Sox17 dependence distinguishes the transcriptional regulation of fetal from adult hematopoietic stem cells

Impact of gallbladder hypoplasia on hilar hepatic ducts in biliary atresia

BACKGROUND

Biliary atresia (BA) is an intractable disease of unknown cause that develops in the neonatal period. It causes jaundice and liver damage due to the destruction of extrahepatic biliary tracts,. We have found that heterozygous knockout mice of the SRY related HMG-box 17 (Sox17) gene, a master regulator of stem/progenitor cells in the gallbladder wall, exhibit a condition like BA. However, the precise contribution of hypoplastic gallbladder wall to the pathogenesis of hepatobiliary disease in Sox17 heterozygous embryos and human BA remains unclear.

METHODS

We employed cholangiography and histological analyses in the mouse BA model. Furthermore, we conducted a retrospective analysis of human BA.

RESULTS

We show that gallbladder wall hypoplasia causes abnormal multiple connections between the hilar hepatic bile ducts and the gallbladder-cystic duct in Sox17 heterozygous embryos. These multiple hilar extrahepatic ducts fuse with the developing intrahepatic duct walls and pull them out of the liver parenchyma, resulting in abnormal intrahepatic duct network and severe cholestasis. In human BA with gallbladder wall hypoplasia (i.e., abnormally reduced expression of SOX17), we also identify a strong association between reduced gallbladder width (a morphometric parameter indicating gallbladder wall hypoplasia) and severe liver injury at the time of the Kasai surgery, like the Sox17-mutant mouse model.

CONCLUSIONS

Together with the close correlation between gallbladder wall hypoplasia and liver damage in both mouse and human cases, these findings provide an insight into the critical role of SOX17-positive gallbladder walls in establishing functional bile duct networks in the hepatic hilus of neonates.

Lineage-tracing hematopoietic stem cell origins in vivo to efficiently make human HLF+ HOXA+ hematopoietic progenitors from pluripotent stem cells

The developmental origin of blood-forming hematopoietic stem cells (HSCs) is a longstanding question. Here, our non-invasive genetic lineage tracing in mouse embryos pinpoints that artery endothelial cells generate HSCs. Arteries are transiently competent to generate HSCs for 2.5 days (∼E8.5-E11) but subsequently cease, delimiting a narrow time frame for HSC formation in vivo. Guided by the arterial origins of blood, we efficiently and rapidly differentiate human pluripotent stem cells (hPSCs) into posterior primitive streak, lateral mesoderm, artery endothelium, hemogenic endothelium, and >90% pure hematopoietic progenitors within 10 days. hPSC-derived hematopoietic progenitors generate T, B, NK, erythroid, and myeloid cells in vitro and, critically, express hallmark HSC transcription factors HLF and HOXA5-HOXA10, which were previously challenging to upregulate. We differentiated hPSCs into highly enriched HLF+ HOXA+ hematopoietic progenitors with near-stoichiometric efficiency by blocking formation of unwanted lineages at each differentiation step. hPSC-derived HLF+ HOXA+ hematopoietic progenitors could avail both basic research and cellular therapies.

Characterization of gene regulatory networks underlying key properties in human hematopoietic stem cell ontogeny

Human hematopoiesis starts at early yolk sac and undergoes site- and stage-specific changes over development. The intrinsic mechanism underlying property changes in hematopoiesis ontogeny remains poorly understood. Here, we analyzed single-cell transcriptome of human primary hematopoietic stem/progenitor cells (HSPCs) at different developmental stages, including yolk-sac (YS), AGM, fetal liver (FL), umbilical cord blood (UCB) and adult peripheral blood (PB) mobilized HSPCs. These stage-specific HSPCs display differential intrinsic properties, such as metabolism, self-renewal, differentiating potentialities etc. We then generated highly co-related gene regulatory network (GRNs) modules underlying the differential HSC key properties. Particularly, we identified GRNs and key regulators controlling lymphoid potentiality, self-renewal as well as aerobic respiration in human HSCs. Introducing selected regulators promotes key HSC functions in HSPCs derived from human pluripotent stem cells. Therefore, GRNs underlying key intrinsic properties of human HSCs provide a valuable guide to generate fully functional HSCs in vitro.

