HoxB4 confers definitive lymphoid-myeloid engraftment potential on embryonic stem cell and yolk sac hematopoietic progenitors

The adult environment promotes the transcriptional maturation of human iPSC-derived muscle grafts

Pluripotent stem cell (PSC)-based cell therapy is an attractive option for the treatment of multiple human disorders, including muscular dystrophies. While in vitro differentiating PSCs can generate large numbers of human lineage-specific tissue, multiple studies evidenced that these cell populations mostly display embryonic/fetal features. We previously demonstrated that transplantation of PSC-derived myogenic progenitors provides long-term engraftment and functional improvement in several dystrophic mouse models, but it remained unknown whether donor-derived myofibers mature to match adult tissue. Here, we transplanted iPAX7 myogenic progenitors into muscles of non-dystrophic and dystrophic mice and compared the transcriptional landscape of human grafts with respective in vitro-differentiated iPAX7 myotubes as well as human skeletal muscle biospecimens. Pairing bulk RNA sequencing with computational deconvolution of human reads, we were able to pinpoint key myogenic changes that occur during the in vitro-to-in vivo transition, confirm developmental maturity, and consequently evaluate their applicability for cell-based therapies.

Post-transcriptional (re)programming of B lymphocyte development: From bench to bedside?

Hematopoiesis, a process which generates blood and immune cells, changes significantly during mammalian development. Definitive hematopoiesis is marked by the emergence of long-term hematopoietic stem cells (HSCs). Here, we will focus on the post-transcriptional differences between fetal liver (FL) and adult bone marrow (ABM) HSCs. It remains unclear how or why exactly FL HSCs transition to ABM HSCs, but we aim to leverage their differences to revive an old idea: in utero HSC transplantation. Unexpectedly, the expression of certain RNA-binding proteins (RBPs) play an important role in HSC specification, and can be employed to convert or reprogram adult HSCs back to a fetal-like state. Among other features, FL HSCs have a broad differentiation capacity that includes the ability to regenerate both conventional B and T cells, as well as innate-like or unconventional lymphocytes such as B-1a and marginal zone B (MzB) cells. This chapter will focus on RNA binding proteins, namely LIN28B and IGF2BP3, that are expressed during fetal life and how they promote B-1a cell development. Furthermore, this chapter considers a potential clinical application of synthetic co-expression of LIN28B and IGF2BP3 in HSCs.

The evolving views of hematopoiesis: from embryo to adulthood and from in vivo to in vitro

The hematopoietic system composed of hematopoietic stem and progenitor cells (HSPCs) and their differentiated lineages serves as an ideal model to uncover generic principles of cell fate transitions. From gastrulation onwards, there successively emerge primitive hematopoiesis (that produces specialized hematopoietic cells), pro-definitive hematopoiesis (that produces lineage-restricted progenitor cells), and definitive hematopoiesis (that produces multipotent HSPCs). These nascent lineages develop in several transient hematopoietic sites and finally colonize into lifelong hematopoietic sites. The development and maintenance of hematopoietic lineages are orchestrated by cell-intrinsic gene regulatory networks and cell-extrinsic microenvironmental cues. Owing to the progressive methodology (e.g., high-throughput lineage tracing and single-cell functional and omics analyses), our understanding of the developmental origin of hematopoietic lineages and functional properties of certain hematopoietic organs has been updated; meanwhile, new paradigms to characterize rare cell types, cell heterogeneity and its causes, and comprehensive regulatory landscapes have been provided. Here, we review the evolving views of HSPC biology during developmental and postnatal hematopoiesis. Moreover, we discuss recent advances in the in vitro induction and expansion of HSPCs, with a focus on the implications for clinical applications.

Haematopoietic development and HSC formation in vitro: promise and limitations of gastruloid models

Haematopoietic stem cells (HSCs) are the most extensively studied adult stem cells. Yet, six decades after their first description, reproducible and translatable generation of HSC in vitro remains an unmet challenge. HSC production in vitro is confounded by the multi-stage nature of blood production during development. Specification of HSC is a late event in embryonic blood production and depends on physical and chemical cues which remain incompletely characterised. The precise molecular composition of the HSC themselves is incompletely understood, limiting approaches to track their origin in situ in the appropriate cellular, chemical and mechanical context. Embryonic material at the point of HSC emergence is limiting, highlighting the need for an in vitro model of embryonic haematopoietic development in which current knowledge gaps can be addressed and exploited to enable HSC production. Gastruloids are pluripotent stem cell-derived 3-dimensional (3D) cellular aggregates which recapitulate developmental events in gastrulation and early organogenesis with spatial and temporal precision. Gastruloids self-organise multi-tissue structures upon minimal and controlled external cues, and are amenable to live imaging, screening, scaling and physicochemical manipulation to understand and translate tissue formation. In this review, we consider the haematopoietic potential of gastruloids and review early strategies to enhance blood progenitor and HSC production. We highlight possible strategies to achieve HSC production from gastruloids, and discuss the potential of gastruloid systems in illuminating current knowledge gaps in HSC specification.

An interactive resource of molecular signalling in the developing human haematopoietic stem cell niche

The emergence of definitive human haematopoietic stem cells (HSCs) from Carnegie Stage (CS) 14 to CS17 in the aorta-gonad-mesonephros (AGM) region is a tightly regulated process. Previously, we conducted spatial transcriptomic analysis of the human AGM region at the end of this period (CS16/CS17) and identified secreted factors involved in HSC development. Here, we extend our analysis to investigate the progression of dorso-ventral polarised signalling around the dorsal aorta over the entire period of HSC emergence. Our results reveal a dramatic increase in ventral signalling complexity from the CS13-CS14 transition, coinciding with the first appearance of definitive HSCs. We further observe stage-specific changes in signalling up to CS17, which may underpin the step-wise maturation of HSCs described in the mouse model. The data-rich resource is also presented in an online interface enabling in silico analysis of molecular interactions between spatially defined domains of the AGM region. This resource will be of particular interest for researchers studying mechanisms underlying human HSC development as well as those developing in vitro methods for the generation of clinically relevant HSCs from pluripotent stem cells.

The oncogenic fusion protein TAZ::CAMTA1 promotes genomic instability and senescence through hypertranscription

TAZ::CAMTA1 is a fusion protein found in over 90% of Epithelioid Hemangioendothelioma (EHE), a rare vascular sarcoma with an unpredictable disease course. To date, how TAZ::CAMTA1 initiates tumour formation remains unexplained. To study the oncogenic mechanism leading to EHE initiation, we developed a model system whereby TAZ::CAMTA1 expression is induced by doxycycline in primary endothelial cells. Using this model, we establish that upon TAZ::CAMTA1 expression endothelial cells rapidly enter a hypertranscription state, triggering considerable DNA damage. As a result, TC-expressing cells become trapped in S phase. Additionally, TAZ::CAMTA1-expressing endothelial cells have impaired homologous recombination, as shown by reduced BRCA1 and RAD51 foci formation. Consequently, the DNA damage remains unrepaired and TAZ::CAMTA1-expressing cells enter senescence. Knockout of Cdkn2a, the most common secondary mutation found in EHE, allows senescence bypass and uncontrolled growth. Together, this provides a mechanistic explanation for the clinical course of EHE and offers novel insight into therapeutic options.

