Study Reveals the Genetic Start-up of a Human Embryo

Study Reveals the Genetic Start-up of a Human Embryo

Thursday, 03 September 2015

An international team of scientists led from Sweden’s Karolinska Institutet has for the first time mapped all the genes that are activated in the first few days of a fertilised human egg. The study, which is being published in the journal Nature Communications, provides an in-depth understanding of early embryonic development in human – and scientists now hope that the results will help finding for example new therapies against infertility.

At the start of an individual’s life there is a single fertilised egg cell. One day after fertilisation there are two cells, after two days four, after three days eight and so on, until there are billions of cells at birth. The order in which our genes are activated after fertilisation has remained one of the last uncharted territories of human development.

Juha Kere is a Professor of Molecular Genetics at

Karolinska Institutet. Credit: Ulf Sirborn.

There are approximately 23,000 human genes in total. In the current study, scientists found that only 32 of these genes are switched on two days after fertilization, and by day three there are 129 activated genes. Seven of the genes found and characterised had not been discovered previously.

“These genes are the ‘ignition key’ that is needed to turn on human embryonic development. It is like dropping a stone into water and then watching the waves spread across the surface”, says principal investigator Juha Kere, professor at theDepartment of Biosciences and Nutrition at Karolinska Institutet and also affiliated to the SciLifeLab facility in Stockholm.

The researchers had to develop a new way of analysing the results in order to find the new genes. Most genes code for proteins but there are a number of repeated DNA sequences that are often considered to be so-called ‘junk DNA’, but are in fact important in regulating gene expression.

Treatment of infertility

In the current study, the researchers show that the newly identified genes can interact with the ‘junk DNA’, and that this is essential to the start of development.

Outi Hovatta is a Professor of Obstetrics and

Gynaecology at Karolinska Institutet. Credit:

Ulf Sirborn.

“Our results provide novel insights into the regulation of early embryonic development in human. We identified novel factors that might be used in reprogramming cells into so-called pluripotent stem cells for possible treatment of a range of diseases, and potentially also in the treatment of infertility”, says Outi Hovatta, professor at Karolinska Institutet’s Department of Clinical Science, Intervention and Technology, and a senior author.

The study was a collaboration between three research groups from Sweden and Switzerland that each provided a unique set of skills and expertise. The work was supported by the Karolinska Institutet Distinguished Professor Award, the Swedish Research Council, the Strategic Research Program for Diabetes funding at Karolinska Institutet, Stockholm County, the Jane & Aatos Erkko Foundation, the Instrumentarium Science Foundation, and the Åke Wiberg and Magnus Bergvall foundations. The computations were performed on resources provided by SNIC through Uppsala Multidisciplinary Center for Advanced Computational Science (UPPMAX).

Source: Karolinska Institutet

Contact: KI Press Office

Reference:

Novel PRD-like homeodomain transcription factors and retrotransposon elements in early human development

Virpi Töhönen, Shintaro Katayama, Liselotte Vesterlund, Eeva-Mari Jouhilahti, Mona Sheikhi, Elo Madissoon, Giuditta Filippini-Cattaneo, Marisa Jaconi, Anna Johnsson, Thomas R. Bürglin, Sten Linnarsson, Outi Hovatta and Juha Kere

Nature Communications, 3 September 2015, doi: 10.1038/NCOMMS9207

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The ISSCR Issues Statement on Human Germ Line Genome Modification

The International Society for Stem Cell Research has released a statement calling for a moratorium on attempts to apply nuclear genome editing of the human germ line in clinical practice

Sunday, 22 March 2015

In a statement released on Thursday, the International Society for Stem Cell Research called for a moratorium on attempts at clinical application of nuclear genome editing of the human germ line to enable more extensive scientific analysis of the potential risks of genome editing and broader public discussion of the societal and ethical implications.

Technologies used to introduce changes into the DNA sequence of cells have advanced rapidly, making genome editing increasingly simple. Genome editing is feasible, not just in the somatic cells of an adult organism, but also in early embryos, as well as the gametes (sperm and egg) that carry the inheritable, germ line DNA. Research involving germ line nuclear genome editing has been performed to date in many organisms, including mice and monkeys, and applications to human embryos are possible.

The ISSCR statement raises significant ethical, societal and safety considerations related to the application of nuclear genome editing to the human germ line in clinical practice. Current genome editing technologies carry risks of unintended genome damage, in addition to unknown consequences. Moreover, consensus is lacking on what, if any, therapeutic applications of germ line genome modification might be permissible.

The statement calls for a moratorium on attempts to apply nuclear genome editing of the human germ line in clinical practice, as scientists currently lack an adequate understanding of the safety and potential long term risks of germ line genome modification. Moreover, the ISSCR asserts that a deeper and more rigorous deliberation on the ethical, legal and societal implications of any attempts at modifying the human germ line is essential if its clinical practice is ever to be sanctioned.

In calling for the above moratorium, the ISSCR is not taking a position on the clinical testing of mitochondrial replacement therapy, a form of germ line modification that entails replacing the mitochondria (found outside the nucleus) in the eggs of women at risk of transmitting certain devastating diseases to their children.

