Stem Cells Age-discriminate Organelles to Maintain Stemness

Stem Cells Age-discriminate Organelles to Maintain Stemness

Thursday, 02 April 2015

Tissue stem cells, that continuously renew our tissues, can divide asymmetrically to produce two types of daughter cells. One will be the new stem cell, whereas the other will give rise to the differentiating cells of the tissue.

A study jointly leads by laboratories in the Institute of Biotechnology, University of Helsinki and Massachusetts Institute of Technology (MIT) investigated whether stem cells may also use asymmetric cell division to reduce accumulation of cellular damage. Damage build-up can cause stem cell exhaustion that result in reduced tissue renewal and aging.

Human mammary stem-like cell apportions

aged mitochondria asymmetrically between

daughter cells. Mitochondria were labelled age-

selectively red 51 hours prior to imaging, leaving

mitochondria that are younger unlabelled. The

daughter cell that will become the new stem cell

(bottom left) receives only few old mitochondria.

Credit: Julia Döhla. 

Researchers developed a novel approach to follow cellular components, such as organelles, age-selectively during cell division. Scientists in David Sabatini's lab studied stem-like cells (SLCs) from cultures of immortalized human mammary epithelial cells. These SLCs were chosen because they express genes associated with the stem-cell state (referred to as stemness), are able to form structures known as mammospheres in culture. To track the destinations of subcellular components during cell division, the researchers, led by former postdoctoral scientist Pekka Katajisto, tagged the components – including lysosomes, mitochondria, Golgi apparatus, ribosomes, and chromatin – with a fluorescent protein that glows when hit by a pulse of ultraviolet light.

"We found that stem cells segregate their old mitochondria to the daughter cell that will differentiate, whereas the new stem cell will receive only young mitochondria" says Pekka Katajisto, a Group leader and Academy research fellow at BI.

By tracing the movements of the glowing organelles, the researchers were able to demonstrate that while the normal epithelial cells distributed all of the tagged components symmetrically to daughter cells, the SLCs localized their older mitochondria distinctly and passed on the lion's share of them to the daughter cells headed for differentiation. The researchers ultimately found that the number of older mitochondria in those cells was roughly six times that in daughter cells whose fate was to remain as stem cells.

Mitochondria appear to be particularly important for stem cells, as other analysed organelles were not similarly age-discriminated, and since inhibition of normal mitochondrial quality control pathways stopped their age-selective segregation.

"There is a fitness advantage to renewing your mitochondria," says David Sabatini, Professor at MIT and Whitehead Institute.

"Stem cells know this and have figured out a way to discard their older components."

“While the mechanism used by stem cells to recognize the age of their mitochondria remains unknown, forced symmetric apportioning of aged mitochondria resulted in loss of stemness in all of the daughter cells," says Katajisto.

"This suggests that the age-selective apportioning of old and potentially damaged organelles may be a way to fight stem cell exhaustion and aging," says Katajisto who now runs a lab at the Institute of Biotechnology at University of Helsinki.

Katajisto laboratory is now exploring how old mitochondria differ from old, and whether this phenomenon occurs in other cell types beyond the human mammary stem-like cells examined here as well as in in vivo.

Source: University of Helsinki

Contact: Pekka Katajisto

Reference:

Asymmetric apportioning of aged mitochondria between daughter cells is required for stemness 

Pekka Katajisto, Julia Döhla, Christine Chaffer, Nalle Pentinmikko, Nemanja Marjanovic, Sharif Iqbal, Roberto Zoncu, Walter Chen, Robert A. Weinberg, David M. Sabatini

Science April 2, .2015, DOI:10.1126/science.1260384

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Researchers Create 'Naïve' Pluripotent Human Embryonic Stem Cells

Researchers Create 'Naïve' Pluripotent Human Embryonic Stem Cells

Saturday, 26 July 2014

Phase and fluorescence images of conventional

(primed) human embryonic stem cells (ESCs)

and naïve human ESCs generated in the

presence of 5 small molecule inhibitors.

The naïve human ESCs exhibit activation of a

fluorescent reporter linked to an enhancer of

theOCT4 gene that is specifically used in

the naïve state. 40X magnification. Credit:

Courtesy of Thorold Theunissen. 