Induced pluripotent stem cell-derived hematopoietic stem and progenitor cells induce mixed chimerism and donor-specific allograft tolerance

In transplantation using allogeneic induced pluripotent stem cells (iPSCs), strategies focused on major histocompatibility complexes were adopted to avoid immune rejection. We showed that minor antigen mismatches are a risk factor for graft rejection, indicating that immune regulation remains one of the most important issues. In organ transplantation, it has been known that mixed chimerism using donor-derived hematopoietic stem/progenitor cells (HSPCs) can induce donor-specific tolerance. However, it is unclear whether iPSC-derived HSPCs (iHSPCs) can induce allograft tolerance. We showed that 2 hematopoietic transcription factors, Hoxb4 and Lhx2, can efficiently expand iHSPCs with a c-Kit+Sca-1+Lineage- phenotype, which possesses long-term hematopoietic repopulating potential. We also demonstrated that these iHSPCs can form hematopoietic chimeras in allogeneic recipients and induce allograft tolerance in murine skin and iPSC transplantation. With mechanistic analyses, both central and peripheral mechanisms were suggested. We demonstrated the basic concept of tolerance induction using iHSPCs in allogeneic iPSC-based transplantation.

Prolonged generation of multi-lineage blood cells in wild-type animals from pluripotent stem cells

Regenerating prolonged multi-lineage hematopoiesis from pluripotent stem cells (PSCs), an unlimited cell source, is a crucial aim of regenerative hematology. In this study, we used a gene-edited PSC line and revealed that simultaneous expression of three transcription factors, Runx1, Hoxa9, and Hoxa10, drove the robust emergence of induced hematopoietic progenitor cells (iHPCs). The iHPCs engrafted successfully in wild-type animals and repopulated abundant and complete myeloid-, B-, and T-lineage mature cells. The generative multi-lineage hematopoiesis distributed normally in multiple organs, persisted over 6 months, and eventually declined over time with no leukemogenesis. Transcriptome characterization of generative myeloid, B, and T cells at the single-cell resolution further projected their identities to natural cell counterparts. Thus, we provide evidence that co-expression of exogenous Runx1, Hoxa9, and Hoxa10 simultaneously leads to long-term reconstitution of myeloid, B, and T lineages using PSC-derived iHPCs as the cell source.

De Novo Generation of Human Hematopoietic Stem Cells from Pluripotent Stem Cells for Cellular Therapy

The ability to manufacture human hematopoietic stem cells (HSCs) in the laboratory holds enormous promise for cellular therapy of human blood diseases. Several differentiation protocols have been developed to facilitate the emergence of HSCs from human pluripotent stem cells (PSCs). Most approaches employ a stepwise addition of cytokines and morphogens to recapitulate the natural developmental process. However, these protocols globally lack clinical relevance and uniformly induce PSCs to produce hematopoietic progenitors with embryonic features and limited engraftment and differentiation capabilities. This review examines how key intrinsic cues and extrinsic environmental inputs have been integrated within human PSC differentiation protocols to enhance the emergence of definitive hematopoiesis and how advances in genomics set the stage for imminent breakthroughs in this field.

Using Pluripotent Stem Cells to Understand Normal and Leukemic Hematopoietic Development

Several decades have passed since the generation of the first embryonic stem cell (ESC) lines both in mice and in humans. Since then, stem cell biologists have tried to understand their potential biological and clinical uses for their implementation in regenerative medicine. The hematopoietic field was a pioneer in establishing the potential use for the development of blood cell products and clinical applications; however, early expectations have been truncated by the difficulty in generating bonafide hematopoietic stem cells (HSCs). Despite some progress in understanding the origin of HSCs during embryonic development, the reproduction of this process in vitro is still not possible, but the knowledge acquired in the embryo is slowly being implemented for mouse and human pluripotent stem cells (PSCs). In contrast, ESC-derived hematopoietic cells may recapitulate some leukemic transformation processes when exposed to oncogenic drivers. This would be especially useful to model prenatal leukemia development or other leukemia-predisposing syndromes, which are difficult to study. In this review, we will review the state of the art of the use of PSCs as a model for hematopoietic and leukemia development.

Gastruloids as in vitro models of embryonic blood development with spatial and temporal resolution

Gastruloids are three-dimensional embryonic organoids that reproduce key features of early mammalian development in vitro with unique scalability, accessibility, and spatiotemporal similarity to real embryos. Recently, we adapted the gastruloid culture conditions to promote cardiovascular development. In this work, we extended these conditions to capture features of embryonic blood development through a combination of immunophenotyping, detailed transcriptomics analysis, and identification of blood stem/progenitor cell potency. We uncovered the emergence of blood progenitor and erythroid-like cell populations in late gastruloids and showed the multipotent clonogenic capacity of these cells, both in vitro and after transplantation into irradiated mice. We also identified the spatial localization near a vessel-like plexus in the anterior portion of gastruloids with similarities to the emergence of blood stem cells in the mouse embryo. These results highlight the potential and applicability of gastruloids to the in vitro study of complex processes in embryonic blood development with spatiotemporal fidelity.

Hematopoietic Stem Cells and Regeneration

Hematopoietic stem cell (HSC) regeneration is the remarkable process by which extremely rare, normally inactive cells of the bone marrow can replace an entire organ if called to do so by injury or harnessed by transplantation. HSC research is arguably the first quantitative single-cell science and the foundation of adult stem cell biology. Bone marrow transplant is the oldest and most refined technique of regenerative medicine. Here we review the intertwined history of the discovery of HSCs and bone marrow transplant, the molecular and cellular mechanisms of HSC self-renewal, and the use of HSCs and their derivatives for cell therapy.

Generation and clinical potential of functional T lymphocytes from gene-edited pluripotent stem cells

Engineered T cells have been shown to be highly effective in cancer immunotherapy, although T cell exhaustion presents a challenge for their long-term function. Additional T-cell sources must be exploited to broaden the application of engineered T cells for immune defense and reconstitution. Unlimited sources of pluripotent stem cells (PSCs) have provided a potential opportunity to generate precise-engineered therapeutic induced T (iT) cells. Single-cell transcriptome analysis of PSC-derived induced hematopoietic stem and progenitor cells (iHSPC)/iT identified the developmental pathways and possibilities of generating functional T cell from PSCs. To date, the PSC-to-iT platforms encounter several problems, including low efficiency of conventional T subset specification, limited functional potential, and restrictions on large-scale application, because of the absence of a thymus-like organized microenvironment. The updated PSC-to-iT platforms, such as the three-dimensional (3D) artificial thymic organoid (ATO) co-culture system and Runx1/Hoxa9-enforced iT lymphopoiesis, provide fresh perspectives for coordinating culture conditions and transcription factors, which may greatly improve the efficiency of T-cell generation greatly. In addition, the improved PSC-to-iT platform coordinating gene editing technologies will provide various functional engineered unconventional or conventional T cells. Furthermore, the clinical applications of PSC-derived immune cells are accelerating from bench to bedside.

