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Continuation of mammalian species requires the formation and development of the sexually dimorphic germ cells. Cultured embryonic stem cells are generally considered pluripotent rather than totipotent because of the failure to detect germline cells under differentiating conditions. Here we show that mouse embryonic stem cells in culture can develop into oogonia that enter meiosis, recruit adjacent cells to form follicle-like structures, and later develop into blastocysts. Oogenesis in culture should contribute to various areas, including nuclear transfer and manipulation of the germ tine, and advance studies on fertility treatment and germ and somatic cell interaction and differentiation., In the early mammalian embryo, the germ line and soma are indistinguishable from each other. In the mouse, germ cell competence is induced at embryonic day 6.5 in proximal epiblast [...]

Stem ceils that naturally reside in adult tissues, such as muscle stem ceils (MuSCs), exhibit robust regenerative capacity in vivo that is rapidly lost in culture. Using a bioengineered substrate to recapitulate key biophysical and biochemical niche features in conjunction with a highly automated single-cell tracking algorithm, we show that substrate elasticity is a potent regulator of MuSC fate in culture. Unlike MuSCs on rigid plastic dishes ([~10.sup.6] kilopascals), MuSCs cultured on soft hydrogel substrates that mimic the elasticity of muscle (12 kilopascals) self-renew in vitro and contribute extensively to muscle regeneration when subsequently transplanted into mice and assayed histologically and quantitatively by noninvasive bioluminescence imaging. Our studies provide novel evidence that by recapitulating physiological tissue rigidity, propagation of adult muscle stem cells is possible, enabling future cell-based therapies for muscle-wasting diseases. 10.1126/science.1191035

Adult stem cells are crucial for physiological tissue renewal and regeneration after injury. Prevailing models assume the existence of a single quiescent population of stem cells residing in a specialized niche of a given tissue. Emerging evidence indicates that both quiescent (out of cell cycle and in a lower metabolic state) and active (in cell cycle and not able to retain DNA labels) stem cell subpopulations may coexist in several tissues, in separate yet adjoining locations. Here, we summarize these findings and propose that quiescent and active stem cell populations have separate but cooperative functional roles. 10.1126/science.1180794

Stem cell niches are Locations where stem cells reside and self-renew. Although studies have shown how niches maintain stem cell fate during tissue homeostasis, less is known about their roles in establishing stem cells. The adult Drosophila midgut is maintained by intestinal stem cells (ISCs); however, how they are established is unknown. Here, we show that an ISC progenitor generates a niche cell via Notch signaling. This niche uses the bone morphogenetic protein 2/4 homolog, decapentaplegic, to allow progenitors to divide in an undifferentiated state and subsequently breaks down and dies, resulting in the specification of ISCs in the adult midgut. Our results demonstrate a paradigm for stem cell--niche biology, where progenitors generate transient niches that determine stem cell fate and may give insights into stem cell specification in other tissues. 10.1126/science.1181958

Haploid embryonic stem (ES) cells combine haploidy and pluripotency, enabling direct genetic analyses of recessive phenotypes in vertebrate cells. Haploid cells have been elusive for culture, due to their inferior growth and genomic instability. Here, we generated gynogenetic medaka embryos and obtained three haploid ES cell lines that retained pluripotency and competitive growth. Upon nuclear transfer into unfertilized oocytes, the haploid ES cells, even after genetic engineering, generated viable offspring capable of germline transmission. Hence, haploid medaka ES cells stably maintain normal growth, pluripotency, and genomic integrity. Mosaic oocytes created by combining a mitotic nucleus and a meiotic nucleus can generate fertile fish offspring. Haploid ES ceils may offer a yeast-like system for analyzing recessive phenotypes in numerous cell lineages of vertebrates in vitro. 10.1126/science.1175151

Stem cell fate is influenced by a number of factors and interactions that require robust control for safe and effective regeneration of functional tissue. Coordinated interactions with soluble factors, other ceils, and extracellular matrices define a focal biochemical and mechanical niche with complex and dynamic regulation that stem cells sense. Decellularized tissue matrices and synthetic polymer niches are being used in the clinic, and they are also beginning to clarify fundamental aspects of how stem ceils contribute to homeostasis and repair, for example, at sites of fibrosis. Multifaceted technologies are increasingly required to produce and interrogate ceils ex vivo, to build predictive models, and, ultimately, to enhance stem cell integration in vivo for therapeutic benefit.

