Novel Theory for Mammalian Stem Cell Regulation
Friday, 29 January 2010
Linheng Li, Ph.D., Investigator, at Stowers Institute for Medical Research, together with Hans Clevers, M.D., Ph.D., Director of the Hubrecht Institute in Utrecht, Netherlands, co-authored a prospective review published today by the journal Science that proposes a new model of mammalian adult stem cell regulation. This model may explain how the coexistence of two disparate stem cell states regulates both stem cell maintenance and simultaneously supports rapid tissue regeneration.
Adult stem cells are crucial for physiological tissue renewal and regeneration following injury. Current models assume the existence of a single quiescent (resting) population of stem cells residing in a single niche of a given tissue.
The Linheng Li Lab and others have previously reported that primitive blood-forming stem cells can be further separated into quiescent (reserved) and active (primed) sub-populations. Emerging evidence indicates that quiescent and active stem cell sub-populations also co-exist in several tissues — including hair follicle, intestine, bone marrow, and potentially in the neural system — in separate yet adjacent microenvironments. In the review, Dr. Li proposes that quiescent and active stem cell populations have separate but cooperative functional roles.
"Both quiescent and active stem cells co-exist in separate 'zones' in the same tissue," explained Dr. Li.
"Active stem cells are the 'primed' sub-population that account for the generation of corresponding tissues, whereas quiescent stem cells function as a 'back-up' or 'reserved' sub-population, which can be activated in response to the loss of active stem cells or to tissue damage."
The new model would explain how the balance can be regulated between stem cell maintenance and simultaneous support of rapid tissue regeneration, not only at the individual cell level but also at the stem cell population level. The advantage of maintaining 'zoned' sub-populations of stem cells is to increase longevity of stem cells within organisms that have long life spans and large bodies.
The existence of two sub-populations of adult stem cells offers another advantage in the rapidly regenerating tissues in mammals by reducing the risk for mutations that cause tumours.
Intriguingly, cancers may utilize this same mechanism to maintain co-existing active-quiescent pools of stem cell sub-populations that support fast tumour growth (by active stem cells) while preserving the root of malignancy (by quiescent stem cells). This may explain the basis of drug resistance to cancer treatment.
"If this hypothesis is true, the critical question will be how to target quiescent drug-resistant cancer stem cells," said Dr. Li.
"We will test this model in cancers in an effort to determine how to activate quiescent (drug-resistant) cancer stem cells for further targeting."
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ZenMaster
For more on stem cells and cloning, go to CellNEWS at
http://cellnews-blog.blogspot.com/
It's about stem cells, cloning, bioethics and genetics.
Friday, 29 January 2010
Wednesday, 27 January 2010
New Way to Grow Embryonic Stem Cells
Holds promise of dramatic reduction in animal use
Wednesday, 27 January 2010
A new method of priming early embryos to form embryonic stem (ES) cells has allowed ES cells to be derived from mice used in diabetes research for the first time.
This could dramatically reduce the number of animals used to study the genetic basis of type 1 diabetes and has the potential to do the same for mouse models of other diseases too.
Understanding the genetic basis of type 1 diabetes is an important area of research. Researchers often use a strain of mouse, known as the non-obese diabetic (NOD) mouse, which spontaneously develops type 1 diabetes. Previously, it was impossible to generate ES cells from NOD mice, so the only way to study a gene of interest was to breed the NOD mouse with a strain of mouse that could be genetically modified. This involved extensive breeding programmes, involving many hundreds of animals, and taking up to two years.
The research has been awarded this year's annual NC3Rs 3Rs Prize. The prize, sponsored by GlaxoSmithKline, was awarded to Dr Jennifer Nichols, University of Cambridge, and her co-authors who used a precise cocktail of molecules to control the growth of the cells to generate ES cells from the NOD mouse. The resulting ES cells can be directly manipulated to disable or repair a specific gene of interest and then injected into early mouse embryos to breed a NOD mouse with the desired genetic makeup, reducing the overall number of mice required.
Because ES cells can be transformed into all other cell types in the body many more experiments can be conducted in vitro than before, potentially leading to further reduction of animal use.
"We are already looking to turn these embryonic stem cells into beta cells found in the pancreas which are known to be involved in the onset of type 1 diabetes. Because these mice spontaneously develop type 1 diabetes we will be able to do experiments in vitro that were previously impossible," Dr Nichols said.
Dr Vicky Robinson, chief executive of the NC3Rs, said:
"This is an exciting and impressive piece of research. The potential for reducing animal use and advancing the field of diabetes research is huge. Importantly, the new method has implications for other areas of research involving mice."
Dr Gianni a dal-Negro, Director of Animal Research Responsibility at GlaxoSmithKline said:
"As sponsor of this award, GSK are delighted to see such an innovative application of science to the 3Rs. This project demonstrates an originality in applying emerging stem cell science with genetics and immunology in a complicated disease. It will no doubt contribute to new understandings in diseases processes and drug discovery and improved animal welfare."
Dr Nichols and her collaborator Professor Anne Cooke have already made the NOD ES cells freely available to the research community, potentially reducing the number of mice used in type 1 diabetes research worldwide. They plan to use the £10k prize winners' grant to host researchers from other groups so they can learn the culture technique and it can be quickly and widely disseminated.
"The technique for extracting the embryonic stem cells is very visual and therefore difficult to learn from written instructions. Getting researchers to visit us will help encourage quicker uptake of this new approach," Dr Nichols said.
About 1 in 250 of the UK population develops Type 1 diabetes at some stage, usually as children or young adults. In Type 1 diabetes the body stops making insulin because the pancreatic beta cells are selectively destroyed, leading to a very high blood glucose level. Treatment to control the blood glucose level is with insulin injections and a healthy diet. Although the cause of type 1 diabetes is still not fully understood it is believed to be of immunological origin, but the development is thought to be governed by both genetic and environmental factors.
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ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Researchers Directly Turn Mouse Skin Cells into Neurons
Researchers Directly Turn Mouse Skin Cells into Neurons
Wednesday, 27 January 2010
Even Superman needed to retire to a phone booth for a quick change. But now scientists at the Stanford University School of Medicine have succeeded in the ultimate switch: transforming mouse skin cells in a laboratory dish directly into functional nerve cells with the application of just three genes. The cells make the change without first becoming a pluripotent type of stem cell — a step long thought to be required for cells to acquire new identities.
The finding could revolutionize the future of human stem cell therapy and recast our understanding of how cells choose and maintain their specialties in the body.
"We actively and directly induced one cell type to become a completely different cell type," said Marius Wernig, MD, assistant professor of pathology and a member of Stanford's Institute for Stem Cell Biology and Regenerative Medicine.
"These are fully functional neurons. They can do all the principal things that neurons in the brain do."
That includes making connections with and signalling to other nerve cells — critical functions if the cells are eventually to be used as therapy for Parkinson's disease or other disorders.
Wernig is the senior author of the research, which will be published online Jan. 27 in Nature. Graduate student Thomas Vierbuchen is the lead author.
Although previous research has suggested that it is possible to coax specialized cells to exhibit some properties of other cell types, this is the first time that skin cells have been converted into fully functional neurons in a laboratory dish. The change happened within a week and with an efficiency of up to nearly 20 percent. The researchers are now working to duplicate the feat with human cells.
"This study is a huge leap forward," said Irving Weissman, MD, director of Stanford's Institute for Stem Cell Biology and Regenerative Medicine.
"The direct reprogramming of these adult skin cells into brain cells that can show complex, appropriate behaviours like generating electrical currents and forming synapses establishes a new method to study normal and disordered brain cell function. Finally we may be able to capture and study conditions like Parkinson's or Alzheimer's or heritable mental diseases in the laboratory dish for the first time."
Until recently, it has been thought that cellular specialization, or differentiation, was a one-way path: pluripotent embryonic stem cells give rise to all the cell types in the body, but as the daughter cells become more specialized, they also become more biologically isolated. Like a tree trunk splitting first into branches and then into individual leaves, the cells were believed to be consigned to one developmental fate by physical modifications — called epigenetic changes — added to their DNA along the way. A skin cell could no more become a nerve cell than a single leaf could flit from branch to branch or Superman could become Clark Kent in midair.
That view began to change when Dolly the sheep was cloned from an adult cell in 1997, showing that, under certain conditions, a specialized cell could shed these restrictions and act like an embryonic stem cell.
And in 2007, researchers announced the creation of induced pluripotent stem cells, or iPS cells, from human skin cells by infecting them with four stem-cell-associated proteins called transcription factors. Once the cells had achieved a pluripotent state, the researchers coaxed them to develop into a new cell type. The process was often described in concept as moving the skin cells backward along the differentiation pathway (in the leaves analogy, reversing down the branch to the tree's trunk) and then guiding them forward again along a different branch into a new lineage.
Finally, in 2008, Doug Melton, PhD, a co-director of Harvard's Stem Cell Institute, showed it was possible in adult mice to reprogram one type of cell in the pancreas to become another pancreatic cell type by infecting them with a pool of viruses expressing just three transcription factors.
As a result, Wernig, who as a postdoctoral fellow in Rudolf Jaenisch's laboratory at the Whitehead Institute in Massachusetts participated in the initial development of iPS cells, began to wonder whether the pluripotent pit stop was truly necessary. Thomas Südhof, the Avram Goldstein Professor in the Stanford School of Medicine, also collaborated on the research.
To test the theory, Wernig, Vierbuchen and graduate student Austin Ostermeier amassed a panel of 19 genes involved in either epigenetic reprogramming or neural development and function. They used a virus called a lentivirus to infect skin cells from embryonic mice with the genes, and then monitored the cells' response. After 32 days they saw that some of the former skin cells now looked like neural cells and expressed neural proteins.
The researchers, which included postdoctoral scholar Zhiping Pang, PhD, used a mix-and-match approach to winnow the original pool of 19 genes down to just three. They also tested the procedure on skin cells from the tails of adult mice. They found that about 20 percent of the former skin cells transformed into neural cells in less than a week. That may not, at first, sound like a quick change, but it is vast improvement over iPS cells, which can take weeks. What's more, the iPS process is very inefficient: Usually only about 1 to 2 percent of the original cells become pluripotent.
