Identification and characterization of hemoangiogenic progenitors during cynomolgus monkey embryonic stem cell differentiation

Single-Cell RNA-seq Analysis of a Human Embryonic Stem Cell to Endothelial Cell System Based on Transcription Factor Overexpression

BACKGROUND

Human embryonic stem cell (hESC)-derived endothelial cells (ECs) possess therapeutic potential in many diseases. Cytokine supplementation induction and transcription factor overexpression have become two mainstream methods of hESC-EC induction. Single-cell RNA-seq technology has been widely used to analyse dynamic processes during hESC-EC induction and components of induced endothelial cells. However, studies that used single-cell RNA-seq are mainly based on cytokine supplementation methods. In this study, we used a high-efficiency human embryonic stem cell-endothelial cell line (hESC-EC) called the "FLI1-PKC system" as a research model and employed single-cell RNA sequencing (scRNA-seq) to investigate the transcriptional landscape and cellular dynamics.

METHODS

The high-efficiency hESC-EC induction (FLI1-PKC) system was established in our previous study. We applied single-cell RNA sequencing (scRNA-seq) of the differentiated cells at different time points and investigated the gene expression profiles.

RESULTS

The FLI1-PKC induction system can directionally differentiate hESCs into mature endothelial cells with all the requisite functions. Unlike other hES-EC induction protocols, the FLI1-PKC method follows a different induction route; nonetheless, the transcriptome of induced endothelial cells (iECs) remains the same. The elevated number of activated transcription factors may explain why the FLI1-PKC system is more effective than other hES-EC protocols.

CONCLUSION

Our study has presented a single-cell transcriptional overview of a high-efficiency hESC-EC induction system, which can be used as a model and reference for further improvement in other hESC induction systems.

Pluripotent stem cell model of Shwachman-Diamond syndrome reveals apoptotic predisposition of hemoangiogenic progenitors

Shwachman-Diamond syndrome (SDS), an autosomal recessive disorder characterized by bone marrow failure, exocrine pancreatic insufficiency, and skeletal abnormalities, is caused by mutations in the Shwachman-Bodian-Diamond syndrome (SBDS) gene, which plays a role in ribosome biogenesis. Although the causative genes of congenital disorders frequently involve regulation of embryogenesis, the role of the SBDS gene in early hematopoiesis remains unclear, primarily due to the lack of a suitable experimental model for this syndrome. In this study, we established induced pluripotent stem cells (iPSCs) from patients with SDS (SDS-iPSCs) and analyzed their in vitro hematopoietic and endothelial differentiation potentials. SDS-iPSCs generated hematopoietic and endothelial cells less efficiently than iPSCs derived from healthy donors, principally due to the apoptotic predisposition of KDR⁺CD34⁺ common hemoangiogenic progenitors. By contrast, forced expression of SBDS gene in SDS-iPSCs or treatment with a caspase inhibitor reversed the deficiency in hematopoietic and endothelial development, and decreased apoptosis of their progenitors, mainly via p53-independent mechanisms. Patient-derived iPSCs exhibited the hematological abnormalities associated with SDS even at the earliest hematopoietic stages. These findings will enable us to dissect the pathogenesis of multiple disorders associated with ribosomal dysfunction.

Hematopoietic Stem and Progenitor Cells (HSPCs)

Hematopoietic stem/progenitor cells (HSPCs) isolated from bone marrow have been successfully employed for 50 years in hematological transplantations. Currently, these cells are more frequently isolated from mobilized peripheral blood or umbilical cord blood. In this chapter, we overview several topics related to these cells including their phenotype, methods for isolation, and in vitro and in vivo assays to evaluate their proliferative potential. The successful clinical application of HSPCs is widely understood to have helped establish the rationale for the development of stem cell therapies and regenerative medicine.

FLI1 and PKC co-activation promote highly efficient differentiation of human embryonic stem cells into endothelial-like cells