For years, researchers and patients have hoped that embryonic stem cells (ESCs) — capable of forming nearly any cell type in the body — could provide insight into numerous diseases perhaps even be used to treat them. Yet progress has been hampered by the inability to transfer research and tools from mouse ESC studies to their human counterparts, in part because human ESCs are "primed" and slightly less plastic than the mouse cells.

Now Thorold Theunissen, Benjamin Powell, and Haoyi Wang, who are scientists in the lab of Whitehead Institute Founding Member Rudolf Jaenisch, have discovered how to manipulate and maintain human ESCs in a "naïve" or base pluripotent state similar to that of mouse ESCs without the use of any reprogramming factors. Their work is described in this week's issue of the journal Cell Stem Cell.

Naïve mice ESCs are well-studied, and scientists have a strong understanding of how they function and mature into more specialized cells. But this understanding is of limited use in human ESC research, as the human cells look different, grow differently, and rely on different genes than mouse ESCs. According to Theunissen, the disparities between mouse and human ESCs are attributable not to species-specific differences but rather to differences of cell state.

In naïve mouse ESCs, a particular enhancer of the gene OCT4 is active, prompting the researchers to look for the presence of this marker as a means to identify rare naïve human ESCs. With this unbiased reporter system in hand, the Jaenisch team determined that a cocktail of five small molecules with a few additional growth factors can induce and support the conversion of primed human ESCs to a naïve state with or without using reprogramming factors to jumpstart the process.

By applying this cocktail to human blastocysts, the scientists could also isolate naïve human stem cells.

"This is important because if this cocktail only works in existing lines of human ESCs, you might wonder, does this really capture a distinct state or is this artificial?" says Theunissen.

"Since the cocktail works directly on human blastocysts, I think it suggests that we're really capturing a cell state that is already present in the early human embryo."

Although other labs have recently reported creating naïve human ESCs, Theunissen, Powell, and Wang question these results as the cells produced through these techniques lack the gene expression and epigenetic profiles of naïve human ESCs. Yet, the Jaenisch lab believes they have now finally unlocked a way to create and maintain this important type of cell and are looking forward to exploring its potential.

"We have discovered a new pathway to generate something we believe is a totally different state of pluripotency in human ESCs that is very close to the mouse naïve state," says Jaenisch, who is also a professor of biology at MIT.

"These cells may be essential for ESC technology, and that is an area we're looking forward to investigating. Now the big question for us is, does this state exist in vivo in embryos? Right now, we don't know, and that is a very interesting line of research."

Source: Whitehead Institute for Biomedical Research 

Contact: Nicole Giese Rura

Reference:

Systematic Identification of Culture Conditions for Induction and Maintenance of Naive Human Pluripotency

Thorold W. Theunissen, Benjamin E. Powell, Haoyi Wang, Maya Mitalipova, Dina A. Faddah, Jessica Reddy, Zi Peng Fan, Dorothea Maetzel, Kibibi Ganz, Linyu Shi, Tenzin Lungjangwa, Sumeth Imsoonthornruksa, Yonatan Stelzer, Sudharshan Rangarajan, Ana D'Alessio, Jianming Zhang, Qing Gao, Meelad M. Dawlaty, Richard A. Young, Nathanael S. Gray, and Rudolf Jaenisch

Cell Stem Cell, July 24, 2014, http://www.cell.com/cell-stem-cell/abstract/S1934-5909(14)00298-7

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Regenerating Our Kidneys

Tel Aviv University research uses new technique to uncover the building blocks of kidney regeneration

Tuesday, 17 June 2014

Doctors and scientists have for years been astonished to observe patients with kidney disease experiencing renal regeneration. The kidney, unlike its neighbour the liver, was universally understood to be a static organ once it had fully developed.

Now a new study conducted by researchers at Sheba Medical Center, Tel Aviv University and Stanford University turns that theory on its head by pinpointing the precise cellular signalling responsible for renal regeneration and exposing the multi-layered nature of kidney growth. The research, in Cell Reports, was conducted by principal investigators Dr. Benjamin Dekel of TAU's Sackler School of Medicine and Sheba Medical Center and Dr. Irving L. Weissman of Stanford University's School of Medicine, working with teams of researchers from both universities.

"We wanted to change the way people thought about kidneys – about internal organs altogether," said Dr. Dekel, who specializes in stem-cell research, genetics, and nephrology.

"Very little is known even now about the way our internal organs function at the single cell level. This study flips the paradigm that kidney cells are static – in fact, kidney cells are continuously growing, all the time."