Source: International Society for Stem Cell Research

Contact: Michelle Quivey

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Mitochondrial Donation: How Many Women Could Benefit?

Two and a Half Thousand Women Could Benefit from Mitochondrial Donation in the UK

Thursday, 29 January 2015

Almost 2,500 women of child-bearing age in the UK are at risk of transmitting mitochondrial disease to their children, according to the most recent estimates published today in the New England Journal of Medicine.

The research offers the most recent evidence yet of how many families could potentially be helped by new IVF techniques to prevent mitochondrial disease, which would be permitted by new regulations on which a vote in parliament is imminent.

Mitochondrial diseases are caused by inherited mutations in the DNA contained in mitochondria - tiny structures present in every cell that generate energy. Mitochondrial diseases can be devastating and particularly affect tissues that have high energy demands - brain, muscle (including heart), liver and kidney.

New IVF-based techniques have been developed which have the potential to prevent the transmission of serious mitochondrial disease. Known as 'mitochondrial donation' the techniques involve removing faulty mitochondria inherited from the mother and replacing them with the healthy mitochondria of another woman. The nuclear DNA, containing 99.9% of genetic material from the mother and father, remains unchanged.

Researchers at the Wellcome Trust Centre for Mitochondrial Research at Newcastle University, which will be the first to offer mitochondrial donation if parliament agrees to new regulations of the Human Fertilisation and Embryology Act (1990), have now calculated how many women have disease-causing mutations in their mitochondrial DNA in order to estimate how many could potentially benefit. The new regulations only allow for mitochondrial donation to prevent mitochondrial disease and set no precedent for genetic manipulation of nuclear DNA.

They calculate that 2,473 women in the UK, and 12,423 women in the US, aged between 15 and 44 years, are at risk of passing on potentially lethal mitochondrial DNA disease to their children. This equates to an average of 152 births per year in the UK, and 778 births per year in the US.

The estimates were made by identifying the number of women in North East England who are at risk of passing on mitochondrial disease to their children and extrapolating the figure to the rest of the UK, based on the relative number of women of child-bearing age in the North East compared to the UK as a whole. A similar method was used for the US figures. The study did not account for variance due to ethnicity or potentially different fertility rates in different parts of the UK.

Researchers also assessed the fertility of women with mitochondrial DNA mutations. To do this they compared fertility data from their patients' to data about the general population, obtained from the UK Office for National Statistics. They found that mitochondrial mutation has no statistically significant effect on fertility rate.

Dr Gráinne Gorman from the Wellcome Trust Centre for Mitochondrial Research at Newcastle University, and joint first author of the paper, said:

"Our estimate of how many women could benefit from mitochondrial donation is based on our data from North East England, where we have very detailed insight into how many women are affected. We are confident that there are a similar number of women across the UK at risk of passing on mitochondrial disease to their children."

Professor Doug Turnbull, Director of the Wellcome Trust Centre for Mitochondrial Research at Newcastle University, and an author of the paper, said:

"Our findings have considerable implications for all countries that are considering allowing mitochondrial donation techniques. In the UK we are waiting for parliament to decide whether to support these regulations. This would allow women who carry these mutations greater reproductive choice. "

Source: Wellcome Trust 

Contact: Clare Ryan 

Reference:

Mitochondrial Donation: How many women could benefit? 

Gráinne S. Gorman, John P. Grady, Yi Ng, Andrew M. Schaefer, Richard J. McNally, Patrick F. Chinnery, Patrick Yu Wai Man, Mary Herbert, Robert W. Taylor, Robert McFarland, and Doug M. Turnbull

New England Journal of Medicine, January 28, 2015 DOI: 10.1056/NEJMc1500960

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World's first child born after uterus transplantation

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Father's Age Influences Rate of Evolution

Chimpanzee.

Father's Age Influences Rate of Evolution

Friday, 13 June 2014

The offspring of chimpanzees inherit 90% of new mutations from their father, and just 10% from their mother, a finding which demonstrates how mutation differs between humans and our closest living relatives, and emphasises the importance of father's age on evolution.

Published today in Science, researchers from the Wellcome Trust Centre for Human Genetics and the Biomedical Primate research Centre in the Netherlands looked at whether, in chimpanzees, there was a heightened risk of fathers passing on mutations to their children compared to humans.

In humans, each individual inherits, on average, about 70 new mutations from their parents. However, this number is influenced by paternal age such that older fathers tend to result in more mutations – in humans each extra year of age results in two extra mutations.

Mutation risk is linked to father's age because the sperm lineage in males keeps dividing, while females have all the eggs they are ever going to produce present at birth. Paternal age is an established risk factor in a number of disorders including schizophrenia and autism.

The study found that the number of new mutations inherited by chimpanzees from their parents is, on average, very similar to that in humans, but that the effect of the father's age is much stronger – each additional year of father's age results in three extra mutations.

The results suggest that sexual selection can influence the rate of evolution through its effect on the male mutation rate.