Rationale-endothelial cells (ECs) play important roles in various regeneration processes and can be used in a variety of therapeutic applications, such as cardiac regeneration, gene therapy, tissue-engineered vascular grafts and prevascularized tissue transplants. ECs can be acquired from pluripotent and adult stem cells. To acquire ECs from human embryonic stem cells (hESCs) in a fast, efficient and economic manner. We established a conditional overexpression system in hESCs based on 15 transcription factors reported to be responsible for hematopoiesis lineage. Among them, only overexpression of FLI1 could induce hESCs to a hematopoietic lineage. Moreover, simultaneous overexpression of FLI1 and activation of PKC rapidly and efficiently induced differentiation of hESCs into induced endothelial cells (iECs) within 3 days, while neither FLI1 overexpression nor PKC activation alone could derive iECs from hESCs. During induction, hESCs differentiated into spindle-like cells that were consistent in appearance with ECs. Flow cytometric analysis revealed that 92.2-98.9% and 87.2-92.6% of these cells were CD31+ and CD144+, respectively. Expression of vascular-specific genes dramatically increased, while the expression of pluripotency genes gradually decreased during induction. iECs incorporated acetylated low-density lipoproteins, strongly expressed vWF and bound UEA-1. iECs also formed capillary-like structures both in vitro and in vivo. RNA-seq analysis verified that these cells closely resembled their in vivo counterparts. Our results showed that co-activation of FLI1 and PKC could induce differentiation of hESCs into iECs in a fast, efficient and economic manner.

Differentiation of induced pluripotent stem cell-derived neutrophil granulocytes from common marmoset monkey (Callithrix jacchus)

BACKGROUND

Inherited and acquired marrow failure syndromes most commonly lead to defect in myeloid and/or neutrophil differentiation and/or function. Besides this, neutropenia induced by cancer-adjusted chemotherapy is a frequent clinical problem. In both cases, cell replacement therapy is a well-established, but due to necessity of donors limited and perilous procedure. Therefore, autologous cell replacement from patients' own marrow-derived cells lowers risk and bares new possibilities for therapy. Since the immune system of the marmoset monkey is known to show high similarity to humans, preclinical studies with these animals bare high hopes for immunologic research and cell replacement therapy.

STUDY DESIGN AND METHODS

Marmoset-induced pluripotent stem (iPS) cells (cj-iPSC) were first cultivated on mouse embryonic feeder cells in medium containing recombinant human vascular endothelial growth factor. After 13 days, CD34+/vascular endothelial growth factor receptor-2 (VEGFR2)- cells were sorted, treated with interleukin (IL-3), thrombopoietin, and stem cell factor for 20 days and further cultivated with granulocyte-colony-stimulating factor (G-CSF) and IL-3 for 10 days.

RESULTS

CD34+/VEGFR2- cells could be generated in high amounts (39.65 ± 6.01%; 2.31 × 10⁵ cells). Afterward, these hematopoietic progenitors could be successfully differentiated into mature cj-iPSC-derived neutrophils showing similar morphology, specific surface antigens, and neutrophil-specific gene products and in vitro phagocytic activity.

CONCLUSION

cj-iPSC-derived neutrophils bare high hopes in hematologic cell replacement therapy. They exhibit high morphologic similarity to native neutrophils and present neutrophil-specific surface antigens, antimicrobial proteins, and gene products yielding an auspicious approach for continuative experiments including tests in living animals.

GSK3β Inhibition Promotes Efficient Myeloid and Lymphoid Hematopoiesis from Non-human Primate-Induced Pluripotent Stem Cells

Advances in the scalable production of blood cells from induced pluripotent stem cells (iPSCs) open prospects for the clinical translation of de novo generated blood products, and evoke the need for preclinical evaluation of their efficacy, safety, and immunogenicity in large animal models. Due to substantial similarities with humans, the outcomes of cellular therapies in non-human primate (NHP) models can be readily extrapolated to a clinical setting. However, the use of this model is hampered by relatively low efficiency of blood generation and lack of lymphoid potential in NHP-iPSC differentiation cultures. Here, we generated transgene-free iPSCs from different NHP species and showed the efficient induction of mesoderm, myeloid, and lymphoid cells from these iPSCs using a GSK3β inhibitor. Overall, our studies enable scalable production of hematopoietic progenitors from NHP-iPSCs, and lay the foundation for preclinical testing of iPSC-based therapies for blood and immune system diseases in an NHP model.

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Generation of transgene-free iPSCs from various non-human primate (NHP) species

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GSK3β inhibition is essential for induction of mesoderm and blood from NHP-iPSCs

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Efficient generation of CD34⁺CD45⁺CD90⁺CD38⁻CD45RA⁻ progenitors from NHP-iPSCs

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Efficient T and NK cell production from NHP-iPSCs

Prognostic significance of aminopeptidase-N (CD13) in hepatoblastoma

BACKGROUND

Hepatoblastoma is a rare childhood malignant tumor that originates from immature hepatic cells. Aminopeptidase-N(CD13), an ectopeptidase that promotes tumor invasion and metastasis, is expressed in fetal stage hepatic progenitor cells, although its role in hepatoblastoma remains unclear.

