Tissue-restricted Stem Cells Research Articles

Tissue-Restricted Stem Cells as Starting Cell Source for Efficient Generation of Pluripotent Stem Cells: An Overview.

Induced pluripotent stem cells (iPSCs) have vast biomedical potential concerning disease modeling, drug screening and discovery, cell therapy, tissue engineering, and understanding organismal development. In the year 2006, a groundbreaking study reported the generation of iPSCs from mouse embryonic fibroblasts by viral transduction of four transcription factors, namely, Oct4, Sox2, Klf4, and c-Myc. Subsequently, human iPSCs were generated by reprogramming fibroblasts as a starting cell source using two reprogramming factor cocktails [(i) OCT4, SOX2, KLF4, and c-MYC, and (ii) OCT4, SOX2, NANOG, and LIN28]. The wide range of applications of these human iPSCs in research, therapeutics, and personalized medicine has driven the scientific community to optimize and understand this reprogramming process to achieve quality iPSCs with higher efficiency and faster kinetics. One of the essential criteria to address this is by identifying an ideal cell source in which pluripotency can be induced efficiently to give rise to high-quality iPSCs. Therefore, various cell types have been studied for their ability to generate iPSCs efficiently. Cell sources that can be easily reverted to a pluripotent state are tissue-restricted stem cells present in the fetus and adult tissues. Tissue-restricted stem cells can be isolated from fetal, cord blood, bone marrow, and other adult tissues or can be obtained by differentiation of embryonic stem cells or trans-differentiation of other tissue-restricted stem cells. Since these cells are undifferentiated cells with self-renewal potential, they are much easier to reprogram due to the inherent characteristic of having an endogenous expression of few pluripotency-inducing factors. This review presents an overview of promising tissue-restricted stem cells that can be isolated from different sources, namely, neural stem cells, hematopoietic stem cells, mesenchymal stem cells, limbal epithelial stem cells, and spermatogonial stem cells, and their reprogramming efficacy. This insight will pave the way for developing safe and efficient reprogramming strategies and generating patient-specific iPSCs from tissue-restricted stem cells derived from various fetal and adult tissues.

Stem cells and the evolving notion of cellular identity.

Stem cells are but one class of the myriad types of cells within an organism. With potential to self-renew and capacity to differentiate, stem cells play essential roles at multiple stages of development. In the early embryo, pluripotent stem cells represent progenitors for all tissues while later in development, tissue-restricted stem cells give rise to cells with highly specialized functions. As best understood in the blood, skin and gut, stem cells are the seeds that sustain tissue homeostasis and regeneration, while in other tissues like the muscle, liver, kidney and lung, various stem or progenitor cells play facultative roles in tissue repair and response to injury. Here, I will provide a brief perspective on the evolving notion of cellular identity and how reprogramming and transcription factor-mediated conversions of one cell type into another have fundamentally altered our assumptions about the stability of cell identity, with profound long-term implications for biomedical research and regenerative medicine.

GROWTH AND DEVELOPMENT SYMPOSIUM: Participation of adult tissue-restricted stem cells to livestock growth and development1

GROWTH AND DEVELOPMENT SYMPOSIUM: Participation of adult tissue-restricted stem cells to livestock growth and development1

Stem cells in gastroenterology and hepatology

Cellular and tissue regeneration in the gastrointestinal tract and liver depends on stem cells with properties of longevity, self-renewal and multipotency. Progress in stem cell research and the identification of potential esophageal, gastric, intestinal, colonic, hepatic and pancreatic stem cells provides hope for the use of stem cells in regenerative medicine and treatments for disease. Embryonic stem cells and induced pluripotent stem cells have the potential to give rise to any cell type in the human body, but their therapeutic application remains challenging. The use of adult or tissue-restricted stem cells is emerging as another possible approach for the treatment of gastrointestinal diseases. The same self-renewal properties that allow stem cells to remain immortal and generate any tissue can occasionally make their proliferation difficult to control and make them susceptible to malignant transformation. This Review provides an overview of the different types of stem cell, focusing on tissue-restricted adult stem cells in the fields of gastroenterology and hepatology and summarizing the potential benefits and risks of using stems cells to treat gastroenterological and liver disorders.