In Wernig's experiments, the cells not only looked like neurons, they also expressed neural proteins and even formed functional synapses with other neurons in laboratory dish.
"We were very surprised by both the timing and the efficiency," said Wernig.
"This is much more straightforward than going through iPS cells, and it's likely to be a very viable alternative."
Quickly making neurons from a specific patient may allow researchers to study particular disease processes such as Parkinson's in a laboratory dish, or one day to even manufacture cells for therapy.
The research suggests that the pluripotent stage, rather than being a required touchstone for identity-shifting cells, may simply be another possible cellular state. Wernig speculates that finding the right combination of cell-fate-specific genes may trigger a domino effect in the recipient cell, wiping away restrictive DNA modifications and imprinting a new developmental fate on the genomic landscape.
"It may be hard to prove, but I no longer think that the induction of iPS cells is a reversal of development,” said Wernig.
“It is probably more of a direct conversion like what we are seeing here, from one cell type to another that just happens to be more embryonic-like. This tips our ideas about epigenetic regulation upside down."
Reference:
Direct conversion of fibroblasts to functional neurons by defined factors
Thomas Vierbuchen, Austin Ostermeier, Zhiping P. Pang, Yuko Kokubu, Thomas C. Südhof & Marius Wernig
Nature advance online publication 27 January 2010, doi:10.1038/nature08797
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ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Friday, 22 January 2010
New Transcription Factor Reprograms Differentiated Cells into Pluripotent Stem Cells
Singapore scientists' surprising discovery potentially relevant to cell-therapy-based medicine
Friday, 22 January 2010
In the new issue of the journal Cell Stem Cell, Singapore scientists report the surprising discovery that a novel transcription factor, Nr5a2, can replace one of the classical reprogramming factors, Oct 4, to significantly increase the efficiency of reprogramming differentiated stem cells into induced pluripotent stem cells (iPS cells).
Previous research revealed that the reprogramming of differentiated cells into induced iPS cells could be achieved by the three transcription factors, Oct4, Sox2 and Klf4.
In this latest finding, which is potentially relevant to cell therapy-based medicine, Genome Institute of Singapore (GIS) and National University of Singapore (NUS) scientists determined that Nr5a2 can replace Oct4. Thus, a new combination of Nr5a2, Sox2 and Klf4 can reprogram differentiated cells into iPS cells.
"This is a very exciting moment," said GIS Senior Group Leader Ng Huck Hui, Ph.D.
"Fundamental research in embryonic stem cells is extremely important for us to harness the full potentials of these cells, and this study provides valuable and crucial insights into the mechanism of reprogramming.”
"Given Oct4's critical role in embryonic stem cells and reprogramming, we were very surprised with the discovery that Nr5a2 could replace Oct4," added Dr. Ng, senior author of the paper.
"This study highlights the prospect of finding more surprises in the field of reprogramming."
"This paper represents significant addition to the very active field of cellular reprogramming," added Davor Solter, M.D., Ph.D., Senior Principal Investigator at Singapore's Institute of Medical Biology (IMB).
Both GIS and IMB are part of Singapore's A*STAR (Agency for Science, Technology and Research).
"The authors show that gene coding for nuclear receptor Nr5a2 can replace one of the classical reprogramming factors Oct 4," Dr. Solter said.
"In addition they presented evidence that this and another nuclear receptor can significantly increase the efficiency of reprogramming. These results have great basic and practical significance."
The reprogramming of differentiated cells into iPS cells is one of the most important breakthroughs in stem cell research, because iPS cells can give rise to all other differentiated cell types that make up the human body.
Because they behave like embryonic stem cells, iPS cells are important starting points for the creation of organs for replacement or transplantation.
The Cell Stem Cell paper, published on Jan. 21, 2010, is the second research report on iPS cell science by Dr. Ng's research group. In Jan. 2009, Dr. Ng and his colleagues reported in Nature Cell Biology that the transcription factor Esrrb could replace Klf4 in the combination of Oct4, Sox2 and Klf4 for iPS cell creation.
Reference:
The Nuclear Receptor Nr5a2 can replace Oct4 in the Reprogramming of Murine Somatic Cells to Pluripotent Cells
Jian-Chien Dominic Heng, Bo Feng, Jianyong Han, Jianming Jiang, Petra Kraus, Jia-Hui Ng, Yuriy L. Orlov, Mikael Huss, Lin Yang, Thomas Lufkin, Bing Lim, Huck-Hui Ng
Cell Stem Cell, Jan. 21, 2010 online issue, 10.1016/j.stem.2009.12.009
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ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Thursday, 21 January 2010
Functional Blood Vessel Cells Generated From Human Stem Cells
Weill Cornell Medical College study lays groundwork for new treatments for cardiovascular disease and other conditions
Thursday, 21 January 2010
In a significant step toward restoring healthy blood circulation to treat a variety of diseases, a team of scientists at Weill Cornell Medical College has developed a new technique and described a novel mechanism for turning human embryonic and pluripotent stem cells into plentiful, functional endothelial cells, which are critical to the formation of blood vessels. Endothelial cells form the interior "lining" of all blood vessels and are the main component of capillaries, the smallest and most abundant vessels. In the near future, the researchers believe, it will be possible to inject these cells into humans to heal damaged organs and tissues.
The new approach allows scientists to generate virtually unlimited quantities of durable endothelial cells – more than 40-fold the quantity possible with previous approaches. Based on insights into the genetic mechanisms that regulate how embryonic stem cells form vascular endothelial cells, the approach may also yield new ways to study genetically inherited vascular diseases. The study appears in the advance online issue of Nature Biotechnology.
"This technique is the first of its kind with serious potential as a treatment for a diverse array of diseases, especially cardiovascular disease, stroke and vascular complications of diabetes," says Dr. Shahin Rafii, the study's senior author. Dr. Rafii is the Arthur B. Belfer Professor in Genetic Medicine and co-director of the Ansary Stem Cell Institute at Weill Cornell Medical College, and an investigator of the Howard Hughes Medical Institute.
In recent years, enormous hopes have been pinned on stem cells as the source of future cures and treatments. Indeed, human embryonic stem cells have the potential to become any one of the more than 200 types of adult cells. However, the factors and pathways that govern their differentiation to abundant derivatives that could be used to repair organs have remained poorly understood.
A major challenge for Dr. Rafii's lab has been to improve their understanding, and hence control, of the differentiation process (how stem cells convert to various cell types), and then to generate enough vascular endothelial cells – many millions – so they can be used therapeutically.
To meet this challenge, the scientists first screened for molecular factors that come into play when stem cells turn into endothelial cells. Their findings led them to a strategy that significantly boosts the efficiency of producing these cells.
Then, the researchers tracked the differentiation process in real-time using a green fluorescent protein marker developed by Dr. Daylon James, the study's first author and assistant research professor in the Department of Reproductive of Medicine at Weill Cornell Medical College. They found that when they exposed stem cells to a compound that blocks TGF-beta (a growth factor involved in cell specialization) at just the right time during cell culturing, the propagation of endothelial cells dramatically increased.
Even more striking, they found that the cells worked properly when injected into mice. The cells were quickly assimilated into the animals' circulatory systems, and functioned alongside normal vasculature.
To achieve long-lasting clinical benefits, there remain additional hurdles to exploiting endothelial cells generated in vitro. Indeed, a fundamental prerequisite to using vascular cells in regenerative medicine has been the proper assembly in vivo of new blood vessels from stem-cell-derived cells, according to Dr. Sina Rabbany, who is an adjunct professor at Weill Cornell Medical College and professor of bioengineering at Hofstra University. Dr. Rabbany emphasizes that, in addition to manipulating biological factors implicated in endothelial cell differentiation, the impact of blood flow on endothelial cells is critical to engineering durable, vascularised organs. With the plentiful supply of endothelial cells that the new methods provide, Dr. Rabbany's team is working to build biological scaffolds that model the microenvironment of the vasculature, so that the vessels they generate will be functional and long-lasting in patients.
Another major obstacle to clinical use of cultured endothelial cells is the potential of immune rejection when the cells are injected into a patient. To address this risk, one approach would be to create a large, genetically diverse bank of human embryonic stem cells that, on demand, could be converted into endothelial cells that are compatible with specific patients.
"Given the success rate our group has shown in generating human embryonic stem cells from donated normal and diseased embryos, this new approach has broad implications not only for regenerative medicine, but also for the study of genetic diseases of the vasculature," states Dr. Zev Rosenwaks, who is director and physician-in-chief of the Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine as well as the director of the Tri-Institutional Stem Cell Initiative Derivation Unit at Weill Cornell Medical College.
The new endothelial cell culture is currently being validated in ongoing research at Weill Cornell using a number of stem cell "lines," or "families" of stem cells.
"Employing a highly sophisticated derivation technology, we have been able to generate 11 normal and diseased human embryonic cell lines from discarded embryos at the Tri-Institute Derivation Unit at Weill Cornell," states Dr. Nikica Zaninovic, an assistant professor at the Department of Reproductive of Medicine who is spearheading the human embryonic stem cell derivation effort. Using the new differentiation methods, several of these new embryonic stem cell lines have been turned into vascular cells.
Testing in humans is the next major step in verifying the ability of this breakthrough cell-based approach to restore blood supply to injured organs. Armed with this new technology and under the umbrella of support from the Ansary Stem Cell Institute and Tri-Institutional Stem Cell Initiative (Tri-SCI), this team of scientists is hoping to transfer their methods to the clinic within the next five years.
The current study sheds light on the generation of human embryonic vasculature in ways that have not previously been feasible due to obstacles associated with the use of human embryonic tissue.
As Dr. James explains:
"The unbiased screening technique we used is a major technological advance that opens up possibilities for discovery of how human embryonic stem cells morph into the specific mature cells that compose the brain, liver, pancreas, and so on. Our general approach can be applied to additional human tissues and help other stem cell research groups develop and maintain specialized cell types in the larger effort to understand human development – and to heal many different kinds of human diseases and injuries."
