Meet Zhong Zhong and Hua Hua

The first monkey clones produced by method that made Dolly
Sunday, 28 January 2018

The first primate clones made by somatic cell nuclear transfer are two genetically identical long-tailed macaques born recently at the Chinese Academy of Sciences Institute of Neuroscience in Shanghai. Researchers named the newborns Zhong Zhong and Hua Hua - born eight and six weeks ago, respectively - after the Chinese adjective "Zhonghua," which means Chinese nation or people. The technical milestone, presented January 24 in the journal Cell, makes it a realistic possibility for labs to conduct research with customizable populations of genetically uniform monkeys.

"There are a lot of questions about primate biology that can be studied by having this additional model," says senior author Qiang Sun, Director of the Nonhuman Primate Research Facility at the Chinese Academy of Sciences Institute of Neuroscience.

"You can produce cloned monkeys with the same genetic background except the gene you manipulated. This will generate real models not just for genetically based brain diseases, but also cancer, immune, or metabolic disorders and allow us to test the efficacy of the drugs for these conditions before clinical use."

 CAPTION: This is a photograph of Zhong Zhong, one of the first two monkeys created by somatic cell nuclear transfer. CREDIT: Qiang Sun and Mu-ming Poo/Chinese Academy of Sciences.

Zhong Zhong and Hua Hua are not the first primate clones - the title goes to Tetra, a rhesus monkey born in 1999 through a simpler method called embryo splitting (Chan et al., Science 287, 317-319). This approach is how twins arise naturally but can only generate up to four offspring at a time. Zhong Zhong and Hua Hua are the product of somatic cell nuclear transfer (SCNT), the technique used to create Dolly the sheep over 20 years ago, in which researchers remove the nucleus from an egg cell and replace it with another nucleus from differentiated body cells. This reconstructed egg then develops into a clone of whatever donated the replacement nucleus.

 CAPTION: This is a photograph of Hua Hua, one of the first monkey clones made by somatic cell nuclear transfer. CREDIT: Qiang Sun and Mu-ming Poo/Chinese Academy of Sciences.

Differentiated monkey cell nuclei, compared to other mammals such as mice or cows, have proven resistant to SCNT. Sun and his colleagues overcame this challenge primarily by introducing epigenetic modulators after the nuclear transfer that switch on or off the genes that are inhibiting embryo development. The researchers found their success rate increased by transferring nuclei taken from fetal differentiated cells, such as fibroblasts, a cell type in the connective tissue. Zhong Zhong and Hua Hua are clones of the same macaque fetal fibroblasts. Adult donor cells were also used, but those clones only lived for a few hours after birth.

"We tried several different methods, but only one worked," says Sun.

"There was much failure before we found a way to successfully clone a monkey."

The first author Zhen Liu, a postdoctoral fellow, spent three years practicing and optimizing the SCNT procedure. He tested various methods to quickly and precisely remove the nuclear materials from the egg cell and promote the fusion of the nucleus-donor cell and enucleated egg. With the additional help of epigenetic modulators that re-activate the suppressed genes in the differentiated nucleus, he was able to achieve much higher rates of normal embryo development and pregnancy in the surrogate female monkeys.

"The SCNT procedure is rather delicate, so the faster you do it, the less damage to the egg you have, and Dr. Liu has a green thumb for doing this," says Muming Poo, a co-author on the study who directs the Institute of Neuroscience of CAS Center for Excellence in Brain Science and Intelligence Technology and helps to supervise the project.

"It takes a lot of practice. Not everybody can do the enucleation and cell fusion process quickly and precisely, and it is likely that the optimization of transfer procedure greatly helped us to achieve this success."

The researchers plan to continue improving the technique, which will also benefit from future work in other labs, and monitoring Zhong Zhong and Hua Hua for their physical and intellectual development. The babies are currently bottle fed and are growing normally compared to monkeys their age. The group is also expecting more macaque clones to be born over the coming months.