Professor Gil McVean, from the Wellcome Trust Centre for Human Genetics at the University of Oxford said:

"In humans, a father's age is known to affect how many new mutations he passes on to his children, and is also an established risk factor in a number of mental health disorders.”

"This study finds that in chimpanzees the father's age has a much stronger effect on mutation rate – about one and a half times that in humans. As a consequence, a greater fraction of new mutations enter the population through males, around 90 per cent, compared to humans, where fathers account for 75 per cent of new mutations."

In the study, Wellcome Trust-funded researchers sequenced the genomes of nine western chimpanzees from a three generation family living at the biomedical primate research centre in the Netherlands.

To establish the number of new mutations a child inherits researchers sequence children and their parents and compare the genetic sequence – any change in the sequence that doesn't exist in either parent genome is a new mutation. To find out which parent the mutation comes from you need to sequence members of the next generation of the family.

One explanation for this difference is that chimpanzees, as a result of their mating system, have evolved to produce many more sperm than humans – their testes are over three times the relative size of a human. This means there are likely to be more cycles of sperm production, increasing the opportunity for new mutations to emerge.

The authors suggest that more work needs to be done across other species to investigate the impact of mating behaviour on mutation rates and male mutation bias.

Source: Wellcome Trust 

Contact: Clare Ryan

Reference:

Strong male bias drives germ line mutation in chimpanzees

Oliver Venn, Isaac Turner, Iain Mathieson, Natasja de Groot, Ronald Bontrop, Gil McVean

Science 13 June 2014, Vol. 344 no. 6189 pp. 1272-1275, DOI: 10.1126/science.344.6189.1272

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How Stem Cells Produce Different Kinds of Cells

How Stem Cells Produce Different Kinds of Cells

Sunday, 05 May 2013

The human body contains trillions of cells, all derived from a single cell, or zygote, made by the fusion of an egg and a sperm. That single cell contains all the genetic information needed to develop into a human, and passes identical copies of that information to each new cell as it divides into the many diverse types of cells that make up a complex organism like a human being.

If each cell is genetically identical, however, how does it grow to be a skin, blood, nerve, bone or other type of cell? How do stem cells read the same genetic code but divide into very different types?

The apical tip of fruit fly testis containing germ line 

stem cells and differentiating germ cells. Copies of 

Y chromosome are marked with either red or blue. 

Using this method, the authors discovered that 

germ line stem cells inherit specific copies of Y (and 

X) chromosomes. Credit: Yukiko Yamashita. 

Researchers at the University of Michigan have found the first direct evidence that cells can distinguish between seemingly identical copies of chromosomes during stem cell division, pointing to the possibility that distinct information on the chromosome copies might underlie the diversification of cell types.

Scientists in the lab of Life Sciences Institute researcher Yukiko Yamashita explained how stem cells can distinguish between two identical copies of chromosomes and distribute them to the daughter cells in a process called non-random chromosome segregation. They also described the genes responsible. Their work is scheduled to be published online May 5 in Nature.

"If we can figure out how and why cells are dividing this way, we might be able to get a glimpse of how we develop into a complete human, starting from a single cell," Yamashita said.

"It is very basic science, but understanding fundamental biological processes always has wide-ranging implications that could be exploited in therapeutics and drug discovery."

During the cell division cycle, the mother cell duplicates its chromosomes, generating two identical sets. When the cell divides to become two cells, each cell inherits one set of chromosome copies. In many divisions, the daughter cells are identical to the mother — one skin cell becomes two, for instance.

But in a process called asymmetric division, a cell divides into two daughters that are not identical — a skin stem cell divides into another skin stem cell and a regular skin cell, for example. In that case, the genetic information within the chromosome copies remains the same, but the type of cell, or "cell fate," is different.

The Yamashita lab used stem cells from the testes of the fruit fly Drosophila to study the process of cell division.

"The Drosophila germ line stem cell can be identified at a single-cell resolution, so they are an ideal model," Yamashita said.

The stem cells cluster and are easy to identify; they divide to produce another germ line stem cell and a differentiating cell called a gonialblast, which goes on to eventually become a sperm cell.

The researchers marked the copies of each chromosome in the Drosophila stem cells as they divided. Using this method, they tracked the tendency of the X and the Y chromosome copies to move to the daughter germ line stem cell or to the gonialblast. They were able to demonstrate that copies of X and Y chromosomes (but not other chromosomes) are distinguished and delivered to the daughter cells with a striking bias.

This is the first direct evidence that cells indeed have an ability to distinguish identical copies of chromosomes and separate them in a regulated manner. This ability has been suspected and hypothesized, but never proven.

"We do not know yet why copies of X and Y chromosomes segregate non-randomly," Yamashita said.

"We think maybe specific epigenetic information is transmitted to the germ line stem cell and to the gonialblast."

The findings suggest that the information on the X and Y chromosomes that makes this division possible is primed during gametogenesis — the process of creating ovum or sperm cells — in the parents.

Many other cells throughout the body are able to divide into two different types, especially during embryonic development. Yamashita's next steps are to explore whether the non-random chromosome segregation seen in Drosophila is a widespread phenomenon that is shared by mammals, including humans.