The Tri-Institutional Stem Cell Initiative, supported by a generous gift from The Starr Foundation, is a collaborative venture of Memorial Sloan-Kettering Cancer Center, The Rockefeller University, and Weill Cornell Medical College.
Ansary Stem Cell Institute
The Ansary Stem Cell Institute, established at Weill Cornell Medical College in 2004 through the generous donation of Shahla and Hushang Ansary, brings together a premier team of scientists to focus on stem cells – the primitive, unspecialized cells with an unrivalled capacity to form all types of cells, tissues and organs in the body. The vision of the Ansary Institute is to help lead the way in 21st-century medicine by employing this new field of research with tremendous potential to relieve human suffering. The Institute permits the multidisciplinary collaboration and creativity of Weill Cornell's researchers, as well as helps to attract the best and brightest young researchers in the field. Scientists at the Institute hope to discover the wellspring of adult stem cells in the body and ways to manipulate them to treat human illness. In particular, they hope to understand the regulation of cells that give rise to such essential components as blood vessels, insulin-producing cells in the pancreas (which are damaged in diabetics), and neurons of the brain and nervous system.
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ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Wednesday, 20 January 2010
Transplanted Stem Cells Form Proper Brain Connections
Neurons developed from embryonic stem cells successfully wired with other brain regions in mice
Wednesday, 20 January 2010
Transplanted neurons grown from embryonic stem cells can fully integrate into the brains of young animals, according to new research in the Jan. 20 issue of The Journal of Neuroscience. Healthy brains have stable and precise connections between cells that are necessary for normal behaviour. This new finding is the first to show that stem cells can be directed not only to become specific brain cells, but to link correctly.
In this study, a team of neuroscientists led by James Weimann, PhD, of Stanford Medical School focused on cells that transmit information from the brain's cortex, some of which are responsible for muscle control. It is these neurons that are lost or damaged in spinal cord injuries and amyotrophic lateral sclerosis (ALS).
"These stem cell-derived neurons can grow nerve fibres between the brain's cerebral cortex and the spinal cord, so this study confirms the use of stem cells for therapeutic goals," Weimann said.
To integrate new cells into a brain successfully, the researchers first had to condition unspecialized cells to become specific cells in the brain's cortex. Cells that were precursors to cortical neurons were grown in a Petri dish until they displayed many of the same characteristics as mature neurons. The young neurons were then transplanted into the brains of newborn mice — specifically, into regions of the cortex responsible for vision, touch, and movement.
Until now, making these proper cellular connections has been a fundamental problem in nervous system transplant therapy. In this case, the maturing neurons extended to the appropriate brain structures, and, just as importantly, avoided inappropriate areas. For example, cells transplanted into the visual cortex reached two deep brain structures called the superior colliculus and the pons, but not to the spinal cord; cells placed into the motor area of the cortex stretched into the spinal cord but avoided the colliculus.
"The authors show that appropriate connectivity for one important class of projection neurons can be obtained in newborn animals," said Mahendra Rao, MD, PhD, an expert in stem cell biology at Life Technology, who was unaffiliated with the study.
The researchers also compared two methods used to grow transplantable cells, only one of which produced the desired results.
"The authors provide a protocol for how to get the right kind of neurons to show appropriate connectivity," Rao said.
"It's a huge advance in the practical use of these cells."
Researchers will now explore whether the same results can be achieved in adult animals and, ultimately, humans. Weimann and his colleagues also hope to understand how the transplanted cells "knew" to connect in precisely the right way, and whether they can generate the right behaviours, such as vision and movement.
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ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Transplanted neurons grown from embryonic stem cells can fully integrate into the brains of young animals, according to new research in the Jan. 20 issue of The Journal of Neuroscience. Healthy brains have stable and precise connections between cells that are necessary for normal behaviour. This new finding is the first to show that stem cells can be directed not only to become specific brain cells, but to link correctly.
In this study, a team of neuroscientists led by James Weimann, PhD, of Stanford Medical School focused on cells that transmit information from the brain's cortex, some of which are responsible for muscle control. It is these neurons that are lost or damaged in spinal cord injuries and amyotrophic lateral sclerosis (ALS).
"These stem cell-derived neurons can grow nerve fibres between the brain's cerebral cortex and the spinal cord, so this study confirms the use of stem cells for therapeutic goals," Weimann said.
To integrate new cells into a brain successfully, the researchers first had to condition unspecialized cells to become specific cells in the brain's cortex. Cells that were precursors to cortical neurons were grown in a Petri dish until they displayed many of the same characteristics as mature neurons. The young neurons were then transplanted into the brains of newborn mice — specifically, into regions of the cortex responsible for vision, touch, and movement.
Until now, making these proper cellular connections has been a fundamental problem in nervous system transplant therapy. In this case, the maturing neurons extended to the appropriate brain structures, and, just as importantly, avoided inappropriate areas. For example, cells transplanted into the visual cortex reached two deep brain structures called the superior colliculus and the pons, but not to the spinal cord; cells placed into the motor area of the cortex stretched into the spinal cord but avoided the colliculus.
"The authors show that appropriate connectivity for one important class of projection neurons can be obtained in newborn animals," said Mahendra Rao, MD, PhD, an expert in stem cell biology at Life Technology, who was unaffiliated with the study.
The researchers also compared two methods used to grow transplantable cells, only one of which produced the desired results.
"The authors provide a protocol for how to get the right kind of neurons to show appropriate connectivity," Rao said.
"It's a huge advance in the practical use of these cells."
Researchers will now explore whether the same results can be achieved in adult animals and, ultimately, humans. Weimann and his colleagues also hope to understand how the transplanted cells "knew" to connect in precisely the right way, and whether they can generate the right behaviours, such as vision and movement.
.........
ZenMaster For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Thursday, 14 January 2010
Dog Genome Researchers Track Paw Prints of Selective Breeding
Genes are being tested for roles in most conspicuous variations among dogs
Thursday, 14 January 2010
From the Dachshund's stubby legs to the Shar-Pei's wrinkly skin, breeding for certain characteristics has left its mark on the dog genome. Researchers have identified 155 regions on the canine genome that appear to have been influenced by selective breeding.
With more than 400 distinct breeds, dogs come in a wide range of shapes, sizes, fur-styles, and temperaments. The curly-haired toy poodle, small enough to sit in a teacup, barely looks or acts like the smooth-coated Great Dane tall enough to peer like a periscope out of a car's sunroof. Not so apparent are breed differences in how the dogs' bodies function and their susceptibility to various diseases.
Although domestication of dogs began over 14,000 years ago, according to Dr. Joshua Akey, University of Washington (UW) assistant professor of genome sciences, the spectacular diversity among breeds is thought to have originated during the past few centuries through intense artificial selection of and strict breeding for desired characteristics. Akey is the lead author of the effort to map canine genome regions that show signs of recent selection and that contain genes that are prime candidates for further investigation. Those genes are being examined for their possible roles in the most conspicuous variations among dog breeds: size, coat colour and texture, behaviour, physiology, and skeleton structure.
The researchers performed the largest genome-wide scan to date for targets of selection in purebred dogs. The genomes came from 275 unrelated dogs representing 10 breeds that were very unlike each other. The breeds were: Beagle, Border Collie, Brittany, Dachshund, German Shepherd, Greyhound, Jack Russell Terrier, Labrador Retriever, Shar-Pei, and Standard Poodle.
The study was conducted, the researchers said, because the canine genome, the product of centuries of strong selection, contains many important lessons about the genetic architecture of physical and behavioural variations and the mechanisms of rapid, short-term evolution. The findings, the researchers said, "provide a detailed glimpse into the genetic legacy of centuries of breeding practices."
Their results were published Jan. 11 in the Proceedings of the National Academy of Science, in the article "Tracking footprints of artificial selection in the dog genome."
The researchers catalogued more than 21,000 tiny variations in the genome. In investigating the relationships among the 10 breeds, they found that, genetically, the German Shepherd, Shar-Pei, Beagle, and Greyhound were especially distinct.
Their list of most differentiated regions of the dog genome included five genes already linked to hallmark traits of certain breeds: one for small size, one for short limbs like those in Dachshunds and other stubby-legged dogs, and three for coats.
In calculating the overlap of the signatures marking selection in the genome, the researchers found that approximately 66 percent occurred in only one or two breeds. They noted it was likely that these genome regions contain genes that confer qualities that distinguish a breed, such as skin wrinkling in the Shar-Pei. In contrast, signatures of selection found in five or more breeds tended to sort the dogs into classes, and include, for example, a gene that governs the miniature size of breeds in the toy group.
A gene associated with dwarfism in mice, the study reports, appears to mediate variations in dog breed size and weight. Small-size breeds, like Dachshund, Beagle, Jack Russell Terrier, and Brittany have enormous differentiation in this gene, compared to larger-size breeds. Another region of peak differentiation in the dog genome, in an area thought to regulate muscle cell formation in embryos, seems to separate the German Shepherd, Jack Russell Terrier, Border Collie and Greyhound from the Dachshund, Beagle, Brittany, and Shar-Pei.
The 155 regions of the genome that appear to have been influenced by selective breeding contain 1,630 known or predicted protein-coding genes. The researchers tried to obtain a broad overview of the molecular functions of these genes. The were surprised to discover that genes involved in immunity and defence were overrepresented in the 155 regions, a phenomenon also discovered in genome analysis of selection in natural populations. Natural and artificial selection were not expected to act on similar classes of genes, the researchers noted, but immune-related genes may be frequent targets of selection because of their critical role in defending against ever-changing infections.
The researchers honed in on a particular genome region in the Shar-Pei. Many of these dogs have excessive wrinkles, but some are smooth. A gene in this region may govern the degree of skin folding correlates with levels of certain molecules whose production. Rare mutations in this same gene also cause severe skin wrinkling in people. Tiny genetic variations in this gene seemed linked to whether a Shar-Pei would be smooth or wrinkled, and a rare genetic mutation was found in the Shar-Pei but not in other dogs.
The researchers explained that, despite the many insights emerging from their data, there were several limitations to their study and in interpreting the findings. They pointed out that a pattern of variation that is unusual to the dog genome at large does not prove that specific genome region is under selection.
