WNT3A promotes hematopoietic or mesenchymal differentiation from hESCs depending on the time of exposure

Dependence of cell fate potential and cadherin switching on primitive streak coordinate during differentiation of human pluripotent stem cells

During gastrulation, the primitive streak (PS) forms and begins to differentiate into mesendodermal subtypes. This process involves an epithelial-mesenchymal transition (EMT), which is marked by cadherin switching, where E-Cadherin is downregulated, and N-Cadherin is upregulated. To understand the relationships between differentiation, EMT, and cadherin switching, we made measurements of these processes during differentiation of human pluripotent stem cells (hPSCs) to PS and subsequently to mesendoderm subtypes using established protocols, as well as variants in which signaling through key pathways including Activin, BMP, and Wnt were modulated. We found that perturbing signaling so that cells acquired identities ranging from anterior to posterior PS had little impact on the subsequent differentiation potential of cells but strongly impacted the degree of cadherin switching. The degree of E-Cadherin downregulation and N-Cadherin upregulation were uncorrelated and had different dependence on signaling. The exception to the broad potential of cells throughout the PS was the loss of definitive endoderm potential in cells with mid to posterior PS identities. Thus, cells induced to different PS coordinates had similar potential within the mesoderm but differed in cadherin switching. Consistently, E-Cadherin knockout did not alter cell fates outcomes during differentiation. Overall, cadherin switching and EMT are modulated independently of cell fate commitment in mesendodermal differentiation.

The Role of Aplnr Signaling in the Developmental Regulation of Mesenchymal Stem Cell Differentiation from Human Pluripotent Stem Cells

Stem cells are invaluable resources for personalized medicine. Mesenchymal stem cells (MSCs) have received great attention as therapeutic tools due to being a safe, ethical, and accessible option with immunomodulatory and controlled differentiation properties. Apelin receptor (Aplnr) signaling is reported to be involved in biological events, including gastrulation, mesoderm migration, proliferation of MSCs. However, the knowledge about the exact role and mechanism of Aplnr signaling during mesoderm and MSCs differentiation is still primitive. The current study aims to unveil the role of Aplnr signaling during mesoderm and MSC differentiation from pluripotent stem cells (PSCs) through peptide/small molecule activation, overexpression, knock down or CRISPR/Cas9 mediated knock out of the pathway components. Morphological changes, gene and protein expression analysis, including antibody array, LC/MS, mRNA/miRNA sequencing, reveal that Aplnr signaling promotes mesoderm commitment possibly via EGFR and TGF-beta signaling pathways and enhances migration of cells during mesoderm differentiation. Moreover, Aplnr signaling positively regulates MSCs differentiation from hPSCs and increases MSC characteristics and differentiation capacity by regulating pathways, such as EGFR, TGFβ, Wnt, PDGF, and FGF. Osteogenic, chondrogenic, adipogenic, and myogenic differentiations are significantly enhanced with Aplnr signaling activity. This study generates an important foundation to generate high potential MSCs from PSCs to be used in personalized cell therapy.

The RNA-binding protein CSDE1 promotes hematopoietic stem and progenitor cell generation via translational control of Wnt signaling

In vertebrates, the earliest hematopoietic stem and progenitor cells (HSPCs) are derived from a subset of specialized endothelial cells, hemogenic endothelial cells, in the aorta-gonad-mesonephros region through endothelial-to-hematopoietic transition. HSPC generation is efficiently and accurately regulated by a variety of factors and signals; however, the precise control of these signals remains incompletely understood. Post-transcriptional regulation is crucial for gene expression, as the transcripts are usually bound by RNA-binding proteins (RBPs) to regulate RNA metabolism. Here, we report that the RBP protein Csde1-mediated translational control is essential for HSPC generation during zebrafish early development. Genetic mutants and morphants demonstrated that depletion of csde1 impaired HSPC production in zebrafish embryos. Mechanistically, Csde1 regulates HSPC generation through modulating Wnt/β-catenin signaling activity. We demonstrate that Csde1 binds to ctnnb1 mRNAs (encoding β-catenin, an effector of Wnt signaling) and regulates translation but not stability of ctnnb1 mRNA, which further enhances β-catenin protein level and Wnt signal transduction activities. Together, we identify Csde1 as an important post-transcriptional regulator and provide new insights into how Wnt/β-catenin signaling is precisely regulated at the post-transcriptional level.

Mesodermal Derivatives of Pluripotent Stem Cells Route to Scarless Healing

Scar formation during normal tissue regeneration in adults may result in noticeable cosmetic and functional defects and have a significant impact on the quality of life. In contrast, fetal tissues in the mid-gestation period are known to be capable of complete regeneration with the restitution of the initial architecture, organization, and functional activity. Successful treatments that are targeted to minimize scarring can be realized by understanding the cellular and molecular mechanisms of fetal wound regeneration. However, such experiments are limited by the inaccessibility of fetal material for comparable studies. For this reason, the molecular mechanisms of fetal regeneration remain unknown. Mesenchymal stromal cells (MSCs) are central to tissue repair because the molecules they secrete are involved in the regulation of inflammation, angiogenesis, and remodeling of the extracellular matrix. The mesodermal differentiation of human pluripotent stem cells (hPSCs) recapitulates the sequential steps of embryogenesis in vitro and provides the opportunity to generate the isogenic cell models of MSCs corresponding to different stages of human development. Further investigation of the functional activity of cells from stromal differon in a pro-inflammatory microenvironment will procure the molecular tools to better understand the fundamental mechanisms of fetal tissue regeneration. Herein, we review recent advances in the generation of clonal precursors of primitive mesoderm cells and MSCs from hPSCs and discuss critical factors that determine the functional activity of MSCs-like cells in a pro-inflammatory microenvironment in order to identify therapeutic targets for minimizing scarring.