Human pluripotent stem cell-derived myogenic progenitors undergo maturation to quiescent satellite cells upon engraftment

Human pluripotent stem cell (hPSC)-derived myogenic progenitor cell (MPC) transplantation is a promising therapeutic approach for a variety of degenerative muscle disorders. Here, using an MPC-specific fluorescent reporter system (PAX7::GFP), we demonstrate that hPSC-derived MPCs can contribute to the regeneration of myofibers in mice following local injury and in mice deficient of dystrophin (mdx). We also demonstrate that a subset of PAX7::GFP MPCs engraft within the basal lamina of regenerated myofibers, adopt a quiescent state, and contribute to regeneration upon reinjury and in mdx mouse models. This subset of PAX7::GFP MPCs undergo a maturation process and remodel their molecular characteristics to resemble those of late-stage fetal MPCs/adult satellite cells following in vivo engraftment. These in-vivo-matured PAX7::GFP MPCs retain a cell-autonomous ability to regenerate and can repopulate in the niche of secondary recipient mice, providing a proof of principle for future hPSC-based cell therapy for muscle disorders.

Kap1 Regulates the Stability of Lin28A in Embryonic Stem Cells

Lin28A is an RNA-binding protein that controls mammalian development and maintenance of the pluripotency of embryonic stem cells (ESCs) via regulating the processing of the microRNA let-7. Lin28A is highly expressed in ESCs, and ectopic expression of this protein facilitates reprogramming of somatic cells to induced pluripotent stem cells. However, the mechanisms underlying the post-translational regulation of Lin28A protein stability in ESCs remain unclear. In the present study, we identified Kap1 (KRAB-associated protein 1) as a novel Lin28A-binding protein using affinity purification and mass spectrometry. Kap1 specifically interacted with the N-terminal region of Lin28A through its coiled-coil domain. Kap1 overexpression significantly attenuated Lin28A ubiquitination and increased its stability. However, small interfering RNA-mediated knockdown of Kap1 promoted the ubiquitination of Lin28A, leading to its proteasomal degradation. Trim71, an E3 ubiquitin ligase, induced Lin28A degradation and Kap1 knockdown accelerated the Trim71-dependent degradation of Lin28A. Mutation of the lysine 177 residue of Lin28A to arginine abrogated the ubiquitination and degradation of Lin28A which were accelerated by Kap1 silencing. Moreover, Kap1 overexpression led to the accumulation of Lin28A in the cytoplasm, but not in the nucleus, and reduced the levels of let-7 subtypes. These results suggest that Kap1 plays a key role in regulation of the stability of Lin28A by modulating the Trim71-mediated ubiquitination and subsequent degradation of Lin28A, thus playing a pivotal role in the regulation of ESC self-renewal and pluripotency.

Germline specification from pluripotent stem cells

Reproduction is a key event in life guaranteeing the propagation and evolution of a species. Infertility caused by abnormal germ cell development is a topic of extensive concern. Herein, in vitro germline specification studies provide a modeling platform to investigate gametogenesis. The differentiation of pluripotent stem cells (PSCs) into germ cells has been studied for more than 30 years, and there have been many astonishing breakthroughs in the last decade. Fertile sperm and oocytes can be obtained from mouse embryonic stem cells (ESCs) through a primordial germ cell (PGC)-based method. Moreover, human PGC-like cells (PGCLCs) can be derived with a similar strategy as that used for mouse PGCLC derivation. In this review, we describe the reconstitution of PGCs and the subsequent meiosis, as well as the signaling pathways and factors involved in these processes.

Hematopoietic stem cells characteristics: from isolation to transplantation

Abstract:

Hematopoietic stem cells (HSCs) have a self-renewal as well as pluripotency properties and are responsible to produce all types of blood cells. These cells are generated during embryonic development and transit through various anatomical niches (bone marrow microenvironment). Today, they are easily enriched from some sources including peripheral blood, bone marrow, and umbilical cord blood (UCB). HSCs have been used for many years to treat a variety of cancers and blood disorders such as various types of leukemia, lymphoma, myelodysplastic, myeloproliferative syndromes etc. Although almost 50 years have passed since the discovery of stem cells and many investigations have been done on cell therapy and regenerative medicine, further studies need to be conducted in this regard. This manuscript review the history, location, evolution, isolation, and therapeutic approaches of HSCs.

Fli1 Promotes Vascular Morphogenesis by Regulating Endothelial Potential of Multipotent Myogenic Progenitors

[Figure: see text].

Quantitative control of noise in mammalian gene expression by dynamic histone regulation

Fluctuation ('noise') in gene expression is critical for mammalian cellular processes. Numerous mechanisms contribute to its origins, yet the mechanisms behind large fluctuations that are induced by single transcriptional activators remain elusive. Here, we probed putative mechanisms by studying the dynamic regulation of transcriptional activator binding, histone regulator inhibitors, chromatin accessibility, and levels of mRNAs and proteins in single cells. Using a light-induced expression system, we showed that the transcriptional activator could form an interplay with dual functional co-activator/histone acetyltransferases CBP/p300. This interplay resulted in substantial heterogeneity in H3K27ac, chromatin accessibility, and transcription. Simultaneous attenuation of CBP/p300 and HDAC4/5 reduced heterogeneity in the expression of endogenous genes, suggesting that this mechanism is universal. We further found that the noise was reduced by pulse-wide modulation of transcriptional activator binding possibly as a result of alternating the epigenetic states. Our findings suggest a mechanism for the modulation of noise in synthetic and endogenous gene expression systems.

Enhanced HSC-like cell generation from mouse pluripotent stem cells in a 3D induction system cocultured with stromal cells

BACKGROUND

Decades of efforts have attempted to differentiate the pluripotent stem cells (PSCs) into truly functional hematopoietic stem cells (HSCs), yet the problems of low differentiation efficiency in vitro and poor hematopoiesis reconstitution in vivo still exist, mainly attributing to the lack of solid, reproduced, or pursued differentiation system.

METHODS

In this study, we established an in vitro differentiation system yielding in vivo hematopoietic reconstitution hematopoietic cells from mouse PSCs through a 3D induction system followed by coculture with OP9 stromal cells. The in vivo hematopoietic reconstitution potential of c-kit⁺ cells derived from the mouse PSCs was evaluated via m-NSG transplantation assay. Flow cytometry analysis, RNA-seq, and cell cycle analysis were used to detect the in vitro hematopoietic ability of endothelial protein C receptor (EPCR, CD201) cells generated in our induction system.

RESULTS

The c-kit⁺ cells from 3D self-assembling peptide induction system followed by the OP9 coculture system possessed apparently superiority in terms of in vivo repopulating activity than that of 3D induction system followed by the 0.1% gelatin culture. We interestingly found that our 3D+OP9 system enriched a higher percentage of CD201⁺c-kit⁺cells that showed more similar HSC-like features such as transcriptome level and CFU formation ability than CD201^-c-kit⁺cells, which have not been reported in the field of mouse PSCs hematopoietic differentiation. Moreover, CD201⁺ hematopoietic cells remained in a relatively slow cycling state, consistent with high expression levels of P57 and Ccng2. Further, we innovatively demonstrated that notch signaling pathway is responsible for in vitro CD201⁺ hematopoietic cell induction from mouse PSCs.