Dr. Dekel began researching the subject three years ago while on sabbatical at Stanford University. While the laboratory experiments and stem cell research were conducted at Stanford, the results were analysed by researchers at TAU and Stanford.

According to Dr. Dekel, scientists knew kidney cells could reproduce outside the body, but the physiological process taking place inside the body at the single cell level was never explored. Uncovering that process became the focus of his efforts.

Dr. Dekel and his research team conducted a study using a "rainbow mouse" model developed at Stanford's Weissman lab, a mouse genetically altered to express one of four alternative fluorescent markers called "reporters" in each cell. The markers allowed researchers to trace cell growth in vivo — growth, they were surprised to find, that was sectional and multi-directional.

"We were amazed to find that renal growth does not depend on a single stem cell, but is rather compartmentalized," said Dr. Dekel.

"Each part of the nephron is responsible for its own growth, each segment responsible for its own development, like a tree trunk and branches – each branch grows at a different pace and in a different direction."

Using the rainbow mouse, the researchers were able to pinpoint a specific molecule responsible for renal cellular growth called the "WNT signal". Once activated in specific precursor cells in each kidney segment, the WNT signal results in robust renal cellular growth and generation of long branches of cells.

"Our aim was to use a new technique to analyse an old problem," said Dr. Dekel.

"No one had ever used a rainbow mouse model to monitor development of kidney cells. It was exciting to use these genetic tricks to discover that cellular growth was occurring all the time in the kidney – that, in fact, the kidney was constantly remodelling itself in a very specific mode."

Dr. Dekel and the research team are paving the way for novel cellular and molecular therapeutics to achieve human kidney regeneration and alleviate shortage of kidney organs for transplantation.

"This study teaches us that in order to regenerate the entire kidney segments different precursor cells grown outside of our bodies will have to be employed," he said.

"In addition, if we were able to further activate the WNT pathway, then in cases of disease or trauma we could activate the phenomena for growth and really boost kidney regeneration to help patients. This is a platform for the development of new therapeutics, allowing us to follow the growth and expansion of cells following treatment."

Source: American Friends of Tel Aviv University 

Contact: George Hunka

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Protein Switch Dictates Cellular Fate

Stem cell or neuron

Thursday, 13 February 2014

Human neural progenitor cells isolated under

selective culture conditions from the developing

human brain and directed through lineage

differentiation. Neural progenitor cells are

stained green; differentiated astrocytes are

orange. Nuclei are stained blue. Credit: Image

courtesy of the National Institute of Neurological

Disorders and Stroke. 

Researchers at the University of California, San Diego School of Medicine have discovered that a well-known protein has a new function: It acts in a biological circuit to determine whether an immature neural cell remains in a stem-like state or proceeds to become a functional neuron.

The findings, published in the February 13 online issue of Cell Reports, more fully illuminate a fundamental but still poorly understood cellular act – and may have significant implications for future development of new therapies for specific neurological disorders, including autism and schizophrenia.

Postdoctoral fellow Chih-Hong Lou, working with principal investigator Miles F. Wilkinson, PhD, professor in the Department of Reproductive Medicine and a member of the UC San Diego Institute for Genomic Medicine, and other colleagues, discovered that this critical biological decision is controlled by UPF1, a protein essential for the nonsense-mediated RNA decay (NMD) pathway.

NMD was previously established to have two broad roles. First, it is a quality control mechanism used by cells to eliminate faulty messenger RNA (mRNA) – molecules that help transcribe genetic information into the construction of proteins essential to life. Second, it degrades a specific group of normal mRNAs. The latter function of NMD has been hypothesized to be physiologically important, but until now it had not been clear whether this is the case.

Wilkinson and colleagues discovered that in concert with a special class of RNAs called microRNA, UPF1 acts as a molecular switch to determine when immature (non-functional) neural cells differentiate into non-dividing (functional) neurons. Specifically, UPF1 triggers the decay of a particular mRNA that encodes for a protein in the TGF-b signalling pathway that promotes neural differentiation. By degrading that mRNA, the encoded protein fails to be produced and neural differentiation is prevented. Thus, Lou and colleagues identified for the first time a molecular circuit in which NMD acts to drive a normal biological response.

NMD also promotes the decay of mRNAs encoding proliferation inhibitors, which Wilkinson said may explain why NMD stimulates the proliferative state characteristic of stem cells.