METHODS

The expression pattern of CD13 was investigated on immunohistochemistry in 30 tissue samples from 27 hepatoblastoma patients (16 with predominantly embryonal [pE] histology and 14 with predominantly fetal [pF] histology). Immunoreactive score (IRS) was used to quantify staining data, and the relationship between CD13 expression, clinicopathological factors, and clinical outcome was investigated. The biological function of CD13 was also examined in the hepatoblastoma cell lines Huh6 and HepG2.

RESULTS

All specimens stained positive for CD13, with higher CD13 expression in pE than in pF hepatoblastoma samples (median IRS, 4; range, 2-9 vs 2; range, 1-4). Strong CD13 expression was correlated with vascular invasion. Five year event-free survival and overall survival were better in patients with CD13(low) than in those with CD13(high) tumors (100% vs 51.0%, P = 0.026; and 100% vs 74.0%, P = 0.114, respectively). A CD13-neutralizing antibody and the potent CD13 inhibitor, Ubenimex, suppressed invasive activity in HepG2 cells in vitro.

CONCLUSIONS

CD13 expression is associated with hepatoblastoma invasiveness and could be a novel prognostic marker for hepatoblastoma.

A novel serum-free monolayer culture for orderly hematopoietic differentiation of human pluripotent cells via mesodermal progenitors

Elucidating the in vitro differentiation of human embryonic stem (ES) and induced pluripotent stem (iPS) cells is important for understanding both normal and pathological hematopoietic development in vivo. For this purpose, a robust and simple hematopoietic differentiation system that can faithfully trace in vivo hematopoiesis is necessary. In this study, we established a novel serum-free monolayer culture that can trace the in vivo hematopoietic pathway from ES/iPS cells to functional definitive blood cells via mesodermal progenitors. Stepwise tuning of exogenous cytokine cocktails induced the hematopoietic mesodermal progenitors via primitive streak cells. These progenitors were then differentiated into various cell lineages depending on the hematopoietic cytokines present. Moreover, single cell deposition assay revealed that common bipotential hemoangiogenic progenitors were induced in our culture. Our system provides a new, robust, and simple method for investigating the mechanisms of mesodermal and hematopoietic differentiation.

Neutrophil differentiation from human-induced pluripotent stem cells

Induced pluripotent stem (iPS) cells are of potential value not only for regenerative medicine, but also for disease investigation. The present study describes the development of a neutrophil differentiation system from human iPS cells (hiPSCs) and the analysis of neutrophil function and differentiation. The culture system used consisted of the transfer of hiPSCs onto OP9 cells and their culture with vascular endothelial growth factor (VEGF). After 10 days, TRA 1-85(+) CD34(+) VEGF receptor-2 (VEGFR-2)(high) cells were sorted and co-cultured with OP9 cells in the presence of hematopoietic cytokines for 30 days. Floating cells were collected and subjected to morphological and functional analysis. These hiPSC-derived neutrophils were similar to peripheral blood mature neutrophils in morphology, contained functional neutrophil specific granules, and were equipped with the basic functions such as phagocytosis, superoxide production, and chemotaxis. In the process of differentiation, myeloid cells appeared sequentially from immature myeloblasts to mature segmented neutrophils. Expression patterns of surface antigen, transcription factors, and granule proteins during differentiation were also similar to those of granulopoiesis in normal bone marrow. In conclusion, differentiation of mature neutrophils from hiPSCs was successfully induced in a similar process to normal granulopoiesis using an OP9 co-culture system. This system may be applied to elucidate the pathogenesis of various hematological diseases that affect neutrophils.

LRF is an essential downstream target of GATA1 in erythroid development and regulates BIM-dependent apoptosis

GATA-1-dependent transcription is essential for erythroid differentiation and maturation. Suppression of programmed cell death is also thought to be critical for this process; however, the link between these two features of erythropoiesis has remained elusive. Here, we show that the POZ-Krüppel family transcription factor, LRF (also known as Zbtb7a/Pokemon), is a direct target of GATA1 and plays an essential antiapoptotic role during terminal erythroid differentiation. We find that loss of Lrf leads to lethal anemia in embryos, due to increased apoptosis of late-stage erythroblasts. This programmed cell death is Arf and p53 independent and is instead mediated by upregulation of the proapoptotic factor Bim. We identify Lrf as a direct repressor of Bim transcription. In strong support of this mechanism, genetic Bim loss delays the lethality of Lrf-deficient embryos and rescues their anemia phenotype. Thus, our data define a key transcriptional cascade for effective erythropoiesis, whereby GATA-1 suppresses BIM-mediated apoptosis via LRF.