CONCLUSIONS

Altogether, our findings lay a foundation for improving the efficiency of hematopoietic differentiation and generating in vivo functional HSC-like cells from mouse PSCs for clinical application.

Zbtb46-dependent altered developmental program in embryonic stem cell-derived blood cell progenitors

Zbtb46 is a recently identified dendritic cell (DC)-specific transcription factor with poorly defined biology. Although Zbtb46 is highly expressed in conventional DCs, evidence also points to its presence in erythroid progenitors and endothelial cells suggesting that this factor might influence the early hematopoietic development. Here, we probe the effect of this transcription factor in embryonic stem cell (ESC)-derived blood cell progenitors using chemically inducible mouse cell lines. Unexpectedly, forced expression of this protein elicited a broad repressive effect at the early stage of ESC differentiation. Ectopic expression of Zbtb46 interfered with the mesoderm formation and cell proliferation was also negatively impacted. More importantly, reduced number of CD11b+ myeloid blood cells were generated from ESC-derived Flk1+ mesoderm cells in the presence of Zbtb46. Consistent with this finding, our gene expression profiling revealed that numerous myeloid and immune response related genes, including Irf8, exhibited lower expression in the Zbtb46-primed cells. Despite these repressive effects, however, Zbtb46 overexpression was associated with enhanced formation of erythroid blood cell colonies and increased adult hemoglobin (Hbb-b1) expression at the early phase of ESC differentiation. Moreover, elevated percent of CD105 (Endoglin) positive cells were detected in the Zbtb46-primed samples. In summary, our results support that Zbtb46 suppresses the ESC-derived myeloid development and diverts mesoderm cells toward erythroid developmental pathway. Moreover, our transcriptomic data provide a resource for exploration of the Zbtb46 regulatory network in ESC-derived progenitors.

Running the full human developmental clock in interspecies chimeras using alternative human stem cells with expanded embryonic potential

Human pluripotent stem cells (hPSCs) can generate specialized cell lineages that have great potential for regenerative therapies and disease modeling. However, the developmental stage of the lineages generated from conventional hPSC cultures in vitro are embryonic in phenotype, and may not possess the cellular maturity necessary for corrective regenerative function in vivo in adult recipients. Here, we present the scientific evidence for how adult human tissues could generate human–animal interspecific chimeras to solve this problem. First, we review the phenotypes of the embryonic lineages differentiated from conventional hPSC in vitro and through organoid technologies and compare their functional relevance to the tissues generated during normal human in utero fetal and adult development. We hypothesize that the developmental incongruence of embryo-stage hPSC-differentiated cells transplanted into a recipient adult host niche is an important mechanism ultimately limiting their utility in cell therapies and adult disease modeling. We propose that this developmental obstacle can be overcome with optimized interspecies chimeras that permit the generation of adult-staged, patient-specific whole organs within animal hosts with human-compatible gestational time-frames. We suggest that achieving this goal may ultimately have to await the derivation of alternative, primitive totipotent-like stem cells with improved embryonic chimera capacities. We review the scientific challenges of deriving alternative human stem cell states with expanded embryonic potential, outline a path forward for conducting this emerging research with appropriate ethical and regulatory oversight, and defend the case of why current federal funding restrictions on this important category of biomedical research should be liberalized.

LHPP-Mediated Histidine Dephosphorylation Suppresses the Self-Renewal of Mouse Embryonic Stem Cells

Self-renewal of embryonic stem cells (ESCs) is orchestrated by a vast number of genes at the transcriptional and translational levels. However, the molecular mechanisms of post-translational regulatory factors in ESC self-renewal remain unclear. Histidine phosphorylation, also known as hidden phosphorylation, cannot be detected by conventional experimental methods. A recent study defined phospholysine phosphohistidine inorganic pyrophosphate phosphatase (LHPP) as a histidine phosphatase, which regulates various biological behaviors in cells via histidine dephosphorylation. In this study, the doxycycline (DOX)-induced hLHPP-overexpressing mouse ESCs and mouse LHPP silenced mESCs were constructed. Quantitative polymerase chain reaction (qPCR), western blotting analysis, immunofluorescence, Flow cytometry, colony formation assays, alkaline phosphatase (AP) and bromodeoxyuridine (Brdu) staining were performed. We found that the histidine phosphorylation level was strikingly reduced following LHPP overexpression. Besides, the expression of Oct4 and Lefty1, indispensable genes in the process of ESCs self-renewal, was significantly down-regulated, while markers related to the differentiation were markedly elevated. Moreover, LHPP-mediated histidine dephosphorylation induced G_0/G₁ phase arrest in mESCs, suggesting LHPP was implicated in cell proliferation and cell cycle. Conversely, silencing of Lhpp promoted the self-renewal of mESCs and reversed the RA induced increased expression of genes associated with differentiation. Mechanistically, our findings suggested that the enzymatic active site of LHPP was the cysteine residue at position 226, not 53. LHPP-mediated histidine dephosphorylation lowered the expression levels of β-catenin and the cell cycle-related genes CDK4 and CyclinD1, while it up-regulated the cell cycle suppressor genes P21 and P27. Taken together, our findings reveal that LHPP-mediated histidine dephosphorylation plays a role in the self-renewal of ESCs. LHPP-mediated histidine dephosphorylation inhibited the self-renewal of ESCs by negatively regulating the Wnt/β-catenin pathway and downstream cell cycle-related genes, providing a new perspective and regulatory target for ESCs self-renewal.

The hemogenic endothelium: a critical source for the generation of PSC-derived hematopoietic stem and progenitor cells

In vitro generation of hematopoietic cells and especially hematopoietic stem cells (HSCs) from human pluripotent stem cells (PSCs) are subject to intensive research in recent decades, as these cells hold great potential for regenerative medicine and autologous cell replacement therapies. Despite many attempts, in vitro, de novo generation of bona fide HSCs remains challenging, and we are still far away from their clinical use, due to insufficient functionality and quantity of the produced HSCs. The challenges of generating PSC-derived HSCs are already apparent in early stages of hemato-endothelial specification with the limitation of recapitulating complex, dynamic processes of embryonic hematopoietic ontogeny in vitro. Further, these current shortcomings imply the incompleteness of our understanding of human ontogenetic processes from embryonic mesoderm over an intermediate, specialized hemogenic endothelium (HE) to their immediate progeny, the HSCs. In this review, we examine the recent investigations of hemato-endothelial ontogeny and recently reported progress for the conversion of PSCs and other promising somatic cell types towards HSCs with the focus on the crucial and inevitable role of the HE to achieve the long-standing goal—to generate therapeutically applicable PSC-derived HSCs in vitro.