"There are many potential clinical ramifications for these findings," Wilkinson said.

"One is that by promoting the stem-like state, NMD may be useful for reprogramming differentiated cells into stem cells more efficiently.”

"Another implication follows from the finding that NMD is vital to the normal development of the brain in diverse species, including humans. Humans with deficiencies in NMD have intellectual disability and often also have schizophrenia and autism. Therapies to enhance NMD in affected individuals could be useful in restoring the correct balance of stem cells and differentiated neurons and thereby help restore normal brain function."

Source: University of California - San Diego 

Contact: Scott LaFee

Reference:

Posttranscriptional Control of the Stem Cell and Neurogenic Programs by the Nonsense-Mediated RNA Decay Pathway

Chih H. Lou, Ada Shao, Eleen Y. Shum, Josh L. Espinoza, Lulu Huang, Rachid Karam, and Miles F. Wilkinson 

Cell Reports, 13 February 2014, 10.1016/j.celrep.2014.01.028

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Rewiring Stem Cells

Rewiring Stem Cells

Friday, 10 January 2014

This is a set of chromosomes in haploid mouse 
embryonic stem cells. Credit: Martin Leeb. 

A fast and comprehensive method for determining the function of genes could greatly improve our understanding of a wide range of diseases and conditions, such as heart disease, liver disease and cancer.

The method uses stem cells with a single set of chromosomes, instead of the two sets found in most cells, to reveal what causes the "circuitry" of stem cells to be rewired as they begin the process of conversion into other cell types. The same method could also be used to understand a range of biological processes.

Embryonic stem cells rely on a particular gene circuitry to retain their original, undifferentiated state, making them self-renewing. The dismantling of this circuitry is what allows stem cells to start converting into other types of cells - a process known as cell differentiation - but how this happens is poorly understood.

Researchers from the University of Cambridge Wellcome Trust-MRC Stem Cell Institute have developed a technique which can pinpoint the factors which drive cell differentiation, including many that were previously unidentified. The method, outlined in the Thursday (9 January) edition of the journal Cell Stem Cell, uses stem cells with a single set of chromosomes to uncover how cell differentiation works.

Cells in mammals contain two sets of chromosomes – one set inherited from the mother and one from the father. This can present a challenge when studying the function of genes, however: as each cell contains two copies of each gene, determining the link between a genetic change and its physical effect, or phenotype, is immensely complex.

"The conventional approach is to work gene by gene, and in the past people would have spent most of their careers looking at one mutation or one gene," said Dr Martin Leeb, who led the research, in collaboration with Professor Austin Smith.

"Today, the process is a bit faster, but it's still a methodical gene by gene approach because when you have an organism with two sets of chromosomes that's really the only way you can go."

Dr Leeb used unfertilised mouse eggs to generate embryonic stem cells with a single set of chromosomes, known as haploid stem cells. These haploid cells show all of the same characteristics as stem cells with two sets of chromosomes, and retain the same full developmental potential, making them a powerful tool for determining how the genetic circuitry of mammalian development functions.

The researchers used transposons – "jumping genes" – to make mutations in nearly all genes. The effect of a mutation can be seen immediately in haploid cells because there is no second gene copy. Additionally, since embryonic stem cells can convert into almost any cell type, the haploid stem cells can be used to investigate any number of conditions in any number of cell types. Mutations with important biological effects can then rapidly be traced to individual genes by next generation DNA sequencing.

"This is a powerful and revolutionary new tool for discovering how gene circuits operate," said Dr Leeb.

"The cells and the methodology we've developed could be applied to a huge range of biological questions."

Source: University of Cambridge 

Contact: Sarah Collins

Reference:

Genetic Exploration of the Exit from Self-Renewal Using Haploid Embryonic Stem Cells

Martin Leeb, Sabine Dietmann, Maike Paramor, Hitoshi Niwa, Austin Smith

Cell Stem Cell, 09 January 2014, 10.1016/j.stem.2013.12.008

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Why Stem Cells Need to Stick With Their Friends

Why Stem Cells Need to Stick With Their Friends

Thursday, 07 November 2013

Embryonic stem cells stick together (green, left

image) while they express Oct4 protein in their

nuclei (magenta, left). When Oct4 is removed

their shape changes and their adhesion to each

other is reduced (right panel, nuclei in blue).

Credit: DanStem. 

