Think Gene Think Gene RSS

a bio blog about genetics, genomics, and biotechnology

DNA Helix

Posts Tagged ‘stem cells’

Pittsburgh researchers identify source of multipotent stem cells with broad regenerative potential

In a promising finding for the field of regenerative medicine, stem cell researchers at Children’s Hospital of Pittsburgh of UPMC have identified a source of adult stem cells found on the walls of blood vessels with the unlimited potential to differentiate into human tissues such as bone, cartilage and muscle.

The scientists, led by Bruno Péault, PhD, deputy director of the Stem Cell Research Center at Children’s Hospital, identified cells known as pericytes that are multipotent, meaning they have broad developmental potential. Pericytes are found on the walls of small blood vessels such as capillaries and microvessels throughout the body and have the potential to be extracted and grown into many types of tissues, according to the study.

“This finding marks the first direct evidence of the source of multipotent adult stem cells known as mesenchymal stem cells. We believe pericytes represent one of the most promising sources of multipotent stem cells that scientists have been searching for in the quest to make regenerative medicine possible,” Dr. Péault said. “The encouraging aspect of this source is that blood vessels are the one structure that all tissues in the human body have in common. These cells can be extracted easily and painlessly from convenient sources such as fat tissue, dental pulp, umbilical cord and placental tissue, then grown in culture to large numbers and, possibly, re-injected into the patient to heal a broken bone, a failing joint or an injured muscle.”

Results of the study are published in the September issue of the journal Cell Stem Cell.

In their laboratory in the John G. Rangos Sr. Research Center, researchers were able to identify pericytes in all human tissues they analyzed, including muscle, fat, pancreas, placenta and many other samples. Through purification in the lab, these pericytes could then be coaxed into becoming whatever type of tissue the scientists desired. For instance, the researchers took pericytes from the pancreas and then reinjected them into an injured muscle. The cells immediately began regenerating muscle tissue.

Source: Children’s Hospital of Pittsburgh

Gene directs stem cells to build the heart

Josh: It’s only a matter of time before we can regenerate organs…

Researchers have shown that they can put mouse embryonic stem cells to work building the heart, potentially moving medical science a significant step closer to a new generation of heart disease treatments that use human stem cells.

Scientists at Washington University School of Medicine in St. Louis report in Cell Stem Cell that the Mesp1 gene locks mouse embryonic stem cells into becoming heart parts and gets them moving to the area where the heart forms. Researchers are now testing if stem cells exposed to Mesp1 can help fix damaged mouse hearts.

“This isn’t the only gene we’ll need to get stem cells to repair damaged hearts, but it’s a key piece of the puzzle,” says senior author Kenneth Murphy, M.D., Ph.D., professor of pathology and immunology and a Howard Hughes Medical Institute investigator. “This gene is like the first domino in a chain: the Mesp1 protein activates genes that make other important proteins, and these in turn activate other genes and so on. The end result of these falling genetic dominoes is your whole cardiovascular system.” … Continue Reading »

New technique produces genetically identical stem cells

Adult cells of mice created from genetically reprogrammed cells—so-called induced pluripotent stem (IPS) stem cells—can be triggered via drug to enter an embryonic-stem-cell-like state, without the need for further genetic alteration.

The discovery, which promises to bring new efficiencies to embryonic stem cell research, is reported in the July 1, 2008, online issue of Nature Biotechnology.

“This technical advancement will allow thousands of identical reprogrammed cells to be used in experiments,” says Marius Wernig, one of the paper’s two lead authors and a postdoctoral researcher in Whitehead Member Rudolf Jaenisch’s lab.

“Using these cells could help define the milestones of how cells are reprogrammed and screen for drug-like molecules that replace the potentially cancer-causing viruses used for reprogramming,” adds Christopher Lengner, the other lead author and also a postdoctoral researcher in the Jaenisch’s lab.

In the current work, Wernig and Lengner made mice created in part from the embryonic-stem-cell-like cells known as IPS cells. The IPS cells were created by reprogramming adult skin cells using lentiviruses to randomly insert four genes (Oct4, Sox2, c-Myc and Klf4) into the cells’ DNA. The IPS cells also were modified to switch on these four genes when a drug trigger, doxycycline, is added to the cells.

Wernig and Lengner then took cells from each IPS mouse and introduced the doxycycline trigger, thereby changing the adult mouse cells into IPS cells.