Bone marrow engraftment but limited expansion of hematopoietic cells from multipotent germline stem cells derived from neonatal mouse testis

OBJECTIVE

Multipotent germline stem (mGS) cells derived from neonatal mouse testis, similar to embryonic stem (ES) cells, differentiate into various types of somatic cells in vitro and produce teratomas after inoculation into mice. In the present work, we examined mGS cells for hematopoietic progenitor potential in vitro and in vivo.

MATERIALS AND METHODS

mGS cells were differentiated on OP9 stromal cells and induced into Flk1(+) cells. Flk1(+) cells were sorted and replated on OP9 stromal cells with various cytokines and emerging hematopoietic cells were analyzed for lineage marker expression by fluorescein-activated cell sorting, progenitor activity by colony assay, and stem cell transplantation assay.

RESULTS

mGS cells, like ES cells, produce hematopoietic progenitors, including both primitive and definitive erythromyeloid, megakaryocyte, and B- and T-cell lineages via Flk1(+) progenitors. When transplanted into the bone marrow (BM) of nonobese diabetic/severe combined immunodeficient (NOD/SCID) gammac(null) mice directly, mGS-derived green fluorescent protein (GFP)-positive cells were detected 4 months later in the BM and spleen. GFP(+) donor cells were also identified in the Hoechst33342 side population, a feature of hematopoietic stem cells. However, these mGS-derived hematopoietic cells did not proliferate in vivo, even after exposure to hematopoietic stressors, such as 5-fluorouracil (5FU) injection or serial transplantation.

CONCLUSION

mGS cells produced multipotent hematopoietic progenitor cells with myeloid and lymphoid lineage potential in vitro and localized in the BM after intra-BM injection but, like ES cells, failed to expand or show stem cell repopulating ability in vivo.

Orderly hematopoietic development of induced pluripotent stem cells via Flk-1(+) hemoangiogenic progenitors

Induced pluripotent stem (iPS) cells, reprogrammed somatic cells with embryonic stem (ES) cell-like characteristics, are generated by the introduction of combinations of specific transcription factors. Little is known about the differentiation of iPS cells in vitro. Here we demonstrate that murine iPS cells produce various hematopoietic cell lineages when incubated on a layer of OP9 stromal cells. During this differentiation, iPS cells went through an intermediate stage consisting of progenitor cells that were positive for the early mesodermal marker Flk-1 and for the sequential expression of other genes that are associated with hematopoietic and endothelial development. Flk-1(+) cells differentiated into primitive and definitive hematopoietic cells, as well as into endothelial cells. Furthermore, Flk-1(+) populations contained common bilineage progenitors that could generate both hematopoietic and endothelial lineages from single cells. Our results demonstrate that iPS cell-derived cells, like ES cells, can follow a similar hematopoietic route to that seen in normal embryogenesis. This finding highlights the potential use of iPS cells in clinical areas such as regenerative medicine, disease investigation, and drug screening.

Hemangioblasts from human embryonic stem cells generate multilayered blood vessels with functional smooth muscle cells

Background: The formation and regeneration of functional vasculatures require both endothelial cells (ECs) and vascular smooth muscle cells (SMCs). Identification and isolation of progenitors with potential for both EC and SMC lineage differentiation from an inexhaustible source, such as human embryonic stem (hES) or induced pluripotent stem cells, will be desirable for cell replacement therapy. Method: Recently, we have developed a serum-free and animal feeder-free differentiation system to generate blast cells (BCs) from hESCs. These cells possess the characteristics of hemangioblasts in vitro and are capable of repairing damaged retinal vasculatures, restoring blood flow in hind-limb ischemia and reducing the mortality rate after myocardial infarction in vivo. We demonstrate here that BCs express markers of SMCs and differentiate into smooth muscle-like cells (SMLCs), in addition to ECs and hematopoietic cells. Results: When BCs from individual blast colonies were cultured in SMC medium, they differentiated into both ECs and SMLCs, which formed capillary-vascular-like structures after replating on Matrigel™. The SMLCs expressed SMC-specific markers (α-SM actin and calponin) and contracted upon treatment with carbachol. When implanted in nude mice, these cells formed microvasculature with ECs in Matrigel plaques. The BCs differentiated into both ECs and SMLCs, and incorporated into blood vessels after injection into ischemic tissue. Conclusion: These results demonstrate that hemangioblasts (BCs) generated from hESCs are tripotential and can provide a potentially inexhaustible source of cells for the treatment of human blood and vascular diseases.