Scientists at University of Copenhagen and University of Edinburgh have identified a core set of functionally relevant factors which regulates embryonic stem cells' ability for self-renewal. A key aspect is the protein Oct4 and how it makes stem cells stick together. The identification of these factors will be an important tool in devising better and safer ways of making specialised cells for future regenerative cell therapies for treatment of diseases like diabetes and Parkinson's disease. The results have just been published in the scientific journal Current Biology.

Scientists have known that the protein Oct4 plays a key role in maintaining the embryonic stem cells in pure form by turning on stem cell genes, however up until now it has not been know which of the 8.000 or more possible genes that Oct4 can choose from actually support self-renewal.

By comparing the evolution of stem cells in frogs, mice and humans, scientists at the Danish Stem Cell Center (DanStem) and the MRC Centre for Regenerative Medicine in Edinburgh have now been able to link the protein Oct4 with the ability of cells to stick together. They found that for embryonic stem cells to thrive they need to stick together and Oct4's role is to make sure they stay that way.

"Embryonic stem cells can stay forever young unless they become grown-up cells with a specialised job in a process called differentiation. Our study shows that Oct4 prevents this process by pushing stem cells to stick to each other," says Dr Alessandra Livigni, Research Fellow at the University of Edinburgh.

Identification of specific genes

The research teams in Edinburgh and Copenhagen successfully identified 53 genes, out of more than 8.000 possible candidates that together with Oct4, functionally regulate cell adhesion. Almost like finding needles in a haystack the scientists have paved the way for a more efficient way of maintaining stem cells as stem cells.

"Embryonic stem cells are characterized, among other things, by their ability to perpetuate themselves indefinitely and differentiate into all the cell types in the body – a trait called pluripotency. Though to be able to use them medically, we need to be able to maintain them as stem cells, until they're needed. When we want to turn a stem cell into a specific cell for example; an insulin producing beta cell, or a nerve cell like those in the brain, we'd like this process to occur accurately and efficiently. We cannot do this if we don't understand how to maintain stem cells as stem cells," says Professor Joshua Brickman from DanStem, University of Copenhagen.

Future potential

As well as maintaining embryonic stem cells in their pure state more effectively, this new insight will also enable scientists to more efficiently manipulate adult cells to revert to a stem cell like stage known as induced pluripotent stem cells (iPS cells). These cells have many of the same traits and characteristics as embryonic stem cells but can be derived from the patients to both help study degenerative disease and eventually treat them.

"This research knowledge has the potential for us to change the way we grow stem cells, enabling us to use them in a less costly and more efficient way. It will help us devise better and safer ways to create specialised cells for future regenerative medicine therapies," concludes Professor Joshua

Source: University of Copenhagen 

Contact: Joshua Brickman

Reference:

A Conserved Oct4/POUV-Dependent Network Links Adhesion and Migration to Progenitor Maintenance

Alessandra Livigni, Hanna Peradziryi, Alexei A. Sharov, Gloryn Chia, Fella Hammachi, Rosa Portero Migueles, Woranop Sukparangsi, Salvatore Pernagallo, Mark Bradley, Jennifer Nichols, Minoru S.H. Ko, Joshua M. Brickman

Current Biology, 07 November 2013, 10.1016/j.cub.2013.09.048

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Reprogramming in situ: Spanish Team is First to Produce Embryonic Stem Cells in Living Adult Organisms

The characteristics of the obtained stem cells correspond to a primitive totipotent state that has never before been obtained

Wednesday, 11 September 2013

A team from the Spanish National Cancer Research Centre (CNIO) has become the first to make adult cells from a living organism retreat in their evolutionary development to recover the characteristics of embryonic stem cells.

Pictured are Manuel Serrano and Maria Abad

in his laboratory at the CNIO. Credit: Spanish

National Cancer Research Center (CNIO).

Researchers have also discovered that these embryonic stem cells, obtained directly from the inside of the organism, have a broader capacity for differentiation than those obtained via in vitro culture. Specifically, they have the characteristics of totipotent cells: a primitive state never before obtained in a laboratory.

The study, carried out by CNIO, was led by Manuel Serrano, the director of the Molecular Oncology Programme and head of the Tumoural Suppression Laboratory. The study was supported by Manuel Manzanares's team from the Spanish National Cardiovascular Research Centre (CNIC).

