Restoring Vision with Stem Cells

Researchers have succeed in producing photoreceptors from human embryonic stem cells

Tuesday, 06 October 2015

Age-related macular degeneration (AMRD) could be treated by transplanting photoreceptors produced by the directed differentiation of stem cells, thanks to findings published today by Professor Gilbert Bernier of the University of Montreal and its affiliated Maisonneuve-Rosemont Hospital. ARMD is a common eye problem caused by the loss of cones. Bernier's team has developed a highly effective in vitro technique for producing light sensitive retina cells from human embryonic stem cells.

"Our method has the capacity to differentiate 80% of the stem cells into pure cones," Professor Gilbert explained.

"Within 45 days, the cones that we allowed to grow towards confluence spontaneously formed organised retinal tissue that was 150 microns thick. This has never been achieved before."

In order to verify the technique, Bernier injected clusters of retinal cells into the eyes of healthy mice. The transplanted photoreceptors migrated naturally within the retina of their host.

Age-related macular degeneration could be

treated by transplanting photoreceptors

produced by the directed differentiation of stem

cells, thanks to findings published today by

Professor Gilbert Bernier of the University of

Montreal and its affiliated Maisonneuve-

Rosemont Hospital. This image illustrates the 3D

reconstruction of the tissue that was produced in

vitro and labelled with antibodies against

photoreceptor-specific proteins. Credit: G.

Bernier, Université de Montréal.

"Cone transplant represents a therapeutic solution for retinal pathologies caused by the degeneration of photoreceptor cells," Bernier explained.

"To date, it has been difficult to obtain great quantities of human cones."

His discovery offers a way to overcome this problem, offering hope that treatments may be developed for currently non-curable degenerative diseases, like Stargardt disease and ARMD.

"Researchers have been trying to achieve this kind of trial for years," he said.

"Thanks to our simple and effective approach, any laboratory in the world will now be able to create masses of photoreceptors. Even if there's a long way to go before launching clinical trials, this means, in theory, that will be eventually be able to treat countless patients."

The findings are particularly significant in the light of improving life expectancies and the associated increase in cases of ARMD. ARMD is in fact the greatest cause of blindness amongst people over the age of 50 and affects millions of people worldwide. And as we age, it is more and more difficult to avoid - amongst people over 80, this accelerated aging of the retina affects nearly one in four. People with ARMD gradually lose their perception of colours and details to the point that they can no longer read, write, watch television or even recognize a face.

ARMD is due to the degeneration of the macula, which is the central part of the retina that enables the majority of eyesight. This degeneration is caused by the destruction of the cones and cells in the retinal pigment epithelium (RPE), a tissue that is responsible for the reparation of the visual cells in the retina and for the elimination of cells that are too worn out. However, there is only so much reparation that can be done as we are born with a fixed number of cones. They therefore cannot naturally be replaced. Moreover, as we age, the RPE's maintenance is less and less effective - waste accumulates, forming deposits.

"Differentiating RPE cells is quite easy. But in order to undertake a complete therapy, we need neuronal tissue that links all RPE cells to the cones. That is much more complex to develop," Bernier explains, noting nonetheless that he believes his research team is up to the challenge.

Bernier has been interested in the genes that code and enable the induction of the retina during embryonic development since completing his PhD in Molecular Biology in 1997.

"During my post-doc at the Max-Planck Institute in Germany, I developed the idea that there was a natural molecule that must exist and be capable of forcing embryonic stem cells into becoming cones," he said.

Indeed, bioinformatics analysis led him to predict the existence of a mysterious protein: COCO, a "recombinational" human molecule that is normally expressed within photoreceptors during their development.

In 2001, he launched his laboratory at Maisonneuve-Rosemont Hospital and immediately isolated the molecule. But it took several years of research to demystify the molecular pathways involved in the photoreceptors development mechanism. His latest research shows that in order to create cones, COCO can systematically block all the signalling pathways leading to the differentiation of the other retinal cells in the eye. It's by uncovering this molecular process that Bernier was able to produce photoreceptors. More specifically, he has produced S-cones, which are photoreceptor prototypes that are found in the most primitive organisms.