New light on the biology and developmental potential of haematopoietic stem cells and progenitor cells

Even though stem cells have been identified in several tissues, one of the best understood somatic stem cells is the bone marrow residing haematopoietic stem cell (HSC). These cells are able to generate all types of blood cells found in the periphery over the lifetime of an animal, making them one of the most profound examples of tissue-restricted stem cells. HSC therapy also represents one of the absolutely most successful cell-based therapies applied both in the treatment of haematological disorders and cancer. However, to fully explore the clinical potential of HSCs we need to understand the molecular regulation of cell maturation and lineage commitment. The extensive research effort invested in this area has resulted in a rapid development of the understanding of the relationship between different blood cell lineages and increased understanding for how a balanced composition of blood cells can be generated. In this review, several of the basic features of HSCs, as well as their multipotent and lineage-restricted offspring, are addressed, providing a current view of the haematopoietic development tree. Some of the basic mechanisms believed to be involved in lineage restriction events including activities of permissive and instructive external signals are also discussed, besides transcription factor networks and epigenetic alterations to provide an up-to-date view of early haematopoiesis.

Ezh2 Orchestrates Gene Expression for the Stepwise Differentiation of Tissue-Specific Stem Cells

Although in vitro studies of embryonic stem cells have identified polycomb repressor complexes (PRCs) as key regulators of differentiation, it remains unclear as to how PRC-mediated mechanisms control fates of multipotent progenitors in developing tissues. Here, we show that an essential PRC component, Ezh2, is expressed in epidermal progenitors but diminishes concomitant with embryonic differentiation and with postnatal decline in proliferative activity. We show that Ezh2 controls proliferative potential of basal progenitors by repressing the Ink4A-Ink4B locus and tempers the developmental rate of differentiation by preventing premature recruitment of AP1 transcriptional activator to the structural genes that are required for epidermal differentiation. Together, our studies reveal that PRCs control epigenetic modifications temporally and spatially in tissue-restricted stem cells. They maintain their proliferative potential and globally repressing undesirable differentiation programs while selectively establishing a specific terminal differentiation program in a stepwise fashion.

Flow-cytometric phosphoprotein analysis reveals agonist and temporal differences in responses of murine hematopoietic stem/progenitor cells.

Hematopoietic stem cells (HSCs) are probably the best-studied adult tissue-restricted stem cells. Although methods for flow cytometric detection of phosphoproteins in hematopoeitic progenitors and mature cells are available, analogous protocols for HSC are lacking. We present a robust method to study intracellular signaling in immunophenotypically-defined murine HSC/progenitor cell (HPC)-enriched populations. Using this method, we uncover differences in the response dynamics of several phosphoproteins representative of the Ras/MAP-Kinase(K), PI3K, mTOR and Jak/STAT pathways in HSC/HPCs stimulated by Scf, Thpo, as well as several other important HSC/HPC agonists.

Foreword

Stem cell biology is emerging as a field in biology with tremendous therapeutic potential. Making this potential a reality requires an international effort. The recognition that such a promising yet multifaceted discipline needs fostering led to the establishment of the International Society for Stem Cell Research (ISSCR). Central to the efforts of the ISSCR is the development of tools to ensure the success of stem cell researchers. What better way to do this than to collaborate with Current Protocols to develop this valuable compendium of protocols in stem cell biology? Stem cell researchers have developed a number of breakthrough techniques, from the derivation and manipulation of pluripotent embryonic stem cells to purification and transplantation of tissue-restricted stem cells from adult organs. A number of laboratories have become leaders in the field as a result of developing such techniques. The more efficient scientists are at implementing new and powerful methodologies in their own laboratories, the faster stem cell biology will advance our understanding of normal development and lead to the development of therapies. Thus, the availability of quality protocols will have a major impact on the success of the entire field. Current Protocols has long been the premier volume for proven in-depth protocols regarding many aspects of biology, and this volume on stem cell biology will prove a valuable addition to researchers worldwide. Experiments in stem cell biology must be interpreted with great caution as well as openness to alternative explanations. For example, the recently discovered phenomenon of cell fusion in vivo or the existence of tissue-restricted blood stem cells in peripheral tissues were initially misinterpreted as evidence for stem cell trans-differentiation. It is very important that this compendium of protocols highlight potential pitfalls as well as maintain the opportunity for clarification and correction when the need arises. The fact that these protocols will be provided online will help ensure that researchers always have the latest, most up-to-date protocols available to them. The stem cell field is burgeoning, and, as I have seen within the ISSCR, there is a genuine push to share information and interact so that the field can move forward quickly. There is a drive to develop not only excellent basic research skills but to bring the findings to clinical use so that patients can benefit. As a Hematology Attending Physician at Children's Hospital Boston, I treat children who have pediatric blood diseases or leukemia and am drawn by the need to translate our research findings into therapies to help treat a number of diseases. The promise is great, but we need to deliver, and I believe Current Protocols in Stem Cell Biology will help tremendously.