While earlier reprogramming experiments have typically induced pluripotency in adult skin cells, Wernig and Lengner were able to employ this novel method to successfully reprogram multiple cell and tissue types, including cells of the intestine, brain, muscle, kidney, adrenal gland, and bone marrow. Importantly, the technique allows researchers to create large numbers of genetically identical IPS cells, because all cells in the mouse contain the same number of viral integrations in the same location within the genome. With previous approaches, each reprogrammed cell differed because the viruses used to insert the reprogramming genes could integrate anywhere in the cell’s DNA with varying frequency.

Wernig and Lengner’s method also increases the reprogramming efficiency from one in a thousand cells to one in twenty.

The large numbers of IPS cells that can be created by this method can aid experiments requiring millions of identical cells for reprogramming, such as large-scale chemical library screening assays.

“In experiments, the technique will eliminate many of the reprogramming process’s unpredictable variables and simplify enormously the research on the reprogramming mechanism and the screening for virus replacements,” says Jaenisch, who is also a professor of biology at Massachusetts Institute of Technology.

Source: Whitehead Institute for Biomedical Research

A drug-inducible transgenic system for direct reprogramming of multiple somatic cell types. Marius Wernig, Christopher J Lengner, Jacob Hanna, Michael A Lodato, Eveline Steine, Ruth Foreman, Judith Staerk, Styliani Markoulaki & Rudolf Jaenisch. Nature Biotechnology. Published online: 01 July 2008; | doi:10.1038/nbt1483

Josh:

I made mention of the techniques used in the earlier paper in an April Fools joke this year. When reading this press release, I first thought it must be incorrect when it says the new technique “replace[s] the potentially cancer-causing viruses used for reprogramming”, since lentiviruses are still used to introduce the vector. However, upon reading the paper, they authors make the same claim! Perhaps I’m just missing something (such as the lentiviral DNA not integrating into the host genome) or am misreading, but this seems very misleading. They say a virus is used to introduce the genes, and then say that the technique eliminates the need to use a virus. What the technique does ensure, however, is that the cells have the same number of integrations and are identical to one another, which would help in these types of experiments.

Wealth of genomic hotspots discovered in embryonic stem cells

In a paper published in Cell on June 13, 2008, Singapore scientists at the Genome Institute of Singapore (GIS) and the National University of Singapore (NUS) unveil an atlas that showing the location of “genomic hotspots” of essential protein “switches” (transcription factors) that are critical for maintaining the embryonic stem (ES) cell state.

Using advanced high throughput sequencing technology, the scientists discovered over 3,000 hotspots. These findings could improve understanding of the unique properties of stem cells that enable them to maintain their intriguing ability to grow and differentiate to virtually any cell type.

“This is the first time such a large scale study has been conducted in Singapore and obtaining such groundbreaking results has caused much excitement,” said Wei Chia Lin, Ph.D., Senior Group Leader at GIS. “This blueprint that we obtained is like a treasure map, pointing us to specific sites where we can further study how these switches interact within the cell. Hopefully, this will eventually allow us unlock the secrets of stem cells.”

Ng Huck Hui, Ph.D., also a Senior Group Leader at GIS, added, “we think that these ‘stemness’ hotspots are the most critical points in the genetic blueprint of ES cells. By targeting these hotspots, we may be able to reconnect the wiring in non-stem cells and jump-start the stem cell program in them. This can potentially create an inexhaustible source of clinically useful cells for regenerative medicine or cell based therapies in the future.” The team has already started work to investigate further into this area of research.

“Using cutting edge sequencing technology, scientists from the GIS and NUS have identified hotspots in embryonic stem cells,” said Prof. Lee Eng Hin, Executive Director of A*STAR’s Biomedical Research Council. “These are important hubs of the genome of embryonic stem cells. This piece of work illustrates how scientists from different disciplines and across institutions can come together to define fundamental features of these intriguing cells.”

“In this new paper in Cell, the team at the GIS continues their remarkable progress in defining the precise DNA sequences to which an important group of 13 transcriptional factors bind in mouse embryonic stem cells,” said Alan Colman, Ph.D., Executive Director of Singapore’s Stem Cell Consortium. “This particular group of factors is responsible for maintaining the self renewal and pluripotency of the embryonic stem cells. The team shows that many of the factors which bind to the same gene regions (‘hotspots’) and their work provide a working model of the transcriptional networks at play within the cells, and how these intracellular networks are linked to events that can be influenced by external stimuli.”

The researchers performed genome-wide mapping of the in vivo binding sites for 13 sequence-specific transcription factors in ES cells. These transcription factors play different roles in self-renewal, pluripotency, reprogramming and chromatin insulation. This study uncovers two major modes of binding that give rise to transcription factor co-localization hotspots. The Nanog/Oct4/Sox2 centric hotspots are commonly co-bound by Smad1 and STAT3 and they represent points of integration for the intrinsic and external signaling pathways. The combinatorial wiring of transcription factors is important in deciphering the code behind gene expression program in ES cells.