Wnt3a-Loaded Extracellular Vesicles Promote Alveolar Epithelial Regeneration after Lung Injury

Compromised regeneration resulting from the deactivation of Wnt/β-catenin signaling contributes to the progression of chronic obstructive pulmonary disease (COPD) with limited therapeutic options. Extracellular cytokine-induced Wnt-based signaling provides an alternative option for COPD treatment. However, the hydrophobic nature of Wnt proteins limits their purification and use. This study devises a strategy to deliver the membrane-bound wingless-type MMTV integration site family, member 3A (Wnt3a) over a long distance by anchoring it to the surface of extracellular vesicles (EVs). The newly engineered Wnt3aWG EVs are generated by co-expressing Wnt3a with two genes encoding the membrane protein, WLS, and an engineered glypican, GPC6ΔGPI -C1C2. The bioactivity of Wnt3aWG EVs is validated using a TOPFlash assay and a mesoderm differentiation model of human pluripotent stem cells. Wnt3aWG EVs activate Wnt signaling and promote cell growth following human alveolar epithelial cell injury. In an elastase-induced emphysema model, impaired pulmonary function and enlarged airspace are greatly restored by the intravenous delivery of Wnt3aWG EVs. Single-cell RNA sequencing-based analyses further highlight that Wnt3aWG EV-activated regenerative programs are responsible for its beneficial effects. These findings suggest that EV-based Wnt3a delivery represents a novel therapeutic strategy for lung repair and regeneration after injury.

Wnt regulation of hematopoietic stem cell development and disease

Hematopoietic stem cells (HSCs) are multipotent stem cells that give rise to all cells of the blood and most immune cells. Due to their capacity for unlimited self-renewal, long-term HSCs replenish the blood and immune cells of an organism throughout its life. HSC development, maintenance, and differentiation are all tightly regulated by cell signaling pathways, including the Wnt pathway. Wnt signaling is initiated extracellularly by secreted ligands which bind to cell surface receptors and give rise to several different downstream signaling cascades. These are classically categorized either β-catenin dependent (BCD) or β-catenin independent (BCI) signaling, depending on their reliance on the β-catenin transcriptional activator. HSC development, homeostasis, and differentiation is influenced by both BCD and BCI, with a high degree of sensitivity to the timing and dosage of Wnt signaling. Importantly, dysregulated Wnt signals can result in hematological malignancies such as leukemia, lymphoma, and myeloma. Here, we review how Wnt signaling impacts HSCs during development and in disease.

Wnt signaling in stem cells during development and cell lineage specification

During embryo development, cell proliferation, cell fate specification and tissue patterning are coordinated and tightly regulated by a handful of evolutionarily conserved signaling pathways activated by secreted growth factor families including fibroblast growth factor (FGF), Nodal/bone morphogenetic protein (BMP), Hedgehog and Wnt. The spatial and temporal activation of these signaling pathways elicit context-specific cellular responses that ultimately shape the different tissues of the embryo. Extensive efforts have been dedicated to identifying the molecular mechanisms underlying these signaling pathways during embryo development, adult tissue homeostasis and regeneration. In this review, we first describe the role of the Wnt/β-catenin signaling pathway during early embryo development, axis specification and cell differentiation as a prelude to highlight how this knowledge is being leveraged to manipulate Wnt/β-catenin signaling activity with small molecules and biologics for the directed differentiation of pluripotent stem cells into various cell lineages that are physiologically relevant for stem cell therapy and regenerative medicine.

Impact of airborne total suspended particles (TSP) and fine particulate matter (PM2.5 )-induced developmental toxicity in zebrafish (Danio rerio) embryos

Airborne total suspended particles (TSP) and particulate matter (PM_2.5 ) threaten global health and their potential impact on cardiovascular and respiratory diseases are extensively studied. Recent studies attest premature deaths, low birth weight, and congenital anomalies in the fetus of pregnant women exposed to air pollution. In this regard, only few studies have explored the effects of TSP and PM_2.5 on cardiovascular and cerebrovascular development. As both TSP and PM_2.5 differ in size and composition, this study is attempted to assess the variability in toxicity effects between TSP and PM_2.5 on the development of cardiovascular and cerebrovascular systems and the underlying mechanisms in a zebrafish model. To explore the potential toxic effects of TSP and PM_2.5 , zebrafish embryos/larvae were exposed to 25, 50, 100, 200, and 400 μg/ml of TSP and PM_2.5 from 24 to 120 hpf (hours post-fertilization). Both TSP and PM_2.5 exposure increased the rate of mortality, malformations, and oxidative stress, whereas locomotor behavior, heart rate, blood flow velocity, development of cardiovasculature and neurovasculature, and dopaminergic neurons were reduced. The expression of genes involved in endoplasmic reticulum stress (ERS), Wnt signaling, and central nervous system (CNS) development were altered in a dose- and time-dependent manner. This study provides evidence for acute exposure to TSP and PM_2.5 -induced cardiovascular and neurodevelopmental toxicity, attributed to enhanced oxidative stress and aberrant gene expression. Comparatively, the effects of PM_2.5 were more pronounced than TSP.