Induced pluripotent stem cell models of myeloid malignancies and clonal evolution

Reprogramming of cells from patients with genetic disorders to pluripotency is a promising avenue to understanding disease biology. A number of induced pluripotent stem cell (iPSC) models of inherited monogenic blood disorders have been reported over the past decade. However, the application of iPSCs for modeling of hematological malignancies has only recently been explored. Blood malignancies comprise a spectrum of genetically heterogeneous disorders marked by the acquisition of somatic mutations and chromosomal aberrations. This genetic heterogeneity presents unique challenges for iPSC modeling, but also opportunities to capture genetically distinct states and generate models of stepwise progression from normal to malignant hematopoiesis. Here we briefly review the current state of this field, highlighting current models of acquired pre-malignant and malignant blood disorders and clonal evolution, and challenges including barriers to reprogramming and differentiation of iPSCs into bona fide hematopoietic stem cells.

Hematopoietic stem cells from pluripotent stem cells: Clinical potential, challenges, and future perspectives

The generation of hematopoietic stem cells (HSCs) from induced pluripotent stem cells (iPSCs) is an active and promising area of research; however, generating engraftable HSCs remains a major obstacle. Ex vivo HSC derivation from renewable sources such as iPSCs offers an experimental tool for studying developmental hematopoiesis, disease modeling, and drug discovery, and yields tremendous therapeutic potential for malignant and nonmalignant hematological disorders. Although initial attempts mostly recapitulated yolk sac primitive/definitive hematopoiesis with inability to engraft, recent advances suggest the feasibility of engraftable HSC derivation from iPSCs utilizing ectopic transcription factor expression. Strategic development for de novo HSC generation includes further investigations of HSC ontogeny, and elucidation of critical signaling pathways, epigenetic modulations, HSC and iPSC microenvironment, and cell-cell interactions that contribute to stem cell biology and function.

Regulation of Hemogenic Endothelial Cell Development and Function

Embryonic definitive hematopoiesis generates hematopoietic stem and progenitor cells (HSPCs) essential for establishment and maintenance of the adult blood system. This process requires the specification of a subset of vascular endothelial cells to become blood-forming, or hemogenic, and the subsequent endothelial-to-hematopoietic transition to generate HSPCs therefrom. The mechanisms that regulate these processes are under intensive investigation, as their recapitulation in vitro from human pluripotent stem cells has the potential to generate autologous HSPCs for clinical applications. In this review, we provide an overview of hemogenic endothelial cell development and highlight the molecular events that govern hemogenic specification of vascular endothelial cells and the generation of multilineage HSPCs from hemogenic endothelium. We also discuss the impact of hemogenic endothelial cell development on adult hematopoiesis.

Kap1 regulates the self-renewal of embryonic stem cells and cellular reprogramming by modulating Oct4 protein stability

Oct4 plays a crucial role in the regulation of self-renewal of embryonic stem cells (ESCs) and reprogramming of somatic cells to induced pluripotent stem cells. However, the molecular mechanisms underlying posttranslational regulation and protein stability of Oct4 remain unclear. Using affinity purification and mass spectrometry analysis, we identified Kap1 as an Oct4-binding protein. Silencing of Kap1 reduced the protein levels of Oct4 in ESCs, whereas the overexpression of Kap1 stimulated the levels of Oct4. In addition, Kap1 overexpression stimulated the self-renewal of ESCs and attenuated the spontaneous differentiation of ESCs in response to LIF withdrawal. Kap1 overexpression increased the stability of Oct4 by inhibiting the Itch-mediated ubiquitination of Oct4. Silencing of Kap1 augmented Itch-mediated ubiquitination and inhibited the stability of Oct4. We identified the lysine 133 (K133) residue in Oct4 as a ubiquitination site responsible for the Kap1-Itch-dependent regulation of Oct4 stability. Preventing ubiquitination at the lysine residue by mutation to arginine augmented the reprogramming of mouse embryonic fibroblasts to induced pluripotent stem cells. These results suggest that Kap1 plays a crucial role in the regulation of the pluripotency of ESCs and somatic cell reprogramming by preventing Itch-mediated ubiquitination and the subsequent degradation of Oct4.

HOXC4 up-regulates NF-κB signaling and promotes the cell proliferation to drive development of human hematopoiesis, especially CD43+ cells

The hematopoietic function of HOXC4 has not been extensively investigated. Our research indicated that induction of HOXC4 in co-culture system from D10 significantly promoted productions of most hematopoietic progenitor cells. CD34−CD43+ cells could be clearly classified into CD34−CD43^low and CD34−CD43^high sub-populations at D14. The former cells had greater myelogenic potential, and their production was not significantly influenced by induction of HOXC4. By contrast, the latter cells had greater potential to differentiate into megakaryocytes and erythroid cells, and thus had properties of erythroid–megakaryocyte common progenitors, which abundance was increased by ∼2-fold when HOXC4 was induced from D10. For CD34−CD43^low, CD34+CD43+, and CD34−CD43^high sub-populations, CD43 level served as a natural index for the tendency to undergo hematopoiesis. Induction of HOXC4 from D10 caused more CD43+ cells sustain in S-phase with up-regulation of NF-κB signaling, which could be counteracted by inhibition of NF-κB signaling. These observations suggested that promotion of hematopoiesis by HOXC4 is closely related to NF-κB signaling and a change in cell-cycle status, which containing potential of clinical applications.

Environmental Optimization Enables Maintenance of Quiescent Hematopoietic Stem Cells Ex Vivo

Hematopoietic stem cells (HSCs) maintain lifelong hematopoiesis by remaining quiescent in the bone marrow niche. Recapitulation of a quiescent state in culture has not been achieved, as cells rapidly proliferate and differentiate in vitro. After exhaustive analysis of different environmental factor combinations and concentrations as a way to mimic physiological conditions, we were able to maintain engraftable quiescent HSCs for 1 month in culture under very low cytokine concentrations, hypoxia, and very high fatty acid levels. Exogenous fatty acids were required likely due to suppression of intrinsic fatty acid synthesis by hypoxia and low cytokine conditions. By contrast, high cytokine concentrations or normoxia induced HSC proliferation and differentiation. Our culture system provides a means to evaluate properties of steady-state HSCs and test effects of defined factors in vitro under near-physiological conditions.

Activated HoxB4-induced hematopoietic stem cells from murine pluripotent stem cells via long-term programming

Hematopoietic stem cells (HSCs) are multipotent cells that form the entire blood system and have the potential to cure several pathogenic conditions directly or indirectly arising from defects within the HSC compartment. Pluripotent stem cells (PSCs) or induced pluripotent stem cells (iPSCs) can give rise to all embryonic cell types; however, efficient in vitro differentiation of HSCs from PSCs remains challenging. HoxB4 is a key regulator orchestrating the differentiation of PSCs into all cells types across the mesodermal lineage, including HSCs. Moreover, the ectopic expression of HoxB4 enhances the in vitro generation and expansion of HSCs. However, several aspects of HoxB4 biology including its regulatory functions are not fully understood. Here, we describe the role of HoxB4 in indirectly inhibiting the emergence of mature CD45⁺ HSCs from iPSCs in vitro. Forced activation of HoxB4 permitted long-term maintenance of functional hematopoietic stem and progenitor cells (HSPCs), which efficiently reconstituted hematopoiesis upon transplantation. Our method enables an easy and scalable in vitro platform for the generation of HSCs from iPSCs, which will ultimately lead to a better understanding of HSC biology and facilitate preparation of the roadma for producing an unrestricted supply of HSCs for several curative therapies.