Beyond the clinical applications, Professor Bernier's findings could enable the modelling of human retinal degenerative diseases through the use of induced pluripotent stem cells, offering the possibility of directly testing potential avenues for therapy on the patient's own tissues.

Source: University of Montréal

Contact: William Raillant-Clark

Reference:

Differentiation of human embryonic stem cells into cone photoreceptors through simultaneous inhibition of BMP, TGFβ and Wnt signaling

Shufeng Zhou, Anthony Flamier, Mohamed Abdouh, Nicolas Tétreault, Andrea Barabino, Shashi Wadhwa and Gilbert Bernier

Development, 42, 3294-3306, October 1, 2015, doi: 10.1242/dev.125385

.........

ZenMaster

---

For more on stem cells and cloning, go to CellNEWS at

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

---

From Pluripotency to Totipotency

Scientists discover mechanism that may lead to more efficient reprogramming of somatic cells

Wednesday, 05 August 2015

Human embryonic stem cells have the potential

to form in vitro neural tube-like structures of the

embryo. Credit: Inserm/Benchoua Alexandra.

While it is already possible to obtain in vitro pluripotent cells (i.e., cells capable of generating all tissues of an embryo) from any cell type, researchers from Maria-Elena Torres-Padilla's team from Institut de Génétique et de Biologie Moléculaire et Cellulaire, have pushed the limits of science even further. They managed to obtain totipotent cells with the same characteristics as those of the earliest embryonic stages and with even more interesting properties. Obtained in collaboration with Juanma Vaquerizas from the Max Planck Institute for Molecular Biomedicine (Münster, Germany), these results are published on 3rd of August in the journal Nature Structural & Molecular Biology.

Totipotency vs pluripotency

Just after fertilization, when the embryo is comprised of only 1 or 2 cells, cells are "totipotent", that is to say, capable of producing an entire embryo as well as the placenta and umbilical cord that accompany it. During the subsequent rounds of cell division, cells rapidly lose this plasticity and become "pluripotent". At the blastocyst stage (about thirty cells), the so-called "embryonic stem cells" can differentiate into any tissue, although they alone cannot give birth to a foetus anymore. Pluripotent cells then continue to specialise and form the various tissues of the body through a process called cellular differentiation.

For some years, it has been possible to re-programme differentiated cells into pluripotent ones, but not into totipotent cells. Now, the team of Maria-Elena Torres-Padilla has studied the characteristics of totipotent cells of the embryo and found factors capable of inducing a totipotent-like state.

“Totipotency is a much more flexible state than the pluripotent state and its potential applications are extraordinary”, says Maria-Elena Torres-Padilla, who led the study.

Looking for the keys of totipotency

When culturing pluripotent stem cells in vitro, a small amount of totipotent cells appear spontaneously; these are called "2C-like cells" (named after their resemblance to the 2-cell stage embryo). The researchers compared these cells to those present in early embryos in order to find their common characteristics and those that make them different from pluripotent cells. In particular, the teams found that the DNA was less condensed in totipotent cells and that the amount of the protein complex CAF1 was diminished. A closer look revealed that CAF1 – already known for its role in the assembly of chromatin (the organised state of DNA) – is responsible for maintaining the pluripotent state by ensuring that the DNA is wrapped around histones. Based on this hypothesis, the Torres-Padilla team was able to induce a totipotent state by inactivating the expression of the CAF1 complex, which led to chromatin reprogramming into a less condensed state.

A 2C-like cell (green) is different from an

embryonic stem cell (magenta). Credit:

IGBMC/Maria-Elena Torres-Padilla.

In order to carefully examine at a molecular level the similarities between 2-cell stage embryos, 2C-like cells and those induced by inactivating the CAF1 complex, the Torres-Padilla team then joined forces with the Vaquerizas laboratory to analyse, in a genome-wide fashion, the gene expression programmes of these cells. The scientists found that the induced, CAF1-depleted, totipotent cells overexpressed a significant amount of 2-cell stage embryo genes.