The lab is following strict international guidelines for animal research set by the US National Institutes of Health, but Sun and Poo encourage the scientific community to discuss what should or should not be acceptable practices when it comes to cloning of non-human primates.

"We are very aware that future research using non-human primates anywhere in the world depends on scientists following very strict ethical standards," Poo says.

This work was supported by grants from Chinese Academy of Sciences, the CAS Key Technology Talent Program, the Shanghai Municipal Government Bureau of Science and Technology, the National Postdoctoral Program for Innovative Talents and the China Postdoctoral Science Foundation.

Source: CELL PRESS

Contact: Joseph Caputo jcaputo@cell.com

Reference:

Cloning of macaque monkeys by somatic cell nuclear transfer

Zhen Liu, Yijun Cai, Yan Wang, Yanhong Nie, Chenchen Zhang, Yuting Xu, Xiaotong Zhang, Yong Lu, Zhanyang Wang, Muming Poo, Qiang Sun

Cell, DOI: http://dx.doi.org/10.1016/j.cell.2018.01.020

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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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Researchers Reconstruct Early Stages of Embryo Development

Researchers Reconstruct Early Stages of Embryo Development

Tuesday, 04 November 2014

Researchers at the University of Cambridge have managed to reconstruct the early stage of mammalian development using embryonic stem cells, showing that a critical mass of cells – not too few, but not too many – is needed for the cells to being self-organising into the correct structure for an embryo to form.

All organisms develop from embryos: a cell divides generating many cells. In the early stages of this process, all cells look alike and tend to aggregate into a featureless structure, more often than not a ball. Then, the cells begin to 'specialise' into different types of cell and space out asymmetrically, forming an axis which begins to provide a structure for the embryo to develop along.

In animal embryos this stage is followed by a process known as gastrulation: a choreographed movement of the cells that, using the initial axis as a reference, positions the head and the tail, the front and the back. During the process, the cells begin to form three distinct layers: the endoderm, mesoderm and ectoderm, determining which tissues or organs the cells will then develop into.

Professor Alfonso Martinez-Arias from the Department of Genetics at the University of Cambridge, who led the research, says:

"Gastrulation was described by biologist Professor Lewis Wolpert as being 'truly the most important event in your life' because it creates the blueprint of an organism. Axis formation and gastrulation are the two central processes that initiate the development of an organism and are inextricably associated with the embryo. We have managed to recreate this for the first time in the lab."

Professor Martinez-Arias and colleagues, supported by the European Research Council and the Wellcome Trust, have reconstructed these early stages of development using mouse embryonic stem cells. Embryonic stem cells, discovered in the Department of Genetics in the 1980s (for which Sir Martin Evans was awarded the Nobel Prize in Physiology or Medicine 2007), have become an important tool for developmental biology, understanding disease, and in regenerative medicine due to the ability to give rise to all cell types in culture. Over the last few years, they have been used to 'grow' organs including the eye and the cerebral cortex; surprisingly, these structures develop without an axis.

In research published today in the journal Development, the researchers report a way to coax cells to reorganize in the manner that they do in an embryo, creating an axis and undergoing movements and organisations that mimic the process of gastrulation. Over the years researchers have been making aggregates of embryonic stem cells to obtain certain cell types, for example red blood cells. However, these aggregates lack structure and the different cell types emerge in a disorganised fashion. This is the first time that researchers have been able to elicit axis formation, spatial organisation and gastrulation-like movements from aggregates of embryonic stem cells.

The researchers show that if the number of cells aggregated initially is similar to that of a mouse embryo, the cells generate a single axis and this serves as a template for a sequence of events that mimics those of the early embryo. By manipulating the signals that the cells see at a particular time, the researchers were able to influence what type of cell they become and how they are organised. In one of the experiments, for example, activation of a particular signal at the correct time elicits the appearance of the mesoderm, endoderm and ectoderm – the precursors of all cell types – with a spatial organization similar to that of an embryo.