Aberrant stem cell and developmental programs in pediatric leukemia

Hematopoiesis is a finely orchestrated process, whereby hematopoietic stem cells give rise to all mature blood cells. Crucially, they maintain the ability to self-renew and/or differentiate to replenish downstream progeny. This process starts at an embryonic stage and continues throughout the human lifespan. Blood cancers such as leukemia occur when normal hematopoiesis is disrupted, leading to uncontrolled proliferation and a block in differentiation of progenitors of a particular lineage (myeloid or lymphoid). Although normal stem cell programs are crucial for tissue homeostasis, these can be co-opted in many cancers, including leukemia. Myeloid or lymphoid leukemias often display stem cell-like properties that not only allow proliferation and survival of leukemic blasts but also enable them to escape treatments currently employed to treat patients. In addition, some leukemias, especially in children, have a fetal stem cell profile, which may reflect the developmental origins of the disease. Aberrant fetal stem cell programs necessary for leukemia maintenance are particularly attractive therapeutic targets. Understanding how hijacked stem cell programs lead to aberrant gene expression in place and time, and drive the biology of leukemia, will help us develop the best treatment strategies for patients.

SOX17/ETV2 improves the direct reprogramming of adult fibroblasts to endothelial cells

An autologous source of vascular endothelial cells (ECs) is valuable for vascular regeneration and tissue engineering without the concern of immune rejection. The transcription factor ETS variant 2 (ETV2) has been shown to directly convert patient fibroblasts into vascular EC-like cells. However, reprogramming efficiency is low and there are limitations in EC functions, such as eNOS expression. In this study, we directly reprogram adult human dermal fibroblasts into reprogrammed ECs (rECs) by overexpressing SOX17 in conjunction with ETV2. We find several advantages to rEC generation using this approach, including improved reprogramming efficiency, increased enrichment of EC genes, formation of large blood vessels carrying blood from the host, and, most importantly, expression of eNOS in vivo. From these results, we present an improved method to reprogram adult fibroblasts into functional ECs and posit ideas for the future that could potentially further improve the reprogramming process.

Maternal inflammation regulates fetal emergency myelopoiesis

Neonates are highly susceptible to inflammation and infection. Here, we investigate how late fetal liver (FL) mouse hematopoietic stem and progenitor cells (HSPCs) respond to inflammation, testing the hypothesis that deficits in the engagement of emergency myelopoiesis (EM) pathways limit neutrophil output and contribute to perinatal neutropenia. We show that fetal HSPCs have limited production of myeloid cells at steady state and fail to activate a classical adult-like EM transcriptional program. Moreover, we find that fetal HSPCs can respond to EM-inducing inflammatory stimuli in vitro but are restricted by maternal anti-inflammatory factors, primarily interleukin-10 (IL-10), from activating EM pathways in utero. Accordingly, we demonstrate that the loss of maternal IL-10 restores EM activation in fetal HSPCs but at the cost of fetal demise. These results reveal the evolutionary trade-off inherent in maternal anti-inflammatory responses that maintain pregnancy but render the fetus unresponsive to EM activation signals and susceptible to infection.