A major impetus behind studying dog genomics, the researchers pointed out, is its potential to advance knowledge about the genetic basis of human form variations and of differences in disease susceptibility among people. In many cases, the researchers said, it may be easier to locate the genetic targets of selection in dogs, and then map these to related regions in the human genome. Scientists are intrigued by the possibility that recent selection may have affected genome regions common to both human and dog lineages.
"This research has shown that artificial selection in dogs has acted on many of the same genes as natural selection in humans, and that many of these genes are regulators of gene activity," said Dr. Irene Eckstrand, who oversees evolution grants at the National Institute of General Medical Sciences at the National Institutes of Health.
"The statistical and computational approaches used in this study will be of great value in deciphering the organization of human genetic variation, and in identifying the genetic basis of human characteristics."
The researchers also said that a better understanding of artificial selection in dogs may reveal the molecular mechanisms of rapid, short-term evolution. Future work, they hope, may uncover the gene activities responsible for shaping the incredible diversity among the world's dogs.
.........
ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
With more than 400 distinct breeds, dogs come in a wide range of shapes, sizes, fur-styles, and temperaments. The curly-haired toy poodle, small enough to sit in a teacup, barely looks or acts like the smooth-coated Great Dane tall enough to peer like a periscope out of a car's sunroof. Not so apparent are breed differences in how the dogs' bodies function and their susceptibility to various diseases.
Although domestication of dogs began over 14,000 years ago, according to Dr. Joshua Akey, University of Washington (UW) assistant professor of genome sciences, the spectacular diversity among breeds is thought to have originated during the past few centuries through intense artificial selection of and strict breeding for desired characteristics. Akey is the lead author of the effort to map canine genome regions that show signs of recent selection and that contain genes that are prime candidates for further investigation. Those genes are being examined for their possible roles in the most conspicuous variations among dog breeds: size, coat colour and texture, behaviour, physiology, and skeleton structure.
The researchers performed the largest genome-wide scan to date for targets of selection in purebred dogs. The genomes came from 275 unrelated dogs representing 10 breeds that were very unlike each other. The breeds were: Beagle, Border Collie, Brittany, Dachshund, German Shepherd, Greyhound, Jack Russell Terrier, Labrador Retriever, Shar-Pei, and Standard Poodle.
The study was conducted, the researchers said, because the canine genome, the product of centuries of strong selection, contains many important lessons about the genetic architecture of physical and behavioural variations and the mechanisms of rapid, short-term evolution. The findings, the researchers said, "provide a detailed glimpse into the genetic legacy of centuries of breeding practices."
Their results were published Jan. 11 in the Proceedings of the National Academy of Science, in the article "Tracking footprints of artificial selection in the dog genome."
The researchers catalogued more than 21,000 tiny variations in the genome. In investigating the relationships among the 10 breeds, they found that, genetically, the German Shepherd, Shar-Pei, Beagle, and Greyhound were especially distinct.
Their list of most differentiated regions of the dog genome included five genes already linked to hallmark traits of certain breeds: one for small size, one for short limbs like those in Dachshunds and other stubby-legged dogs, and three for coats.
In calculating the overlap of the signatures marking selection in the genome, the researchers found that approximately 66 percent occurred in only one or two breeds. They noted it was likely that these genome regions contain genes that confer qualities that distinguish a breed, such as skin wrinkling in the Shar-Pei. In contrast, signatures of selection found in five or more breeds tended to sort the dogs into classes, and include, for example, a gene that governs the miniature size of breeds in the toy group.
A gene associated with dwarfism in mice, the study reports, appears to mediate variations in dog breed size and weight. Small-size breeds, like Dachshund, Beagle, Jack Russell Terrier, and Brittany have enormous differentiation in this gene, compared to larger-size breeds. Another region of peak differentiation in the dog genome, in an area thought to regulate muscle cell formation in embryos, seems to separate the German Shepherd, Jack Russell Terrier, Border Collie and Greyhound from the Dachshund, Beagle, Brittany, and Shar-Pei.
The 155 regions of the genome that appear to have been influenced by selective breeding contain 1,630 known or predicted protein-coding genes. The researchers tried to obtain a broad overview of the molecular functions of these genes. The were surprised to discover that genes involved in immunity and defence were overrepresented in the 155 regions, a phenomenon also discovered in genome analysis of selection in natural populations. Natural and artificial selection were not expected to act on similar classes of genes, the researchers noted, but immune-related genes may be frequent targets of selection because of their critical role in defending against ever-changing infections.
The researchers honed in on a particular genome region in the Shar-Pei. Many of these dogs have excessive wrinkles, but some are smooth. A gene in this region may govern the degree of skin folding correlates with levels of certain molecules whose production. Rare mutations in this same gene also cause severe skin wrinkling in people. Tiny genetic variations in this gene seemed linked to whether a Shar-Pei would be smooth or wrinkled, and a rare genetic mutation was found in the Shar-Pei but not in other dogs.
The researchers explained that, despite the many insights emerging from their data, there were several limitations to their study and in interpreting the findings. They pointed out that a pattern of variation that is unusual to the dog genome at large does not prove that specific genome region is under selection.
A major impetus behind studying dog genomics, the researchers pointed out, is its potential to advance knowledge about the genetic basis of human form variations and of differences in disease susceptibility among people. In many cases, the researchers said, it may be easier to locate the genetic targets of selection in dogs, and then map these to related regions in the human genome. Scientists are intrigued by the possibility that recent selection may have affected genome regions common to both human and dog lineages.
"This research has shown that artificial selection in dogs has acted on many of the same genes as natural selection in humans, and that many of these genes are regulators of gene activity," said Dr. Irene Eckstrand, who oversees evolution grants at the National Institute of General Medical Sciences at the National Institutes of Health.
"The statistical and computational approaches used in this study will be of great value in deciphering the organization of human genetic variation, and in identifying the genetic basis of human characteristics."
The researchers also said that a better understanding of artificial selection in dogs may reveal the molecular mechanisms of rapid, short-term evolution. Future work, they hope, may uncover the gene activities responsible for shaping the incredible diversity among the world's dogs.
.........
ZenMaster For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
China Stakes Claim as Global Centre for Scientific Research
China Stakes Claim as Global Centre for Scientific Research
Thursday, 14 January 2010
Contrary to popular belief, China is doing much more than exporting clothing, toys, electronics, and other popular consumer goods. The country is on a scientific roll, to the point where it could conceivably be regarded as the emerging global centre for scientific research, a new report indicates. It describes an amazing growth in chemical patenting and publishing that could bring new and innovative products to the world market ranging from pharmaceuticals to microchips, according to an article in the current issue of Chemical & Engineering News, (C&EN) ACS' weekly newsmagazine.
C&EN Senior Editor Sophie L. Rovner reports that China in 2009 became the world leader in the number of chemistry patent applications published annually. China published 67,000 patent applications in 2009, compared to 52,000 for Japan and 41,000 for the United States. Publication of scientific papers originating in China increased faster than any other nation during the last 10 years. The output of papers with Chinese authors more than quadrupled — from 20,000 papers in 1998 to more than 112,000 in 2008. The publication of U.S. scientific papers rose by barely 30 percent during that period.
In achieving this growth, scientists in China are embracing collaborators in the U.S. and other countries. It is becoming increasingly clear that the country is changing the "world map of research," with China conceivably at its centre, the article suggests.
This story is available at China Ascendant.
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ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Gene Mutations in Patients with Becker Muscular Dystrophy
Gene Mutations in Patients with Becker Muscular Dystrophy
Thursday, 14 January 2010
Investigators in The Research Institute at Nationwide Children's Hospital have identified a link between specific modifications of the dystrophin gene and the age of cardiac disease onset in patients with Becker muscular dystrophy (BMD). This information could help clinicians provide early cardiac intervention for BMD patients based on genetic testing results performed on a blood sample. These findings are a result of analysis of the largest number of BMD patients to date and are published in the December issue of the journal Circulation: Cardiovascular Genetics.
Becker muscular dystrophy is a genetic disorder that usually begins in adolescence causing progressive muscle weakness of the legs and pelvis. Most patients – more than 70 percent – will also develop cardiac disease that is likely to go unnoticed until it has reached an advanced stage. To date, clinicians cannot predict when cardiac disease will occur and which patients would most benefit from early heart screenings.
"Our study findings revealed areas of gene mutation most associated with early onset of heart disease," said the study's lead author, Rita Wen Kaspar, BSN, RN, a PhD student at The Ohio State University College of Nursing who conducted this research at the Center for Gene Therapy in The Research Institute at Nationwide Children's Hospital.
"By identifying which dystrophin mutations are most likely to cause early-onset heart conditions, our research could help clinicians identify at-risk patients, provide early intervention and ultimately prolong patient survival."
Investigators collected data from 78 patients with BMD or X-linked dilated cardiomyopathy from Nationwide Children's Hospital, The Ohio State University, the Utah Dystrophinopathy Project, the Leiden Open Variation Database and published case reports. They then correlated genetic mutations with the onset age of heart disease.
Federica Montanaro, PhD, the study's corresponding author and a principal investigator in the Center for Gene Therapy at Nationwide Children's, described the study as an important example of collaboration between basic scientists and clinicians.
"The results from this study are important at two levels," explained Dr. Montanaro, also a faculty member of The Ohio State University College of Medicine.
"First, as genetic screening becomes more widely available, clinicians will now be able to use this information to deliver more personalized care to BMD patients. Second, our findings provide new clues as to the functions of dystrophin in the heart. These clinical findings are now being brought back to the research laboratory to help design more effective treatments for heart disease in BMD patients as well as in children that suffer from the more severe form of this disease known as Duchenne Muscular Dystrophy."
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ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Wednesday, 13 January 2010
The Viruses Within and What Keeps Them There
Biologists wake dormant viruses and uncover mechanism for survival
Wednesday, 13 January 2010
It is known that viral "squatters" comprise nearly half of our genetic code. These genomic invaders inserted their DNA into our own millions of years ago when they infected our ancestors. But just how we keep them quiet and prevent them from attack was more of a mystery until EPFL researchers revived them.