Using this experimental system, the researchers were able to generate the early stages of a spinal cord, which they showed forms as part of the process of gastrulation. This finding complements previous research from the University of Edinburgh and the National Institute for Medical Research which showed that embryonic stem cells can be coaxed into this spinal cord cells; however, the Cambridge researchers showed that in the embryo-like aggregates, the structural organization is more robust and allows for the polarised growth of the tissue.

Professor Martinez-Arias adds:

"It is early days but this system promises insights into the early stages of development and what determines the specification of the different cell types. This will allow more robust protocols for differentiation with cues that mimic those that the cells are subject to in embryos.”

"Most significantly, the system will provide a means to test, experimentally, how a homogeneous group of cells organizes itself in space, a central process in the development of any organism, and the ability to recreate in culture the niches that adult stem cells create during embryogenesis and which have remained elusive experimentally."

Source: University of Cambridge

Contact: Craig Brierley

References:

Symmetry breaking, germ layer specification and axial organisation in aggregates of mouse ES cells

Susanne C. van den Brink, Peter Baillie-Johnson, Tina Balayo, Anna-Katerina Hadjantonakis, Sonja Nowotschin, David A. Turner, and Alfonso Martinez Arias

Development 2014 141:4231-4242; doi:10.1242/dev.113001

Wnt/β-catenin and FGF signalling direct the specification and maintenance of a neuromesodermal axial progenitor in ensembles of mouse ES cells

David A. Turner, Penelope C. Hayward, Peter Baillie-Johnson, Pau Rué, Rebecca Broome, Fernando Faunes, and Alfonso Martinez Arias

Development; 2014 141:4243-4253; doi:10.1242/dev.112979

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Shopping for an Egg Donor

Is beauty, brains, or health most important?

Tuesday, 21 October 2014

Human egg cell. 

When it comes to picking an egg donor, until recent years, recipients tended to prefer someone with a similar appearance. Donor trait choices are changing, though, and which traits are now more preferable and why is the focus of "Beauty, Brains or Health: Trends in Ovum Recipient Preferences," an article published in Journal of Women's Health, a peer-reviewed publication from Mary Ann Liebert, Inc., publishers. The article is available free on the Journal of Women's Health website at http://online.liebertpub.com/doi/full/10.1089/jwh.2014.4792 until November 20, 2014.

Homero Flores, MD and coauthors from Reproductive Medicine Associates of New York and Icahn School of Medicine at Mount Sinai (New York, NY) reviewed the requests of ovum donor recipients over a 5-year period and assessed their preferences for donor traits, categorizing them by appearance, ethnicity, intellect, ability, and mental health. The authors documented statistically significant increases and decreases in the different categories over the years, with more "practical traits" that would improve offspring's overall quality of life tending to increase compared to "self-reflective" traits.

"As social acceptance of ovum donation has increased, and donor selection has become more sophisticated, couples are changing their preferences for what donor characteristics they value most for their future offspring," says Susan G. Kornstein, MD, Editor-in-Chief of Journal of Women's Health, Executive Director of the Virginia Commonwealth University Institute for Women's Health, Richmond, VA, and President of the Academy of Women's Health.

Source: Mary Ann Liebert, Inc./Genetic Engineering News

Contact: Kathryn Ryan

Reference:

Beauty, Brains or Health: Trends in Ovum Recipient Preferences

Flores Homero, Lee Joseph, Rodriguez-Purata Jorge, Witkin Georgia, Sandler Benjamin, and Copperman Alan B.

Journal of Women's Health. October 2014, 23(10): 830-833. doi:10.1089/jwh.2014.4792

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World's first child born after uterus transplantation

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Some Stem Cell Methods Closer to "Gold Standard" than Others

Nuclear transfer appears superior for creating embryonic stem cells

Thursday, 03 July 2014

Researchers around the world have turned to stem cells, which have the potential to develop into any cell type in the body, for potential regenerative and disease therapeutics.

Now, for the first time, researchers at the Salk Institute, with collaborators from Oregon Health & Science University and the University of California, San Diego, have shown that stem cells created using two different methods are far from identical. The finding could lead to improved avenues for developing stem cell therapies as well as a better understanding of the basic biology of stem cells.