Source: University of Michigan 

Contact: Laura J. Williams

Reference:

Chromosome-specific nonrandom sister chromatid segregation during stem-cell division

Swathi Yadlapalli &  Yukiko M. Yamashita

Nature (2013), doi:10.1038/nature12106

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Human Spermatogonial Stem Cells Can Become Insulin-secreting Pancreatic Cells

Human Spermatogonial Stem Cells Can Become Insulin-secreting Pancreatic Cells
Sunday, 12 December 2010

Insulin-secreting pancreatic islet cells have been generated from human spermatogonial stem cells (SSCs) directly isolated from human testicular tissue, researchers reported today at the American Association of Cell Biology 50th Annual Meeting in Philadelphia.

When grafted into diabetic mice that lacked a transplant-rejecting immune system, the bioengineered cells functioned much like somatic β-islet cells, the Georgetown University (GU) Medical Center researchers said.

By decreasing the animals' blood glucose levels, the human-derived islet cells demonstrated their potential to counter diabetic hyperglycaemia in humans, added G. Ian Gallicano, Ph.D., who heads the GU research team.

Gallicano said that these results represent the first step of a transplant strategy to deliver β-islet cells that would not be rejected by the patient with type 1 diabetes because the stem cells would be obtained from the patient's own SSCs, the earliest precursors of male gamete sperm cells.

This transplant strategy would avoid the host-versus-graft issues that have plagued other transplant treatments for type 1 diabetes, Gallicano explained, because the SSCs would be obtained from male patients, modified in the laboratory to secrete insulin, and transplanted back to the donors.

Although surgeons currently transplant islet tissue from deceased donors into female and male patients with type 1 diabetes, this therapy is hampered by a woeful shortage of suitable donations and by complications resulting from host-versus-graft disease.

Gallicano said that obtaining beta-islet-like cells from the male patient's SSCs could solve the problem of immune rejection in males with type 1 diabetes, since the "treatment based on this research would be 'autologous,' that is, the cells come from the patient and would be recognized as 'self.'"

The fundamental approach of transforming male gametes into pluripotent stem cells might also be applicable to the female counterpart, oocytes, he added.

The β-islet-like cells were engineered from germ-derived pluripotent stem (gPS) cells produced from the SSCs. The engineered β-islet cells secreted insulin and exhibited many of the markers characteristic of normal islet cells including C-peptide (pro-insulin) production and the expression of PDX1, a transcription factor involved in pancreatic development.

Source: American Society for Cell Biology
Contact: Cathy Yarbrough
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Keeping Stem Cells from Changing Fates

Johns Hopkins researchers have determined why certain stem cells are able to stay stem cells
Thursday, 09 September 2010

The report in the June 4 issue of Cell Stem Cell reveals that an enzyme that changes the way DNA is packaged in cells allows specific genes to be turned on and off, thereby preventing a stem cell from becoming another cell type.

Each cell has to fit in 6 feet of highly organized and carefully packaged DNA. Some regions of the DNA are more tightly compacted than others and this structure is dynamic. There are specific enzymes that change how condensed the DNA is to help turn genes on and off. The genes that are turned off generally are found in tightly condensed DNA. To turn genes on, the DNA around those genes is loosened so that activators and other proteins can interact with the DNA.

The Johns Hopkins researchers believed that restructuring the DNA by proteins that make up chromosomes could play a role in deciding if a stem cell was going to change into another cell or stay a stem cell, since change in the DNA packaging would allow for many genes to be turned off and other genes to be turned on.

By genetically engineering flies to lack several proteins involved in packaging DNA, in the stem cells of the testes in fruit flies, the research team found that if the enzyme NURF is removed from testis stem cells, the stem cells disappeared. A constant supply of stem cells in the testes is responsible for making cells that eventually become sperm. More staining of the testes with coloured markers showed that these cells hadn't gone away completely, but were becoming another cell type, sperm cells.

"This experiment was really hard to do," says Erika Matunis, Ph.D., professor of cell biology from the Johns Hopkins Medical Institutions.

"As soon as you remove NURF from these cells, they leave, so you have to take a lot of samples to see how the cells are moving, since we are not looking at living moving cells but rather individual flashes in time."

So how does NURF keep stem cells as stem cells? NURF can both turn on and turn off genes.

"We still don't know what is happening in this case with how NURF regulates genes to keep stem cells from changing," says Matunis.

Matunis' group last year discovered proteins that were able to prevent stem cells from becoming other types of cells in the fruit fly testes. Now they showed that these same proteins also work with NURF to keep stem cells from changing.

"By any means this isn't the only pathway though, it's just the one we know more about" says Matunis.

"It's probably a tangled hair ball of all kinds of signals going on in these cells that prevent these stem cells from differentiating."

NURF keeps stem cells from changing in fruit fly testes, but whether NURF keeps other stem cells from changing still needs to be tested. Matunis believes that proteins similar to NURF will factor into whether a cell decides to change or not in other cell types.