The reason we survive the presence of these endogenous retroviruses — viruses that attack and are passed on through germ cells, the cells that give rise to eggs and sperm — is because something keeps the killers silent. Now, publishing in the journal Nature, Didier Trono and his team from EPFL, in Switzerland, describe the mechanism. Their results provide insights into evolution and suggest potential new therapies in fighting another retrovirus — HIV.
By analysing embryonic stem cells in mice within the first few days of life, Trono and team discovered that mouse DNA codes for an army of auxiliary proteins that recognize the numerous viral sequences littering the genome. The researchers also demonstrated that a master regulatory protein called KAP1 appears to orchestrate these inhibitory proteins in silencing would-be viruses. When KAP1 is removed, for example, the viral DNA "wakes up," multiplies, induces innumerable mutations, and the embryo soon dies.
Because retroviruses tend to mutate their host's DNA, they have an immense power and potential to alter genes. And during ancient pandemics, some individuals managed to silence the retrovirus involved and therefore survived to pass on the ability. Trono explains that the great waves of endogenous retrovirus appearance coincide with times when evolution seemed to leap ahead.
"In our genome we find traces of the last two major waves. The first took place 100 million years ago, at the time when mammals started to develop, and the second about fifty million years ago, just before the first anthropoid primates," he says.
The discovery of the KAP1 mechanism could be of interest in the search for new therapeutic approaches to combat AIDS. The virus that causes AIDS can lie dormant in the red blood cells it infects, keeping it hidden from potential treatments. Waking the virus up could expose it to attack.
To view a YouTube video related to this release, please visit The Viruses Within - Interview with Didier Trono, EPFL.
Reference:
KAP1 controls endogenous retroviruses in embryonic stem cells
Helen M. Rowe, Johan Jakobsson, Daniel Mesnard, Jacques Rougemont, Séverine Reynard, Tugce Aktas, Pierre V. Maillard, Hillary Layard-Liesching, Sonia Verp, Julien Marquis, François Spitz, Daniel B. Constam & Didier Trono
Nature 463, 237-240 (14 January 2010), doi:10.1038/nature08674
.........
ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
It is known that viral "squatters" comprise nearly half of our genetic code. These genomic invaders inserted their DNA into our own millions of years ago when they infected our ancestors. But just how we keep them quiet and prevent them from attack was more of a mystery until EPFL researchers revived them.
The reason we survive the presence of these endogenous retroviruses — viruses that attack and are passed on through germ cells, the cells that give rise to eggs and sperm — is because something keeps the killers silent. Now, publishing in the journal Nature, Didier Trono and his team from EPFL, in Switzerland, describe the mechanism. Their results provide insights into evolution and suggest potential new therapies in fighting another retrovirus — HIV.
By analysing embryonic stem cells in mice within the first few days of life, Trono and team discovered that mouse DNA codes for an army of auxiliary proteins that recognize the numerous viral sequences littering the genome. The researchers also demonstrated that a master regulatory protein called KAP1 appears to orchestrate these inhibitory proteins in silencing would-be viruses. When KAP1 is removed, for example, the viral DNA "wakes up," multiplies, induces innumerable mutations, and the embryo soon dies.
Because retroviruses tend to mutate their host's DNA, they have an immense power and potential to alter genes. And during ancient pandemics, some individuals managed to silence the retrovirus involved and therefore survived to pass on the ability. Trono explains that the great waves of endogenous retrovirus appearance coincide with times when evolution seemed to leap ahead.
"In our genome we find traces of the last two major waves. The first took place 100 million years ago, at the time when mammals started to develop, and the second about fifty million years ago, just before the first anthropoid primates," he says.
The discovery of the KAP1 mechanism could be of interest in the search for new therapeutic approaches to combat AIDS. The virus that causes AIDS can lie dormant in the red blood cells it infects, keeping it hidden from potential treatments. Waking the virus up could expose it to attack.
To view a YouTube video related to this release, please visit The Viruses Within - Interview with Didier Trono, EPFL.
Reference:
KAP1 controls endogenous retroviruses in embryonic stem cells
Helen M. Rowe, Johan Jakobsson, Daniel Mesnard, Jacques Rougemont, Séverine Reynard, Tugce Aktas, Pierre V. Maillard, Hillary Layard-Liesching, Sonia Verp, Julien Marquis, François Spitz, Daniel B. Constam & Didier Trono
Nature 463, 237-240 (14 January 2010), doi:10.1038/nature08674
.........
ZenMaster For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Chimp and Human Y Chromosomes Evolving Faster Than Expected
Chimp and Human Y Chromosomes Evolving Faster Than Expected
Wednesday, 13 January 2010
Contrary to a widely held scientific theory that the mammalian Y chromosome is slowly decaying or stagnating, new evidence suggests that in fact the Y is actually evolving quite rapidly through continuous, wholesale renovation.
By conducting the first comprehensive interspecies comparison of Y chromosomes, Whitehead Institute researchers have found considerable differences in the genetic sequences of the human and chimpanzee Y’s — an indication that these chromosomes have evolved more quickly than the rest of their respective genomes over the 6 million years since they emerged from a common ancestor. The findings are published online this week in the journal Nature.
"The region of the Y that is evolving the fastest is the part that plays a role in sperm production," say Jennifer Hughes, first author on the Nature paper and a postdoctoral researcher in Whitehead Institute Director David Page's lab.
"The rest of the Y is evolving more like the rest of the genome, only a little bit faster."
The chimp Y chromosome is only the second Y chromosome to be comprehensively sequenced. The original chimp genome sequencing completed in 2005 largely excluded the Y chromosome because its hundreds of repetitive sections typically confound standard sequencing techniques. Working closely with the Genome Center at Washington University, the Page lab managed to painstakingly sequence the chimp Y chromosome, allowing for comparison with the human Y, which the Page lab and the Genome Center at Washington University had sequenced successfully back in 2003.
The results overturned the expectation that the chimp and human Y chromosomes would be highly similar. Instead, they differ remarkably in their structure and gene content. The chimp Y, for example, has lost one third to one half of the human Y chromosome genes – a significant change in a relatively short period of time. Page points out that this is not all about gene decay or loss. He likens the Y chromosome changes to a home undergoing continual renovation.
"People are living in the house, but there's always some room that's being demolished and reconstructed," says Page, who is also a Howard Hughes Medical Institute investigator.
"And this is not the norm for the genome as a whole."
Wes Warren, Assistant Director of the Washington University Genome Center, agrees.
"This work clearly shows that the Y is pretty ingenious at using different tools than the rest of the genome to maintain diversity of genes," he says.
"These findings demonstrate that our knowledge of the Y chromosome is still advancing."
Hughes and Page theorize that the divergent evolution of the chimp and human Y chromosomes may be due to several factors, including traits specific to Y chromosomes and differences in mating behaviours.
Because multiple male chimpanzees may mate with a single female in rapid succession, the males' sperm wind up in heated reproductive competition. If a given male produces more sperm, that male would theoretically be more likely to impregnate the female, thereby passing on his superior sperm production genes, some of which may be residing on the Y chromosome, to the next generation.
Because selective pressure to pass on advantageous sperm production genes is so high, those genes may also drag along detrimental genetic traits to the next generation. Such transmission is allowed to occur because, unlike other chromosomes, the Y has no partner with which to swap genes during cell division. Swapping genes between chromosomal partners can eventually associate positive gene versions with each other and eliminate detrimental gene versions. Without this ability, the Y chromosome is treated by evolution as one large entity. Either the entire chromosome is advantageous, or it is not.
In chimps, this potent combination of intense selective pressure on sperm production genes and the inability to swap genes may have fuelled the Y chromosome's rapid evolution. Disadvantages from a less-than-ideal gene version or even the deletion of a section of the chromosome may have been outweighed by the advantage of improved sperm production, resulting in a Y chromosome with far fewer genes than its human counterpart.
To determine whether this rapid rate of evolution affects Y chromosomes beyond those of chimps and humans, the Page lab and the Washington University Genome Center are now sequencing and examining the Y chromosomes of several other mammals.
Reference:
Chimpanzee and human Y chromosomes are remarkably divergent in structure and gene content
Jennifer F. Hughes, Helen Skaletsky, Tatyana Pyntikova, Tina A. Graves, Saskia K. M. van Daalen, Patrick J. Minx, Robert S. Fulton, Sean D. McGrath, Devin P. Locke, Cynthia Friedman, Barbara J. Trask, Elaine R. Mardis, Wesley C. Warren, Sjoerd Repping, Steve Rozen, Richard K. Wilson, David C. Page
Nature, online January 13, 2010, doi:10.1038/nature08700
The fickle Y chromosome: Chimp genome reveals rapid rate of change.
Lizzie Buchen
Nature 463, 149 (2010), doi:10.1038/463149a
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ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Monday, 11 January 2010
Stem Cells Improves Repair of Major Bone Injuries in Rats
Stem Cells Improves Repair of Major Bone Injuries in Rats
Monday, 11 January 2010
A study published this week reinforces the potential value of stem cells in repairing major injuries involving the loss of bone structure.
The study shows that delivering stem cells on a polymer scaffold to treat large areas of missing bone leads to improved bone formation and better mechanical properties compared to treatment with the scaffold alone. This type of therapeutic treatment could be a potential alternative to bone grafting operations.
"Massive bone injuries are among the most challenging problems that orthopaedic surgeons face, and they are commonly seen as a result of accidents as well as in soldiers returning from war," said the study's lead author Robert Guldberg, a professor in Georgia Institute of Technology’s Woodruff School of Mechanical Engineering.
"This study shows that there is promise in treating these injuries by delivering stem cells to the injury site. These are injuries that would not heal without significant medical intervention."
Details of the research were published in the early edition of the journal Proceedings of the National Academy of Sciences on January 11, 2010. The National Institutes of Health and the National Science Foundation funded this work.
The study was conducted in rats in which two bone gaps eight millimetres in length were created to simulate massive injuries. One gap was treated with a polymer scaffold seeded with stem cells and the other with scaffold only. The results showed that injuries treated with the stem cell scaffolds showed significantly more bone growth than injuries treated with scaffolds only.