SOX17 enables immune evasion of early colorectal adenomas and cancers

A hallmark of cancer is the avoidance of immune destruction. This process has been primarily investigated in locally advanced or metastatic cancer1-3; however, much less is known about how pre-malignant or early invasive tumours evade immune detection. Here, to understand this process in early colorectal cancers (CRCs), we investigated how naive colon cancer organoids that were engineered in vitro to harbour Apc-null, KrasG12D and Trp53-null (AKP) mutations adapted to the in vivo native colonic environment. Comprehensive transcriptomic and chromatin analyses revealed that the endoderm-specifying transcription factor SOX17 became strongly upregulated in vivo. Notably, whereas SOX17 loss did not affect AKP organoid propagation in vitro, its loss markedly reduced the ability of AKP tumours to persist in vivo. The small fraction of SOX17-null tumours that grew displayed notable interferon-γ (IFNγ)-producing effector-like CD8+ T cell infiltrates in contrast to the immune-suppressive microenvironment in wild-type counterparts. Mechanistically, in both endogenous Apc-null pre-malignant adenomas and transplanted organoid-derived AKP CRCs, SOX17 suppresses the ability of tumour cells to sense and respond to IFNγ, preventing anti-tumour T cell responses. Finally, SOX17 engages a fetal intestinal programme that drives differentiation away from LGR5+ tumour cells to produce immune-evasive LGR5- tumour cells with lower expression of major histocompatibility complex class I (MHC-I). We propose that SOX17 is a transcription factor that is engaged during the early steps of colon cancer to orchestrate an immune-evasive programme that permits CRC initiation and progression.

The role of m6A mRNA modification in normal and malignant hematopoiesis

Hematopoiesis is a highly orchestrated biological process sustaining the supply of leukocytes involved in the maintenance of immunity, O2 and CO2 exchange, and wound healing throughout the lifetime of an animal, including humans. During early hematopoietic cell development, several waves of hematopoiesis require the precise regulation of hematopoietic ontogeny as well as the maintenance of hematopoietic stem and progenitor cells in the hematopoietic tissues, such as the fetal liver and bone marrow. Recently, emerging evidence has suggested the critical role of m6A messenger RNA (mRNA) modification, an epigenetic modification dynamically regulated by its effector proteins, in the generation and maintenance of hematopoietic cells during embryogenesis. In the adulthood, m6A has also been demonstrated to be involved in the functional maintenance of hematopoietic stem and progenitor cells in the bone marrow and umbilical cord blood, as well as the progression of malignant hematopoiesis. In this review, we focus on recent progress in identifying the biological functions of m6A mRNA modification, its regulators, and downstream gene targets during normal and pathological hematopoiesis. We propose that targeting m6A mRNA modification could offer novel insights into therapeutic development against abnormal and malignant hematopoietic cell development in the future.

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.

E2F1 Mediates SOX17 Deficiency-Induced Pulmonary Hypertension

BACKGROUND

Rare genetic variants and genetic variation at loci in an enhancer in SOX17 (SRY-box transcription factor 17) are identified in patients with idiopathic pulmonary arterial hypertension (PAH) and PAH with congenital heart disease. However, the exact role of genetic variants or mutations in SOX17 in PAH pathogenesis has not been reported.

METHODS

SOX17 expression was evaluated in the lungs and pulmonary endothelial cells (ECs) of patients with idiopathic PAH. Mice with Tie2Cre-mediated Sox17 knockdown and EC-specific Sox17 deletion were generated to determine the role of SOX17 deficiency in the pathogenesis of PAH. Human pulmonary ECs were cultured to understand the role of SOX17 deficiency. Single-cell RNA sequencing, RNA-sequencing analysis, and luciferase assay were performed to understand the underlying molecular mechanisms of SOX17 deficiency-induced PAH. E2F1 (E2F transcription factor 1) inhibitor HLM006474 was used in EC-specific Sox17 mice.