Transplantation Induces Profound Changes in the Transcriptional Asset of Hematopoietic Stem Cells: Identification of Specific Signatures Using Machine Learning Techniques

During the phase of proliferation needed for hematopoietic reconstitution following transplantation, hematopoietic stem/progenitor cells (HSPC) must express genes involved in stem cell self-renewal. We investigated the expression of genes relevant for self-renewal and expansion of HSPC (operationally defined as CD34+ cells) in steady state and after transplantation. Specifically, we evaluated the expression of ninety-one genes that were analyzed by real-time PCR in CD34+ cells isolated from (i) 12 samples from umbilical cord blood (UCB); (ii) 15 samples from bone marrow healthy donors; (iii) 13 samples from bone marrow after umbilical cord blood transplant (UCBT); and (iv) 29 samples from patients after transplantation with adult hematopoietic cells. The results show that transplanted CD34+ cells from adult cells acquire an asset very different from transplanted CD34+ cells from cord blood. Multivariate machine learning analysis (MMLA) showed that four specific gene signatures can be obtained by comparing the four types of CD34+ cells. In several, but not all cases, transplanted HSPC from UCB overexpress reprogramming genes. However, these remarkable changes do not alter the commitment to hematopoietic lineage. Overall, these results reveal undisclosed aspects of transplantation biology.

Improved hematopoietic differentiation of mouse embryonic stem cells through manipulation of the RNA binding protein ARS2

The RNA binding protein ARS2 is highly expressed in hematopoietic progenitor populations and is required for adult hematopoiesis. Recent molecular studies found that ARS2 coordinates interactions between nascent RNA polymerase II transcripts and downstream RNA processing machineries, yet how such interactions influence hematopoiesis remains largely unknown. Techniques to differentiate embryonic stem cells (ESC) to hematopoietic progenitor cells (HPC) and mature blood cells have increased molecular understanding of hematopoiesis. Taking such an in vitro approach to examine the influence of ARS2 on hematopoiesis, we found that ARS2 suppresses expression of some HSC signature genes and differentiation of ESC to a HPC population (CSMD-HPC) identified by markers expressed on bone marrow resident hematopoietic stem cells. In line with ARS2's ability to promote proliferation of cultured cells, ARS2 knockout ESC showed limited expansion and yielded less CSMD-HPC than wild-type ESC. In contrast, transient ARS2 knockdown led to doubling the number of CSMD-HPC generated per ESC without affecting further differentiation into mature T-cells. Overall, data indicate that ARS2 negatively regulates early hematopoietic differentiation of ESC, in stark contrast to its supportive role in adult hematopoiesis. Consequently, manipulation of ARS2 expression and/or function has potential utility in hematopoietic cell engineering and regenerative medicine.

Enhancing Hematopoiesis from Murine Embryonic Stem Cells through MLL1-Induced Activation of a Rac/Rho/Integrin Signaling Axis

The Mixed Lineage Leukemia (MLL1, KMT2A) gene is critical for development and maintenance of hematopoietic stem cells (HSCs), however, whether this protein is limiting for HSC development is unknown due to lack of physiologic model systems. Here, we develop an MLL1-inducible embryonic stem cell (ESC) system and show that induction of wild-type MLL1 during ESC differentiation selectively increases hematopoietic potential from a transitional c-Kit⁺/Cd41⁺ population in the embryoid body and also at sites of hematopoiesis in embryos. Single-cell sequencing analysis illustrates inherent heterogeneity of the c-Kit⁺/Cd41⁺ population and demonstrates that MLL1 induction shifts its composition toward multilineage hematopoietic identities. Surprisingly, this does not occur through increasing Hox or other canonical MLL1 targets but through an enhanced Rac/Rho/integrin signaling state, which increases responsiveness to Vla4 ligands and enhances hematopoietic commitment. Together, our data implicate a Rac/Rho/integrin signaling axis in the endothelial to hematopoietic transition and demonstrate that MLL1 actives this axis.

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Increasing MLL1 enhances hematopoietic potential in vitro and in vivo

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scRNA sequencing illustrates the heterogeneity of an EMP-like population from EBs

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MLL1 activates Rac/Rho/integrin signaling during hematopoietic specification

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MLL1-induced HSPCs are primed for hematopoiesis via integrin-mediated adhesion

Transcriptional control of blood cell emergence

The haematopoietic system is established during embryonic life through a series of developmental steps that culminates with the generation of haematopoietic stem cells. Characterisation of the transcriptional network that regulates blood cell emergence has led to the identification of transcription factors essential for this process. Among the many factors wired within this complex regulatory network, ETV2, SCL and RUNX1 are the central components. All three factors are absolutely required for blood cell generation, each one controlling a precise step of specification from the mesoderm germ layer to fully functional blood progenitors. Insight into the transcriptional control of blood cell emergence has been used for devising protocols to generate blood cells de novo, either through reprogramming of somatic cells or through forward programming of pluripotent stem cells. Interestingly, the physiological process of blood cell generation and its laboratory-engineered counterpart have very little in common.

Haematopoietic stem cell reprogramming and the hope for a universal blood product

Haematopoietic stem cells (HSCs) are the only adult stem cells with a demonstrated clinical use, even though a tractable method to maintain and expand human HSCs in vitro has not yet been found. Owing to the introduction of transplantation strategies for the treatment of haematological malignancies and, more recently, the promise of gene therapy, the need to improve the generation, manipulation and scalability of autologous or allogeneic HSCs has risen steeply over the past decade. In that context, reprogramming strategies based on the expression of exogenous transcription factors have emerged as a means to produce functional HSCs in vitro. These approaches largely stem from the assumption that key master transcription factors direct the expression of downstream target genes thereby triggering haematopoiesis. Both somatic and pluripotent cells have been used to this end, yielding variable results in terms of haematopoietic phenotype and functionality. Here, we present an overview of the haematopoietic reprogramming methods reported to date, provide the appropriate historical context and offer some critical insight about where the field stands at present.

Induction of human hemogenesis in adult fibroblasts by defined factors and hematopoietic coculture

Transcription factor (TF)-based reprogramming of somatic tissues holds great promise for regenerative medicine. Previously, we demonstrated that the TFs GATA2, GFI1B, and FOS convert mouse and human fibroblasts to hemogenic endothelial-like precursors that generate hematopoietic stem progenitor (HSPC)-like cells over time. This conversion is lacking in robustness both in yield and biological function. Herein, we show that inclusion of GFI1 to the reprogramming cocktail significantly expands the HSPC-like population. AFT024 coculture imparts functional potential to these cells and allows quantification of stem cell frequency. Altogether, we demonstrate an improved human hemogenic induction protocol that could provide a valuable human in vitro model of hematopoiesis for disease modeling and a platform for cell-based therapeutics. DATABASE: Gene expression data are available in the Gene Expression Omnibus (GEO) database under the accession number GSE130361.