Guldberg and mechanical engineering graduate student Kenneth Dupont experimented with scaffolds containing two different types of human stem cells – bone marrow-derived mesenchymal adult stem cells and amniotic fluid foetal stem cells.
"We were able to directly evaluate the therapeutic potential of human stem cells to repair large bone defects by implanting them into rats with a reduced immune system," explained Guldberg, who is also the director of the Petit Institute for Bioengineering and Bioscience at Georgia Tech.
Micro-CT measurements showed no significant differences in bone regeneration between the two stem cell groups. However, combining the two types of stem cells produced significantly higher bone volume and strength compared to scaffolds without cellular augmentation.
Although stem cell delivery significantly enhanced bone growth and biomechanical properties, it was not able to consistently repair the injury. Eight weeks after the treatment, new bone bridged the gaps in four of nine defects treated with scaffolds seeded with adult stem cells, one of nine defects treated with scaffolds seeded with foetal stem cells, and none of the defects treated with the scaffold alone.
"We thought that the functional regeneration of the bone defects may have been limited by stem cells migrating away from the injury site, so we decided to investigate the fate and distribution of the delivered cells," said Guldberg.
To do this, Guldberg labelled stem cells with fluorescent quantum dots – nanometre-scale particles that emit light when excited by near-infrared radiation – to track the distribution of stem cells after delivery on the scaffolds and completed the same experiments as previously described.
Throughout the entire study, the researchers observed significant fluorescence at the stem cell scaffold sites. However, beginning seven to 10 days after treatment, signals appeared at the scaffold-only sites. Additional analysis with immunostaining revealed that the quantum dots present at the scaffold-only sites were contained in inflammatory cells called macrophages that had taken up quantum dots released from dead stem cells.
"While our overall study shows that stem cell therapy has a lot of promise for treating massive bone defects, this experiment shows that we still need to develop an improved way of delivering the stem cells so that they stay alive longer and thus remain at the injury site longer," explained Guldberg.
The researchers also found that the quantum dots diminished the function of the transplanted stem cells and thus their therapeutic effect. When the stem cells were labelled with quantum dots, the results showed a failure to enhance bone formation or bridge defects. However, the same low concentration of quantum dots did not affect cell viability or the ability of the stem cells to become bone cells in laboratory studies.
"Although in vitro laboratory studies remain important, this work provides further evidence that well-characterized in vivo models are necessary to test the ability of regenerative tissue strategies to effectively integrate and restore function in complex living organisms," added Guldberg.
"Improved methods of non-invasive cell tracking that do not alter cell function in vivo are needed to optimize stem cell delivery strategies and compare the effectiveness of different stem cell sources for tissue regeneration."
Guldberg is currently exploring alternative cell tracking methods, such as genetically modifying the stem cells to express green fluorescent protein and/or other luminescent enzymes such as luciferase. He is also investigating the addition of programming cues to the scaffold that will direct the stem cells to differentiate into bone cells. These signals may be particularly effective for foetal stem cells, which are believed to be more primitive than adult stem cells, according to Guldberg.
Lessons learned from the current work are also being applied to develop effective stem cell therapies for severe composite injuries to multiple tissues including bone, nerve, vasculature and muscle. This follow-on work is being conducted in the Georgia Tech Center for Advanced Bioengineering for Soldier Survivability in collaboration with Ravi Bellamkonda and Barbara Boyan, professors in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University.
.........
ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
A study published this week reinforces the potential value of stem cells in repairing major injuries involving the loss of bone structure.
The study shows that delivering stem cells on a polymer scaffold to treat large areas of missing bone leads to improved bone formation and better mechanical properties compared to treatment with the scaffold alone. This type of therapeutic treatment could be a potential alternative to bone grafting operations.
"Massive bone injuries are among the most challenging problems that orthopaedic surgeons face, and they are commonly seen as a result of accidents as well as in soldiers returning from war," said the study's lead author Robert Guldberg, a professor in Georgia Institute of Technology’s Woodruff School of Mechanical Engineering.
"This study shows that there is promise in treating these injuries by delivering stem cells to the injury site. These are injuries that would not heal without significant medical intervention."
Details of the research were published in the early edition of the journal Proceedings of the National Academy of Sciences on January 11, 2010. The National Institutes of Health and the National Science Foundation funded this work.
The study was conducted in rats in which two bone gaps eight millimetres in length were created to simulate massive injuries. One gap was treated with a polymer scaffold seeded with stem cells and the other with scaffold only. The results showed that injuries treated with the stem cell scaffolds showed significantly more bone growth than injuries treated with scaffolds only.
Guldberg and mechanical engineering graduate student Kenneth Dupont experimented with scaffolds containing two different types of human stem cells – bone marrow-derived mesenchymal adult stem cells and amniotic fluid foetal stem cells.
"We were able to directly evaluate the therapeutic potential of human stem cells to repair large bone defects by implanting them into rats with a reduced immune system," explained Guldberg, who is also the director of the Petit Institute for Bioengineering and Bioscience at Georgia Tech.
Micro-CT measurements showed no significant differences in bone regeneration between the two stem cell groups. However, combining the two types of stem cells produced significantly higher bone volume and strength compared to scaffolds without cellular augmentation.
Although stem cell delivery significantly enhanced bone growth and biomechanical properties, it was not able to consistently repair the injury. Eight weeks after the treatment, new bone bridged the gaps in four of nine defects treated with scaffolds seeded with adult stem cells, one of nine defects treated with scaffolds seeded with foetal stem cells, and none of the defects treated with the scaffold alone.
"We thought that the functional regeneration of the bone defects may have been limited by stem cells migrating away from the injury site, so we decided to investigate the fate and distribution of the delivered cells," said Guldberg.
To do this, Guldberg labelled stem cells with fluorescent quantum dots – nanometre-scale particles that emit light when excited by near-infrared radiation – to track the distribution of stem cells after delivery on the scaffolds and completed the same experiments as previously described.
Throughout the entire study, the researchers observed significant fluorescence at the stem cell scaffold sites. However, beginning seven to 10 days after treatment, signals appeared at the scaffold-only sites. Additional analysis with immunostaining revealed that the quantum dots present at the scaffold-only sites were contained in inflammatory cells called macrophages that had taken up quantum dots released from dead stem cells.
"While our overall study shows that stem cell therapy has a lot of promise for treating massive bone defects, this experiment shows that we still need to develop an improved way of delivering the stem cells so that they stay alive longer and thus remain at the injury site longer," explained Guldberg.
The researchers also found that the quantum dots diminished the function of the transplanted stem cells and thus their therapeutic effect. When the stem cells were labelled with quantum dots, the results showed a failure to enhance bone formation or bridge defects. However, the same low concentration of quantum dots did not affect cell viability or the ability of the stem cells to become bone cells in laboratory studies.
"Although in vitro laboratory studies remain important, this work provides further evidence that well-characterized in vivo models are necessary to test the ability of regenerative tissue strategies to effectively integrate and restore function in complex living organisms," added Guldberg.
"Improved methods of non-invasive cell tracking that do not alter cell function in vivo are needed to optimize stem cell delivery strategies and compare the effectiveness of different stem cell sources for tissue regeneration."
Guldberg is currently exploring alternative cell tracking methods, such as genetically modifying the stem cells to express green fluorescent protein and/or other luminescent enzymes such as luciferase. He is also investigating the addition of programming cues to the scaffold that will direct the stem cells to differentiate into bone cells. These signals may be particularly effective for foetal stem cells, which are believed to be more primitive than adult stem cells, according to Guldberg.
Lessons learned from the current work are also being applied to develop effective stem cell therapies for severe composite injuries to multiple tissues including bone, nerve, vasculature and muscle. This follow-on work is being conducted in the Georgia Tech Center for Advanced Bioengineering for Soldier Survivability in collaboration with Ravi Bellamkonda and Barbara Boyan, professors in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University.
.........