VEGF, FGF2, and BMP4 regulate transitions of mesoderm to endothelium and blood cells in a human model of yolk sac hematopoiesis

Exogenous growth factors play an important role in mediating hematopoietic differentiation of human pluripotent stem cells. We explored the role of different factors in early human blood cell production using blast colony formation in methylcellulose as a surrogate assay for yolk sac hematopoiesis. A reporter cell line that read out endothelial (SOX17⁺) and hematopoietic (RUNX1C⁺) progenitors facilitated the identification of basic fibroblast growth and vascular endothelial growth factor as critical signals for the progression of mesoderm into endothelium. Bone morphogenetic protein 4 was needed for the subsequent generation of blood from hemogenic endothelium, and this was antagonized by Activin A or high concentrations of the WNT agonist CHIR-99021. Manipulations of the Hedgehog pathway or inhibition of Notch signaling reduced blast colony frequency but did not perturb cell differentiation. These data help to define distinct roles for prerequisite growth factors that commit mesoderm to hemogenic endothelium and subsequently allocate cells to blood lineages.

A Benchmark Side-by-Side Comparison of Two Well-Established Protocols for in vitro Hematopoietic Differentiation From Human Pluripotent Stem Cells

The generation of transplantable hematopoietic stem cells (HSCs) from human pluripotent stem cells (hPSCs) remains challenging. Current differentiation protocols from hPSCs generate mostly hematopoietic progenitors of the primitive HSC-independent program, and it remains unclear what is the best combination of cytokines and hematopoietic growth factors (HGFs) for obtaining functional hematopoietic cells in vitro. Here, we have used the AND1 and H9 hESC lines and the H9:dual-reporter RUNX1C-GFP-SOX17-Cherry to compare the hematopoietic differentiation in vitro based on the treatment of embryoid bodies (EBs) with the ventral mesoderm inducer BMP4 plus HGFs in the absence (protocol 1) or presence (protocol 2) of stage-specific activation of Wnt/β-catenin and inhibition of Activin/Nodal. Despite a slight trend in favor of protocol 1, no statistically significant differences were observed between protocols at any time point analyzed throughout EB development regarding the frequency of hemogenic endothelial (HE) precursors; CD43+ CD45−, CD45+, and CD45 + CD34 + hematopoietic derivatives; or the output of clonogenic progenitors. Similarly, the kinetics of emergence throughout EB development of both SOX17 + HE and RUNX1C + definitive hematopoiesis was very similar for both protocols. The expression of the early master mesendodermal transcription factors Brachyury, MIXL1, and KDR revealed similar gene expression kinetics prior to the emergence of RUNX1C + definitive hematopoiesis for both protocols. Collectively, the simpler protocol 1 is, at least, as efficient as protocol 2, suggesting that supplementation with additional morphogens/HGFs and modulation of Activin/Nodal and Wnt/β-catenin pathways seem dispensable for in vitro hematopoietic differentiation of hPSCs.

Selective activation of FZD7 promotes mesendodermal differentiation of human pluripotent stem cells

WNT proteins are secreted symmetry breaking signals that interact with cell surface receptors of the FZD family to regulate a multitude of developmental processes. Studying selectivity between WNTs and FZDs has been hampered by the paucity of purified WNT proteins and by their apparent non-selective interactions with the FZD receptors. Here, we describe an engineered protein, called F7L6, comprised of antibody-derived single-chain variable fragments, that selectively binds to human FZD7 and the co-receptor LRP6. F7L6 potently activates WNT/β-catenin signaling in a manner similar to Wnt3a. In contrast to Wnt3a, F7L6 engages only FZD7 and none of the other FZD proteins. Treatment of human pluripotent stem (hPS) cells with F7L6 initiates transcriptional programs similar to those observed during primitive streak formation and subsequent gastrulation in the mammalian embryo. This demonstrates that selective engagement and activation of FZD7 signaling is sufficient to promote mesendodermal differentiation of hPS cells.

MicroRNA-361-3p Inhibit the Progression of Lymphoma by the Wnt/β-Catenin Signaling Pathway

Background

MicroRNA is involved in the development of lymphoma. It is reported that miR-361-3p has a tumor inhibitory effect, but its role in lymphoma is still unclear. The purpose of this study is to examine whether miR-361-3p can inhibit the development of lymphoma and further explore the related potential mechanism.

Methods

In this study, we first analyzed the biological function of miR-361-3p in transfected Raji that mimicked miRNA. We also analyzed the biological function of the whole population in stably expressed miR-361-3p transgenic cells. Next, we conducted a complete micro-gene network to test the genetic profile of differential expression of stable gene-modified cells.

Results

We found that miR-361-3p expression was often reduced in lymphoma cell lines. Cellular assays have shown a significant role in inhibiting the growth of miR-361-3p by inhibiting lymphoma proliferation and migration, and severely inhibiting the Wnt/β-catenin series protein signal. Bioinformatics analysis shows that Wnt10A is a new target of miR-361-3p, which is confirmed by our mechanism research. It is confirmed that restoring Wnt10A can reduce the tumor inhibition of Wnt/β-catenin during lymphoma progression and restore the normal signal of Wnt/β-catenin series proteins.

Discussion

Our data indicate that miR-361-3p inhibits the Wnt/β-catenin protein signal by locking Wnt10A, which is an important factor in inhibiting the tumor in the pathogenesis of lymphoma. The miR-361-3p/Wnt10A axis may be a promising target for the treatment of lymphoma.