Source: Johns Hopkins Medical Institutions
Contact: Vanessa McMains

Reference:
Epigenetic Regulation of Stem Cell Maintenance in the Drosophila Testis via the Nucleosome-Remodeling Factor NURF
Christopher M. Cherry, Erika L. Matunis
Cell Stem Cell, Volume 6, Issue 6, 557-567, 4 June 2010, 10.1016/j.stem.2010.04.018
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NIH Stem Cell Guidelines Should Be Modified

NIH Stem Cell Guidelines Should Be Modified Friday, 19 February 2010 A UCSF team, led by bioethicist Bernard Lo, MD, recommends that the National Institutes of Health ethics guidelines for embryonic stem cell research be modified to better protect the rights of individuals donating egg or sperm to patients undergoing in vitro fertilization. The recommendation is reported in the February 19, 2010 issue of Science. Third parties frequently donate sperm and egg, or “gametes,” for patients attempting to create embryos in the in vitro fertilization clinic. Under current practice in the United States, gamete donors sign a form giving the IVF patient unrestricted legal authority to determine how to dispose of any embryos that may be leftover following fertility treatments. Donor banks and IVF clinics are not required to brief gamete donors about the various options for disposition, which include donating the embryos for stem cell research, thereby enabling scientists to derive new human embryonic stem cell lines; discarding the embryos, or donating them to other IVF patients. While many state, national, and international scientific committees and agencies have recommended that third-party gamete donors give formal “informed consent” for stem cell research with embryos remaining after infertility treatment, the NIH did not stipulate this requirement in its guidelines issued in March 2009. As these guidelines determine which human embryonic stem cell (hESC) lines may be studied under NIH research grants – which are expected to play a growing role in funding stem cell research – the ethical implications are significant, says Lo, chair of the UCSF Gamete, Embryonic Stem Cell Research Committee, members of which published the Science paper. “We urge the NIH to revise its guidelines to require that gamete donors be advised that embryos containing their sperm or egg could be used for embryonic stem cell research, before they grant dispositional authority over embryos to the IVF patient,” he says. “Because some gamete donors may not approve of embryonic stem cell research, we consider this the ethically appropriate position.” In their paper, the team recommends a process that is less complex than the detailed “informed consent” process carried out when IVF patients donate embryos for research. They suggest the disclosure to gamete donors may be made through oral discussion or brochures before donors sign a form authorizing the IVF patient to determine the disposition of embryos. Importantly, says Lo, the gamete donors’ instructions would not disrupt the IVF process. IVF patients would learn of a gamete donor’s restrictions in advance of selecting embryos for IVF treatment, and could select other gamete donors if not satisfied with the donors’ disposition restrictions. The recommendation is consistent with that of the National Academy of Sciences and the International Society for Stem Cell Research says Lo, a member of the ethics committee of the ISSCR, and the co-chair of the Standards Working Group of the California Institute for Regenerative Medicine. “It would be highly desirable to have consistency among standards and regulations,” he says. “If such harmonization were achieved, many university Institutional Review Boards and other research oversight bodies would likely allow NIH-eligible human embryonic stem cell lines to be used for any otherwise acceptable hESC research.” “It’s critical that we consider all parties involved in the creation of embryos and honor their wishes,” says co-author Arnold Kriegstein, MD, PhD, director of the Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research at UCSF. “The field of human embryonic stem cell research offers enormous promise for patients suffering from devastating diseases. We want to build this field on an ethical foundation of which we can be proud.” Exceptions to the guideline could be justified for hESC lines already in existence if there were strong scientific reasons to use the cell lines and the third-party gamete donor had granted rights to the IVF patient to determine disposition of the embryos. Reference: NIH Guidelines for Stem Cell Research and Gamete Donors Bernard Lo, Lindsay Parham, Marcelle Cedars, Susan Fisher, Elena Gates, Linda Giudice, Dina Gould Halme, William Hershon, Arnold Kriegstein, Radhika Rao, Clifford Roberts, and Richard Wagner Science 19 February 2010, Vol. 327. no. 5968, pp. 962 – 963, DOI: 10.1126/science.1180725 ......... ZenMaster

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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

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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

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Researchers Make Stem Cells from Developing Sperm

