Stem Cells Make Similar Decisions to Humans

Stem Cells Make Similar Decisions to Humans

Wednesday, 25 March 2015

Pancreas explant. 

Scientists at the University of Copenhagen have captured thousands of progenitor cells of the pancreas on video. They have filmed the cells making decisions to both divide and expand the organ or to specialize into the endocrine cells that regulate our blood sugar levels.

The new study reveals that stem cells behave as people in a society, making individual choices but with enough interactions to bring them to their end-goal. The results could eventually lead to a better control over the production of insulin-producing endocrine cells for diabetes therapy.

The research is published in the scientific journal PLOS Biology.

Why one cell matters

In a joint collaboration between the University of Copenhagen and University of Cambridge, Professor Anne Grapin- Botton and a team of researchers including Assistant Professor Yung Hae Kim from DanStem focused on marking the progenitor of the embryonic pancreas, commonly referred to as ‘mothers’, and their ‘daughters’ in different fluorescent colours and then captured them on video to analyse how they make decisions.

Prior to this work, there were methods to predict how specific types of pancreas cells would evolve as the embryo develops. However, by looking at individual cells, the scientists found that even within one group of cells presumed to be of the same type, some will divide many times to make the organ bigger while others will become specialized and will stop dividing.

The scientists witnessed interesting occurrences where the ‘mother’ of two ‘daughters’ made a decision and passed it on to the two ‘daughters’ who then acquired their specialization in synchrony. By observing enough cells, they were able to extract logic rules of decision-making, and with the help of Dr Pau Rué, a mathematician from the University of Cambridge, they developed a mathematical model to make long-term predictions over multiple generations of cells.

Stem cell movies

"It is the first time we have made movies of a quality that is high enough to follow thousands of individual cells in this organ, for periods of time that are long enough for us to follow the slow decision process. The task seemed daunting and technically challenging, but fascinating,” says Professor Grapin-Botton. 

"With these movies we can see and quantify the dynamics of decisions in each cell in the context of the organ, in a way that will inspire the study of many other organs," says Assistant Professor Yung Hae Kim.

"To complement the movies, which are done on isolated pancreas, we developed a method to visualize the family tree of cells in the untouched organ. We initially focused on one generation but now we are also observing their descendants over multiple generations," Kim elaborates.

Next steps in diabetes therapy

The project has been focused on basic research and is highly theoretical, but it now provides tools to control whether a cell should expand or specialize into an endocrine cell on its way to producing insulin.

“It is a worldwide quest to produce such insulin-producing cells from stem cells, for their transplantation in diabetic patients. In the future, this could be done by increasing the probability of specialization or by pushing ‘mother’ cells to pass on the decision to specialize to their two daughters”, Grapin-Botton concludes.

Source: University of Copenhagen

Contact: Yung Hae Kim

Reference:

Cell Cycle–Dependent Differentiation Dynamics Balances Growth and Endocrine Differentiation in the Pancreas

Yung Hae Kim , Hjalte List Larsen, Pau Rué, Laurence A. Lemaire, Jorge Ferrer and Anne Grapin-Botton 

PLOS Biology, March 18, 2015, DOI: 10.1371/journal.pbio.1002111

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Tumour Suppressor Also Inhibits Key Property of Stem Cells

Tumour Suppressor Also Inhibits Key Property of Stem Cells

Friday, 14 November 2014

A protein that plays a critical role in preventing the development of many types of human cancers has been shown also to inhibit a vital stem cell property called pluripotency, according to a study by researchers at the Stanford University School of Medicine.

Blocking expression of the protein, called retinoblastoma, in mouse cells allowed the researchers to more easily transform them into what are known as induced pluripotent stem cells, or iPS cells. Pluripotent is a term used to describe a cell that is similar to an embryonic stem cell and can become any tissue in the body.

The study provides a direct and unexpected molecular link between cancer and stem cell science through retinoblastoma, or Rb, one of the best known of a class of proteins called tumour suppressors. Although Rb has long been known to control the rate of cell division, the researchers found that it also directly binds and inhibits the expression of genes involved in pluripotency.

"We were very surprised to see that retinoblastoma directly connects control of the cell cycle with pluripotency," said Julien Sage, PhD, associate professor of paediatrics and of genetics.

"This is a completely new idea as to how retinoblastoma functions. It physically prevents the reacquisition of stem cell-ness and pluripotency by inhibiting gene expression."

"The loss of Rb appears to directly change a cell's identity. Without the protein, the cell is much more developmentally fluid and is easier to reprogram into an iPS cell," said Marius Wernig, MD, associate professor of pathology.

Wernig and Sage, both members of the Stanford Cancer Institute, share senior authorship of the study, which will be published online Nov. 13 in Cell Stem Cell. Postdoctoral scholar Michael Kareta, PhD, is the lead author.