Human yolk sac-like haematopoiesis generates RUNX1-, GFI1- and/or GFI 1B-dependent blood and SOX17-positive endothelium

The genetic regulatory network controlling early fate choices during human blood cell development are not well understood. We used human pluripotent stem cell reporter lines to track the development of endothelial and haematopoietic populations in an in vitro model of human yolk-sac development. We identified SOX17⁻CD34⁺CD43⁻ endothelial cells at day 2 of blast colony development, as a haemangioblast-like branch point from which SOX17⁻CD34⁺CD43⁺ blood cells and SOX17⁺CD34⁺CD43⁻ endothelium subsequently arose. Most human blood cell development was dependent on RUNX1. Deletion of RUNX1 only permitted a single wave of yolk sac-like primitive erythropoiesis, but no yolk sac myelopoiesis or aorta-gonad-mesonephros (AGM)-like haematopoiesis. Blocking GFI1 and/or GFI1B activity with a small molecule inhibitor abrogated all blood cell development, even in cell lines with an intact RUNX1 gene. Together, our data define the hierarchical requirements for RUNX1, GFI1 and/or GFI1B during early human haematopoiesis arising from a yolk sac-like SOX17-negative haemogenic endothelial intermediate.

Highlighted Article: The hierarchical requirements for RUNX1, GFI1 and/or GFI1B during early human haematopoiesis arising from a yolk sac-like haemogenic endothelial intermediate.

A p53-Dependent Checkpoint Induced upon DNA Damage Alters Cell Fate during hiPSC Differentiation

The ability of human induced pluripotent stem cells (hiPSCs) to differentiate in vitro to each of the three germ layer lineages has made them an important model of early human development and a tool for tissue engineering. However, the factors that disturb the intricate transcriptional choreography of differentiation remain incompletely understood. Here, we uncover a critical time window during which DNA damage significantly reduces the efficiency and fidelity with which hiPSCs differentiate to definitive endoderm. DNA damage prevents the normal reduction of p53 levels as cells pass through the epithelial-to-mesenchymal transition, diverting the transcriptional program toward mesoderm without induction of an apoptotic response. In contrast, TP53-deficient cells differentiate to endoderm with high efficiency after DNA damage, suggesting that p53 enforces a "differentiation checkpoint" in early endoderm differentiation that alters cell fate in response to DNA damage.

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.

Origin and function of the yolk sac in primate embryogenesis

Human embryogenesis is hallmarked by two phases of yolk sac development. The primate hypoblast gives rise to a transient primary yolk sac, which is rapidly superseded by a secondary yolk sac during gastrulation. Moreover, primate embryos form extraembryonic mesoderm prior to gastrulation, in contrast to mouse. The function of the primary yolk sac and the origin of extraembryonic mesoderm remain unclear. Here, we hypothesise that the hypoblast-derived primary yolk sac serves as a source for early extraembryonic mesoderm, which is supplemented with mesoderm from the gastrulating embryo. We discuss the intricate relationship between the yolk sac and the primate embryo and highlight the pivotal role of the yolk sac as a multifunctional hub for haematopoiesis, germ cell development and nutritional supply.

Transcriptional dynamics of pluripotent stem cell-derived endothelial cell differentiation revealed by single-cell RNA sequencing

AIMS

Pluripotent stem cell-derived endothelial cell products possess therapeutic potential in ischaemic vascular disease. However, the factors that drive endothelial differentiation from pluripotency and cellular specification are largely unknown. The aims of this study were to use single-cell RNA sequencing (scRNA-seq) to map the transcriptional landscape and cellular dynamics of directed differentiation of human embryonic stem cell-derived endothelial cells (hESC-EC) and to compare these cells to mature endothelial cells from diverse vascular beds.

METHODS AND RESULTS

A highly efficient directed 8-day differentiation protocol was used to generate a hESC-derived endothelial cell product (hESC-ECP), in which 66% of cells co-expressed CD31 and CD144. We observed largely homogeneous hESC and mesodermal populations at Days 0 and 4, respectively, followed by a rapid emergence of distinct endothelial and mesenchymal populations. Pseudotime trajectory identified transcriptional signatures of endothelial commitment and maturation during the differentiation process. Concordance in transcriptional signatures was verified by scRNA-seq analysis using both a second hESC line RC11, and an alternative hESC-EC differentiation protocol. In total, 105 727 cells were subjected to scRNA-seq analysis. Global transcriptional comparison revealed a transcriptional architecture of hESC-EC that differs from freshly isolated and cultured human endothelial cells and from organ-specific endothelial cells.

CONCLUSION

A transcriptional bifurcation into endothelial and mesenchymal lineages was identified, as well as novel transcriptional signatures underpinning commitment and maturation. The transcriptional architecture of hESC-ECP was distinct from mature and foetal human EC.

The Role Played by Wnt/β-Catenin Signaling Pathway in Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is an aggressive hematologic neoplastic disorder that arises from the clonal expansion of transformed T-cell or B-cell precursors. Thanks to progress in chemotherapy protocols, ALL outcome has significantly improved. However, drug-resistance remains an unresolved issue in the treatment of ALL and toxic effects limit dose escalation of current chemotherapeutics. Therefore, the identification of novel targeted therapies to support conventional chemotherapy is required. The Wnt/β-catenin pathway is a conserved signaling axis involved in several physiological processes such as development, differentiation, and adult tissue homeostasis. As a result, deregulation of this cascade is closely related to initiation and progression of various types of cancers, including hematological malignancies. In particular, deregulation of this signaling network is involved in the transformation of healthy HSCs in leukemic stem cells (LSCs), as well as cancer cell multi-drug-resistance. This review highlights the recent findings on the role of Wnt/β-catenin in hematopoietic malignancies and provides information on the current status of Wnt/β-catenin inhibitors with respect to their therapeutic potential in the treatment of ALL.