Skeletal Muscle Stem Cells from PSC-Derived Teratomas Have Functional Regenerative Capacity

Derivation of functional skeletal muscle stem cells from pluripotent cells without genetic modification has proven elusive. Here we show that teratomas formed in adult skeletal muscle differentiate in vivo to produce large numbers of α7-Integrin+ VCAM-1+ myogenic progenitors. When FACS-purified and transplanted into diseased muscles, mouse teratoma-derived myogenic progenitors demonstrate very high engraftment potential. As few as 40,000 cells can reconstitute ∼80% of the tibialis anterior muscle volume. Newly generated fibers are innervated, express adult myosins, and ameliorate dystrophy-related force deficit and fatigability. Teratoma-derived myogenic progenitors also contribute quiescent PAX7+ muscle stem cells, enabling long-term maintenance of regenerated muscle and allowing muscle regeneration in response to subsequent injuries. Transcriptional profiling reveals that teratoma-derived myogenic progenitors undergo embryonic-to-adult maturation when they contribute to the stem cell compartment of regenerated muscle. Thus, teratomas are a rich and accessible source of potent transplantable skeletal muscle stem cells. VIDEO ABSTRACT.

Retinoid-Sensitive Epigenetic Regulation of the Hoxb Cluster Maintains Normal Hematopoiesis and Inhibits Leukemogenesis

Hox genes modulate the properties of hematopoietic stem cells (HSCs) and reacquired Hox expression in progenitors contributes to leukemogenesis. Here, our transcriptome and DNA methylome analyses revealed that Hoxb cluster and retinoid signaling genes are predominantly enriched in LT-HSCs, and this coordinate regulation of Hoxb expression is mediated by a retinoid-dependent cis-regulatory element, distal element RARE (DERARE). Deletion of the DERARE reduced Hoxb expression, resulting in changes to many downstream signaling pathways (e.g., non-canonical Wnt signaling) and loss of HSC self-renewal and reconstitution capacity. DNA methyltransferases mediate DNA methylation on the DERARE, leading to reduced Hoxb cluster expression. Acute myeloid leukemia patients with DNMT3A mutations exhibit DERARE hypomethylation, elevated HOXB expression, and adverse outcomes. CRISPR-Cas9-mediated specific DNA methylation at DERARE attenuated HOXB expression and alleviated leukemogenesis. Collectively, these findings demonstrate pivotal roles for retinoid signaling and the DERARE in maintaining HSCs and preventing leukemogenesis by coordinate regulation of Hoxb genes.

Generation of hematopoietic cells from mouse pluripotent stem cells in a 3D culture system of self-assembling peptide hydrogel

In vitro generation of hematopoietic stem cells from pluripotent stem cells (PSCs) can be regarded as novel therapeutic approaches for replacing bone marrow transplantation without immune rejection or graft versus host disease. To date, many different approaches have been evaluated in terms of directing PSCs toward different hematopoietic cell types, yet, low efficiency and no function restrict the further hematopoietic differentiation study, our research aims to develop a three dimension (3D) hematopoietic differentiation approach that serves as recapitulation of embryonic development in vitro to a degree of complexity not achievable in a two dimension culture system. We first found that mouse PSCs could be efficiently induced to hematopoietic differentiation with an expression of hematopoietic makers, such as c-kit, CD41, and CD45 within self-assembling peptide hydrogel. Colony-forming cells assay results suggested mouse PSCs (mPSCs) could be differentiated into multipotential progenitor cells and 3D induction system derived hematopoietic colonies owned potential of differentiating into lymphocyte cells. In addition, in vivo animal transplantation experiment showed that mPSCs (CD45.2) could be embedded into nonobese diabetic/severe combined immunodeficiency mice (CD45.1) with about 3% engraftment efficiency after 3 weeks transplantation. This study demonstrated that we developed the 3D induction approach that could efficiently promote the hematopoietic differentiation of mPSCs in vitro and obtained the multipotential progenitors that possessed the short-term engraftment potential.

Induced pluripotent stem cells in disease modelling and drug discovery

The derivation of induced pluripotent stem cells (iPSCs) over a decade ago sparked widespread enthusiasm for the development of new models of human disease, enhanced platforms for drug discovery and more widespread use of autologous cell-based therapy. Early studies using directed differentiation of iPSCs frequently uncovered cell-level phenotypes in monogenic diseases, but translation to tissue-level and organ-level diseases has required development of more complex, 3D, multicellular systems. Organoids and human-rodent chimaeras more accurately mirror the diverse cellular ecosystems of complex tissues and are being applied to iPSC disease models to recapitulate the pathobiology of a broad spectrum of human maladies, including infectious diseases, genetic disorders and cancer.

Development of Hematopoietic Stem Cells in the Early Mammalian Embryo

Hematopoietic stem cells (HSCs) were the first stem cells discovered in humans. A. A. Maximov proposed an idea of blood stem cells that was confirmed later by McCulloch and Till experimentally. HSCs were the first type of stem cells to be used in clinics and ever since are being continually used. Indeed, a single HSC transplanted intravenously is capable of giving rise to all types of blood cells. In recent decades, human and animal HSC origin, development, hierarchy, and gene signature have been extensively investigated. Due to the constant need for donor blood and HSCs suitable for therapeutic transplants, the experimental possibility of obtaining HSCs in vitro by directed differentiation of pluripotent stem cells (PSCs) has been considered in recent years. However, despite all efforts, it is not yet possible to reproduce in vitro the ontogenesis of HSCs and obtain cells capable of long-term maintenance of hematopoiesis. The study of hematopoiesis in embryonic development facilitates the establishment and improvement of protocols for deriving blood cells from PCSs and allows a better understanding of the pathogenesis of various types of proliferative blood diseases, anemia, and immunodeficiency. This review focuses on the development of hematopoiesis in mammalian ontogenesis.

Doxycycline Masks the Genuine Effect of the Doxycycline-Inducible Transgene by Promoting Dopaminergic Neuron Differentiation from Human Pluripotent Stem Cells

Doxycycline (DOX), an antibacterial drug, has been widely used in the inducible gene expression system. However, its effect was largely ignored when studying functions of the inducible transgene. By using a DOX-inducible Tet-ON system, we identified that DOX alone dramatically promoted dopaminergic (DA) neuron differentiation from human pluripotent stem cells (hPSCs), whereas the studied gene had no significant effects after considering the confounding factor DOX. These findings suggest that the effect of DOX should be taken into consideration when it is used in the inducible system especially during DA neuron differentiation from hPSCs. Meanwhile, it also suggests that DOX can be used as an efficient and inexpensive molecule to increase DA neuron differentiation efficacy from hPSCs for cell therapy.