Researchers Make Stem Cells from Developing Sperm Thursday, 06 August 2009 The promise of stem cell therapy may lie in uncovering how adult cells revert back into a primordial, stem cell state, whose fate is yet to be determined. Now, cell scientists at the Johns Hopkins University School of Medicine have identified key molecular players responsible for this reversion in fruit fly sperm cells. Reporting online this week in Cell Stem Cell, researchers show that two proteins are responsible redirecting cells on the way to becoming sperm back to stem cells. "We knew from our previous work that cells destined to be sperm could revert back to being stem cells, but we didn't know how," says Erika Matunis, Ph.D., an associate professor of cell biology at the Johns Hopkins University School of Medicine. "Since, dedifferentiation is an interesting phenomenon probably occurring in a lot of different stem cell populations, we wanted to know more about the process." Like all stem cells, each of the nine stem cells in the fly testis divides to form two daughter cells: One stays a stem cell and the other differentiates into an adult cell, in this case, a sperm cell. To figure out what might cause sperm cells to revert or dedifferentiate, Matunis's research team genetically altered the flies so that both cells become sperm, reducing the stem cell population in the testis to nothing. About a week later, the team examined these fly testes and found that the stem cells had been repopulated. To figure out how this was happening, the researchers first suspected two proteins — Jak and STAT — known to act together to help stem cells maintain their stem cell-ness. The team genetically altered flies to reduce the activity of Jak and STAT in the testis. Counting the number of cells, they found that the loss of Jak-STAT caused fewer cells to revert to stem cells; only 60 percent of testes regained stem cells compared to 97 percent in normal Jak-STAT-containing testes. "We now know that in the fly testis, interfering with Jak-STAT signalling interferes with the process of dedifferentiation," says Matunis. Next, Matunis would like to figure out how Jak and STAT control dedifferentiation. "We don't know if a cell is just reversing all of the steps to go back to being a stem cell or if it is doing something totally new and different, but we're eager to find out," she says. Reference: Dedifferentiating Spermatogonia Outcompete Somatic Stem Cells for Niche Occupancy in the Drosophila Testis X. Rebecca Sheng, Crista M. Brawley and Erika L. Matunis Cell Stem Cell, Volume 5, Issue 2, 191-203, 7 August 2009, doi:10.1016/j.stem.2009.05.024 ......... ZenMaster

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Male Germ Cells Directly Converted into Other Cell Types

Male Germ Cells Directly Converted into Other Cell Types Wednesday, 29 July 2009 Researchers have found a way to directly convert spermatogonial stem cells, the precursors of sperm cells, into tissues of the prostate, skin and uterus. Their approach, described this month in the journal Stem Cells, may prove to be an effective alternative to the medical use of embryonic stem cells. The hunt for alternatives to embryonic stem cells has led to some promising yet problematic approaches, some of which involve spermatogonial stem cells (SSCs). Researchers recently observed, for example, that SSCs grown in the laboratory will eventually give rise to a few cells that look and act like embryonic stem cells. This process can take months, however, and only a small percentage of the SSCs are converted into "embryonic stem-like" cells. Other researchers have used viruses to insert genes into SSCs that will spur them to turn into ES-like cells. But this approach is problematic and the use of viruses to ferry in the needed genes has caused concern. The new method, recently developed at the University of Illinois, takes advantage of the unusual interaction of two tissue types: the epithelium and the mesenchyme. The epithelium lines the cavities and surfaces of glands and many organs and secretes enzymes and other factors that are essential to the function of these tissues. The mesenchyme is the connective tissue in embryos. (In adults, the connective tissue is called stroma.) In the 1950s, scientists discovered that the epithelium takes its developmental instructions from the mesenchyme. For example, when researchers put bladder epithelial cells on the mesenchyme of a prostate gland, the bladder cells were changed into prostatic epithelium. The prostatic mesenchyme had altered the fate of the bladder epithelium. "The mesenchyme – it's the director; it's controlling the show," said University of Illinois veterinary biosciences professor Paul Cooke, who led the new study with postdoctoral researcher Liz Simon. Cooke began the effort with what even he considered an unlikely proposition. "Could we take spermatogonial stem cells and cause them to directly change into other cell types by putting them with various mesenchymes and growing them in the body?" he said. "I thought it was possible, but I didn't think it would work." The experiment did work, however. When Simon placed SSCs from inbred mice on prostate mesenchyme and grafted the combination into living mice, the SSCs became prostatic epithelium. When combined with skin mesenchyme and grown in vivo, the SSCs became skin epithelium. The researchers were even able to convert SSCs into uterine epithelium by using uterine mesenchyme. The newly formed tissues had all the physical characteristics of prostate, skin or uterus, and produced the telltale markers of those tissue types, Cooke said. They also stopped looking and behaving like SSCs. To assure that their tests were not contaminated with epithelial cells from the source of the mesenchyme cells, the researchers repeated the experiments using a mouse whose cells contained a gene that fluoresces green under ultraviolet light. The SSCs were obtained from a green-fluorescing mouse, but the mesenchyme came from a non-fluorescing mouse. This enabled the researchers to trace the fate of the SSCs. If the newly formed prostatic epithelium glowed green even though the mesenchyme did not, for example, the researchers knew that the SSCs had been converted into prostatic epithelium. Cooke hopes that a more streamlined approach can be developed that makes use of a man's own SSCs and stroma (the adult equivalent of the mesenchyme) to produce new skin cells or other tissues when needed – for example, to replace skin damaged in a burn. And his team is investigating the use of ovarian stem cells instead of SSCs to see if the same results can be obtained with ovarian tissue. Reference: Direct Transdifferentiation of Stem/Progenitor Spermatogonia Into Reproductive and Nonreproductive Tissues of All Germ Layers Liz Simon, Gail C. Ekman, Natalia Kostereva, Zhen Zhang, Rex A. Hess, Marie-Claude Hofmann, Paul S. Cooke Stem Cells Vol. 27 No. 7 July 2009, pp. 1666 -1675, doi:10.1002/stem.93 ......... ZenMaster

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How to Make Human Sperm in the Lab