BMP4 and perivascular cells promote hematopoietic differentiation of human pluripotent stem cells in a differentiation stage-specific manner

The efficient and reproducible derivation and maturation of multipotent hematopoietic progenitors from human pluripotent stem cells (hPSCs) requires the recapitulation of appropriate developmental stages and the microenvironment. Here, using serum-, xeno-, and feeder-free stepwise hematopoietic induction protocols, we showed that short-term and high-concentration treatment of hPSCs with bone morphogenetic protein 4 (BMP4) strongly promoted early mesoderm induction followed by increased hematopoietic commitment. This method reduced variations in hematopoietic differentiation among hPSC lines maintained under chemically defined Essential 8 medium compared to those maintained under less-defined mTeSR medium. We also found that perivascular niche cells (PVCs) significantly augmented the production of hematopoietic cells via paracrine signaling mechanisms only when they were present during the hematopoietic commitment phase. A protein array revealed 86 differentially expressed (>1.5-fold) secretion factors in PVC-conditioned medium compared with serum-free control medium, of which the transforming growth factor-β inducible gene H3 significantly increased the number of hematopoietic colony-forming colonies. Our data suggest that BMP4 and PVCs promote the hematopoietic differentiation of hPSCs in a differentiation stage-specific manner. This will increase our understanding of hematopoietic development and expedite the development of hPSC-derived blood products for therapeutic use.

Adding a vital regulatory molecule and support cells to the culture medium can help in the derivation of blood products from stem cells. A team led by Seok-Ho Hong from Kangwon National University in Chuncheon, South Korea, followed a clinical-grade protocol for converting embryonic stem cells or induced pluripotent stem cells from adults into blood cell precursors. The researchers showed that incorporating high doses of a growth factor called bone morphogenetic protein 4 into the standard culture medium for a short period promoted early differentiation toward blood cells. Incorporating so-called perivascular cells taken from umbilical cord blood also enhanced the process through the secretion of signaling molecules that further pushed the stem cells toward differentiating into blood cells. The findings could help improve protocols for making blood products from stem cells for therapeutic purposes.

A critical look: Challenges in differentiating human pluripotent stem cells into desired cell types and organoids

Too many choices can be problematic. This is certainly the case for human pluripotent stem cells (hPSCs): they harbor the potential to differentiate into hundreds of cell types; yet it is highly challenging to exclusively differentiate hPSCs into a single desired cell type. This review focuses on unresolved and fundamental questions regarding hPSC differentiation and critiquing the identity and purity of the resultant cell populations. These are timely issues in view of the fact that hPSC-derived cell populations have or are being transplanted into patients in over 30 ongoing clinical trials. While many in vitro differentiation protocols purport to "mimic development," the exact number and identity of intermediate steps that a pluripotent cell takes to differentiate into a given cell type in vivo remains largely unknown. Consequently, most differentiation efforts inevitably generate a heterogeneous cellular population, as revealed by single-cell RNA-sequencing and other analyses. The presence of unwanted cell types in differentiated hPSC populations does not portend well for transplantation therapies. This provides an impetus to precisely control differentiation to desired ends-for instance, by logically blocking the formation of unwanted cell types or by overexpressing lineage-specifying transcription factors-or by harnessing technologies to selectively purify desired cell types. Conversely, approaches to differentiate three-dimensional "organoids" from hPSCs intentionally generate heterogeneous cell populations. While this is intended to mimic the rich cellular diversity of developing tissues, whether all such organoids are spatially organized in a manner akin to native organs (and thus, whether they fully qualify as organoids) remains to be fully resolved. This article is categorized under: Adult Stem Cells > Tissue Renewal > Regeneration: Stem Cell Differentiation and Reversion Gene Expression > Transcriptional Hierarchies: Cellular Differentiation Early Embryonic Development: Gastrulation and Neurulation.

The mesenchymoangioblast, mesodermal precursor for mesenchymal and endothelial cells

Mesenchymoangioblast (MB) is the earliest precursor for endothelial and mesenchymal cells originating from APLNR+PDGFRα+KDR+ mesoderm in human pluripotent stem cell cultures. MBs are identified based on their capacity to form FGF2-dependent compact spheroid colonies in a serum-free semisolid medium. MBs colonies are composed of PDGFRβ+CD271+EMCN+DLK1+CD73- primitive mesenchymal cells which are generated through endothelial/angioblastic intermediates (cores) formed during first 3-4 days of clonogenic cultures. MB-derived primitive mesenchymal cells have potential to differentiate into mesenchymal stromal/stem cells (MSCs), pericytes, and smooth muscle cells. In this review, we summarize the specification and developmental potential of MBs, emphasize features that distinguish MBs from other mesenchymal progenitors described in the literature and discuss the value of these findings for identifying molecular pathways leading to MSC and vasculogenic cell specification, and developing cellular therapies using MB-derived progeny.

WNT9A Is a Conserved Regulator of Hematopoietic Stem and Progenitor Cell Development

Hematopoietic stem cells (HSCs) differentiate into all cell types of the blood and can be used therapeutically to treat hematopoietic cancers and disorders. Despite decades of research, it is not yet possible to derive therapy-grade HSCs from pluripotent precursors. Analysis of HSC development in model organisms has identified some of the molecular cues that are necessary to instruct hematopoiesis in vivo, including Wnt9A, which is required during an early time window in zebrafish development. Although bona fide HSCs cannot be derived in vitro, it is possible to model human hematopoietic progenitor development by differentiating human pluripotent stem cells to hematopoietic cells. Herein, we modulate WNT9A expression during the in vitro differentiation of human embryonic stem cells to hematopoietic progenitor cells and demonstrate that WNT9A also regulates human hematopoietic progenitor cell development in vitro. Overexpression of WNT9A only impacts differentiation to CD34⁺/CD45⁺ cells during early time windows and does so in a dose-dependent manner. The cells that receive the Wnt signal—not the cells that secrete WNT9A—differentiate most efficiently to hematopoietic progenitors; this mimics the paracrine action of Wnt9a during in vivo hematopoiesis. Taken together, these data indicate that WNT9A is a conserved regulator of zebrafish and human hematopoietic development.