Source: Agency for Science, Technology and Research (A*STAR), Singapore

Integration of External Signaling Pathways with the Core Transcriptional Network in Embryonic Stem Cells. Xi Chen, Han Xu, Ping Yuan, Fang Fang, Mikael Huss, Vinsensius B. Vega, Eleanor Wong, Yuriy L. Orlov, Weiwei Zhang, Jianming Jiang, Yuin-Han Loh, Hock Chuan Yeo, Zhen Xuan Yeo, Vipin Narang, Kunde Ramamoorthy Govindarajan, Bernard Leong, Atif Shahab, Yijun Ruan, Guillaume Bourque, Wing-Kin Sung, Neil D. Clarke, Chia-Lin Wei, and Huck-Hui Ng. Cell. June 13, 2008: 133 (6).

Josh says:

Previous reports showed that these transcription factors are sufficient to induce pluripotent stem cells, but this is unique in that it shows what genes these transcription factors activate.

Stem cell discovery sheds light on placenta development

Researchers studying embryonic stem cells have explored the first fork in the developmental road, getting a new look at what happens when fertilized eggs differentiate to build either an embryo or a placenta.

By manipulating a specific gene in a mouse blastocyst — the structure that develops from a fertilized egg but is not yet an actual embryo — scientists with the University of Florida’s McKnight Brain Institute and the Harvard Stem Cell Institute caused cells destined to build an embryo to instead change direction and build the cell mass that leads to the placenta.

Writing in today’s (Monday, June 9) online edition of Nature Genetics, the scientists reveal a cellular signaling mechanism in place at the earliest developmental stage.

Understanding the conditions that cause these cells to go off to different fates may have a bearing on health problems such as ectopic pregnancy, which occurs when the embryo develops outside of the womb in about 1 of 60 pregnancies, or molar pregnancy, which is abnormal tissue growth within the uterus that affects about 1 in every 1,000 pregnancies.

“We originally were exploring factors that might cause embryonic stem cells to become malignant — there is a concern that these cells may cause tumors,” said Chi-Wei Lu, Ph.D., an associate neuroscientist at the UF College of Medicine and lead author of the study. “Our experiments led us to discover the signal that initiates the process of embryonic tissue differentiation.”

By activating a gene called Ras in cells bathed in a very specific culture medium, scientists were able to cause embryonic stem cells — which originate from the inner cell mass of the blastocyst — to become more like the trophoblastic stem cells that give rise to the placenta from the outer portion of the blastocyst.

Researchers marked these newly minted cells, which they called ES-TS cells, and injected them into mouse embryos. Instead of joining the stem cells that build the embryo, ES-TS cells joined the stem cells that build the placenta. Furthermore, when scientists transferred the engineered mouse embryos to foster mothers, the ES-TS cells went to work exclusively laying the foundation for the placenta.

“This paper highlights the value of embryonic stem cells for understanding early development,” said senior author George Q. Daley, M.D., Ph.D., an associate professor of biological chemistry and molecular pharmacology at Harvard Medical School and an associate professor of pediatrics at Children’s Hospital Boston. “Embryonic stem cells are more plastic than we had thought. By simply activating the Ras gene, we changed the fate of embryonic stem cells to an entirely unexpected tissue — the placenta. This surprising result has given us an unanticipated insight into early embryo development.”

The technique of genetically modifying the cells and growing them in a special medium could be valuable for additional research.

“This is exciting because events that only occur in the early stages of embryonic development are very difficult to study,” Lu said. “Just a few models exist, and even in mice, only a limited amount of embryos can be harvested. Now we can culture these cells and have unlimited material to study.”

Researchers are only beginning to understand the natural chemical environments that allow for production of different tissues.

“What is nice is that what she has observed in cultures appears to be quite similar to what goes on in early development in animals,” said R. Michael Roberts, D.Phil., a professor of molecular biology at the C.S. Bond Life Sciences Center at the University of Missouri-Columbia who did not participate in the research. “Normally, mouse embryonic stem cells aren’t easily converted along the pathway to form placental cells, while human embryonic stem cells undergo this transition quite easily. This has always been a puzzle. What she has shown is you can make mouse embryonic stem cells convert unidirectionally to trophoblasts by activating a single gene. This is very helpful for understanding how the placenta develops.”