Tumour Suppressor

Pluripotent stem cells are able to become any tissue in the body. In 2006, researchers in Shinya Yamanaka's laboratory in Kyoto University found that it's possible to push a fully specialized adult cell, such as a skin cell, backward along the developmental pathway to assume a pluripotent state. They did so by adding four proteins – Sox2, Oct4, c-Myc and Klf4 – that are normally found in cells only very early in embryonic development. The resulting cells were called induced pluripotent stem cells.

Rb was first identified as a tumour suppressor because of its role in a rare but rapidly developing childhood cancer of the retina. It has since been shown to be missing or functionally inactive in nearly all human cancers. Intact Rb prevents cancer by acting as a natural brake on the cell cycle, the process by which cells divide to make daughter cells. Loss of Rb allows a cell to divide more quickly and potentially accumulate more cancer-causing mutations. However, the new research shows that Rb's effect on pluripotency is independent of its role in cell cycle control.

Cancerous cells often appear less mature than their noncancerous peers. They persist in dividing in the face of external cues that curb the proliferation of normal cells, and they often seem to regress developmentally, assuming the form and mimicking the behaviour of their more developmentally flexible ancestors. A similar cascade of events occurs when researchers create iPS cells from specialized adult cells.

"The process of creating iPS cells from fully differentiated, or specialized, cells is in many ways very similar to what happens when a cell becomes cancerous," said Sage, who holds the Harriet and Mary Zelencik Endowed Professorship in Pediatrics.

"We wondered if we could learn more about both processes by investigating whether the loss of Rb affects reprogramming efficiency."

Previous studies in other laboratories have suggested that Rb may also be involved in promoting cellular differentiation – a cell's developmental progression toward a more specialized state.

Link between Rb and Pluripotency

The researchers found that embryonic mouse cells unable to express functional Rb were much more efficiently and quickly converted to iPS cells than were cells in which Rb was present. Conversely, cells with higher-than-normal levels of the Rb protein were more difficult to reprogram into iPS cells. When the researchers compared the rate of division of the control cells with those in which Rb expression was lost, they found no significant differences.

"It didn't change the cell proliferation rates at all," said Wernig.

"This indicated that Rb's mechanism of action on reprogramming was something completely different than what we had expected."

Further investigation showed that Rb directly binds to many genes involved in the acquisition of pluripotency, including those encoding two of the proteins often used by researchers to create iPS cells: Sox2 and Oct4. Loss of Rb increased the expression of the proteins, thereby affecting a large "pluripotency network."

"We saw a global effect on a network of genes involved in pluripotency," said Sage.

The net effect, according to the researchers, is an overall reduction in the natural barrier that exists to prevent specialized adult cells from dedifferentiating – that is, spontaneously becoming pluripotent, an occurrence that could easily wreak havoc on a multicellular organism that depends on an orderly arrangement of tissues.

The researchers also showed that Rb's effect on the pluripotency network is an important driver of cancer in a mouse model. Animals in which Rb expression is blocked typically develop pituitary tumours within a few months. However, the researchers found the cancers didn't occur when Sox2 was also removed.

"It's clear that Sox2 expression is also required for the development of cancers in the animals," said Wernig.

"This implies that Rb's effect on Sox2 expression is critical for cancer development."

The researchers plan to continue their investigations into the relationship between Rb and pluripotency. In particular, Wernig is interested in learning whether Rb expression plays a role in a phenomenon he discovered called direct conversion, in which one cell type, such as a skin cell, can be directly converted into another, such as a neuron, without first entering a pluripotent state.

Source: Stanford University Medical Center

Contact: Krista Conger

Reference:

Inhibition of Pluripotency Networks by the Rb Tumor Suppressor Restricts Reprogramming and Tumorigenesis

Michael S. Kareta, Laura L. Gorges, Sana Hafeez, Bérénice A. Benayoun, Samuele Marro, Anne-Flore Zmoos, Matthew J. Cecchini, Damek Spacek, Luis F.Z. Batista, Megan O’Brien, Yi-Han Ng, Cheen Euong Ang, Dedeepya Vaka, Steven E. Artandi, Frederick A. Dick, Anne Brunet, Julien Sage, Marius Wernig

Cell Stem Cell, November 13, 2014, DOI: http://dx.doi.org/10.1016/j.stem.2014.10.019

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ZenMaster

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Stem Cells Hold Keys to Body's Plan

Case Western Reserve University research team discovers 'seeds' of stem cells' development

Thursday, 05 June 2014

Case Western Reserve researchers have discovered landmarks within pluripotent stem cells that guide how they develop to serve different purposes within the body. This breakthrough offers promise that scientists eventually will be able to direct stem cells in ways that prevent disease or repair damage from injury or illness. The study and its results appear in the June 5 edition of the journal Cell Stem Cell.