Human haematopoietic stem cell development: from the embryo to the dish

Haematopoietic stem cells (HSCs) emerge during embryogenesis and give rise to the adult haematopoietic system. Understanding how early haematopoietic development occurs is of fundamental importance for basic biology and medical sciences, but our knowledge is still limited compared with what we know of adult HSCs and their microenvironment. This is particularly true for human haematopoiesis, and is reflected in our current inability to recapitulate the development of HSCs from pluripotent stem cells in vitro In this Review, we discuss what is known of human haematopoietic development: the anatomical sites at which it occurs, the different temporal waves of haematopoiesis, the emergence of the first HSCs and the signalling landscape of the haematopoietic niche. We also discuss the extent to which in vitro differentiation of human pluripotent stem cells recapitulates bona fide human developmental haematopoiesis, and outline some future directions in the field.

Generation of hematopoietic stem cells from human embryonic stem cells using a defined, stepwise, serum-free, and serum replacement-free monolayer culture method

Background

Embryonic stem cells (ESCs) can be expanded infinitely in vitro and have the potential to differentiate into hematopoietic stem cells (HSCs); thus, they are considered a useful source of cells for HSC production. Although several technical in vitro methods for engineering HSCs from pluripotent stem cells have been developed, clinical application of HSCs engineered from pluripotent stem cells is restricted because of the possibility of xenogeneic contamination resulting from the use of murine materials.

Methods

Human ESCs (CHA-hES15) were cultured on growth factor-reduced Matrigel-coated dishes in the mTeSR1 serum-free medium. When the cells were 70% confluent, we initiated HSC differentiation by three methods involving (1) knockout serum replacement (KSR), cytokines, TGFb1, EPO, and FLT3L; (2) KSR, cytokines, and bFGF; or (3) cytokines and bFGF.

Results

Among the three differentiation methods, the minimal number of cytokines without KSR resulted in the greatest production of HSCs. The optimized method resulted in a higher proportion of CD34⁺CD43⁺ hematopoietic progenitor cells (HPCs) and CD34⁺CD45⁺ HPCs compared to the other methods. In addition, the HSCs showed the potential to differentiate into multiple lineages of hematopoietic cells in vitro.

Conclusion

In this study, we optimized a two-step, serum-free, animal protein-free, KSR-free, feeder-free, chemically defined monolayer culture method for generation of HSCs and hematopoietic stem and progenitor cells (HSPCs) from human ESCs.

Mapping the Pairwise Choices Leading from Pluripotency to Human Bone, Heart, and Other Mesoderm Cell Types

Stem-cell differentiation to desired lineages requires navigating alternating developmental paths that often lead to unwanted cell types. Hence, comprehensive developmental roadmaps are crucial to channel stem-cell differentiation toward desired fates. To this end, here, we map bifurcating lineage choices leading from pluripotency to 12 human mesodermal lineages, including bone, muscle, and heart. We defined the extrinsic signals controlling each binary lineage decision, enabling us to logically block differentiation toward unwanted fates and rapidly steer pluripotent stem cells toward 80%-99% pure human mesodermal lineages at most branchpoints. This strategy enabled the generation of human bone and heart progenitors that could engraft in respective in vivo models. Mapping stepwise chromatin and single-cell gene expression changes in mesoderm development uncovered somite segmentation, a previously unobservable human embryonic event transiently marked by HOPX expression. Collectively, this roadmap enables navigation of mesodermal development to produce transplantable human tissue progenitors and uncover developmental processes. VIDEO ABSTRACT.

Understanding kidney morphogenesis to guide renal tissue regeneration

The treatment of renal failure has seen little change in the past 70 years. Patients with end-stage renal disease (ESRD) are treated with renal replacement therapy, including dialysis or organ transplantation. The growing imbalance between the availability of donor organs and prevalence of ESRD is pushing an increasing number of patients to undergo dialysis. Although the prospect of new treatment options for patients through regenerative medicine has long been suggested, advances in the generation of human kidney cell types through the directed differentiation of human pluripotent stem cells over the past 2 years have brought this prospect closer to delivery. These advances are the result of careful research into mammalian embryogenesis. By understanding the decision points made within the embryo to pattern the kidney, it is now possible to recreate self-organizing kidney tissues in vitro. In this Review, we describe the key decision points in kidney development and how these decisions have been mimicked experimentally. Recreation of human nephrons from human pluripotent stem cells opens the door to patient-derived disease models and personalized drug and toxicity screening. In the long term, we hope that these efforts will also result in the generation of bioengineered organs for the treatment of kidney disease.