The researchers discovered that stem cells created by moving genetic material from a skin cell into an empty egg cell — rather than coaxing adult cells back to their embryonic state by artificially turning on a small number of genes — more closely resemble human embryonic stem cells, which are considered the gold standard in the field.

Joseph R. Ecker, Professor, Genomic Analysis

Laboratory. Credit: Courtesy of the Salk

Institute for Biological Studies. 

"These cells created using eggs' cytoplasm have fewer reprogramming issues, fewer alterations in gene expression levels and are closer to real embryonic stem cells," says co-senior author Joseph R. Ecker, professor and director of Salk's Genomic Analysis Laboratory and co-director of the Center of Excellence for Stem Cell Genomics. The results of the study were published today in Nature.

Human embryonic stem cells (hESCs) are directly pulled from unused embryos discarded from in-vitro fertilization, but ethical and logistical quandaries have restricted their access. In the United States, federal funds have limited the use of hESCs so researchers have turned to other methods to create stem cells. Most commonly, scientists create induced pluripotent stem (iPS) cells by starting with adult cells (often from the skin) and adding a mixture of genes that, when expressed, regress the cells to a pluripotent stem-cell state. Researchers can then coax the new stem cells to develop into cells that resemble those in the brain or in the heart, giving scientists a valuable model for studying human disease in the lab.

Over the past year, a team at OHSU built upon a technique called somatic cell nuclear transfer (the same that is used for cloning an organism, such as Dolly the sheep) to transplant the DNA-containing nucleus of a skin cell into an empty human egg, which then naturally matures into a group of stem cells.

Shoukhrat Mitalipov, Ph.D., Oregon Health &

Science University, led a team that found that a

process called "somatic cell nuclear transfer" is

much better and more accurate at

reprogramming human skin cells to become

embryonic stem cells. Credit: Oregon Health &

Science University.

Ecker, holder of the Salk International Council Chair in Genetics, teamed up with Shoukhrat Mitalipov, developer of the new technique and director of the Center for Embryonic Cell and Gene Therapy at OHSU, and UCSD assistant professor Louise Laurent to carry out the first direct comparison of the two approaches. The scientists created four lines of nuclear transfer stem cells all using eggs from a single donor, along with seven lines of iPS cells and two lines of the gold standard hESCs. All cell lines were shown to be able to develop into multiple cell types and had nearly identical DNA content contained within them.

But when they looked closer at the cells, the researchers spotted some differences: the patterns of methylation — chemical flags that are added to genes to control their expression — varied between the cell lines. This indicates a difference in how and when genes, despite having identical sequences, might be expressed. The methylation of nuclear transfer cells more closely resembled hESCs than the iPS cells did. And when the investigators looked at patterns of actual gene expression — by measuring the levels of particular RNA strands produced by each cell — the differences continued. Once again, nuclear transfer cells had RNA levels closer to embryonic cells, making them more accurate for basic research and therapeutic studies.

"Both the DNA methylation and gene expression data show that nuclear transfer does a better job at erasing the signature of the original skin cell," says Laurent, who is a co-senior author of the paper.

"If you believe that gene expression is important, which we do, then the closer you get to the gene expression patterns of embryonic stem cells, the better," Ecker says.

"Right now, nuclear transfer cells look closer to the embryonic stem cells than do the iPS cells."

Ecker doesn't expect labs to race to make the switch to nuclear transfer protocols — after all, the method falls within those restricted for federal funding. But he thinks the new observation likely holds lessons that could help improve the protocols for making iPS cells.

"What this is telling us is that you can use the standard mix of genes and they do a pretty good job of creating iPS cells," Ecker says.

"But they're not perfect. The material in an egg does a better job than just those four genes alone."

If researchers can pin down what it is within an egg that drives the production of pluripotent stem cells, they may be able to integrate that knowledge into iPS methods to improve stem cell therapy for disease.

"At this point, nuclear transfer stem cells combine the key advantages of both hESCs and iPS cells and, as such, are ideal for clinical applications in regenerative therapy," adds Mitalipov.