Pluripotent stem cells are so named because they can evolve into any of the cell types that exist within the body. Their immense potential captured the attention of two accomplished faculty with complementary areas of expertise.

“We had a unique opportunity to bring together two interdisciplinary groups,” said co-senior author Paul Tesar, PhD, Assistant Professor of Genetics and Genome Sciences at CWRU School of Medicine and the Dr. Donald and Ruth Weber Goodman Professor.

"We have exploited the Tesar lab’s expertise in stem cell biology and my lab’s expertise in genomics to uncover a new class of genetic switches, which we call seed enhancers,” said co-senior author Peter Scacheri, PhD, Associate Professor of Genetics and Genome Sciences at CWRU School of Medicine.

“Seed enhancers give us new clues to how cells morph from one cell type to another during development."

The breakthrough came from studying two closely related stem cell types that represent the earliest phases of development — embryonic stem cells and epiblast stem cells, first described in research by Tesar in 2007.

“These two stem cell types give us unprecedented access to the earliest stages of mammalian development,” said Daniel Factor, graduate student in the Tesar lab and co-first author of the study.

Olivia Corradin, graduate student in the Scacheri lab and co-first author, agrees.

“Stem cells are touted for their promise to make replacement tissues for regenerative medicine,” she said.

“But first, we have to understand precisely how these cells function to create diverse tissues.”

Enhancers are sections of DNA that control the expression of nearby genes. By comparing these two closely related types of pluripotent stem cells (embryonic and epiblast), Corradin and Factor identified a new class of enhancers, which they refer to as seed enhancers. Unlike most enhancers, which are only active in specific times or places in the body, seed enhancers play roles from before birth to adulthood.

They are present, but dormant, in the early mouse embryonic stem cell population. In the more developed mouse epiblast stem cell population, they become the primary enhancers of their associated genes. As the cells mature into functional adult tissues, the seed enhancers grow into super enhancers. Super enhancers are large regions that contain many enhancers and control the most important genes in each cell type.

“These seed enhancers have wide-ranging potential to impact the understanding of development and disease,” said Stanton Gerson, MD, Asa & Patricia Shiverick and Jane Shiverick (Tripp) Professor of Hematological Oncology and Director of the National Center for Regenerative Medicine at Case Western Reserve University.

“In the stem cell field, this understanding should rapidly enhance the ability to generate clinically useful cell types for stem cell-based regenerative medicine.”

“Our next step is to understand if miss-regulation of these seed enhancers might play a role in human diseases,” Tesar said.

“The genes controlled by seed enhancers are powerful ones, and it’s possible that aberrations could contribute to things like heart disease or neurodegenerative disorders.”

“It is also clear that cancer can be driven by changes in enhancers, and we are interested in understanding the role of seed enhancers in cancer onset and progression,” Scacheri added.

Source: Case Western Reserve University 

Contact: Jeannette Spalding

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ZenMaster

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Automated Tissue Engineering on Demand