Stepwise Clearance of Repressive Roadblocks Drives Cardiac Induction in Human ESCs

Cardiac induction requires stepwise integration of BMP and WNT pathway activity. Human embryonic stem cells (hESCs) are developmentally and clinically relevant for studying the poorly understood molecular mechanisms downstream of these cascades. We show that BMP and WNT signaling drive cardiac specification by removing sequential roadblocks that otherwise redirect hESC differentiation toward competing fates, rather than activating a cardiac program per se. First, BMP and WNT signals pattern mesendoderm through cooperative repression of SOX2, a potent mesoderm antagonist. BMP signaling promotes miRNA-877 maturation to induce SOX2 mRNA degradation, while WNT-driven EOMES induction transcriptionally represses SOX2. Following mesoderm formation, cardiac differentiation requires inhibition of WNT activity. We found that WNT inhibition serves to restrict expression of anti-cardiac regulators MSX1 and CDX2/1. Conversely, their simultaneous disruption partially abrogates the requirement for WNT inactivation. These results suggest that human cardiac induction depends on multi-stage repression of alternate lineages, with implications for deriving expandable cardiac stem cells.

From pluripotency to myogenesis: a multistep process in the dish

Pluripotent stem cells (PSCs), such as embryonic stem cells or induced pluripotent stem cells are a promising source of cells for regenerative medicine as they can differentiate into all cell types building a mammalian body. However, protocols leading to efficient and safe in vitro generation of desired cell types must be perfected before PSCs can be used in cell therapies or tissue engineering. In vivo, i.e. in developing mouse embryo or teratoma, PSCs can differentiate into skeletal muscle, but in vitro their spontaneous differentiation into myogenic cells is inefficient. Numerous attempts have been undertaken to enhance this process. Many of them involved mimicking the interactions occurring during embryonic myogenesis. The key regulators of embryonic myogenesis, such as Wnts proteins, fibroblast growth factor 2, and retinoic acid, have been tested to improve the frequency of in vitro myogenic differentiation of PSCs. This review summarizes the current state of the art, comparing spontaneous and directed myogenic differentiation of PSCs as well as the protocols developed this far to facilitate this process.

Gene Signature of Human Oral Mucosa Fibroblasts: Comparison with Dermal Fibroblasts and Induced Pluripotent Stem Cells

Oral mucosa is a useful material for regeneration therapy with the advantages of its accessibility and versatility regardless of age and gender. However, little is known about the molecular characteristics of oral mucosa. Here we report the first comparative profiles of the gene signatures of human oral mucosa fibroblasts (hOFs), human dermal fibroblasts (hDFs), and hOF-derived induced pluripotent stem cells (hOF-iPSCs), linking these with biological roles by functional annotation and pathway analyses. As a common feature of fibroblasts, both hOFs and hDFs expressed glycolipid metabolism-related genes at higher levels compared with hOF-iPSCs. Distinct characteristics of hOFs compared with hDFs included a high expression of glycoprotein genes, involved in signaling, extracellular matrix, membrane, and receptor proteins, besides a low expression of HOX genes, the hDFs-markers. The results of the pathway analyses indicated that tissue-reconstructive, proliferative, and signaling pathways are active, whereas senescence-related genes in p53 pathway are inactive in hOFs. Furthermore, more than half of hOF-specific genes were similarly expressed to those of hOF-iPSC genes and might be controlled by WNT signaling. Our findings demonstrated that hOFs have unique cellular characteristics in specificity and plasticity. These data may provide useful insight into application of oral fibroblasts for direct reprograming.

Mixl1 and Flk1 Are Key Players of Wnt/TGF-β Signaling During DMSO-Induced Mesodermal Specification in P19 cells

Dimethyl sulfoxide (DMSO) is widely used to induce multilineage differentiation of embryonic and adult progenitor cells. To date, little is known about the mechanisms underlying DMSO-induced mesodermal specification. In this study, we investigated the signaling pathways and lineage-determining genes involved in DMSO-induced mesodermal specification in P19 cells. Wnt/β-catenin and TGF-β superfamily signaling pathways such as BMP, TGF-β and GDF1 signaling were significantly activated during DMSO-induced mesodermal specification. In contrast, Nodal/Cripto signaling pathway molecules, required for endoderm specification, were severely downregulated. DMSO significantly upregulated the expression of cardiac mesoderm markers but inhibited the expression of endodermal and hematopoietic lineage markers. Among the DMSO-activated cell lineage markers, the expression of Mixl1 and Flk1 was dramatically upregulated at both the transcript and protein levels, and the populations of Mixl1+, Flk1+ and Mixl1+/Flk1+ cells also increased significantly. DMSO modulated cell cycle molecules and induced cell apoptosis, resulting in significant cell death during EB formation of P19 cells. An inhibitor of Flk1, SU5416 significantly blocked expressions of TGF-β superfamily members, mesodermal cell lineage markers and cell cycle molecules but it did not affect Wnt molecules. These results demonstrate that Mixl1 and Flk1 play roles as key downstream or interacting effectors of Wnt/TGF-β signaling pathway during DMSO-induced mesodermal specification in P19 cells.

Progress and challenges in generating functional hematopoietic stem/progenitor cells from human pluripotent stem cells

The generation of hematopoietic stem cells (HSCs) from human pluripotent stem cells (hPSCs) in vitro holds great potential for providing alternative sources of donor cells for clinical HSC transplantation. However, the low efficiency of current protocols for generating blood lineages and the dysfunction identified in hPSC-derived hematopoietic cells limit their use for full hematopoietic reconstitution in clinics. This review outlines the current understanding of in vitro hematopoietic differentiation from hPSCs, emphasizes the intrinsic and extrinsic molecular mechanisms that are attributed to the aberrant phenotype and function in hPSC-derived hematopoietic cells, pinpoints the current challenges to develop the truly functional HSCs from hPSCs for clinical applications and explores their potential solutions.