Newcastle University researchers make human sperm from embryonic stem cells Wednesday, 08 July 2009 Human sperm have been created using embryonic stem cells for the first time in a scientific development which will lead researchers to a better understanding of the causes of infertility. Researchers led by Professor Karim Nayernia at Newcastle University and the NorthEast England Stem Cell Institute (NESCI) have developed a new technique which has made the creation of human sperm possible in the laboratory. The work is published today (8th July 2009) in the academic journal Stem Cells and Development. The NorthEast England Stem Cell Institute (NESCI) is a collaboration between Newcastle and Durham Universities, Newcastle NHS Foundation Trust and other partners. Professor Nayernia says: "This is an important development as it will allow researchers to study in detail how sperm forms and lead to a better understanding of infertility in men – why it happens and what is causing it. This understanding could help us develop new ways to help couples suffering infertility so they can have a child which is genetically their own." "It will also allow scientists to study how cells involved in reproduction are affected by toxins, for example, why young boys with leukaemia who undergo chemotherapy can become infertile for life – and possibly lead us to a solution." The team also believe that studying the process of forming sperm could lead to a better understanding of how genetic diseases are passed on. In the technique developed at Newcastle, stem cells with XY chromosomes (male) were developed into germline stem cells which were then prompted to complete meiosis - cell division with halving of the chromosome set. These were shown to produce fully mature, sperm called scientifically, In Vitro Derived sperm (IVD sperm). In contrast, stem cells with XX chromosomes (female) were prompted to form early stage sperm, spermatagonia, but did not progress further. This demonstrates to researchers that the genes on a Y chromosome are essential for meiosis and for sperm maturation. IVD sperm The IVD sperm will not and cannot be used for fertility treatment. As well as being prohibited by UK law, the research team say fertilization of human eggs and implantation of embryos would hold no scientific merit for them as they want to study the process as a model for research. "While we can understand that some people may have concerns, this does not mean that humans can be produced 'in a dish' and we have no intention of doing this. This work is a way of investigating why some people are infertile and the reasons behind it. If we have a better understanding of what's going on it could lead to new ways of treating infertility," adds Professor Nayernia. Technique The Newcastle University team have developed a method for establishing early stage sperm from human embryonic stem cells in the laboratory. The embryonic stem cells were cultured in a new medium containing vitamin A derivative (retinoic acid), in a new technique established by the team. Based on this technique, the cells differentiated into germline stem cells. These expressed a protein which was stained with a green fluorescent marker and they were separated out by FACSTM (Fluorescence-activated cell sorting) using a laser. After further differentiation, these in vitro derived germline stem cells expressed markers which are specific to primordial germ cells, spermatogonial stem cells, meiotic (spermatocytes) and post meiotic germ cells (spermatids and sperm). These results indicated maturation of the primordial germ cells to haploid male gametes – called IVD sperm – characterised by containing half a chromosome set (23 chromosomes). ......... ZenMaster

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Call for Public Debates on Future Uses of Stem Cells

Science is running ahead of public debate and guidelines to grapple with use of stem cell-derived eggs and sperm Thursday, 02 July 2009 More than 40 scientists, bioethicists, lawyers and science journal editors are calling on their colleagues, policy makers and the public to begin developing guidelines for the research and reproductive use of stem cell-derived eggs and sperm, even though such use may be a decade or more away. "Science has always moved faster than social debate or society's ability to grapple with these issues," says Debra Mathews, Ph.D., lead author of a paper published in the July issue of Cell Stem Cell and assistant director of science programs at the Johns Hopkins Berman Institute of Bioethics. The paper calls for all parties to begin engaging in open discussion and debates, and describes the need for informed social policy well in advance of the eventual use of eggs and sperm derived from pluripotent stem cells. Mathews said stem cell researchers need to be better prepared to address public questions about uses of so-called pluripotent stem cell-derived gametes – regardless of how realistic or soon those uses may be. Such uses would potentially include reproductive uses such as the creation of sperm and eggs for in vitro fertilization, embryo selection based on genetic profile, and the creation of embryos from the tissues of foetuses, children and the deceased. The issues are too complex, and the stakes are too high, the authors suggest, for the public to be caught unaware by some new capability for using stem cell-derived gametes, and the research already is moving rapidly toward generation of sperm and eggs capable of making human embryos and potentially children. "Because derived-gamete research will require the creation and destruction of human embryos, this line of research will be morally objectionable to those who imbue human embryos with full moral status, and those objections must be addressed," the authors state. In their paper, the Johns Hopkins-led team described an analysis of the current state of pluripotent stem cell science and suggested a framework for the debates that need to take place. There was consensus by the authors that policymakers should not restrict scientific inquiry solely because ethical or moral disagreement exists about the use of these cells. Instead, they offered recommendations for guidelines that would be the focus of social debate. Among them were that restrictions should be specific to those aspects of the technology that are deemed morally unacceptable in a given nation or state, and that specific consent should be required of tissue donors whose cells will be used to derive gametes for use in reproduction. This approach would rule out using for reproduction any tissue from foetuses, minors and the deceased. Consent, they said, need not be required in situations involving laboratory studies that produce no embryos. The authors emphasized that significant oversight rules must be in place before any reproductive uses of gametes even begins, and early attempts to use gametes for these purposes should take place only as part of clinical research that follows the highest ethical standards. Assuming that reproductive use of stem cell-derived gametes does occur, the health of women carrying the resulting foetuses, and of children born to them, should be monitored rigorously and tracked in long-term studies. Pluripotent stem cell-derived gamete research brings together several of today's most contentious ethical issues, including the use of embryonic stem cells, the increasing ability to identify and understand risks associated with particular parts of the human genome, advanced reproductive technologies to treat infertility and interest in "human enhancement." Mathews noted that pluripotent stem cell-derived gamete research already is producing significant advances in basic understanding of how eggs and sperm develop from germ cells, infertility, genetic diseases and some cancers. Mathews said the most difficult scientific issue the study team faced was predicting how long it would take to get from a human stem cell to a set of gametes capable of successful test-tube fertilization, and how long, if ever, it would be until such gametes are used in clinical care. The group believes it will take at least a decade to develop derived human gametes and that clinical applications likely will not be available for several years beyond that. Whatever the time frame, she said determining whether pluripotent stem cell-derived gametes can function reliably and normally is critical for both non-reproductive and reproductive purposes. Scientists and the public also must prepare, Mathews noted, for the potential production of large numbers of human gametes that facilitate multigenerational laboratory studies of human genetics and disease. "Although many welcome the prospects for disease prevention and health promotion that such research should facilitate, many others will find the treatment of human embryos in such blatantly manipulative ways to be ethically unacceptable," the authors said in their paper. Reference: Pluripotent Stem Cell-Derived Gametes: Truth and (Potential) Consequences Debra J.H. Mathews, Peter J. Donovan, John Harris, Robin Lovell-Badge, Julian Savulescu and Ruth Faden Cell Stem Cell, Volume 5, Issue 1, 11-14, 2 July 2009, doi:10.1016/j.stem.2009.06.005 ......... ZenMaster