Other researchers on the study were Ryan C. O'Neil, Yupeng He, Matthew D. Schultz, Manoj Heriharan, Joseph R. Nery, and Rosa Castanon of the Salk Institute for Biological Studies; Hong Ma, Brittany Daughtry, Masahito Tachibana, Eunju Kang, Rebecca Tippner-Hedges, Riffat Ahmed, Nuria Marti Gutierrez, Crystal Van Dyken, Alimujiang Fulati, Atsushi Sugawara, Michelle Sparman, Paula Amato and Don P. Wolf of Oregon Health & Science University; Robert Morey, Karen Sabatini and Rathi D. Thiagarajan of the University of California, San Diego; and Sumita Gokhale of the Boston University School of Medicine.

Source: Salk Institute for Biological Studies

Contact: Kristina Grifantini

Reference:

Abnormalities in human pluripotent cells due to reprogramming mechanisms

Hong Ma, Robert Morey, Ryan C. O'Neil, Yupeng He, Brittany Daughtry, Matthew D. Schultz, Manoj Hariharan, Joseph R. Nery, Rosa Castanon, Karen Sabatini, Rathi D. Thiagarajan, Masahito Tachibana, Eunju Kang, Rebecca Tippner-Hedges, Riffat Ahmed, Nuria Marti Gutierrez, Crystal Van Dyken, Alim Polat, Atsushi Sugawara, Michelle Sparman, Sumita Gokhale, Paula Amato, Don P.Wolf, Joseph R. Ecker, Louise C. Laurent & Shoukhrat Mitalipov

Nature (2014), doi:10.1038/nature13551

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Reconstructing the Life History of a Single Cell

Cell's unique mutations used to trace history back to its origins in the embryo

Sunday, 29 June 2014

Researchers have developed new methods to trace the life history of individual cells back to their origins in the fertilised egg. By looking at the copy of the human genome present in healthy cells, they were able to build a picture of each cell's development from the early embryo on its journey to become part of an adult organ.

Reconstruction of early cell divisions of two

mouse embryos: Each white-filled large circle

represents an individual cell from a mouse

embryo and the unique combination of

mutations in its DNA. Each mutation is

represented by a number and those highlighted in

yellow were acquired in the most recent cell

division. The smaller colour-filled circles are the

final sets of cells taken from different parts of

the mouse and there are an unknown number of

cell generations between each set of cells and its

closest identifiable precursor cell. [DOI:

10.1038/nature13448]

During the life of an individual, all cells in the body develop mutations, known as somatic mutations, which are not inherited from parents or passed on to offspring. These somatic mutations carry a coded record of the lifetime experiences of each cell.

By looking at the numbers and types of mutations in a cell's DNA, researchers were able to assess whether the cell had divided a few times or many times and detect the imprints, known as signatures, of the processes of DNA damage and repair that the cells had been exposed to during the life of the individual. Furthermore, comparing each cell's mutations with those of other cells in the body enabled scientists to map out a detailed tree of development from the fertilised egg.

"With this novel approach, we can peer back into an organism's development," says Dr Sam Behjati, first author from the Wellcome Trust Sanger Institute.

"If we can better understand how normal, healthy cells mutate as they divide over a person's lifetime, we will gain a fundamental insight into what can be considered normal and how this differs from what we see in cancer cells."

The team looked at mouse cells from the stomach, small bowel, large bowel and prostate. The single cells were grown to produce enough DNA to be sequenced accurately. Eventually, single-cell sequencing technology will develop so that this type of experiment can be conducted using just one cell. However, the tiny amounts of DNA in single cells mean that mutation data are not currently precise enough to reconstruct accurate lineages.

The researchers recorded differences in the numbers of mutations in cells from the different tissues studied, likely attributable to differences in rates of cell division. Moreover, different patterns of mutation were found in cells from different tissues, suggesting that they have been exposed to different processes of DNA damage and repair, reflecting different lifetime experiences.