Cyclosporin A induces cardiac differentiation but inhibits hemato-endothelial differentiation of P19 cells

Little is known about the mechanisms underlying the effects of Cyclosporin A (CsA) on the fate of stem cells, including cardiomyogenic differentiation. Therefore, we investigated the effects and the molecular mechanisms behind the actions of CsA on cell lineage determination of P19 cells. CsA induced cardiomyocyte-specific differentiation of P19 cells, with the highest efficiency at a concentration of 0.32 μM during embryoid body (EB) formation via activation of the Wnt signaling pathway molecules, Wnt3a, Wnt5a, and Wnt8a, and the cardiac mesoderm markers, Mixl1, Mesp1, and Mesp2. Interestingly, cotreatment of P19 cells with CsA plus dimethyl sulfoxide (DMSO) during EB formation significantly increases cardiac differentiation. In contrast, mRNA expression levels of hematopoietic and endothelial lineage markers, including Flk1 and Er71, were severely reduced in CsA-treated P19 cells. Furthermore, expression of Flk1 protein and the percentage of Flk1+ cells were severely reduced in 0.32 μM CsA-treated P19 cells compared to control cells. CsA significantly modulated mRNA expression levels of the cell cycle molecules, p53 and Cyclins D1, D2, and E2 in P19 cells during EB formation. Moreover, CsA significantly increased cell death and reduced cell number in P19 cells during EB formation. These results demonstrate that CsA induces cardiac differentiation but inhibits hemato-endothelial differentiation via activation of the Wnt signaling pathway, followed by modulation of cell lineage-determining genes in P19 cells during EB formation.

Wnt signaling controls the specification of definitive and primitive hematopoiesis from human pluripotent stem cells

Efforts to derive hematopoietic stem cells (HSCs) from human pluripotent stem cells (hPSCs) are complicated by the fact that embryonic hematopoiesis consists of two programs, primitive and definitive, that differ in developmental potential. As only definitive hematopoiesis generates HSCs, understanding how this program develops is essential for being able to produce this cell population in vitro. Here we show that both hematopoietic programs transition through hemogenic endothelial intermediates and develop from KDR⁺CD34⁻CD144⁻ progenitors that are distinguished by CD235a expression. Generation of primitive progenitors (KDR⁺CD235a⁺) depends on stage-specific Activin-nodal signaling and inhibition of the Wnt-β-catenin pathway, whereas specification of definitive progenitors (KDR⁺CD235a⁻) requires Wnt-β-catenin signaling during this same time frame. Together, these findings establish simple selective differentiation strategies for the generation of primitive or definitive hematopoietic progenitors via Wnt-β-catenin manipulation, and in doing so provide access to enriched populations for future studies on hPSC-derived hematopoietic development.

Wnt and Bmp fit germ cells to a T

Reporting in Developmental Cell, Aramaki et al. (2013) identify T as a key mediator of primordial germ cell (PGC) specification in the embryo. Deconstruction of how Bmp and Wnt signals regulate the expression and targeting of T to regulatory elements of either mesodermal or PGC genes has implications for differentiation in vitro.

Efficient endoderm induction from human pluripotent stem cells by logically directing signals controlling lineage bifurcations

Human pluripotent stem cell (hPSC) differentiation typically yields heterogeneous populations. Knowledge of signals controlling embryonic lineage bifurcations could efficiently yield desired cell types through exclusion of alternate fates. Therefore, we revisited signals driving induction and anterior-posterior patterning of definitive endoderm to generate a coherent roadmap for endoderm differentiation. With striking temporal dynamics, BMP and Wnt initially specified anterior primitive streak (progenitor to endoderm), yet, 24 hr later, suppressed endoderm and induced mesoderm. At lineage bifurcations, cross-repressive signals separated mutually exclusive fates; TGF-β and BMP/MAPK respectively induced pancreas versus liver from endoderm by suppressing the alternate lineage. We systematically blockaded alternate fates throughout multiple consecutive bifurcations, thereby efficiently differentiating multiple hPSC lines exclusively into endoderm and its derivatives. Comprehensive transcriptional and chromatin mapping of highly pure endodermal populations revealed that endodermal enhancers existed in a surprising diversity of "pre-enhancer" states before activation, reflecting the establishment of a permissive chromatin landscape as a prelude to differentiation.

The negative impact of Wnt signaling on megakaryocyte and primitive erythroid progenitors derived from human embryonic stem cells

The Wnt gene family consists of structurally related genes encoding secreted signaling molecules that have been implicated in many developmental processes, including regulation of cell fate and patterning during embryogenesis. Previously, we found that Wnt signaling is required for primitive or yolk sac-derived-erythropoiesis using the murine embryonic stem cell (ESC) system. Here, we examine the effect of Wnt signaling on the formation of early hematopoietic progenitors derived from human ESCs. The first hematopoietic progenitor cells in the human ESC system express the pan-hematopoietic marker CD41 and the erythrocyte marker, glycophorin A or CD235. We have developed a novel serum-free, feeder-free, adherent differentiation system that can efficiently generate large numbers of CD41+CD235+ cells. We demonstrate that this cell population contains progenitors not just for primitive erythroid and megakaryocyte cells but for the myeloid lineage as well and term this population the primitive common myeloid progenitor (CMP). Treatment of mesoderm-specified cells with Wnt3a led to a loss of hematopoietic colony-forming ability while the inhibition of canonical Wnt signaling with DKK1 led to an increase in the number of primitive CMPs. Canonical Wnt signaling also inhibits the expansion and/or survival of primitive erythrocytes and megakaryocytes, but not myeloid cells, derived from this progenitor population. These findings are in contrast to the role of Wnt signaling during mouse ESC differentiation and demonstrate the importance of the human ESC system in studying species-specific differences in development.