We have identified two genes, smedwi-1 and smedwi-2, expressed in the dividing adult stem cells (neoblasts) of the planarian Schmidtea mediterranea. Both genes encode proteins that belong to the Argonaute/PIWI protein family and that share highest homology with those proteins defined by Drosophila PIWI. RNA interference (RNAi) of smedwi-2 blocks regeneration, even though neoblasts are present, irradiation-sensitive, and capable of proliferating in response to wounding; smedwi-2(RNAi) neoblast progeny migrate to sites of cell turnover but, unlike normal cells, fail at replacing aged tissue. We suggest that SMEDWI-2 functions within dividing neoblasts to support the generation of cells that promote regeneration and homeostasis., Members of the PIWI/Argonaute family of proteins fall into two main classes, one named after Arabidopsis Argonaute and the other after Drosophila PIWI (1). Members of this protein family contain [...]

The shoot apical meristem (SAM) is a collection of stem cells that resides at the tip of each shoot and provides the cells of the shoot. It is divided into functional regions. The central zone (CZ) at the tip of the meristem is the domain of expression of the CLAVATA3 (CLV3) gene, encoding a putative ligand for a transmembrane receptor kinase, CLAVATA1, active in cells of the rib meristem (RM), located just below the CZ. We show here that CLV3 restricts its own domain of expression (the CZ) by preventing differentiation of peripheral zone cells (PZ), which surround the CZ, into CZ cells and restricts overall SAM size by a separate, long-range effect on cell division rate., Pattern formation in the SAM is a dynamic process that results from active orchestration of spatial and temporal patterns of gene expression and of cellular behavior, by cell-cell communication. In [...]

Transforming growth factor-β (TGF-β) and TGF-β-related proteins, such as the bone morphogenetic proteins, have emerged as key regulators of stem cell renewal and differentiation. These proteins have disparate roles in regulating the biology of embryonic stem cells and tumor suppression, and they help define the selection of cell fate and the progression of differentiation along a lineage. Here we illustrate their roles in embryonic stem cells and in the differentiation of neural, hematopoietic, mesenchymal, and gastrointestinal epithelial stem cells., Stem cells are characterized by their undifferentiated state, their ability to give rise to fully differentiated cells, and their capacity for self-renewal. Embryonic stem (ES) cells are pluripotent cells derived [...]

We have explored the use of embryonic stem cells as an alternative to oocytes for reprogramming human somatic nuclei. Human embryonic stem (hES) cells were fused with human fibroblasts, resulting in hybrid cells that maintain a stable tetraploid DNA content and have morphology, growth rate, and antigen expression patterns characteristic of hES cells. Differentiation of hybrid cells in vitro and in vivo yielded cell types from each embryonic germ layer. Analysis of genome-wide transcriptional activity, reporter gene activation, allele-specific gene expression, and DNA methylation showed that the somatic genome was reprogrammed to an embryonic state. These results establish that hES cells can reprogram the transcriptional state of somatic nuclei and provide a system for investigating the underlying mechanisms., The generation of embryonic stem (ES) cell lines and cloned animals by somatic cell nuclear transfer has demonstrated that the cytoplasm of an oocyte can reprogram the genome of a [...]

A key process in organ homeostasis is the mobilization of stem cells out of their niches. We show through analysis of mouse models that telomere length, as well as the catalytic component of telomerase, Tert, are critical determinants in the mobilization of epidermal stem cells. Telomere shortening inhibited mobilization of stem cells out of their niche, impaired hair growth, and resulted in suppression of stem cell proliferative capacity in vitro. In contrast, Tert overexpression in the absence of changes in telomere length promoted stem cell mobilization, hair growth, and stem cell proliferation in vitro. The effects of telomeres and telomerase on stem cell biology anticipate their role in cancer and aging., Tumor formation and aging are associated with alterations in the number or functional competence of tissue stem cells (1-3). Both processes have also been linked to alterations at the telomere [...]

Shortly before Congressman James Langevin cast his vote last month to relax federal rules on funding of stem cell research, the Rhode Island Democrat told his colleagues, 'I believe one [...]