This experiment used healthy mice. If mutation rates are similar in human cells, these techniques could be used to provide an insight into the life histories of normal human cells.

"The adult human body is composed of 100 million million cells, all of which have originated from a single fertilised egg," says Professor Mike Stratton, senior author and Director of the Sanger Institute.

"Much more extensive application of this approach will allow us to provide a clear picture of how adult cells have developed from the fertilised egg. Furthermore, by looking at the numbers and types of mutation in each cell we will be able to obtain a diary, writ in DNA, of what each healthy cell has experienced during its lifetime, and then explore how this changes in the range of human diseases."

Source: Wellcome Trust Sanger Institute 

Contact: Mark Thomson

Reference:

Genome sequencing of normal cells reveals developmental lineages and mutational processes

Sam Behjati, Meritxell Huch, Ruben van Boxtel, Wouter Karthaus, David C. Wedge, Asif U. Tamuri, Iñigo Martincorena, Mia Petljak, Ludmil B. Alexandrov, Gunes Gundem, Patrick S. Tarpey, Sophie Roerink, Joyce Blokker, Mark Maddison, Laura Mudie, Ben Robinson, Serena Nik-Zainal, Peter Campbell, Nick Goldman, Marc van de Wetering, Edwin Cuppen, Hans Clevers & Michael R. Stratton

Nature 2014, DOI: 10.1038/nature13448

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Three Parents and a Baby

Scientists advise caution with regard to artificial insemination method

Wednesday, 18 June 2014

Already a few dysfunctional mitochondria (in

yellow on top of the picture) could cause a

disease by overgrowing functional ones (in blue).

Credit: Illustration: Iain Johnston. 

Mitochondria are cell organelles located within animal and human cells. They produce energy for the organism, possess their own genetic material - mitochondrial DNA (mtDNA) - and are transmitted exclusively by the mother. Depending on their activity and tasks, different numbers of mitochondria are present in a cell - usually a few hundred to a thousand per body cell.

Inherited mitochondrial disorders or so-called mitochondropathies occur in about one of 10,000 humans throughout the world. Diseases such as diabetes, stroke, cardiac defects, epilepsy, or muscle weakness may originate from mitochondrial defects. Inherited mitochondrial disorders have been incurable so far. Therefore, efforts are now being made to enable women with this disease to bear healthy children by means of nuclear transfer.

Mitochondria multiply at different rates

Jörg Burgstaller, a scientist and member of Gottfried Brem's research group at the Vetmeduni Vienna, has been working for several years on the genetics of mitochondria. It was known before that different types of mitochondria within a cell can proliferate at different rates. However, it was not known whether this is a singular phenomenon or if these cases occur more frequently.

Burgstaller investigated this in four newly bred mouse models which carried different mixtures of mitochondria whose DNA were related to each other to a differing extent.

This meant no health problem for the mice since all mtDNAs are were fully functional.

The outcome was: the more distantly two types of mitochondria within an egg cell were related, the more frequently a growth advantage was noted in favour of one of the two types of mitochondria. When two different mtDNAs were equally common in cells of an organ at the time of birth, one type was completely lost after a while. One mitochondria variant had thus achieved a growth advantage compared to the other variant and superseded the latter. This effect was almost non-existent in genetically very similar mitochondria within the cells; the ratio between the two types of mitochondria was not altered in that case.

The effect is of significance in reproduction medicine

Burgstaller's results may have effects on the planned introduction of the so called "Three-Parent Baby" in Great Britain. Experts take the cell nucleus of one human egg cell whose mitochondria have a defect and place it in an egg cell with "healthy" mitochondria. The baby resulting from this procedure has three parents, namely the mother whose cell nucleus is used, the mother whose mitochondria are involved, and the father whose sperm inseminated the egg cell.

However, this method raises the following problem: in every nuclear transfer, a small number of defective mitochondria are transferred into the healthy egg cell.