Derivation and characterization of nonhuman primate embryonic stem cells

Embryonic stem (ES) cells are a powerful research tool enabling the generation of mice with custom genetics, the study of the earliest stages of mammalian differentiation in vitro and, with the isolation of human ES cells, the potential of cell-based therapies for a number of diseases including Parkinson's and Type 1 diabetes. ES cells isolated from nonhuman primates (nhpES cells) offer the opportunity to ethically test the developmental potential of primate ES cells in chimeric offspring. If these cells have similar potency to mouse ES cells, this may open a new era of primate models of human disease. Nonhuman primates are the perfect model system for the preclinical testing of ES cell-derived therapies. In this unit, we describe methods for the derivation and characterization of nonhuman primate ES cells. With these protocols, the investigator will be able to isolate nhpES cells and perform the necessary tests to confirm the pluripotent phenotype.

GeneChip analysis of human embryonic stem cell differentiation into hemangioblasts: an in silico dissection of mixed phenotypes

Transcriptional profiling of human embryonic stem cells differentiating into blast cells reveals that erythroblasts are the predominant cell type in the blast cell population. In silico comparisons with publicly available data sets revealed the presence of endothelia, cardiomyocytes and hematopoietic lineages.

Background

Microarrays are being used to understand human embryonic stem cell (hESC) differentiation. Most differentiation protocols use a multi-stage approach that induces commitment along a particular lineage. Therefore, each stage represents a more mature and less heterogeneous phenotype. Thus, characterizing the heterogeneous progenitor populations upon differentiation are of increasing importance. Here we describe a novel method of data analysis using a recently developed differentiation protocol involving the formation of functional hemangioblasts from hESCs. Blast cells are multipotent and can differentiate into multiple lineages of hematopoeitic cells (erythroid, granulocyte and macrophage), endothelial and smooth muscle cells.

Results

Large-scale transcriptional analysis was performed at distinct time points of hESC differentiation (undifferentiated hESCs, embryoid bodies, and blast cells, the last of which generates both hematopoietic and endothelial progenies). Identifying genes enriched in blast cells relative to hESCs revealed a genetic signature indicative of erythroblasts, suggesting that erythroblasts are the predominant cell type in the blast cell population. Because of the heterogeneity of blast cells, numerous comparisons were made to publicly available data sets in silico, some of which blast cells are capable of differentiating into, to assess and characterize the blast cell population. Biologically relevant comparisons masked particular genetic signatures within the heterogeneous population and identified genetic signatures indicating the presence of endothelia, cardiomyocytes, and hematopoietic lineages in the blast cell population.

Conclusion

The significance of this microarray study is in its ability to assess and identify cellular populations within a heterogeneous population through biologically relevant in silico comparisons of publicly available data sets. In conclusion, multiple in silico comparisons were necessary to characterize tissue-specific genetic signatures within a heterogeneous hemangioblast population.

Generation of functional hemangioblasts from human embryonic stem cells

Recent evidence suggests the existence of progenitor cells in adult tissues that are capable of differentiating into vascular structures as well as into all hematopoietic cell lineages. Here we describe an efficient and reproducible method for generating large numbers of these bipotential progenitors-known as hemangioblasts-from human embryonic stem (hES) cells using an in vitro differentiation system. Blast cells expressed gene signatures characteristic of hemangioblasts, and could be expanded, cryopreserved and differentiated into multiple hematopoietic lineages as well as into endothelial cells. When we injected these cells into rats with diabetes or into mice with ischemia-reperfusion injury of the retina, they localized to the site of injury in the damaged vasculature and appeared to participate in repair. Injection of the cells also reduced the mortality rate after myocardial infarction and restored blood flow in hind limb ischemia in mouse models. Our data suggest that hES-derived blast cells (hES-BCs) could be important in vascular repair.