Embryonic stem cells are the main focus for the future of regenerative medicine. They are the only ones capable of generating any cell type from the hundreds of cell types that make up an adult organism, so they are the first step towards curing illnesses such as Alzheimer, Parkinson's disease or diabetes. Nevertheless, this type of cell has a very short lifespan, limited to the first days of embryonic development, and they do not exist in any part of an adult organism.

One of the greatest achievements in recent biomedical research was in 2006 when Shinya Yamanaka managed to create embryonic stem cells (pluripotent stem cells, induced in vitro or in vitro iPSCs) in a laboratory from adult cells, via a cocktail of just four genes. Yamanaka's discovery, for which he was awarded the Nobel Prize in Medicine in 2012, opened a new horizon in regenerative medicine.

CNIO researchers have taken another step forward, by achieving the same as Yamanaka, but this time within the same organism, in mice, without the need to pass through in vitro culture dishes. Generating these cells within an organism brings this technology even closer to regenerative medicine.

The first challenge for CNIO researchers was to reproduce the Yamanaka experiment in a living being. They chose a mouse as a model organism. Using genetic manipulation techniques, researchers created mice in which Yamanaka's four genes could be activated at will. When these genes were activated, they observed that the adult cells were able to retreat in their evolutionary development to become embryonic stem cells in multiple tissues and organs.

María Abad, the lead author of the article and a researcher in Serrano's group, said:

"This change of direction in development has never been observed in nature. We have demonstrated that we can also obtain embryonic stem cells in adult organisms and not only in the laboratory".

Manuel Serrano added that:

"We can now start to think about methods for inducing regeneration locally and in a transitory manner for a particular damaged tissue".

Stem cells obtained in mice also show totipotent characteristics never generated in a laboratory, equivalent to those present in human embryos at the 72-hour stage of development, when they are composed of just 16 cells.

In comparison with the cells obtained with the technique developed by Yamanaka, the stem cells obtained by CNIO therefore represent an even earlier embryonic state, with greater capacity for differentiation.

The authors were even able to induce the formation of pseudo-embryonic structures (teratomas) in the thoracic and abdominal cavities of the mice. These pseudo-embryos displayed the three layers typical of embryos (ectoderm, mesoderm and endoderm), and extra-embryonic structures such as the Vitelline membrane and even signs of blood cell formation.

"This data tell us that our stem cells are much more versatile than Yamanaka's in vitro iPSCs, whose potency generates the different layers of the embryo but never tissues that sustain the development of a new embryo, like the placenta", said the CNIO researcher.

The authors emphasise that the possible therapeutic applications of their work are still distant, but they admit that, without doubt, it might mean a change of direction for stem cell research, for regenerative medicine or for tissue engineering.

"Our stem cells also survive outside of mice, in a culture, so we can also manipulate them in a laboratory", said Abad.

"The next step is studying if these new stem cells are capable of efficiently generating different tissues such as that of the pancreas, liver or kidney".

Source: Centro Nacional de Investigaciones Oncologicas (CNIO) 

Contact: Juan J. Gomez

Reference:

Reprogramming in vivo produces teratomas and iPSCs with totipotency features

María Abad, Lluc Mosteiro, Cristina Pantoja, Marta Cañamero, Teresa Rayón, Inmaculada Ors, Osvaldo Graña, Diego Megías, Orlando Domínguez, Dolores Martínez, Miguel Manzanares, Sagrario Ortega, Manuel Serrano

Nature (2013), DOI: 10.1038/nature12586

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Key Finding in Stem Cell Self-renewal

Key Finding in Stem Cell Self-renewal
Tuesday, 14 February 2012

A University of Minnesota-led research team has proposed a mechanism for the control of whether embryonic stem cells continue to proliferate and stay stem cells, or differentiate into adult cells like brain, liver or skin.

The work has implications in two areas. In cancer treatment, it is desirable to inhibit cell proliferation. But to grow adult stem cells for transplantation to victims of injury or disease, it would be desirable to sustain proliferation until a sufficient number of cells have been produced to make a usable organ or tissue.

The study gives researchers a handle on how those two competing processes might be controlled. It was performed at the university's Hormel Institute in Austin, Minn., using mouse stem cells. The researchers, led by Hormel Institute Executive Director Zigang Dong and Associate Director Ann M. Bode, have published a report in the journal Nature Structure and Molecular Biology.

"This is breakthrough research and provides the molecular basis for development of regenerative medicine," said Dong.