Closely related signals often lead to very different cellular outcomes. We found that the differentiation of human mesenchymal stem cells into boneforming cells is stimulated by epidermal growth factor (EGF) but not platelet-derived growth factor (PDGF). We used mass spectrometry-based proteomics to comprehensively compare proteins that were tyrosine phosphorylated in response to EGF and PDGF and their associated partners. More than 90% of these signaling proteins were used by both ligands, whereas the phosphatidylinositol 3-kinase (P13K) pathway was exclusively activated by PDGF, implicating it as a possible control point. Indeed, chemical inhibition of P13K in PDGF-stimulated cells removed the differential effect of the two growth factors, bestowing full differentiation effect onto PDGF. Thus, quantitative proteomics can directly compare entire signaling networks and discover critical differences capable of changing cell fate., Receptor tyrosine kinases (RTKs) regulate cellular processes ranging from cell growth and proliferation to survival and differentiation. After binding of their cognate ligands, these receptors undergo autophosphorylation on multiple tyrosine [...]

Gene marking with replication-defective retroviral vectors has been used for more than 20 years to track the in vivo fate of cell clones. We demonstrate that retroviral integrations themselves may trigger nonmalignant clonal expansion in murine long-term hematopoiesis. All 29 insertions recovered from clones dominating in serially transplanted recipients affected loci with an established or potential role in the self-renewal or survival of hematopoietic stem cells. Transcriptional dysregulation occurred in all 12 insertion sites analyzed. These findings have major implications for diagnostic gene marking and the discovery of genes regulating stern cell turnover., Because of their unspecific insertion properties, replication-defective retroviral vectors represent unique tools for genetic marking studies, enabling the numbers and progeny of transplanted (stem) cells to be determined (1, 2). [...]

Apoptosis is important in controlling hematopoietic stem cell (HSC) numbers. However, the specific BCL-2 family member(s) that regulate HSC homeostasis are not precisely defined. We tested myeloid leukemia-1 (MCL-1) as an attractive candidate that is highly expressed in HSCs and regulated by growth factor signals. Inducible deletion of Mcl-1 in mice resulted in ablation of bone marrow. This resulted in the loss of early bone marrow progenitor populations, including HSCs. Moreover, growth factors including stem cell factor increased transcription of the Mcl-1 gene and required MCL-1 to augment survival of purified bone marrow progenitors. Deletion of Mcl-1 in other tissues, including liver, did not impair survival. Thus, MCL-1 is a critical and specific regulator essential for ensuring the homeostasis of early hematopoietic progenitors., Hematopoietic stem cells (HSCs), which give rise to all cells of hematopoietic lineages, can undergo several developmental fates. These include self-renewal or differentiation into multipotent progenitors that give rise to [...]

Hair graying is the most obvious sign of aging in humans, yet its mechanism is largely unknown. Here, we used melanocyte-tagged transgenic mice and aging human hair follicles to demonstrate that hair graying is caused by defective self-maintenance of melanocyte stem cells. This process is accelerated dramatically with Bcl2 deficiency, which causes selective apoptosis of melanocyte stem cells, but not of differentiated melanocytes, within the niche at their entry into the dormant state. Furthermore, physiologic aging of melanocyte stem cells was associated with ectopic pigmentation or differentiation within the niche, a process accelerated by mutation of the melanocyte master transcriptional regulator Mitf., Qualitative and quantitative changes in stem and progenitor cells have been implicated in physiological (chronological) aging (1, 2), although the changes are poorly understood and the process of stem-cell aging [...]

Veterinarian Woo Suk Hwang and gynecologist Shin Yong Moon leapt from obscurity to scientific stardom last February when they isolated embryonic stem (ES) cells from cloned human cells, a world [...]

Although the ability of engrafted stem cells to regenerate tissue has received much attention, the molecular mechanisms controlling regeneration are poorly understood. In the Drosophila male germline, local activation of the Janus kinase-signal transducer and activator of transcription (Jak-STAT) pathway maintains stem cells; germline stern cells lacking Jak-STAT signaling differentiate into spermatogonia without self-renewal. By conditionally manipulating Jak-STAT signaling, we find that spermatogonia that have initiated differentiation and are undergoing limited mitotic (transit-amplifying) divisions can repopulate the niche and revert to stem cell identity. Thus, in the appropriate microenvironment, transit-amplifying cells dedifferentiate, becoming functional stern cells during tissue regeneration., In the Drosophila testis, germline stem cells (GSCs) attach to a cluster of quiescent somatic cells called the hub (Fig. 1A), which creates a special localized microenvironment, or niche, by [...]