Automated Tissue Engineering on Demand Monday, 18 May 2009 Skin from a factory – this has long been the dream of pharmacologists, chemists and doctors. Research has an urgent need for large quantities of 'skin models', which can be used to determine if products such as creams and soaps, cleaning agents, medicines and adhesive bandages are compatible with skin, or if they instead will lead to irritation or allergic reactions for the consumer. Such test results are seen as more meaningful than those from animal experiments are, and can even make such experiments largely superfluous. But artificial skin is rare. "The production is complex and involves a great deal of manual work. At this time, even the market's established international companies cannot produce more than 2,000 tiny skin pieces a month. With annual requirements of more than 6.5 million units in the EU area alone, however, the industrial demand far exceeds all currently available production capacities," reports Jörg Saxler. Together with Prof. Heike Mertsching, he is coordinating the "Automated Tissue Engineering on Demand" project within the Fraunhofer-Gesellschaft. Tissue engineering is still in its infancy. "Until now, the offer was limited predominantly to single-layer skin models that consist of a single cell type," explains Mertsching, who heads the Cell Systems Department at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB. "Thanks to developments at our institute, the project team has access to a patent-protected skin model that consists of two layers with different cell types. This gives us an almost perfect copy of human skin, and one that provides more information than any system currently available on the market." An interdisciplinary team of Fraunhofer researchers is currently developing the first fully automatic production system for two-layer skin models. "Our engineers and biologists are the only ones who have succeeded in fully automating the entire process chain for manufacturing two-layer skin models," explains Saxler, who is from the Fraunhofer Institute for Production Technology IPT where he is responsible for technology management and heads the "Life Science Engineering" business unit. In a multi-stage process, first small pieces of skin are sterilized. Then they are cut into small pieces, modified with specific enzymes, and isolated into two cell fractions, which are then propagated separately on cell culture surfaces. The next step in the process combines the two cell types into a two-layer model, with collagen added to the cells that are to form the flexible lower layer, or dermis. This gives the tissue natural elasticity. In a humid incubator kept at body temperature, it takes the cell fractions less than three weeks to grow together and form a finished skin model with a diameter of roughly one centimetre. The technique has already proven its use in practice, but until now, it has been too expensive and complicated for mass production. Mertsching explains, "The production is associated with a great deal of manual work, and this reduces the method's efficiency." The project team, in which engineers, scientists and technicians from four Fraunhofer institutes are cooperating, is currently working at full speed to automate the work steps. The researchers at the IGB and the Fraunhofer Institute for Cell Therapy and Immunology IZI are handling the development of the biological fundamentals and validation of the machine and its sub-modules. Experts from the Fraunhofer Institute for Manufacturing and Automation IPA and the Fraunhofer Institute for Production Technology IPT are taking care of prototype development, automation and integration of the machine into a complete functional system. "At the beginning, our greatest challenge was to overcome existing barriers, because each discipline had its own very different approach," Saxler remembers. "Meanwhile, the four institutes are working together very smoothly – everyone knows that progress is impossible without input from the others." After working together for one year, the project team has already initiated eight patent procedures. At a collective Fraunhofer-Gesellschaft booth at the 2009 BIO in Atlanta, the researchers are presenting a computer model of the overall system, along with the three fundamental sub-modules. The first module prepares the tissue samples and isolates the two cell types; the second proliferates them. The finished skin models are built up and cultivated in the third, and then packed by a robot. The researchers still have a lot of meticulous work ahead before the machine will be finished. The difference between success and failure often depends on details, such as the quality of the skin pieces, processing times of enzymes, and liquid viscosities. Furthermore, the cell cultures must be monitored throughout the entire manufacturing process in order to provide optimal process control and to allow timely detection of any contamination with fungi or bacteria. The skin factory is expected to be finished in two years. "Our goal is a monthly production of 5,000 skin models with perfect quality, and a unit price under 34 euros. These are levels that are attractive for industry," Saxler continues. But chemical, cosmetic, pharmaceutical, and medical technology companies who have to test the reaction of skin to their products are not the only ones interested in Automated Tissue Engineering. In transplantation medicine, surgeons require healthy tissue in order to replace destroyed skin sections when burn injuries cover large portions of the body. The two-layer models that the new machine is intended to produce are not yet suitable for this purpose, however. "They don't have a blood supply, and are consequently rejected by the body after some time," Saxler explains. However, IGB researchers are already working on a full-skin model that will even include blood vessels. Once the research has been completed, fully automatic production of the transplants should also be possible. "We have designed the production system in such a way that it satisfies the high standards for good manufacturing practices (GMP) for the manufacture of products used in medicine," Mertsching explains. "And so they are also suitable for producing artificial skin for transplants." ......... ZenMaster

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For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/ and http://www.geocities.com/giantfideli/index.html

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A New Method for Bone-marrow-derived Liver Stem Cells Isolation

Researchers designed a culture system to isolate, proliferate and differentiate liver stem cells directly from bone marrow cells. Thursday, 16 April 2009 Great interest has been aroused in the identification and isolation of liver stem cells from bone marrow cells. Several subsets of bone marrow cells have been found to have the potential to differentiate into hepatocytes, however, sorting based on immunological methods is difficult because of the complicated surface markers of the stem cells; furthermore, no report of successful passage has been published. A research article to be published on April 7, 2009 in the World Journal of Gastroenterology addresses this question. The research team led by Dr. Yun-Feng Cai and his colleagues from the Affiliated Foshan Hospital and the Second Affiliated Hospital of Sun Yat-sen University established a carefully designed culture system to isolate, proliferate and differentiate liver stem cells directly from bone marrow cells, and they were able to achieve six passages of the stem cells. The results suggest that BDLSCs can be purified and passaged (proliferated). The selecting culture system that contains cholestatic serum can purify BDLSCs directly from bone marrow cells, which provides an easy method to separate stem cells, by avoiding complicated immunological manipulation. The successful passage of the stem cells further verifies the proliferating ability of the cells, although the passage is limited, and further research will provide more experience. In this study, the authors used their original method to retrieve the cells, which are possibly BDLSCs. Then, they used fluorescence-activated cell sorting to determine the cells' characteristics before and after differentiation. This is an interesting and potentially important study, which suggests that bone-marrow-derived cells can be stimulated to expand and then differentiate into hepatocyte-like cells, which can possibly be used to treat liver disease. Reference: Passage of bone marrow-derived liver stem cells with a proliferating culture system Yun-Feng Cai, Ji-Sheng Chen, Shu-Ying Su, Zuo-Jun Zhen, Huan-Wei Chen World J Gastroenterol 2009, 15(13): 1630-1635 ......... ZenMaster

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