RESULTS

SOX17 expression was downregulated in the lung and pulmonary ECs from patients with idiopathic PAH. Mice with Tie2Cre-mediated Sox17 knockdown and EC-specific Sox17 deletion induced spontaneously mild pulmonary hypertension. Loss of endothelial Sox17 in EC exacerbated hypoxia-induced pulmonary hypertension in mice. Loss of SOX17 in lung ECs induced endothelial dysfunctions including upregulation of cell cycle programming, proliferative and antiapoptotic phenotypes, augmentation of paracrine effect on pulmonary arterial smooth muscle cells, impaired cellular junction, and BMP (bone morphogenetic protein) signaling. E2F1 signaling was shown to mediate the SOX17 deficiency-induced EC dysfunction. Pharmacological inhibition of E2F1 in Sox17 EC-deficient mice attenuated pulmonary hypertension development.

CONCLUSIONS

Our study demonstrated that endothelial SOX17 deficiency induces pulmonary hypertension through E2F1. Thus, targeting E2F1 signaling represents a promising approach in patients with PAH.

Engineered hematopoietic and immune cells derived from human pluripotent stem cells

For the past decade, significant advances have been achieved in human hematopoietic stem cell (HSC) transplantation for treating various blood diseases and cancers. However, challenges remain with the quality control, amount, and cost of HSCs and HSC-derived immune cells. The advent of human pluripotent stem cells (hPSCs) may transform HSC transplantation and cancer immunotherapy by providing a cost-effective and scalable cell source for fundamental studies and translational applications. In this review, we discuss the current developments in the field of stem cell engineering for hematopoietic stem and progenitor cell (HSPC) differentiation and further differentiation of HSPCs into functional immune cells. The key advances in stem cell engineering include the generation of HSPCs from hPSCs, genetic modification of hPSCs, and hPSC-derived HSPCs for improved function, further differentiation of HPSCs into functional immune cells, and applications of cell culture platforms for hematopoietic cell manufacturing. Current challenges impeding the translation of hPSC-HSPCs and immune cells as well as further directions to address these challenges are also discussed.

Single-cell multiomics of human fetal hematopoiesis define a developmental-specific population and a fetal signature

Knowledge of human fetal blood development and how it differs from adult blood is highly relevant to our understanding of congenital blood and immune disorders and childhood leukemia, of which the latter can originate in utero. Blood formation occurs in waves that overlap in time and space, adding to heterogeneity, which necessitates single-cell approaches. Here, a combined single-cell immunophenotypic and transcriptional map of first trimester primitive blood development is presented. Using CITE-seq (cellular indexing of transcriptomes and epitopes by sequencing), the molecular profile of established immunophenotype-gated progenitors was analyzed in the fetal liver (FL). Classical markers for hematopoietic stem cells (HSCs), such as CD90 and CD49F, were largely preserved, whereas CD135 (FLT3) and CD123 (IL3R) had a ubiquitous expression pattern capturing heterogenous populations. Direct molecular comparison with an adult bone marrow data set revealed that the HSC state was less frequent in FL, whereas cells with a lymphomyeloid signature were more abundant. An erythromyeloid-primed multipotent progenitor cluster was identified, potentially representing a transient, fetal-specific population. Furthermore, differentially expressed genes between fetal and adult counterparts were specifically analyzed, and a fetal core signature was identified. The core gene set could separate subgroups of acute lymphoblastic leukemia by age, suggesting that a fetal program may be partially retained in specific subgroups of pediatric leukemia. Our detailed single-cell map presented herein emphasizes molecular and immunophenotypic differences between fetal and adult blood cells, which are of significance for future studies of pediatric leukemia and blood development in general.

Maternal IL-10 restricts fetal emergency myelopoiesis

Neonates, in contrast to adults, are highly susceptible to inflammation and infection. Here we investigate how late fetal liver (FL) mouse hematopoietic stem and progenitor cells (HSPC) respond to inflammation, testing the hypothesis that deficits in engagement of emergency myelopoiesis (EM) pathways limit neutrophil output and contribute to perinatal neutropenia. We show that despite similar molecular wiring as adults, fetal HSPCs have limited production of myeloid cells at steady state and fail to activate a classical EM transcriptional program. Moreover, we find that fetal HSPCs are capable of responding to EM-inducing inflammatory stimuli in vitro , but are restricted by maternal anti-inflammatory factors, primarily interleukin-10 (IL-10), from activating EM pathways in utero . Accordingly, we demonstrate that loss of maternal IL-10 restores EM activation in fetal HSPCs but at the cost of premature parturition. These results reveal the evolutionary trade-off inherent in maternal anti-inflammatory responses that maintain pregnancy but render the fetus unresponsive to EM activation signals and susceptible to infection.