ZenMaster For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Friday, 8 January 2010
China A Rising Star in Regenerative Medicine
Enforcing new Chinese rules for clinics may influence lucrative stem cell therapy tourism, but improve international credibility and confidence 08 January 2010 Chinese researchers have become the world's fifth most prolific contributors to peer-reviewed scientific literature on clock-reversing regenerative medicine even as a sceptical international research community condemns the practice of Chinese clinics administering unproven stem cell therapies to domestic and foreign patients. According to a study by the Canadian-based McLaughlin-Rotman Centre for Global Health (MRC), published today by the UK journal Regenerative Medicine, China's government is pouring dollars generously into regenerative medicine (RM) research and aggressively recruiting high-calibre scientists trained abroad in pursuit of its ambition to become a world leader in the field. And its strategy is working: Chinese contributions to scientific journals on RM topics leapt from 37 in year 2000 to 1,116 in 2008, exceeded only by the contributions of experts in the USA, Germany, Japan and the UK. The accomplishment is even more astonishing given that China's international credibility has been and still is severely hindered by global concerns surrounding Chinese clinics, where unproven therapies continue to be administered to thousands of patients. New rules to govern such treatments were recently instituted but need to be strictly enforced in order to repair China's global reputation, according to MRC authors Dominique S. McMahon, Halla Thorsteinsdóttir, Peter A. Singer and Abdallah S. Daar. They drew their conclusions after having gained unprecedented access to almost 50 Chinese researchers, policy makers, clinicians, company executives and regulators for interviews. The research was made possible by funding from the Canadian Institutes of Health Research. "When you look at the issue of stem cells in China, you see the Yin-Yang of a scientific powerhouse mixed with controversial clinical application of stem cell therapies," says Dr. Singer, MRC's Director. "The overall picture at the moment is ambiguous but in the future, given the measures that have been put in place, the science can be expected to rise and the controversy to fall." Regenerative medicine an interdisciplinary field of research and clinical applications focused on the repair, replacement or regeneration of cells, tissues or organs to restore impaired function resulting from any cause, including congenital defects, disease, trauma and aging. It uses a combination of several converging technological approaches, both existing and newly emerging, that moves it beyond traditional transplantation and replacement therapies. The approaches often stimulate and support the body's own self-healing capacity. These approaches may include the use of soluble molecules, gene therapy, stem cell transplants, tissue engineering, and the reprogramming of cell and tissue types. MRC researchers report that until May 2009 clinical trials to determine the effectiveness of stem cell therapies were not required. Now proof of safety and efficacy through clinical trials is required by China's Ministry of Health for all stem cell and gene therapies. The change was made after international experts, joined by top Chinese researchers, protested that treatment centres were acting "against commonly accepted principles of modern scientific research" and successfully called on China to regulate new treatments and ensure patient safety. Despite the new rules, however, stem cell treatments are still available at over 200 hospitals across China to patients of diseases such as ataxia, Lou Gehrig's disease, traumatic brain and spinal cord injury, diabetes, Parkinson's, multiple sclerosis, autism, cerebral palsy, stroke, optic nerve hypoplasia and many others. "To our knowledge, Chinese policy makers and ethicists are working out the regulation details,” says Ms. McMahon, the study's lead author. "Once that is accomplished, we still expect a delay, during which the therapies currently administered by clinics and hospitals will be evaluated individually to determine whether they meet the criteria of China's Ministry of Health." "It is hard to say what impact these new clinical regulations will have in China, although certainly they show the government's commitment to changing the way things are done," she adds. Beike Biotechnology Inc. (Shenzhen) is the largest of the Chinese therapy centres and claims to have treated over 5,000 patients to date, including more than 900 foreigners, offering stem cell injections into spinal fluid, for example. The Stem Cell Center affiliated with Tiantan Puhua Neuroscience Hospital in Beijing, meanwhile, claims to activate and multiply the body's own neural stem cells through oral and intravenous medications and rehabilitation. It also offers a lumbar puncture or brain injection of bone marrow stem cells, foetal neural stem cells, or other stem cell types to allegedly improve symptoms of stroke, cerebral palsy, spinal injury, Parkinson's disease or other neurological diseases. Controversial stem cell therapies provided at Beijing Xishan Institute for Neuroregeneration and Functional Recovery, involve injecting cells from aborted foetuses to treat spinal cord injury and a variety of central nervous system diseases. About 1,500 patients have received this treatment, including roughly 1,000 foreigners. MRC authors say this latter stem cell therapy is the only one discussed in high-impact peer-reviewed academic journals. One study documented a spinal cord injury patient's early motor and sensory improvement; another found no improvement in seven spinal cord injury patients. Another recent publication found the therapy improved some spinal cord injuries in animals but its effectiveness in humans "is not yet established." Despite the absence of randomized clinical trial evidence that these stem cell therapies work, an "increasingly popular but controversial" tourism industry has grown up around them. "This is a matter of international importance, as increasing numbers of foreign patients travel to China to seek unproven stem cell therapies not available in their home countries," according to the MRC. "The International Society for Stem Cell Research (ISSCR) strongly condemns the administration of unproven stem cell therapies… and has written a handbook to help doctors and patients make informed decisions about available stem cell therapies." As for advice to last-resort patients considering Chinese clinic stem cell treatments: "This is not a medical study," says Dr. Singer. "Instead we urge such patients to consult their own medical professionals. The International Society for Stem Cell Research has certainly made their stance clear." "These therapies are sought out by desperate, no-option patients seeking marginal improvements in their quality of life. People should get as much information as possible before committing to any procedures. Each clinic provides a different therapy for a variety of different ailments and there is no systematic evidence that these therapies work." Chinese Firsts While unorthodox activities at Chinese clinics and controversial drug approvals have raised eyebrows both in and outside China, dedicated researchers in the country's labs have been making remarkable contributions to the field. Among the country's scientific firsts:
- By transferring the nucleus of a human skin cell into the immature ovum cell of a rabbit, researchers from a Shanghai hospital successfully produced embryonic human cells (a finding popular scientific journals held off publishing for two years due to scepticism and of mistrust Chinese scientific integrity).
- China to date has created at least 25 human embryonic stem cell lines (some estimate over 70 stem cell lines), four of which are of a specialized type that at that time only two other groups worldwide had managed to create.
- A Shanghai hospital cultivated and reintroduced human brain tissue in 2002 after taking a sample from the end of a chopstick implanted in a patient's frontal lobe following a disagreement at a restaurant.
- Several human tissue types created artificially include blood vessel, tendon, bone, cartilage, skin, cornea and muscle fibre.
Notable Research Underway Current research of note includes the efforts of ChinaSCINet, a consortium of 27 medical facilities, starting phase 2 clinical trials to test the efficacy and safety of using cord blood stem cells and oral lithium to treat about 40 patients with spinal cord injuries. Other clinical trials are underway on the use of stem cell therapies to treat patients of heart attacks, artery obstruction, and liver and neural diseases. Elsewhere in China, studies are underway on the potential use of stem cells to treat Type 1 diabetes, Parkinson's disease, heart, liver and blood diseases, eye cataracts, and to combat aging. Liberal Research Rules Guidelines governing Chinese research are liberal but common to other countries as well. Chinese regulations prohibit reproductive cloning, the use of human embryos past 14 days post-fertilization, the fusion of human and non-human gametes (cells that fuse during fertilization), or the implantation of research embryos into human or animal uterus. Researchers are required to obtain informed consent from subjects and institutes must have an ethics review board to approve research involving human embryonic stem cells. Chinese fertility clinics serve as a source of discarded embryonic stem cells for some research, and cord blood banks may serve as a source of stem cells for clinical applications. Therapeutic cloning is allowed, as is the use of surplus embryos or discarded foetal cells from abortions as well as embryos created with artificial help. "What sets China apart from most of the rest of the world is that these regulations do not prohibit the fusion of human genetic material with nonhuman oocytes (cells from which an egg or ovum develops)," the MRC authors say. As well, the rules for embryonic stem cell research in China are criticized internationally as having limited authority over researchers because they are not legally binding. Adherence is enforced only for those who receive government funding, which applies to most researchers, but financially independent researchers or hospitals must simply answer to their own institution's ethical review board. MRC authors say that while there is no indication embryonic stem cell research rules are being broken, greater regulatory oversight would help ease international concerns. Interviewees agreed that regulation enforcement is a key concern. According to one, a lack of inspection capacity cast doubt on regulatory implementation. Huge Chinese Investment in RM Chinese data show the country now generates 400,000 graduates in science and medicine each year and recruits many high calibre scientists from abroad. China’s gross domestic expenditure on R&D in science and technology has grown from $5.9 billion in 1996 to $44 billion today. Stem cell research, tissue engineering and gene therapy are key areas receiving priority funding, largely centralized in the universities, hospitals and research institutes of China's main urban centres, especially in Beijing and Shanghai. Approximately 78% of China's R&D funding in RM is reserved for product development, with an additional 16.8% for applied research. In addition, China has developed large primate colonies for preclinical testing, and begun clinical trials for a number of therapies. According to the MRC, China's push for clinical applications, which has allowed it to produce new scientific knowledge quickly, has come at the expense of basic research aimed at, for example, overcoming technical challenges such as controlling how stem cells behave and differentiate. Only 5.2% of China's budget for research and development is allocated to basic research, compared with 13 to 19% in Japan, Korea and the USA. Even the funds allocated for basic research favour 'strategic basic research' designed to encourage application. China's Recruitment Policy A Model for Other Developing Countries "China has catapulted itself into the field of regenerative medicine in a relatively short time," says Dr. Thorsteinsdóttir. "The government's policy of attracting highly educated Chinese nationals back to China has contributed significantly to the country's success in the field." "I was amazed that almost all the top Chinese researchers the regenerative medicine field had been educated in the US and the UK and gained extensive working experience there in cutting edge research," she adds. "This is a policy other countries lacking relevant human resources should consider." "New regulations may in time help restore international confidence in Chinese stem cell innovations, but it will take time to evaluate their impact," says Dr. Daar. "The creation of new RM therapies needs a clear regulatory path. There should also be a closer connection between applied research and those providing therapy." "China is an important player in regenerative medicine," says Ms. McMahon. "Despite the media's focus on stem cell tourism, the international community needs to recognize that Chinese researchers are making important contributions to the science of this field, and China should be included in international discourses on standards and regulations." "Regenerative medicine research in China is a source of national pride," she adds. "The Chinese rightly feel their research discoveries can achieve solutions to many global health problems. If China continues to build on its strengths and overcomes its challenges, successful, internationally acclaimed regenerative medicine treatments and therapies are more than likely." This release is available in
Chinese. ......... ZenMasterFor more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Thursday, 7 January 2010
Efficient Genetic Modification of Human Embryonic Stem Cells
Efficient Genetic Modification of Human Embryonic Stem Cells
Thursday, 07 January 2010
Biologists have developed an efficient way to genetically modify human embryonic stem cells. Their approach, which uses bacterial artificial chromosomes to swap in defective copies of genes, will make possible the rapid development of stem cell lines that can both serve as models for human genetic diseases and as testbeds on which to screen potential treatments, they say.
"This will help to open up the whole human embryonic stem cell field. Otherwise, there's really few efficient ways you can study genetics with them," said Yang Xu, professor of biology at the University of California, San Diego who directed the research. Xu and co-authors Hoseok Song and Sun-Ku Chung, both postdoctoral fellows in Xu's research group, describe their technique in the January 8 issue of the journal Cell Stem Cell.
Most attempts to alter the genetic makeup of the cells have proved too inefficient, Xu said. His group used bacterial artificial chromosomes, or BACs, to improve the yield.
BACs are synthesized circles of human DNA, which bacteria will replicate just like their own native chromosomes. Commercially available BACs can be modified within bacterial cells to insert altered copies of specific genes. Once the modified BACs are introduced into human cells, they will sometimes pair up with a matching segment of a human chromosome and swap segments of DNA, a process called homologous recombination.
The advantage of using BACS to alter the genetic code in human cells comes from the long flanking sequences on either side of the modified gene, which increases the chance that the BAC with line up with native DNA in position for a swap. Other genetic approaches have been limited by shorter segments of DNA.
Using BACs, the team was able to substitute modified genes in 20 percent of treated cells. Standard methods of genetic modification typically achieve modification in fewer than one percent of cells, Xu said.