“One could imagine that if cells lose their ability to assemble chromatin, this would affect gene expression”, explains Cells-in-Motion PhD student Rocio Enriquez-Gasca of Juanma Vaquerizas’ lab, who performed the computational analyses of the work.

“So it was really exciting to realise that the resulting gene expression programme in fact significantly overlaps with that of early embryo, totipotent cells”.

Moreover, the teams found that specific classes of repetitive elements (repeated sequences of DNA that form around 50% of the mouse and human genomes) were also up-regulated in induced totipotent-like cells, a hallmark of the 2-cell embryo.

“The computational analysis of expression of repetitive elements is very challenging, since these are found many times in the genome”, says Juanma Vaquerizas.

“Now it is key to understand why these repetitive elements and gene expression programmes are both up-regulated in totipotent cells”.

These results provide new elements for the understanding of pluripotency and could increase the efficiency of reprogramming somatic cells to be used for applications in regenerative medicine.

Source: INSERM

Contact: Maria-Elena Torres-Padilla 

Reference:

Early embryonic-like cells are induced by down-regulation of replication-dependent chromatin assembly

Takashi Ishiuchi, Rocio Enriquez-Gasca, Eiji Mizutani, Ana Boškovi, Celine Ziegler-Birling, Diego Rodriguez-Terrones, Teruhiko Wakayama, Juan M. Vaquerizas & Maria-Elena Torres-Padilla

Nature Structural & Molecular Biology, 3 Aug 2015, doi:10.1038/nsmb.3066

.........

ZenMaster

---

For more on stem cells and cloning, go to CellNEWS at

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

---

Recovery of Sensory Function by Stem Cell Transplants

Recovery of Sensory Function by Stem Cell Transplants

Monday, 08 June 2015

New research from Uppsala University shows promising progress in the use of stem cells for treatment of spinal cord injury. The results, which are published in the scientific journal Scientific Reports, show that human stem cells that are transplanted to the injured spinal cord contribute to restoration of some sensory functions.

Traffic accidents and severe falls can cause ruptures of nerve fibres that enter/exit the spinal cord. Most commonly, these avulsion injuries affect the innervation of the arm and hand, and lead to paralysis, loss of sensation and cause chronic pain. Surgical interventions can help the patient regain some muscle function, but there is currently no treatment able to restore sensory functions. The reason for this is the emergence of a "barrier" at the junction between the ruptured nerve fibres and the spinal cord which prevents them from growing into the spinal cord and restore lost nerve connections.

In a new study the PhD students Jan Hoeber, Niclas König and Carl Trolle, working in Dr.Elena Kozlova's research group transplanted human stem cells to an avulsion injury in mice with the aim to restore a functional route for sensory information from peripheral tissues into the spinal cord.

The results show that the transplanted stem cells act as a "bridge" which allows injured sensory nerve fibres to grow into the spinal cord, rebuilds functional nerve connections, and thereby achieve long term restoration of major parts of the lost sensory functions. The transplanted stem cells differentiated to different types of cells with variable level of maturation, specific for the nervous system. No signs of tumour development or any functional abnormalities from the transplants were observed in the study, outcomes which are important in view of potential risks with transplantation of embryonic stem cells.

The results encourage further research on the use of stem cells for treatment of injury and disease in the spinal cord, and may contribute to the development of novel treatment strategies in these disorders.

Source: Uppsala University

Contact: Elena Kozlova

Reference:

Human embryonic stem cell-derived progenitors assist functional sensory regeneration after dorsal root avulsion injury

Hoeber J, Trolle C, König N, Du Z, Gallo A, Hermans E, Aldskogius H, Shortland P, Zheng, S-C, Deumens R, Kozlova EN. 

Scientific Reports 5, 08 June 2015, Article number: 10666, doi:10.1038/srep10666

.........

ZenMaster

---

For more on stem cells and cloning, go to CellNEWS at

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

---

New Stem Cell May Overcome Hurdles for Regenerative Medicine

Salk Institute scientists discover new type of stem cell that could potentially generate mature, functional tissues

Thursday, 07 May 2015

In this image, a novel type of human stem cell is

shown in green integrating and developing into

the surrounding cells of a nonviable mouse

embryo. Red indicates cells of endoderm lineage.