HIGHLIGHTS

The structure of the HSPC compartment is conserved from late fetal to adult life.Fetal HSPCs have diminished steady-state myeloid cell production compared to adult.Fetal HSPCs are restricted from engaging in emergency myelopoiesis by maternal IL-10.Restriction of emergency myelopoiesis may explain neutropenia in septic neonates.

eTOC BLURB

Fetal hematopoietic stem and progenitor cells are restricted from activating emergency myelopoiesis pathways by maternal IL-10, resulting in inadequate myeloid cell production in response to inflammatory challenges and contributing to neonatal neutropenia.

Pan-cancer Analysis Reveals Cancer-dependent Expression of SOX17 and Associated Clinical Outcomes

BACKGROUND/AIM

SRY-box containing gene 17 (SOX17) plays a pivotal role in cancer onset and progression and is considered a potential target for cancer diagnosis and treatment. However, the expression pattern of SOX17 in cancer and its clinical relevance remains unknown. Here, we explored the relationship between the expression of SOX17 and drug response by examining SOX17 expression patterns across multiple cancer types.

MATERIALS AND METHODS

Single-cell and bulk RNA-seq analyses were used to explore the expression profile of SOX17. Analysis results were verified with qPCR and immunohistochemistry. Survival, drug response, and co-expression analyses were performed to illustrate its correlation with clinical outcomes.

RESULTS

The results revealed that abnormal expression of SOX17 is highly heterogenous across multiple cancer types, indicating that SOX17 manifests as a cancer type-dependent feature. Furthermore, the expression pattern of SOX17 is also associated with cancer prognosis in certain cancer types. Strong SOX17 expression correlates with the potency of small molecule drugs that affect PI3K/mTOR signaling. FGF18, a gene highly relevant to SOX17, is involved in the PI3K-AKT signaling pathway. Single-cell RNA-seq analysis demonstrated that SOX17 is mainly expressed in endothelial cells and barely expressed in other cells but spreads to other cell types during the development of ovarian cancer.

CONCLUSION

Our study revealed the expression pattern of SOX17 in pan-cancer through bulk and single-cell RNA-seq analyses and determined that SOX17 is related to the diagnosis, staging, and prognosis of some tumors. These findings have clinical implications and may help identify mechanistic pathways amenable to pharmacological interventions.

Gastruloid-derived primordial germ cell-like cells develop dynamically within integrated tissues

Primordial germ cells (PGCs) are the early embryonic precursors of gametes - sperm and egg cells. PGC-like cells (PGCLCs) can currently be derived in vitro from pluripotent cells exposed to signalling cocktails and aggregated into large embryonic bodies, but these do not recapitulate the native embryonic environment during PGC formation. Here, we show that mouse gastruloids, a three-dimensional in vitro model of gastrulation, contain a population of gastruloid-derived PGCLCs (Gld-PGCLCs) that resemble early PGCs in vivo. Importantly, the conserved organisation of mouse gastruloids leads to coordinated spatial and temporal localisation of Gld-PGCLCs relative to surrounding somatic cells, even in the absence of specific exogenous PGC-specific signalling or extra-embryonic tissues. In gastruloids, self-organised interactions between cells and tissues, including the endodermal epithelium, enables the specification and subsequent maturation of a pool of Gld-PGCLCs. As such, mouse gastruloids represent a new source of PGCLCs in vitro and, owing to their inherent co-development, serve as a novel model to study the dynamics of PGC development within integrated tissue environments.