Stem cell self-renewal can be specified by local signals from the surrounding microenvironment, or niche. However, the relation between the niche and the mechanisms that ensure the correct balance between stem cell self-renewal and differentiation is poorly understood. Here, we show that dividing Drosophila male germline stem cells use intracellular mechanisms involving centrosome function and cortically localized Adenomatous Polyposis Coli tumor suppressor protein to orient mitotic spindles perpendicular to the niche, ensuring a reliably asymmetric outcome in which one daughter cell remains in the niche and self-renews stem cell identity, whereas the other, displaced away, initiates differentiation., Adult stem cells maintain populations of highly differentiated but short-lived cells such as skin, intestinal epithelium, or sperm through a critical balance between alternate fates: Daughter cells either maintain stem [...]

Mechanisms regulating self-renewal and cell fate decisions in mammalian stem cells are poorly understood. We determined global gene expression profiles for mouse and human hematopoietic stem cells and other stages of the hematopoietic hierarchy. Murine and human hematopoietic stem cells share a number of expressed gene products, which define key conserved regulatory pathways in this developmental system. Moreover, in the mouse, a portion of the genetic program of hematopoietic stem cells is shared with embryonic and neural stem cells. This overlapping set of gene products represents a molecular signature of stem cells., Adult and embryonic stem cells (SCs) hold great promise for regenerative medicine, tissue repair, and gene therapy (1). Hematopoietic stem cells (HSCs) have been the most extensively studied and serve [...]

The transcriptional profiles of mouse embryonic, neural, and hematopoietic stem cells were compared to define a genetic program for stem cells. A total of 216 genes are enriched in all three types of stem cells, and several of these genes are clustered in the genome. When compared to differentiated cell types, stem cells express a significantly higher number of genes (represented by expressed sequence tags) whose functions are unknown. Embryonic and neural stem cells have many similarities at the transcriptional level. These results provide a foundation for a more detailed understanding of stem cell biology., Stem cells (SCs) have the capacity to self-renew as well as the ability to generate differentiated cells. Recently, the field of SC biology has attracted increasing attention because of the [...]

To rigorously test the in vivo cell fate specificity of bone marrow (BM) hematopoietic stem cells (HSCs), we generated chimeric animals by transplantation of a single green fluorescent protein (GFP)-marked HSC into lethally irradiated nontransgenic recipients. Single HSCs robustly reconstituted peripheral brood leukocytes in these animals, but did not contribute appreciably to nonhematopoietic tissues, including brain, kidney, gut, liver, and muscle. Similarly, in GF[P.sup.+]:GF[P.sup.-] parabiotic mice, we found substantial chimerism of hematopoietic but not nonhematopoietic cells. These data indicate that 'transdifferentiation' of circulating HSCs and/or their progeny is an extremely rare event, if it occurs at all., As many recent reports have suggested that BM HSCs may harbor unexpected developmental plasticity (1-14), we set out to test rigorously the cell fate potential of prospectively isolated, long-term reconstituting [...]

The transcription factor Pax5 is essential for initiating B cell lineage commitment, but its role in maintaining commitment is unknown. Using conditional Pax5 inactivation in committed pro-B cells, we demonstrate that Pax5 is required not only to initiate its B lymphoid transcription program, but also to maintain it in early B cell development. As a consequence of Pax5 inactivation, previously committed pro-B cells regained the capacity to differentiate into macrophages in vitro and to reconstitute T. cell development in vivo in [RAG2.sup.-/-] mice. Hence, Pax5 expression is continuously required to maintain B cell lineage commitment, because its loss converts committed pro-B cells into hematopoietic progenitors with multilineage potential., The hematopoietic stem cell gives rise to all lymphoid lineages by differentiating through the intermediary stage of the common lymphoid progenitor (1). Entry of this progenitor into the B cell [...]

Hematopoietic stem cell (HSC) gene therapy for adenosine deaminase (ADA)--deficient severe combined immunodeficiency (SCID) has shown limited clinical efficacy because of the small proportion of engrafted genetically corrected HSCs. We describe an improved protocol for gene transfer into HSCs associated with nonmyeloablative conditioning. This protocol was used in two patients for whom enzyme replacement therapy was not available, which allowed the effect of gene therapy alone to be evaluated. Sustained engraftment of engineered HSCs with differentiation into multiple lineages resulted in increased lymphocyte counts, improved immune functions (including antigen-specific responses), and lower toxic metabolites. Both patients are currently at home and clinically well with normal growth and development. These results indicate the safety and efficacy of HSC gene therapy combined with nonmyeloablative conditioning for the treatment of SCID., Gene therapy trials have demonstrated the safety and feasibility of engineering hematopoietic stem cells (HSCs) for treating inherited hematopoietic diseases (1-6). In these studies, however, the frequency of multipotent genetically [...]