Source: University of Florida

Ras-MAPK signaling promotes trophectoderm formation from embryonic stem cells and mouse embryos. Chi-Wei Lu, Akiko Yabuuchi, Lingyi Chen, Srinivas Viswanathan, Kitai Kim & George Q Daley. Nature Genetics. Published online: 08 June 2008; | doi:10.1038/ng.173

Josh says:

As the one author said, this certainly does show the importance of working with stem cells. It’s interesting though that a cancer gene, Ras, lead to the stem cells becoming placenta.

Neurologically impaired mice improve after receiving human stem cells

Scientists report a dramatic success in what may be the first documented rescue of a congenital brain disorder by transplantation of human neural stem cells. The research, published by Cell Press in the June issue of the journal Cell Stem Cell, may lead the way to new strategies for treating certain hereditary and perinatal neurological disorders.

Nerve cell projections are ensheathed by a fatty substance called myelin that is produced by oligodendrocytes, a type non-nerve cell in the brain and spinal cord. Myelin enhances the speed and coordination of the electrical signals by which nerve cells communicate with one another. When myelin is missing or damaged, electrical signals are not properly transmitted. Previous studies have explored the potential utility of cell transplantation for restoring absent or lost myelination to diseased nerve fibers. Much of this research has made use of the ‘shiverer mouse’ animal model which lacks normal myelin and typically dies within months of birth. Yet to date, no transplantation of human neural stem cells or of their derivatives, called glial progenitor cells, have ever altered the condition or fate of recipient animals. … Continue Reading »

USC stem cell study sheds new light on cell mechanism

Research from the University of Southern California (USC) has discovered a new mechanism to allow embryonic stem cells to divide indefinitely and remain undifferentiated. The study, which will be published in the May 22 issue of the journal Nature, also reveals how embryonic stem cell multiplication is regulated, which may be important in understanding how to control tumor cell growth.

“Our study suggests that what we believe about how embryonic stem cell self-renewal is controlled is wrong,” says Qi-Long Ying, Ph.D., assistant professor of Cell and Neurobiology at the Keck School of Medicine of USC, researcher at the Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research at USC, and lead author of the paper. “Our findings will likely change the research direction of many stem cell laboratories.”

Contrary to the current understanding of stem cell self-renewal and differentiation, the findings suggest that embryonic stem cells will remain undifferentiated if they are shielded from differentiation signals. By applying small molecules that block the chemicals from activating the differentiation process, the natural default of the cell is to self-renew, or multiply, as generic stem cells.

“This study presents a completely new paradigm for understanding how to grow embryonic stem cells in the laboratory,” says Martin Pera, Ph.D., director of the Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research at USC. “The discovery has major implications for large scale production of specialized cells, such as brain, heart muscle and insulin producing cells, for future therapeutic use.”

Embryonic stem cells have only been derived from a very small number of species.

“We believe the process we discovered in mice may facilitate the derivation of embryonic stem cells from species like pigs, cows or other large animals, which have not been done before,” continues Ying. “If deriving embryonic stem cells from cows, for instance, is possible, then perhaps in the future cows might be able to produce milk containing medicines.”

With better understanding of the multiplication process of embryonic stem cells, researchers have additional insight on tumor cell growth as these cells share similar qualities. “Our study reveals part of the little known process of how embryonic stem cells multiplication is regulated. This is important for us in understanding how to control tumor cell growth moving forward in cancer research,” says Ying.

Source: University of Southern California

Qi-Long Ying, Jason Wray, Jennifer Nichols, Laura Batlle-Morera, Bradley Doble, James Woodgett, Philip Cohen and Austin Smith. “The Ground State of Embryonic Stem Cell Self-Renewal,” Nature (2008). Doi: 10.1038/nature06968.

Josh says:

I’m a bit skeptical of this. I haven’t really done any cell culture work, but if the stem cells are grown in a serum free media that doesn’t have any “differentiation signals”, they still differentiate. What they may be doing here is blocking transcription factors that are normally present and cause the cells to differentiate, thereby keeping them undifferentiated.

Embryonic pathway delivers stem cell traits

Studies of how cancer cells spread have led to a surprising discovery about the creation of cells with adult stem cell characteristics, offering potentially major implications for regenerative medicine and for cancer treatment.

Some cancer cells acquire the ability to migrate through the body by re-activating biological programs that have lain dormant since the embryo stage, as the lab of Whitehead Member Robert Weinberg has helped to demonstrate in recent years. Now scientists in the Weinberg lab have shown that both normal and cancer cells that are induced to follow one of these pathways may gain properties of adult stem cells, including the ability to self-renew. … Continue Reading »