A Sox17 downstream gene Rasip1 is involved in the hematopoietic activity of intra-aortic hematopoietic clusters in the midgestation mouse embryo

BACKGROUND

During mouse embryonic development, definitive hematopoiesis is first detected around embryonic day (E) 10.5 in the aorta-gonad-mesonephros (AGM) region. Hematopoietic stem cells (HSCs) arise in the dorsal aorta's intra-aortic hematopoietic cell clusters (IAHCs). We have previously reported that a transcription factor Sox17 is expressed in IAHCs, and that, among them, CD45lowc-Kithigh cells have high hematopoietic activity. Furthermore, forced expression of Sox17 in this population of cells can maintain the formation of hematopoietic cell clusters. However, how Sox17 does so, particularly downstream signaling involved, remains poorly understood. The purpose of this study is to search for new Sox17 targets which contribute to cluster formation with hematopoietic activity.

METHODS

RNA-sequencing (RNA-seq) analysis was done to identify genes that are upregulated in Sox17-expressing IAHCs as compared with Sox17-negative ones. Among the top 7 highly expressed genes, Rasip1 which had been reported to be a vascular-specific regulator was focused on in this study, and firstly, the whole-mount immunostaining was done. We conducted luciferase reporter assay and chromatin immunoprecipitation (ChIP) assay to examine whether Sox17 regulates Rasip1 gene expression via binding to its enhancer element. We also analyzed the cluster formation and the multilineage colony-forming ability of Rasip1-transduced cells and Rasip1-knockdown Sox17-transduced cells.

RESULTS

The increase of the Rasip1 expression level was observed in Sox17-positive CD45lowc-Kithigh cells as compared with the Sox17-nonexpressing control. Also, the expression level of the Rasip1 gene was increased by the Sox17-nuclear translocation. Rasip1 was expressed on the membrane of IAHCs, overlapping with the endothelial cell marker, CD31, and hematopoietic stem/progenitor marker (HSPC), c-Kit. Rasip1 expression was observed in most part of c-Kit+Sox17+ cells in IAHCs. Luciferase reporter assay and ChIP assay indicated that one of the five putative Sox17-binding sites in the Rasip1 enhancer region was important for Rasip1 expression via Sox17 binding. Rasip1 knockdown in Sox17-transduced cells decreased the cluster formation and diminished the colony-forming ability, while overexpression of Rasip1 in CD45lowc-Kithigh cells led to a significant but transient increase in hematopoietic activity.

CONCLUSIONS

Rasip1 knockdown in Sox17-transduced CD45lowc-Kithigh cells displayed a significant decrease in the multilineage colony-forming ability and the cluster size. Rasip1 overexpression in Sox17-untransduced CD45lowc-Kithigh cells led to a significant but transient increase in the multilineage colony-forming ability, suggesting the presence of a cooperating factor for sustained hematopoietic activity.

The dynamic expression of SOX17 in germ cells from human female foetus and adult ovaries after specification

Background

SOX17 has been identified as a critical factor in specification of human primordial germ cells, but whether SOX17 regulates development of germ cells after sex differentiation is poorly understood.

Methods

We collected specimens of gonadal ridge from an embryo (n=1), and ovaries of foetuses (n=23) and adults (n=3). Germ cells were labelled with SOX17, VASA (classic germ cells marker), phosphohistone H3 (PHH3, mitosis marker) and synaptonemal complex protein 3 (SCP3, meiosis marker).

Results

SOX17 was detected in both cytoplasm and nucleus of oogonia and oocytes of primordial and primary follicles from 15 to 28 gestational weeks (GW). However, it was exclusively expressed in cytoplasm of oogonia at 7 GW, and in nucleus of oocytes in secondary follicles. Co-expression rates of SOX17 in VASA+ germ cells ranged from 81.29% to 97.81% in foetuses. Co-staining rates of SOX17 and PHH3 or SCP3 were 0%-34% and 0%-57%, respectively. Interestingly, we distinguished a subpopulation of SOX17+VASA- germ cells in fetal ovaries. These cells clustered in the cortex and could be co-stained with the mitosis marker PHH3 but not the meiosis marker SCP3.