His group successfully transferred a defective copy of the gene p53, which suppresses cancer, into a human embryonic stem cell line. By repeating the process in a second round, they developed a line of cells in which both copies of the genes were disrupted.
They also report success with a different gene, ATM, which when mutated in humans causes Ataxia-telangiectasia, a disease characterized by a host of systemic defects including increased cancer risk, degeneration of specific types of brain cells and degraded telomeres, the protective caps at the end of each chromosome.
Genetically engineered mice with two bad copies of the ATM gene share some of these traits with human patients, but not all. Neurons do not degenerate in ATM mice, for example, and the telomeres are long.
"If you want to study accelerated shortening of telomeres, you can't do it in the mouse. You can only do it in human cells," Xu said.
Those differences propelled Xu's group to develop human cell lines instead, with the hope that some of the processes that go wrong in human patients could be studied in the lab. Already, they have demonstrated that their ATM-deficient embryonic stem cell line has damaged telomeres. Other characteristics, such as the degeneration of specific types of neurons, will be the subject of future experiments, Xu said.
The authors say their approach can easily be adapted to modify other human genes within other stem cells lines. For their initial work, Xu's group used a cell line that easily forms new colonies from single cells, but they also repeated the procedure in a cell line called H9, which has proved difficult to manipulate.
Because H9 was among the few cells lines approved for use by researchers funded by the federal government before new lines began to be approved in mid-December 2009, many researchers already have considerable experience with coaxing the cells into differentiating into specific types of tissues, for example, which would make the ability to genetically modify them particularly valuable.
Reference:
Modeling Disease in Human ESCs Using an Efficient BAC-Based Homologous Recombination System
Hoseok Song, Sun-Ku Chung, Yang Xu
Cell Stem Cell, Volume 6, Issue 1, 80-89, 8 January 2010, 10.1016/j.stem.2009.11.016
.........
ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
Protein Complex Crucial for Triggering Embryo Development
Enzyme wipes developmental slate clean, giving cells a fresh start
Thursday, 07 January 2010
The DNA contained within each of our cells is exactly the same, yet different types of cells – skin cells, heart cells, brain cells – perform very different functions. The ultimate fate of these cells is encoded not just in the DNA, but in a specific pattern of chemical modifications that overlay the DNA structure. These modifications, or epigenetic markers as they are called, are stably carried in our genomes – except for at times when the cells change their fate, such as what occurs when the sperm meets the egg. Then they are erased completely.
Researchers at the UNC School of Medicine have discovered a protein complex that appears to play a significant role in erasing these epigenetic instructions on sperm DNA, essentially creating a blank slate for the different cell types of a new embryo to develop. The protein complex – called elongator – could prove valuable for changing cell fate, such as converting cancer cells to normal cells, as it may be able to reactivate tumor suppressor genes by removing the epigenetic modifications that often prevent them from curbing the proliferation of cancer cells.
The discovery may also have implications for stem cell research by providing a tool to quickly reprogram adult cells to possess the same attributes as embryonic stem cells, but without the ethical or safety issues of cells currently used for such studies. The results of the study appear on-line in the Jan. 6, 2010 issue of the journal Nature.
"The implications of such research have always been clear, and that is why for years researchers have tried to identify a factor responsible for erasing these epigenetic markers," said senior author Yi Zhang, Ph.D., Howard Hughes Medical Institute Investigator and Kenan Distinguished Professor of biochemistry and biophysics at UNC. He is also a member of the UNC Lineberger Comprehensive Cancer Center.
Epigenetic markers are essentially chemical tags attached to the genomes of each cell, determining which genes will be turned on or off and, ultimately, what role that cell type will have in the body. One way this comes about is through DNA methylation, a process by which methyl groups are stamped onto cytosine – one of the four bases of DNA – to produce a characteristic pattern for a particular cell.
During fertilization, the paternal genome derived from the sperm is actively demethylated, removing these methyl tags quickly before cell division, while the maternal genome is demethylated passively. The new methylation pattern will be re-established at a later stage.
"Several previous studies have identified factors that can perform gene-specific DNA demethylation, but ours is the first to link a protein complex to global DNA demethylation that correlates to germ cell to somatic cell transition," Zhang said.
The UNC scientist and his colleagues sought to discover the factor that orchestrates this demethylation. By creating a green fluorescent tag that has affinity to non-methylated DNA, they were able to "watch" the demethylation process under the microscope. With that technology in hand, they began to fish through a dozen candidate factors that they believed could play a role in the process, based on their chemical properties and expression patterns in zygotes, cells formed by the union of sperm and egg.
When they "knocked down" these candidate genes in zygotes, only the loss of the elongator gene prevented the accumulation of the fluorescent tags in the paternal genome, indicating that it was needed for demethylation to occur. The researchers performed a number of experiments to confirm their findings, including sequencing the paternal genome to determine changes in the DNA methylation status.
Zhang says the identification of this gene could have implications for stem cell research, which up until this point has only been possible using two major approaches. One way scientists reprogram adult cell nuclei is by transferring them into an egg, which contains factors that wipe away all epigenetic markers. The other way is to express several critical stem cell factors in adult somatic cells, which coax the cells back to their virginal stem cell state. The first approach involves the use of embryos, which raises ethical concerns; the second involves retroviruses, which can cause cancer and are thus not considered safe.
"But there could be another way," says Zhang.
"Many of the genes that are active in stem cells are not active in adult cells because they are methylated. If elongator can catalyze global demethylation, it could be the critical ingredient to these reprogramming cocktails, enabling us to generate stem cells quickly and safely."
Now Zhang and his colleagues are conducting biochemical experiments to prove that the protein does possess true demethylase activity. It will be a difficult task, Zhang says, because they still do not know all the subunits of the elongator protein complex. At the same time, the researchers are actively investigating the effects of the protein on reprogramming and its implications for stem cell research.
Reference:
A role for the elongator complex in zygotic paternal genome demethylation
Yuki Okada, Kazuo Yamagata, Kwonho Hong, Teruhiko Wakayama & Yi Zhang
Nature advance online publication 6 January 2010, doi:10.1038/nature08732
.........
ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/
The DNA contained within each of our cells is exactly the same, yet different types of cells – skin cells, heart cells, brain cells – perform very different functions. The ultimate fate of these cells is encoded not just in the DNA, but in a specific pattern of chemical modifications that overlay the DNA structure. These modifications, or epigenetic markers as they are called, are stably carried in our genomes – except for at times when the cells change their fate, such as what occurs when the sperm meets the egg. Then they are erased completely.
Researchers at the UNC School of Medicine have discovered a protein complex that appears to play a significant role in erasing these epigenetic instructions on sperm DNA, essentially creating a blank slate for the different cell types of a new embryo to develop. The protein complex – called elongator – could prove valuable for changing cell fate, such as converting cancer cells to normal cells, as it may be able to reactivate tumor suppressor genes by removing the epigenetic modifications that often prevent them from curbing the proliferation of cancer cells.
The discovery may also have implications for stem cell research by providing a tool to quickly reprogram adult cells to possess the same attributes as embryonic stem cells, but without the ethical or safety issues of cells currently used for such studies. The results of the study appear on-line in the Jan. 6, 2010 issue of the journal Nature.
"The implications of such research have always been clear, and that is why for years researchers have tried to identify a factor responsible for erasing these epigenetic markers," said senior author Yi Zhang, Ph.D., Howard Hughes Medical Institute Investigator and Kenan Distinguished Professor of biochemistry and biophysics at UNC. He is also a member of the UNC Lineberger Comprehensive Cancer Center.
Epigenetic markers are essentially chemical tags attached to the genomes of each cell, determining which genes will be turned on or off and, ultimately, what role that cell type will have in the body. One way this comes about is through DNA methylation, a process by which methyl groups are stamped onto cytosine – one of the four bases of DNA – to produce a characteristic pattern for a particular cell.
During fertilization, the paternal genome derived from the sperm is actively demethylated, removing these methyl tags quickly before cell division, while the maternal genome is demethylated passively. The new methylation pattern will be re-established at a later stage.
"Several previous studies have identified factors that can perform gene-specific DNA demethylation, but ours is the first to link a protein complex to global DNA demethylation that correlates to germ cell to somatic cell transition," Zhang said.
The UNC scientist and his colleagues sought to discover the factor that orchestrates this demethylation. By creating a green fluorescent tag that has affinity to non-methylated DNA, they were able to "watch" the demethylation process under the microscope. With that technology in hand, they began to fish through a dozen candidate factors that they believed could play a role in the process, based on their chemical properties and expression patterns in zygotes, cells formed by the union of sperm and egg.
When they "knocked down" these candidate genes in zygotes, only the loss of the elongator gene prevented the accumulation of the fluorescent tags in the paternal genome, indicating that it was needed for demethylation to occur. The researchers performed a number of experiments to confirm their findings, including sequencing the paternal genome to determine changes in the DNA methylation status.
Zhang says the identification of this gene could have implications for stem cell research, which up until this point has only been possible using two major approaches. One way scientists reprogram adult cell nuclei is by transferring them into an egg, which contains factors that wipe away all epigenetic markers. The other way is to express several critical stem cell factors in adult somatic cells, which coax the cells back to their virginal stem cell state. The first approach involves the use of embryos, which raises ethical concerns; the second involves retroviruses, which can cause cancer and are thus not considered safe.
"But there could be another way," says Zhang.
"Many of the genes that are active in stem cells are not active in adult cells because they are methylated. If elongator can catalyze global demethylation, it could be the critical ingredient to these reprogramming cocktails, enabling us to generate stem cells quickly and safely."
Now Zhang and his colleagues are conducting biochemical experiments to prove that the protein does possess true demethylase activity. It will be a difficult task, Zhang says, because they still do not know all the subunits of the elongator protein complex. At the same time, the researchers are actively investigating the effects of the protein on reprogramming and its implications for stem cell research.
Reference:
A role for the elongator complex in zygotic paternal genome demethylation
Yuki Okada, Kazuo Yamagata, Kwonho Hong, Teruhiko Wakayama & Yi Zhang
Nature advance online publication 6 January 2010, doi:10.1038/nature08732
.........
ZenMaster For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/