"This research will aid in the development of the next generation of drugs that make repairs and regeneration within the body possible following damage by such factors as cancer, aging, heart disease, diabetes, or paralysis caused by traumatic injury."

The mechanism centers on a protein called Klf4, which is found in embryonic stem cells and whose activities include keeping those cells dividing and proliferating rather than differentiating. That is, Klf4 maintains the character of the stem cells; this process is called self-renewal. The researchers discovered that two enzymes, called ERK1 and ERK2, inactivate Klf; this allows the cells to begin differentiating into adult cells.

The two enzymes are part of a "bucket brigade" of signals that starts when a chemical messenger arrives from outside the embryonic stem cells. Chemical messages are passed to inside the cells, resulting in, among other things, the two enzymes swinging into action.

The researchers also discovered how the enzymes control Klf4. They attach a small molecule – phosphate, consisting of phosphorus and oxygen – to Klf4. This "tag" marks it for destruction by the cellular machinery that recycles proteins.

Further, they found that suppressing the activity of the two enzymes allows the stem cells to maintain their self-renewal and resist differentiation. Taken together, their findings paint a picture of the ERK1 and ERK2 enzymes as major players in deciding the future of embryonic stem cells – and potentially cancer cells, whose rapid growth mirrors the behavior of the stem cells.

Klf4 is one of several factors used to reprogram certain adult skin cells to become a form of stem cells called iPS (induced pluripotent stem) cells, which behave similarly to embryonic stem cells. Also, many studies have shown that Klf4 can either activate or repress the functioning of genes and, in certain contexts, act as either an oncogene (that promotes cancer) or a tumor suppressor. Given these and their own findings reported here, the Hormel Institute researchers suggest that the self-renewal program of cancer cells might resemble that of embryonic stem cells.

"Although the functions of Klf4 in cancer are controversial, several reports suggest Klf4 is involved in human cancer development," Bode said.

Source: University of Minnesota

Contact: Jeff Falk
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A Single Stem Cell Capable of Regenerating the Entire Blood System

'Pure' Human Blood Stem Cell Discovery Opens Door to Expanding Cells for More Clinical Use
Friday, 08 July 2011

For the first time since stem cells were discovered here 50 years ago, scientists have isolated a human blood stem cell in its purest form – as a single stem cell capable of regenerating the entire blood system. This breakthrough opens the door to harnessing the power of these life-producing cells to treat cancer and other debilitating diseases more effectively.

The research is published today in Science.

"This discovery means we now have an increasingly detailed road map of the human blood development system including the much sought after stem cell," says principal investigator John Dick, who holds a Canada Research Chair in Stem Cell Biology and is a Senior Scientist at the McEwen Centre for Regenerative Medicine and the Ontario Cancer Institute, University Health Network (UHN).

"We have isolated a single cell that makes all arms of the blood system, which is key to maximizing the potential power of stem cells for use in more clinical applications. Stem cells are so rare that this is a little like finding a needle in a haystack."

Dr. Dick, who pioneered the field of cancer stem cells with previous discoveries in human leukemia and colon cancer, also developed a way to replicate the entire human leukemia disease process using genetically engineered mice. As well as being a Senior Scientist at UHN's Princess Margaret and Toronto General Hospitals, he is a Professor in the Department of Molecular Genetics, University of Toronto, and Director of the Cancer Stem Cell Program at the Ontario Institute for Cancer Research.

Dr. Dick works out of UHN's Ontario Cancer Institute (OCI) – the venerable institution where stem-cell science began in 1961 with the original discovery of Drs. James Till and Ernest McCulloch – and McEwen Centre for Regenerative Medicine with the next generation of stem-cell scientists focused on developing better and more effective treatments for heart disease, diabetes, respiratory disease and spinal cord injury.

The 1961 Till and McCulloch discovery quickly led to using stem cells for bone marrow transplantation in leukemia patients, the most successful clinical application so far in what is now known as regenerative medicine and a therapy that is used to treat thousands of patients annually around the world.

"Ever since stem-cell science began," says Dr. Dick, "scientists have been searching for the elusive mother lode – the single, pure stem cell that could be controlled and expanded in culture prior to transplantation into patients. Recently scientists have begun to harness the stem cells found in the umbilical cord blood; however, for many patients a single donor sample is not large enough to use. These new findings are a major step to generate sufficient quantities of stem cells to enable greater clinical use and thus move closer to realizing the promise of regenerative medicine for patients."