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Sperm Delivers More Complex Material than Thought

New study explores dad's role in shaping a healthy baby Monday, 15 June 2009 It was long believed that conception does not involve a meeting of equals. The egg is a relatively large, impressive biological factory compared with the tiny sperm, which delivers to the egg one copy of the father’s genes. However, a new study from Huntsman Cancer Institute (HCI) at the University of Utah reveals that the father’s sperm delivers much more complex genetic material than previously thought. The findings could lead to a diagnostic test to help couples deal with infertility. Researchers discovered particular genes packaged in a special way within the sperm, and that may promote the development of the foetus. “Our findings show that the father plays an active role in packaging his genome to help ensure a healthy baby,” says study co-leader Brad Cairns, Ph.D., investigator with HCI and the Howard Hughes Medical Institute, and professor of oncological sciences at the University of Utah. “However, they also raise the possibility that a man’s aging, health and lifestyle may alter this packaging and negatively affect fertility and embryo development.” During foetal development, certain genes make decisions about organ and tissue development. The new research shows that in sperm, these genes are wrapped in special packaging materials called ‘modified histones.’ These modified histones appear to be key factors in ensuring genes are activated or repressed at the right level, place and time, which helps the fertilized egg develop properly, known as epigenetic inheritance. Chromosomes are long strands of DNA containing thousands of genes, and their packaging helps determine which genes turn on and off. Understanding how these genes are activated or repressed leads to a better understanding of how disorders like birth defects and cancer develop. “Genes have on-and-off switches, and understanding them allows us to target them, leading to possible treatments, cures or prevention strategies,” says Cairns. “That’s the good news.” An implication of this study is that factors such as genetic mutations, age or lifestyle may affect sperm chromosome packaging, leading to infertility. “We are hopeful that this work will soon lead to a clinical diagnostic test that will help couples with infertility problems make better informed decisions regarding their prospects for a healthy child. We will also be testing if aspects of a man’s lifestyle – such as age, diet or health – affect proper packaging and fertility,” says Cairns. Other future work includes how decision-making genes are packaged in eggs, which remains a major mystery. The study is set for publication June 14 in the online edition of the journal Nature. The research involved collaboration between Cairns’ lab at HCI and the University of Utah’s in vitro fertilization (IVF) and andrology lab led by Doug Carrell, along with their joint graduate student, Sue Hammoud. About Huntsman Cancer Institute: Huntsman Cancer Institute (HCI) at the University of Utah marks its 10th anniversary in 2009. HCI was founded by Jon M. Huntsman to fulfil his dream of finding a cure for cancer through genetic research. In the last 10 years, HCI has grown to become one of America’s major cancer research centres. HCI is part of the University of Utah Health Care system and is ranked consistently by U.S. News & World Report as one of the top cancer hospitals in the country. Reference: Distinctive chromatin in human sperm packages genes for embryo development Saher Sue Hammoud, David A. Nix, Haiying Zhang, Jahnvi Purwar, Douglas T. Carrell & Bradley R. Cairns Nature advance online publication 14 June 2009, doi:10.1038/nature08162 ......... ZenMaster

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