"So far it was believed that this minimal 'contamination' is of no consequence for the baby. However, our data show that the effect may have dramatic consequences on the health of the offspring. If the mitochondria of both mothers are genetically very different, it may have the same effects seen in the mouse model," says Burgstaller who developed the theory together with co-author Joanna Poulton, Professor of Mitochondrial Genetics at the John Radcliffe Hospital in Oxford.

"One mitochondrial type may be able to assert itself against the other. If the assertive one happens to carry the defective mtDNA, the benefit of the therapy would be jeopardized."

The solution to the "Three-Parent Baby"-problem

Burgstaller and his colleagues suggest the following solution to the problem: the mtDNA of both mothers, i.e. the donor of the nucleus and the donor of the mitochondria, should be analysed in advance and aligned to each other. So called "matching haplotypes" could prevent the dangerous effect. In the future the effect may even be utilized in a targeted manner to suppress defective mtDNA.

Source: University of Veterinary Medicine – Vienna 

Contact: Joerg Burgstaller

Reference:

mtDNA Segregation in Heteroplasmic Tissues Is Common In Vivo and Modulated by Haplotype Differences and Developmental Stage

Joerg Patrick Burgstaller, Iain G. Johnston, Nick S. Jones, Jana Albrechtová, Thomas Kolbe, Claus Vogl, Andreas Futschik, Corina Mayrhofer, Dieter Klein, Sonja Sabitzer, Mirjam Blattner, Christian Gülly, Joanna Poulton, Thomas Rülicke, Jaroslav Piálek, Ralf Steinborn and Gottfried Brem

Cell Reports. DOI:10.1016/j.celrep.2014.05.020 

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New Stem Cell Line Should Accelerate Embryonic Stem Cell Research

New Stem Cell Line Should Accelerate Embryonic Stem Cell Research

Sunday, 16 March 2014

Researchers at the University of Washington have successfully created a line of human embryonic stem cells that have the ability to develop into a far broader range of tissues than most existing cell lines.

This is Carol Ware, Professor of comparative

medicine, University of Washington. Credit: 
Bryan Donohue. 

"These cells will allow us to gain a much greater understanding of normal embryonic development and have the real potential for use in developing ways to grow new tissues and organs for transplantation," said Carol Ware, a professor in the UW Department of Comparative Medicine and lead author of a paper describing the new cell line appearing in the March 10 issue of the journal Proceedings of the National Academy of Sciences.

The cells, called naïve embryonic stem cells, normally appear at the earliest stages of embryonic development and so retain the ability to differentiate in all the different types of cells of the human body — a capacity called pluripotency.

Researchers had been able to develop naive cells using mouse embryonic stem cells but to create naive human embryonic stem cells has required inserting a set of genes that force the cells to behave like naive cells.

While these "transgenic" cells are valuable research tools, the presence of the artificially introduced genes meant the cells will not develop as normal embryonic cells would nor could they be safely used to create tissues and organs for transplantation.

In an article, Ware and her colleagues from the UW Institute for Stem Cell and Regenerative Medicine describe how they successfully created a line of naive human embryonic stem cells without introducing an artificial set of genes.

They first took embryonic stem cells that are slightly more developed, called primed stem cells, and grew them in a medium that contained factors that switched them back — or "reverse toggled" them — to the naive state.

They then used the reverse toggled cells to develop a culture medium that would keep them in the naive state and create a stable cell line for study and research.

Then having worked out how to maintain the cells in the naive state, Ware and her colleagues harvested naive cells directly from donated human embryos and cultured them in the maintenance medium to see if they could create a stable cell line that had not undergone reverse toggling. After many tries, they succeeded.

While the "reverse toggled" cells are much easier to create and will prove valuable research tools, Ware said, the cells that were directly derived from embryos are the more important advance because they are more likely to behave, grow and develop as embryonic cells do in nature.

The new cell line is called Elf1: "El" for the Ellison Foundation, a major supporter of the lab's work; "f" for female, the sex of the stem cell; and "1" for first.

Source: University of Washington

Contact: Kim Blakeley

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ZenMaster

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http://cellnews-blog.blogspot.com/

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