Along the way, scientists have indeed mapped many vital signposts regarding stem-cell subsets and specialization. Last year, Dr. Dick's team reported isolating the more specialized progenitor cells that lie downstream of the stem cell. The discovery published today was enabled by hi-tech flow cytometry technology: a process that rapidly sorts, sifts and purifies millions of blood cells into meaningful bins for scientific analysis. Now, stem-cell scientists can start mapping the molecular switches that guide how "normal" stem cells behave and endure, and also characterize the core properties that distinguish them from all other blood cell types.

This discovery is the one Dr. Dick has personally been seeking ever since 1988 when he developed the first means of studying human blood stem cells by transplanting them into immune-deficient mice, research that was also published in Science.

"Back then, our goal was to define single human stem cells. With advances made in technology, twenty-three years later, we have."

Source: University Health Network
Contact: Jane Finlayson

Reference:
Isolation of Single Human Hematopoietic Stem Cells Capable of Long-Term Multilineage Engraftment
Faiyaz Notta, Sergei Doulatov. Elisa Laurenti, Armando Poeppl, Igor Jurisica and John E. Dick
Science 8 July 2011, Vol. 333 no. 6039 pp. 218-221, DOI: 10.1126/science.1201219
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ZenMaster

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

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Normal Stem Cells Made to Look and Act Like Cancer Stem Cells

Normal Stem Cells Made to Look and Act Like Cancer Stem Cells
Thursday, 05 May 2011

Researchers at the University of North Carolina School of Medicine at Chapel Hill, after isolating normal stem cells that form the developing placenta, have given them the same properties of stem cells associated with an aggressive type of breast cancer.

From left to right are study co-first

authors Nicole Vincent Jordan and

Amy N. Abell, Ph.D. Credit: Photo

by Les Lang/UNC School of

Medicine.

The scientific first opens the door for developing novel targeted therapies aimed at triple negative breast cancer. Known also as TNBC, this highly recurrent tumour spreads aggressively beyond its original site in the breast and carries a poor prognosis for patients who have it.

The study will be published online Friday, May 6, by the journal Cell Stem Cell.

"We changed only one amino acid in normal tissue stem cells, trophoblast stem cells. While they maintained their self-renewal, these mutant stem cells had properties very similar to what people predict in cancer stem cells: they were highly mobile and highly invasive," said Gary Johnson, PhD, professor and chair of pharmacology at UNC and senior study author.

"No one has ever isolated a stem cell like that." Johnson is also a member of the UNC Lineberger Comprehensive Cancer Center.

In normal development, epithelial stem cells called trophoblasts are involved in the formation of placental tissue. To do so, they must undergo a conversion to tissue-like cells. These then travel to the site in the uterus where they revert to a non-invasive tissue cell.

"But the mutant trophoblast stem cells made in our lab, which would normally invade the uterus and then stop, just keep going," Johnson said.

The study led by the first authors, research assistant professor Amy N. Abell, PhD and graduate student Nicole Vincent Jordan, both working in Johnson's lab, showed that similar to triple-negative breast cancer stem cells, normal tissue stem cells also go through the same program of molecular changes during organ development called epithelial mesenchymal transition, or EMT. This suggests that breast cancer cells utilize this tissue stem cell molecular program for tumour metastasis, or cancer spread.

The discovery was made using a unique mouse model of tissue stem cell EMT developed in the Johnson laboratory. The study identified two proteins that regulate the expression of specific genes in tissue stem cells during organ development that control normal EMT. Inactivation of the proteins MAP3K4 and CBP in trophoblast stem cells causes them to become hyper invasive.

In collaboration with Aleix Prat, PhD and Charles Perou, PhD in the UNC Lineberger Comprehensive Cancer Center, the research team made another discovery: an overlap between the gene expression signature of the mutant tissue stem cells properties during EMT and the triple-negative human breast cancer gene signature that's predictive of invasiveness. The same genes were down regulated.

"This significant genetic intersection between tissue stem cells and TNBC has identified previously unrecognized genes that likely contribute to breast cancer metastasis," said Johnson.

"This newly identified gene signature is currently being investigated in different models of breast cancer with the goal of developing new therapeutic interventions for the treatment of TNBC."

Source: University of North Carolina School of Medicine
Contact: Les Lang
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ZenMaster

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

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