Adult stem cell plasticity: new pathways of tissue regeneration become visible.

There has recently been a significant change in the way we think about organ regeneration. In the adult, organ formation and regeneration was thought to occur through the action of organ-or tissue-restricted stem cells (i.e. haematopoietic stem cells making blood; gut stem cells making gut, etc.). However, there is a large body of recent work that has extended this model. Thanks to lineage tracking techniques, we now believe that stem cells from one organ system, for example the haematopoietic compartment, can develop into the differentiated cells within another organ system, such as liver, brain or kidney. This cellular plasticity not only occurs under experimental conditions, but has also been shown to take place in humans following bone marrow and organ transplants. This trafficking is potentially bi-directional, and even differentiated cells from different organ systems can interchange, with pancreatic cells able to form hepatocytes, for example. In this review we will detail some of these findings and attempt to explain their biological significance.

Transcription factor-mediated lineage switching reveals plasticity in primary committed progenitor cells.

The developmental plasticity of transplanted adult stem cells challenges the notion that tissue-restricted stem cells have stringently limited lineage potential and prompts a re-evaluation of the stability of lineage commitment. Transformed cell systems are inappropriate for such studies, since transformation potentially dysregulates the processes governing lineage commitment. We have therefore assessed the stability of normal lineage commitment in primary adult haematopoietic cells. For these studies we have used prospectively isolated primary bipotent progenitors, which normally display only neutrophil and monocyte differentiation in vitro. In response to ectopic transcription factor expression, these neutrophil/monocyte progenitors were reprogrammed to take on erythroid, eosinophil and basophil-like cell fates, with the resultant colonies resembling the mixed lineage colonies normally generated by multipotential progenitors. Clone-marking and daughter cell experiments identified lineage switching rather than differential cell selection as the mechanism of altered lineage output. These results demonstrate that the cell type-specific programming of apparently committed primary progenitors is not irrevocably fixed, but may be radically re-specified in response to a single transcriptional regulator.

An introduction to stem cells.

1998 saw the publication of two papers describing the growth in vitro of human embryonic stem (ES) cells derived either from the inner cell mass (ICM) of the early blastocyst or the primitive gonadal regions of early aborted fetuses. Work on murine ES cells over many years had already established the amazing flexibility of ES cells, essentially able to differentiate into almost all cells that arise from the three germ layers. The realization of such pluripotentiality (see below) has, of course, resulted in the field of stem cell research going into overdrive, the establishment of many new biotechnology companies (http://www.stemcellresearchnew.com/catalog1677.html), and a genuine belief that stem cell research will deliver a revolution in terms of how we treat cardiovascular disease, neurodegenerative disease, cancer, diabetes, and the like. However, many people believe that early human embryos should be accorded the same status as any sentient being and thus their 'harvesting' for stem cells is morally unjustifiable. With this in mind, other sources of malleable stem cells have been sought. In the adult, organ formation and regeneration was thought to occur through the action of organ- or tissue-restricted stem cells (i.e. haematopoietic stem cells giving rise to all the cells of the blood, neural stem cells making neurons, astrocytes, and oligodendrocytes). However, it is now believed that stem cells from one organ system, for example the haematopoietic compartment can develop into the differentiated cells within another organ system, such as the liver, brain or kidney. Thus, certain adult stem cells may turn out be as malleable as ES cells and so also be useful in regenerative medicine. This brief overview summarizes the important attributes of tissue-based stem cells and clarifies the terms used.