Although not quite the cold fusion of biology, it ignites similar passions. Stem cell 'plasticity'--the ability of cell types from adult tissues to take on surprising new identities--can inspire debates [...]

Spermatogenesis is a precisely regulated process in which the germ cells closely interact with Sertoli cells. The molecular basis of this cell-cell adhesion is unknown. Here, we demonstrate that targeted disruption of Man2a2, a gene encoding α-mannosidase IIx (MX), an enzyme that forms intermediate asparagine-linked carbohydrates (N-glycans), results in Man2a2 null males that are largely infertile. The Man2a2 null spermatogenic cells fail to adhere to Sertoli cells and are prematurely released from the testis to epididymis. We identified an N-glycan structure that plays a key role in germ cell-Sertoli cell adhesion and showed that a specific carbohydrate was required for spermatogenesis., Spermatogenesis is a complex process by which postmeiotic male germ cells differentiate into mature spermatozoa. At all stages of spermatogenic maturation, germ cells, and Sertoli cells communicate through direct cell-cell [...]

Stem cells, which regenerate tissue by producing differentiating cells, also produce cells that renew the stem cell population. Signals from regulatory microenvironments (niches) are thought to cause stem cells to retain self-renewing potential. However, the molecular characterization of niches remains an important goal In Drosophila testes, germ line and somatic stem cells attach to a duster of support cells called the hub. The hub specifically expresses Unpaired, a ligand activating the JAK-STAT (Janus kinase-signal transducer and activator of transcription) signaling cascade. Without JAK-STAT signaling, germ line stem cells differentiate but do not self-renew. Conversely, ectopic JAK-STAT signaling greatly expands both stem cell populations. We conclude that the support cells of the hub signal to adjacent stem cells by activation of the JAK-STAT pathway, thereby defining a niche for stem cell self-renewal, A small population of germ line stem cells (GSCs) in a morphologically well-defined environment sustains Drosophila spermatogenesis (1). GSCs attach to a cluster of nonmitotic somatic support cells at the [...]

The mechanisms controlling neural stem cell proliferation are poorly understood. Here we demonstrate that the PTEN tumor suppressor plays an important role in regulating neural stem/progenitor cells in vivo and [...]

The mouse small intestinal epithelium consists of four principal cell types deriving from one multipotent stem cell: enterocytes, goblet, enteroendocrine, and Paneth cells. Previous studies showed that Math1, a basic helix-loop-helix (bHLH) transcription factor, is expressed in the gut. We find that loss of Math1 leads to depletion of goblet, enteroendocrine, and Paneth cells without affecting enterocytes. Colocalization of Math1 with Ki-67 in some proliferating cells suggests that secretory cells (goblet, enteroendocrine, and Paneth ceils) arise from a common progenitor that expresses Math1, whereas absorptive cells (enterocytes) arise from a progenitor that is Math1-independent. The continuous rapid renewal of these cells makes the intestinal epithelium a model system for the study of stem cell regeneration and lineage commitment., The mouse gut begins developing at embryonic day 7.5 (E7.5). Invagination of the most anterior and posterior endoderm leads to the formation of the foregut and hindgut pockets, respectively, which [...]

Hematopoietic stem cells (HSCs) reside predominantly in bone marrow, but low numbers of HSCs are also found in peripheral blood. We examined the fate of blood-borne HSCs using genetically marked parabiotic mice, which are surgically conjoined and share a common circulation. Parabionts rapidly established stable, functional cross engraftment of partner-derived HSCs and maintained partner-derived hematopoiesis after surgical separation. Determination of the residence time of injected blood-borne progenitor cells suggests that circulating HSCs/progenitors are cleared quickly from the blood. These data demonstrate that HSCs rapidly and constitutively migrate through the blood and play a physiological role in, at least, the functional reengraftment of unconditioned bone marrow., Bone marrow (BM) transplantation is a common procedure wherein suspensions of cells are harvested from marrow cavities and intravenously injected into patients or animals whose blood-forming system is compromised by [...]