Endoderm cells can give rise to tissue that covers

organs from the digestive and respiratory

systems. The new stem cell, developed at the

Salk Institute, holds promise for one day growing

replacement functional cells and tissues. Credit:

Courtesy of the Salk Institute for Biological

Studies.

Scientists at the Salk Institute have discovered a novel type of pluripotent stem cell – cells capable of developing into any type of tissue – whose identity is tied to their location in a developing embryo. This contrasts with stem cells traditionally used in scientific study, which are characterized by their time-related stage of development.

In the paper, published May 6, 2015 in Nature, the scientists report using these new stem cells to develop the first reliable method for integrating human stem cells into nonviable mouse embryos in a laboratory dish in such a way that the human cells began to differentiate into early-stage tissues.

“The region-specific cells we found could provide tremendous advantages in the laboratory to study development, evolution and disease, and may offer avenues for generating novel therapies,” says Salk Professor Juan Carlos Izpisua Belmonte, senior author of the paper and holder of Salk’s Roger Guillemin Chair.

The researchers dubbed this new class of cells “region-selective pluripotent stem cells,” or rsPSCs for short. The rsPSCs were easier to grow in the laboratory than conventional human pluripotent stem cells and offered advantages for large-scale production and gene editing (altering a cell’s DNA), both desirable features for cell replacement therapies.

Juan Carlos Izpisua Belmonte and Jun Wu

Credit: Courtesy of the Salk Institute for

Biological Studies.

To produce the cells, the Salk scientists developed a combination of chemical signals that directed human stem cells in a laboratory dish to become spatially oriented.

They then inserted the spatially oriented human stem cells (human rsPSCs) into specific regions of partially dissected mouse embryos and cultured them in a dish for 36 hours. Separately, they also inserted human stem cells cultured using conventional methods, so that they could compare existing techniques to their new technique.

While the human stem cells derived through conventional methods failed to integrate into the modified embryos, the human rsPSCs began to develop into early stage tissues. The cells in this region of an early embryo undergo dynamic changes to give rise to all cells, tissues and organs of the body. Indeed the human rsPSCs began the process of differentiating into the three major cell layers in early development, known as ectoderm, mesoderm and endoderm. The Salk researchers stopped the cells from differentiating further, but each germ layer was theoretically capable of giving rise to specific tissues and organs.

The new stem cell (green), developed at the Salk

Institute, holds promise for one day growing

replacement functional cells and tissues. Credit:

Courtesy of the Salk Institute for Biological

Studies.

Collaborating with the labs of Salk Professors Joseph Ecker and Alan Saghatelian, the Izpisua Belmonte team performed extensive characterization of the new cells and found rsPSCs showed distinct molecular and metabolic characteristics as well as novel epigenetic signatures – that is, patterns of chemical modifications to DNA that control which genes are turned on or off without changing the DNA sequence.

“The region selective-state of these stem cells is entirely novel for laboratory-cultured stem cells and offers important insight into how human stem cells might be differentiated into derivatives that give rise to a wide range of tissues and organs,” says Jun Wu, a postdoctoral researcher in Izpisua Belmonte’s lab and first author of the new paper.

“Not only do we need to consider the timing, but also the spatial characteristics of the stem cells. Understanding both aspects of a stem cell’s identity could be crucial to generate functional and mature cell types for regenerative medicine.”

Source: Salk Institute

Contact: Salk Communications

Reference:

An alternative pluripotent state confers interspecies chimaeric competency

Authors: Jun Wu, Daiji Okamura, Mo Li, Keiichiro Suzuki, Chongyuan Luo,Li Ma, Yupeng He, Zhongwei Li, Chris Benner, Isao Tamura, Marie N. Krause, Joseph R. Nery, Tingting Du, Zhuzhu Zhang, Tomoaki Hishida, Yuta Takahashi, Emi Aizawa, Na Young Kim, Jeronimo Lajara, Pedro Guillen, Josep M. Campistol, Concepcion Rodriguez Esteban, Pablo J. Ross, Alan Saghatelian, Bing Ren, Joseph R. Ecker and Juan Carlos Izpisua Belmonte

Nature, 06 May 2015, doi:10.1038/nature14413

.........