Cross-Regulation between TDP-43 and Paraspeckles Promotes Pluripotency-Differentiation Transition

RNA-binding proteins (RBPs) and long non-coding RNAs (lncRNAs) are key regulators of gene expression, but their joint functions in coordinating cell fate decisions are poorly understood. Here we show that the expression and activity of the RBP TDP-43 and the long isoform of the lncRNA Neat1, the scaffold of the nuclear compartment "paraspeckles," are reciprocal in pluripotent and differentiated cells because of their cross-regulation. In pluripotent cells, TDP-43 represses the formation of paraspeckles by enhancing the polyadenylated short isoform of Neat1. TDP-43 also promotes pluripotency by regulating alternative polyadenylation of transcripts encoding pluripotency factors, including Sox2, which partially protects its 3' UTR from miR-21-mediated degradation. Conversely, paraspeckles sequester TDP-43 and other RBPs from mRNAs and promote exit from pluripotency and embryonic patterning in the mouse. We demonstrate that cross-regulation between TDP-43 and Neat1 is essential for their efficient regulation of a broad network of genes and, therefore, of pluripotency and differentiation.

Robust hematopoietic specification requires the ubiquitous Sp1 and Sp3 transcription factors

Background

Both tissue-specific and ubiquitously expressed transcription factors, such as Sp-family members, are required for correct development. However, the molecular details of how ubiquitous factors are involved in programming tissue-specific chromatin and thus participate in developmental processes are still unclear. We previously showed that embryonic stem cells lacking Sp1 DNA-binding activity (Sp1^ΔDBD/ΔDBD cells) are able to differentiate into early blood progenitors despite the inability of Sp1 to bind chromatin without its DNA-binding domain. However, gene expression during differentiation becomes progressively deregulated, and terminal differentiation is severely compromised.

Results

Here, we studied the cooperation of Sp1 with its closest paralogue Sp3 in hematopoietic development and demonstrate that Sp1 and Sp3 binding sites largely overlap. The complete absence of either Sp1 or Sp3 or the presence of the Sp1 DNA-binding mutant has only a minor effect on the pattern of distal accessible chromatin sites and their transcription factor binding motif content, suggesting that these mutations do not affect tissue-specific chromatin programming. Sp3 cooperates with Sp1^ΔDBD/ΔDBD to enable hematopoiesis, but is unable to do so in the complete absence of Sp1. Using single-cell gene expression analysis, we show that the lack of Sp1 DNA binding leads to a distortion of cell fate decision timing, indicating that stable chromatin binding of Sp1 is required to maintain robust differentiation trajectories.

Conclusions

Our findings highlight the essential contribution of ubiquitous factors such as Sp1 to blood cell development. In contrast to tissue-specific transcription factors which are required to direct specific cell fates, loss of Sp1 leads to a widespread deregulation in timing and coordination of differentiation trajectories during hematopoietic specification.

Electronic supplementary material

The online version of this article (10.1186/s13072-019-0282-9) contains supplementary material, which is available to authorized users.

Splitomicin, a SIRT1 Inhibitor, Enhances Hematopoietic Differentiation of Mouse Embryonic Stem Cells

Background and Objectives

Embryonic stem (ES) cells have pluripotent ability to differentiate into multiple tissue lineages. SIRT1 is a class III histone deacetylase which modulates chromatin remodeling, gene silencing, cell survival, metabolism, and development. In this study, we examined the effects of SIRT1 inhibitors on the hematopoietic differentiation of mouse ES cells.

Methods and Results

Treatment with the SIRT1 inhibitors, nicotinamide and splitomicin, during the hematopoietic differentiation of ES cells enhanced the production of hematopoietic progenitors and slightly up-regulated erythroid and myeloid specific gene expression. Furthermore, treatment with splitomicin increased the percentage of erythroid and myeloid lineage cells.

Conclusions

Application of the SIRT1 inhibitor splitomicin during ES cell differentiation to hematopoietic cells enhanced the yield of specific hematopoietic lineage cells from ES cells. This result suggests that SIRT1 is involved in the regulation of hematopoietic differentiation of specific lineages and that the modulation of the SIRT1 activity can be a strategy to enhance the efficiency of hematopoietic differentiation.

Pluripotent stem cell-derived myogenic progenitors remodel their molecular signature upon in vivo engraftment

Optimal cell-based therapies for the treatment of muscle degenerative disorders should not only regenerate fibers but provide a quiescent satellite cell pool ensuring long-term maintenance and regeneration. Conditional expression of Pax3/Pax7 in differentiating pluripotent stem cells (PSCs) allows the generation of myogenic progenitors endowed with enhanced regenerative capacity. To identify the molecular determinants underlying their regenerative potential, we performed transcriptome analyses of these cells along with primary myogenic cells from several developmental stages. Here we show that in vitro-generated PSC-derived myogenic progenitors possess a molecular signature similar to embryonic/fetal myoblasts. However, compared with fetal myoblasts, following transplantation they show superior myofiber engraftment and ability to seed the satellite cell niche, respond to multiple reinjuries, and contribute to long-term regeneration. Upon engraftment, the transcriptome of reisolated Pax3/Pax7-induced PSC-derived myogenic progenitors changes toward a postnatal molecular signature, particularly in genes involved in extracellular matrix remodeling. These findings demonstrate that Pax3/Pax7-induced myogenic progenitors remodel their molecular signature and functionally mature upon in vivo exposure to the adult muscle environment.

Combining CRISPR/Cas9-mediated knockout with genetic complementation for in-depth mechanistic studies in human ES cells

Gene regulatory networks that control pluripotency of human embryonic stem cells (hESCs) are of considerable interest for regenerative medicine. RNAi and CRISPR/Cas9 technologies have allowed the identification of hESC regulators on a genome-wide scale. However, these technologies are ill-suited for mechanistic studies because knockdown/knockout clones of essential genes do not grow in culture. We have developed a genetic rescue strategy that combines CRISPR/Cas9-mediated knockout with TALEN-mediated integration of a doxycycline-inducible rescue transgene into a constitutive AASV1 locus. The resulting rescue clones are stable in culture, allow modulation of the rescue transgene dosage by titration of doxycycline in the media and can be combined with various molecular assays, thus providing mechanistic insights into gene function in a variety of cellular contexts.

Long-Term Engraftment of ESC-Derived B-1 Progenitor Cells Supports HSC-Independent Lymphopoiesis

It is generally considered that mouse embryonic stem cell (ESC) differentiation into blood cells in vitro recapitulates yolk sac (YS) hematopoiesis. As such, similar to YS-derived B-progenitors, we demonstrate here that ESC-derived B-progenitors differentiate into B-1 and marginal zone B cells, but not B-2 cells in immunodeficient mice after transplantation. ESC-derived B-1 cells were maintained in the recipients for more than 6 months, secreting natural IgM antibodies in vivo. Gene expression profiling displayed a close relationship between ESC- and YS-derived B-1 progenitors. Because there are no hematopoietic stem cells (HSCs) detectable in our ESC differentiation culture, successful long-term engraftment of ESC-derived functional B-1 cells supports the presence of HSC-independent B-1 cell development.

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ESC-derived B-progenitors mature into B-1 cells and MZ B cells in vivo

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ESC-derived B-1 cells engrafted in vivo long-term and secrete natural antibodies

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ESC-derived B-progenitors are molecularly similar to YS-derived B-progenitors

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Long-term B-1 cell engraftment represents HSC-independent lymphopoiesis