Hematopoietic stem cells (HSCs) supply all blood cells throughout life by making use of their self-renewal and multilineage differentiation capabilities. A monoclonal antibody raised to the mouse homolog of CD34 (mCD34) was used to purify mouse HSCs to near homogeneity. Unlike in humans, primitive adult mouse bone marrow HSCs were detected in the mCD34 low to negative fraction. Injection of a single [mCD34.sup.lo/-], [c-Kit.sup.+], [Sca-1.sup.+], lineage markers negative ([Lin.sup.-]) cell resulted in long-term reconstitution of the lymphohematopoietic system in 21 percent of recipients. Thus, the purified HSC population should enable analysis of the self-renewal and multilineage differentiation of individual HSCs., CD34 is a marker of human HSCs, and all colony-forming activity of human bone marrow (BM) cells is found in the Cd34-positive fraction (1). Clinical transplantation studies that used enriched [...]

Mast cells originate from hematopoietic stem cells, but the mast cell-committed precursor has not been identified. In the study presented here, a cell population in murine fetal blood that fulfills [...]

In the Drosophila embryo, the central nervous system (CNS) develops from a population of neural stem cells (neuroblasts) and midline progenitor cells. Here, the fate and extent of determination of CNS progenitors along the dorsoventral axis was assayed. Dorsal neuroectodermal cells transplanted into the ventral neuroectoderm or into the midline produced CNS lineages consistent with their new position. However, ventral neuroectodermal cells and midline cells transplanted to dorsal sites of the neuroectoderm migrated ventrally and produced CNS lineages consistent with their origin. Thus, inductive signals at the ventral midline and adjacent neuroectoderm may confer ventral identities to CNS progenitors as well as the ability to assume and maintain characteristic positions in the developing CNS. Furthermore, ectopic transplantations of wild-type midline cells into single minded (sim) mutant embryos suggest that the ventral midline is required for correct positioning of the cells., The development of the CNS in insects begins shortly after gastrulation, when about 30 neuroblasts (NBs) per hemisegment delaminate from the neuroectoderm according to a stereotypical spatial and temporal pattern [...]

The Notch/Lin-1 2/Glp-1 receptor family mediates the specification of numerous cell fates during development in Drosophila and Caenorhabditis elegans. Studies on the expression, mutant phenotypes, and developmental consequences of unregulated receptor activation have implicated these proteins in a general mechanism of local cell signaling, which includes interactions between equivalent cells and between different cell types. Genetic approaches in flies and worms have identified putative components of the signaling cascade, including a conserved family of extracellular ligands and two cellular factors that may associate with the Notch Intracellular domain. One factor, the Drosophila Suppressor of Hairless protein, is a DNA-binding protein, which suggests that Notch signaling may involve relatively direct signal transmission from the cell surface to the nucleus. Several vertebrate Notch receptors have also been discovered recently and play important roles in normal development and tumorigenesis., Multicellular development is governed by the combinatorial and sequential activity of genes that gradually restrict the developmental potential of cell lineages during differentiation. Large-scale mutational analyses performed in Drosophila have [...]

In this study, the cytokine-producing profile of progenitor T cells (pro-T cells) was determined. During screening of a complementary DNA library generated from activated mouse pro-T cells, a cytokine designated lymphotactin was discovered. Lymphotactin is similar to members of both the Cys-Cys and Cys-X-Cys chemokine families but lacks two of the four cysteine residues that are characteristic of the chemokines. Lymphotactin is also expressed in activated [CD8.sup.+] T cells and [CD4.sup.-][CD8.sup.-] T cell receptor α[β.sup.+] thymocytes. It has chemotactic activity for lymphocytes but not for monocytes or neutrophils. The gene encoding lymphotactin maps to chromosome one. Taken together, these observations suggest that lymphotactin represents a novel addition to the chemokine superfamily., The pro-T cell is an immature thymocyte subset that is likely to be the final differentiation stage before the onset of T cell receptor (TCR) β chain gene rearrangement (1, [...]

An efficient system was developed that induced the differentiation of embryonic stem (ES) cells into blood cells of erythroid, myeloid, and B cell lineages by coculture with the stromal cell line OP9. This cell line does not express functional macrophage colony-stimulating factor (M-CSF). The presence of M-CSF had inhibitory effects on the differentiation of ES cells to blood cells other than macrophages. Embryoid body formation or addition of exogenous growth factors was not required, and differentiation was highly reproducible even after the selection of ES cells with the antibiotic G418. Combined with the ability to genetically manipulate ES cells, this system will facilitate the study of molecular mechanisms involved in development and differentiation of hematopoietic cells., The mechanisms of determination and differentiation that lead to the formation of hematopoietic cells from the inner cell mass of blastocysts through mesodermal cells are still unelucidated in spite of [...]