ZenMaster

---

For more on stem cells and cloning, go to CellNEWS at

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

---

New Clues into How Stem Cells Get Their Identity

New Clues into How Stem Cells Get Their Identity

Wednesday, 06 May 2015

Scientists at the University of Copenhagen have identified one mechanism that explains how some stem cells choose to become a given cell type: the cells combine specific sets of proteins at precise positions along the DNA. When these particular groups of proteins are combined, the gates are opened so that certain groups of genes can now be used, giving the cells a new identity.

Scientists have now identified one of these combinations, which drive the cells along the path that allow them to become organs such as liver and pancreas. This latest research could lead scientists to a better understanding on how to generate insulin-producing cells in the laboratory to use as therapy for Type I diabetes. The work has just been published in the journal Cell Stem Cell.

Specificity – choosing the combinations

Scientists working under the leadership of Henrik Semb from the DanStem Center at the University of Copenhagen have explained how the acquisition of a new cell identity is achieved; cells respond to information from their surroundings, in turn activating a specific combination of proteins at certain places on the DNA, to turn on a genetic programme.

Stem cells. 

“We added one particular chemical compound to the culture media to promote the generation of new cell types. The information transmitted by this compound is deciphered only by a small number of proteins. We then looked all along the cell’s DNA to find the positions of the proteins that were activated by the compound. We repeated the experiment using additional compounds, to get an idea of how specific the responses were and to categorize the genes that the cells decided to use when being directed toward different cellular fates,” says Assistant Professor Karen Schachter.

Getting the identity right

The work in the field of human pluripotent stem cell research has concentrated on finding the correct combination of drugs or chemical compounds that can be used to drive the cells into specific cell types in the culture dish.

“There is however a lack of understanding of how these compounds activates the genes that give the cells unique identities, which has resulted in a lack of reproducibility of the methods used by different labs. As a comparison; if you use a pre-mixed powder to bake a cake you will face problems if you run out on an important ingredient and do not know how to replace its action. We believe that our study provides useful information that will help us to understand the recipe better, so that we can generate functional cells in a more controlled manner,” adds Post doc Nina Funa.

There is already a lot of focus in the stem cell community to generate cells in the laboratory to use as therapy, so the scientists at DanStem want to emphasize the importance of continuing doing this important basic research work.

“Our ultimate aim is to understand how stem cells make choices, which will also help improve the quality of the work that will put stem cells into therapeutic use,” concludes Funa.

Source: University of Copenhagen

Contact: Assistant Professor Karen Schachter

Reference:

β-Catenin Regulates Primitive Streak Induction through Collaborative Interactions with SMAD2/SMAD3 and OCT4

Nina S. Funa, Karen A. Schachter, Mads Lerdrup, Jenny Ekberg, Katja Hess, Nikolaj Dietrich, Christian Honoré, Klaus Hansen, Henrik Semb

Cell Stem Cell, April 23, 2015, DOI: http://dx.doi.org/10.1016/j.stem.2015.03.008

.........

ZenMaster

---

For more on stem cells and cloning, go to CellNEWS at

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

---

“Open” Stem Cell Chromosomes Reveal New Possibilities for Diabetes

Researchers map chromosomal changes that must take place before stem cells can be used to produce pancreatic and liver cells 

Thursday, 02 April 2015

These are pancreatic cells derived from

embryonic stem cells. Credit: UC San Diego

School of Medicine. 

Stem cells hold great promise for treating a number of diseases, in part because they have the unique ability to differentiate, specializing into any one of the hundreds of cell types that comprise the human body. Harnessing this potential, though, is difficult. In some cases, it takes up to seven carefully orchestrated steps of adding certain growth factors at specific times to coax stem cells into the desired cell type. Even then, cells of the intestine, liver and pancreas are notoriously difficult to produce from stem cells. Writing in Cell Stem Cell April 2, researchers at University of California, San Diego School of Medicine have discovered why.