Differential requirements for hematopoietic commitment between human and rhesus embryonic stem cells

Progress toward clinical application of ESC-derived hematopoietic cellular transplantation will require rigorous evaluation in a large animal allogeneic model. However, in contrast to human ESCs (hESCs), efforts to induce conclusive hematopoietic differentiation from rhesus macaque ESCs (rESCs) have been unsuccessful. Characterizing these poorly understood functional differences will facilitate progress in this area and likely clarify the critical steps involved in the hematopoietic differentiation of ESCs. To accomplish this goal, we compared the hematopoietic differentiation of hESCs with that of rESCs in both EB culture and stroma coculture. Initially, undifferentiated rESCs and hESCs were adapted to growth on Matrigel without a change in their phenotype or karyotype. Subsequent differentiation of rESCs in OP9 stroma led to the development of CD34(+)CD45(-) cells that gave rise to endothelial cell networks in methylcellulose culture. In the same conditions, hESCs exhibited convincing hematopoietic differentiation. In cytokine-supplemented EB culture, rESCs demonstrated improved hematopoietic differentiation with higher levels of CD34(+) and detectable levels of CD45(+) cells. However, these levels remained dramatically lower than those for hESCs in identical culture conditions. Subsequent plating of cytokine-supplemented rhesus EBs in methylcellulose culture led to the formation of mixed colonies of erythroid, myeloid, and endothelial cells, confirming the existence of bipotential hematoendothelial progenitors in the cytokine-supplemented EB cultures. Evaluation of four different rESC lines confirmed the validity of these disparities. Although rESCs have the potential for hematopoietic differentiation, they exhibit a pause at the hemangioblast stage of hematopoietic development in culture conditions developed for hESCs.

alpha4-Integrin(+) endothelium derived from primate embryonic stem cells generates primitive and definitive hematopoietic cells

The mechanism of commencement of hematopoiesis in blood islands of the yolk sac and the aorta-gonad-mesonephros (AGM) region during primate embryogenesis remains elusive. In this study, we demonstrated that VE-cadherin(+)CD45(-) endothelial cells derived from nonhuman primate embryonic stem cells are able to generate primitive and definitive hematopoietic cells sequentially, as revealed by immunostaining of floating erythrocytes and colony-forming assay in cultures. Single bipotential progenitors for hematopoietic and endothelial lineages are included in this endothelial cell population. Furthermore, hemogenic activity of these endothelial cells is observed exclusively in the alpha4-integrin(+) subpopulation; bipotential progenitors are 4-fold enriched in this subpopulation. The kinetics of this hemogenic subpopulation is similar to that of hemogenic endothelial cells previously reported in the yolk sac and the AGM region in vivo in that they emerge for only a limited time. We suggest that VE-cadherin(+)CD45(-)alpha4-integrin(+) endothelial cells are involved in primitive and definitive hematopoiesis during primate embryogenesis, though VE-cadherin(-)CD45(-)alpha4-integrin(+) cells are the primary sources for primitive hematopoiesis.

Sequential analysis of alpha- and beta-globin gene expression during erythropoietic differentiation from primate embryonic stem cells

The temporal pattern of embryonic, fetal, and adult globin expression in the alpha (zeta --> alpha) and beta (epsilon --> gamma and gamma --> beta) clusters were quantitatively analyzed at the transcriptional and translational levels in erythrocytes induced from primate embryonic stem cells in vitro. When vascular endothelial growth factor receptor-2(high) CD34(+) cells were harvested and reseeded onto OP9 stromal cells, two-wave erythropoiesis occurred sequentially. Immunostaining and real-time reverse transcription-polymerase chain reaction analyses of floating mature erythrocytes revealed that globin switches occurred in parallel with the erythropoietic transition. Colony-forming assays showed replacement of primitive clonogenic progenitor cells with definitive cells during culturing. A decline in embryonic zeta- and epsilon-globin expression at the translational level occurred in individual definitive erythroid progenitors. Expression of beta-globin in individual definitive erythroid progenitors was upregulated in the presence of OP9 stromal cells. Thus, this system reproduces early hematopoietic development in vitro and can serve as a model for analyzing the mechanisms of the globin switch in humans.

Hematopoietic Cells from Primate Embryonic Stem Cells

Embryonic stem (ES) cells, derived from early stage embryos, are pluripotent precursors of all of the tissues and organs of the body. ES cells from the mouse have been shown to undergo differentiation in vitro to form a variety of different cell types, including the differentiated progeny of hematopoietic precursors. These hematopoietic cells, however, exhibit numerous differences from those of human cells, and it has become increasingly clear that mouse ES cell differentiation has significant limitations as a model of human developmental biology. The more recent isolation and characterization of nonhuman primate ES cell lines have made available an experimental model with characteristics considerably more close to human biology. We have developed experimental conditions that promote efficient differentiation of these cells to produce progeny cells with considerable similarity to hematopoietic precursors harvested from bone marrow of adult animals.