It turns out that the chromosomes in laboratory stem cells open slowly over time, in the same sequence that occurs during embryonic development. It isn’t until certain chromosomal regions have acquired the “open” state that they are able to respond to added growth factors and become liver or pancreatic cells. This new understanding, say researchers, will help spur advancements in stem cell research and the development of new cell therapies for diseases of the liver and pancreas, such as type 1 diabetes.

“Our ability to generate liver and pancreatic cells from stem cells has fallen behind the advances we’ve made for other cell types,” said Maike Sander, MD, professor of paediatrics and cellular and molecular medicine and director of the Pediatric Diabetes Research Center at UC San Diego.

“So we haven’t yet been able to do things like test new drugs on stem cell-derived liver and pancreatic cells. What we have learned is that if we want to make specific cells from stem cells, we need ways to predict how those cells and their chromosomes will respond to the growth factors.”

Sander led the study, together with co-senior author Bing Ren, PhD, professor of cellular and molecular medicine at UC San Diego and Ludwig Cancer Research member.

Chromosomes are the structures formed by tightly wound and packed DNA. Humans have 46 chromosomes – 23 inherited from each parent. Sander, Ren and their teams first made maps of chromosomal modifications over time, as embryonic stem cells differentiated through several different developmental intermediates on their way to becoming pancreatic and liver cells. Then, in analysing these maps, they discovered links between the accessibility (openness) of certain regions of the chromosome and what they call developmental competence – the ability of the cell to respond to triggers like added growth factors.

“We’re also finding that these chromosomal regions that need to open before a stem cell can fully differentiate are linked to regions where there are variations in certain disease states,” Sander says.

In other words, if a person were to inherit a genetic variation in one of these chromosomal regions and his or her chromosome didn’t open up at exactly the right time, he or she could hypothetically be more susceptible to a disease affecting that cell type. Sander’s team is now working to further investigate what role, if any, these chromosomal regions and their variations play in diabetes.

Source: UCSD

Contact: Heather Buschman

Reference:

Epigenetic Priming of Enhancers Predicts Developmental Competence of hESC-Derived Endodermal Lineage Intermediates

Allen Wang, Feng Yue, Yan Li, Ruiyu Xie, Thomas Harper, Nisha A. Patel, Kayla Muth, Jeffrey Palmer, Yunjiang Qiu, Jinzhao Wang, Dieter K. Lam, Jeffrey C. Raum, Doris A. Stoffers, Bing Ren, Maike Sander

Cell Stem Cell, Volume 16, Issue 4, p386–399, 2 April 2015, DOI: http://dx.doi.org/10.1016/j.stem.2015.02.013

.........

ZenMaster

---

For more on stem cells and cloning, go to CellNEWS at

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

---

Stem Cells Make Similar Decisions to Humans

Stem Cells Make Similar Decisions to Humans

Wednesday, 25 March 2015

Pancreas explant. 

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

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

The research is published in the scientific journal PLOS Biology.

Why one cell matters

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

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

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

Stem cell movies

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

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

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

Next steps in diabetes therapy

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

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

Source: University of Copenhagen

Contact: Yung Hae Kim

Reference:

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

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

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

.........

ZenMaster

---

For more on stem cells and cloning, go to CellNEWS at

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

---

Scientists Pinpoint Molecule that Switches On Stem Cell Genes

Experiments placed Sox9 at the crux of a shift in gene expression associated with hair follicle stem cell identity

Friday, 20 March 2015

Stem cells can have a strong sense of identity. Taken out of their home in the hair follicle, for example, and grown in culture, these cells remain true to themselves. After waiting in limbo, these cultured cells become capable of regenerating follicles and other skin structures once transplanted back into skin. It's not clear just how these stem cells – and others elsewhere in the body – retain their ability to produce new tissue and heal wounds, even under extraordinary conditions.

New research at Rockefeller University has identified a protein, Sox9, which takes the lead in controlling stem cell plasticity. In a paper published March 18 in Nature, the team describes Sox9 as a "pioneer factor" that breaks ground for the activation of genes associated with stem cell identity in the hair follicle.

"We found that in the hair follicle, Sox9 lays the foundation for stem cell plasticity. First, Sox9 makes the genes needed by stem cells accessible, so they can become active. Then, Sox9 recruits other proteins that work together to give these "stemness" genes a boost, amplifying their expression," says study author Elaine Fuchs, Rebecca C. Lancefield Professor, Robin Chemers Neustein Laboratory of Mammalian Cell Biology and Development.

"Without Sox9, this process never happens, and hair follicle stem cells cannot survive."

Sox9 is a type of protein called a transcription factor, which can act like a volume dial for genes. When a transcription factor binds to a segment of DNA known as an enhancer, it cranks up the activity of the associated gene. Recently, scientists identified a less common, but more powerful version: the super-enhancer. Super-enhancers are much longer pieces of DNA, and host large numbers of cell type-specific transcription factors that bind cooperatively. Super-enhancers also contain histones, DNA-packaging proteins, which harbour specific chemical groups – epigenetic marks – that make genes they are associated with accessible so they can be expressed.

Using an epigenetic mark associated specifically with the histones of enhancers, first author Rene Adam, a graduate student in the lab, and colleagues, identified 377 of these high-powered gene-amplifying regions in hair follicle stem cells. The majority of these super-enhancers were bound by at least five transcription factors, often including Sox9. Then, they compared the stem cell super-enhancers to those of short-lived stem cell progeny, which have begun to choose a fate, and so lost the plasticity of stem cells. These two types of cells shared only 32 percent of their super-enhancers, suggesting these regions played an important role in skin cell identity. By switching off super-enhancers associated with stem cell genes, these genes were silenced while new super-enhancers were being activated to turn on hair genes.

To better understand these dynamics, the researchers took a piece of a super-enhancer, called an epicentre, where all the stem cell transcription factors bind, and they linked it to a gene that glowed green whenever the transcription factors were present. In living mice, all the hair follicle stem cells glowed green, but surprisingly, the green gene turned off when the stem cells were taken from the follicle and placed in culture. When they put the cells back into living skin, the green glow returned.

Another clue came from experiments performed by Hanseul Yang, another student in the lab. By examining the new super-enhancers that were gained when the stem cells were cultured, they learned that these new super-enhancers bound transcription factors that were known to be activated during wound-repair. When they used one of these epicentres to drive the green gene, the green glow appeared in culture, but not in skin. When they wounded the skin, then the green glow switched on.

Researchers made stem cells fluoresce green (at

the base of hair follicles above) by labelling their

super-enhancers, regions of the genome bound

by gene-amplifying proteins. It appears one such

protein, Sox9, leads the activation of super-

enhancers that boost genes associated with stem

cell plasticity. Credit: Laboratory of

Mammalian Cell Biology and Development at

the Rockefeller University/Nature. 

"We were learning that some super-enhancers are specifically activated in the stem cells within their native niche, while other super-enhancers specifically switch on during injury," explained Adam.

"By shifting epicentres, you can shift from one cohort of transcription factors to another to adapt to different environments. But we still needed to determine what was controlling these shifts."

The culprit turned out to be Sox9, the only transcription factor expressed in both living tissue and culture. Further experiments confirmed Sox9's importance by showing, for example, that removing it spelled death for stem cells, while expressing it in the epidermis gave the skin cells features of hair follicle stem cells. These powers seemed to be special to Sox9, placing it atop the hierarchy of transcription factors in the stem cells. Sox9 is one of only a few pioneer factors known in biology which can initiate such dramatic changes in gene expression.

"Importantly, we link this pioneer factor to super-enhancer dynamics, giving these domains a 'one-two punch' in governing cell identity. In the case of stem cell plasticity, Sox9 appears to be the lead factor that activates the super-enhancers that amplify genes associated with stemness," Fuchs says.

"These discoveries offer new insights into the way in which stem cells choose their fates and maintain plasticity while in transitional states, such as in culture or when repairing wounds."

Source: Rockefeller University

Contact: Wynne Parry

Reference:

Pioneer factors govern super-enhancer dynamics in stem cell plasticity and lineage choice

Rene C. Adam, Hanseul Yang, Shira Rockowitz, Samantha B. Larsen, Maria Nikolova, Daniel S. Oristian, Lisa Polak, Meelis Kadaja, Amma Asare, Deyou Zheng, and Elaine Fuchs

Nature, March 18, 2015, doi:10.1038/nature14289

.........

ZenMaster

---

For more on stem cells and cloning, go to CellNEWS at

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

---

New Technology Directly Reprograms Skin Fibroblasts for a New Role

Penn study has implications for new skin disease treatments

Tuesday, 16 December 2014

Dermal fibroblasts are directly reprogrammed to

pigmented melanocytes by three transcription

factors (SOX10, MITF and PAX3).

Credit: Ruifeng Yang, Perelman School of

Medicine, University of Pennsylvania. 

As the main component of connective tissue in the body, fibroblasts are the most common type of cell. Taking advantage of that ready availability, scientists from the Perelman School of Medicine at the University of Pennsylvania, the Wistar Institute, Boston University School of Medicine, and New Jersey Institute of Technology have discovered a way to repurpose fibroblasts into functional melanocytes, the body's pigment-producing cells. The technique has immediate and important implications for developing new cell-based treatments for skin diseases such as vitiligo, as well as new screening strategies for melanoma. The work was published this week in Nature Communications.

The new technique cuts out a cellular middleman. Study senior author Xiaowei "George" Xu, MD, PhD, an associate professor of Pathology and Laboratory Medicine, explains.

"Through direct reprogramming, we do not have to go through the pluripotent stem cell stage, but directly convert fibroblasts to melanocytes. So these cells do not have tumourigenicity."

Changing a cell from one type to another is hardly unusual. Nature does it all the time, most notably as cells divide and differentiate themselves into various types as an organism grows from an embryo into a fully-functional being. With stem cell therapies, medicine is learning how to tap into such cell specialization for new clinical treatments. But controlling and directing the process is challenging. It is difficult to identify the specific transcription factors needed to create a desired cell type. Also, the necessary process of first changing a cell into an induced pluripotent stem cell (iPSC) capable of differentiation, and then into the desired type, can inadvertently create tumours.

Xu and his colleagues began by conducting an extensive literature search to identify 10 specific cell transcription factors important for melanocyte development. They then performed a transcription factor screening assay and found three transcription factors out of those 10 that are required for melanocytes: SOX10, MITF, and PAX3, a combination dubbed SMP3.

"We did a huge amount of work," says Xu.

"We eliminated all the combinations of the other transcription factors and found that these three are essential."

The researchers first tested the SMP3 combination in mouse embryonic fibroblasts, which then quickly displayed melanocytic markers. Their next step used a human-derived SMP3 combination in human foetal dermal cells, and again melanocytes (human-induced melanocytes, or hiMels) rapidly appeared. Further testing confirmed that these hiMels indeed functioned as normal melanocytes, not only in cell culture but also in whole animals, using a hair-patch assay, in which the hiMels generated melanin pigment. The hiMels proved to be functionally identical in every respect to normal melanocytes.

Xu and his colleagues anticipate using their new technique in the treatment of a wide variety of skin diseases, particularly those such as vitiligo for which cell-based therapies are the best and most efficient approach.

The method could also provide a new way to study melanoma.

By generating melanocytes from the fibroblasts of melanoma patients, Xu explains: "we can screen not only to find why these patients easily develop melanoma, but possibly use their cells to screen for small compounds that can prevent melanoma from happening."

Perhaps most significantly, say the researchers, is the far greater number of fibroblasts available in the body for reprogramming compared to tissue-specific adult stem cells, which makes this new technique well-suited for other cell-based treatments.

Source: University of Pennsylvania School of Medicine

Contact: Karen Kreeger

.........

ZenMaster

---

For more on stem cells and cloning, go to CellNEWS at

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

---