Conclusions

The dynamic expression of SOX17 was detected in human female germ cells. We discovered a population of SOX17+ VASA- germ cells clustering at the cortex of ovaries. We could not find a relationship between mitosis or meiosis and SOX17 or VASA staining in germ cells. Our findings provide insight into the potential role of SOX17 involving germ cells maturation after specification, although the mechanism is unclear and needs further investigation.

Single-Cell RNA Sequencing of Sox17-Expressing Lineages Reveals Distinct Gene Regulatory Networks and Dynamic Developmental Trajectories

During early embryogenesis, the transcription factor SOX17 contributes to hepato-pancreato-biliary system formation and vascular-hematopoietic emergence. To better understand Sox17 function in the developing endoderm and endothelium, we developed a dual-color temporal lineage-tracing strategy in mice combined with single-cell RNA sequencing to analyze 6934 cells from Sox17-expressing lineages at embryonic days 9.0-9.5. Our analyses showed 19 distinct cellular clusters combined from all 3 germ layers. Differential gene expression, trajectory and RNA-velocity analyses of endothelial cells revealed a heterogenous population of uncommitted and specialized endothelial subtypes, including 2 hemogenic populations that arise from different origins. Similarly, analyses of posterior foregut endoderm revealed subsets of hepatic, pancreatic, and biliary progenitors with overlapping developmental potency. Calculated gene-regulatory networks predict gene regulons that are dominated by cell type-specific transcription factors unique to each lineage. Vastly different Sox17 regulons found in endoderm versus endothelial cells support the differential interactions of SOX17 with other regulatory factors thereby enabling lineage-specific regulatory actions.

SOX18-enforced expression diverts hemogenic endothelium-derived progenitors from T towards NK lymphoid pathways

Hemogenic endothelium (HE) is the main source of blood cells in the embryo. To improve blood manufacturing from human pluripotent stem cells (hPSCs), it is essential to define the molecular determinants that enhance HE specification and promote development of the desired blood lineage from HE. Here, using SOX18-inducible hPSCs, we revealed that SOX18 forced expression at the mesodermal stage, in contrast to its homolog SOX17, has minimal effects on arterial specification of HE, expression of HOXA genes and lymphoid differentiation. However, forced expression of SOX18 in HE during endothelial-to-hematopoietic transition (EHT) greatly increases NK versus T cell lineage commitment of hematopoietic progenitors (HPs) arising from HE predominantly expanding CD34⁺CD43⁺CD235a/CD41a^-CD45^- multipotent HPs and altering the expression of genes related to T cell and Toll-like receptor signaling. These studies improve our understanding of lymphoid cell specification during EHT and provide a new tool for enhancing NK cell production from hPSCs for immunotherapies.

Hematopoietic Jagged1 is a fetal liver niche factor required for functional maturation and engraftment of fetal hematopoietic stem cells

Notch signaling is essential for the emergence of definitive hematopoietic stem cells (HSCs) in the embryo and their development in the fetal liver niche. However, how Notch signaling is activated and which fetal liver cell type provides the ligand for receptor activation in HSCs is unknown. Here we provide evidence that endothelial Jagged1 (Jag1) has a critical early role in fetal liver vascular development but is not required for hematopoietic function during fetal HSC expansion. We demonstrate that Jag1 is expressed in many hematopoietic cells in the fetal liver, including HSCs, and that its expression is lost in adult bone marrow HSCs. Deletion of hematopoietic Jag1 does not affect fetal liver development; however, Jag1-deficient fetal liver HSCs exhibit a significant transplantation defect. Bulk and single-cell transcriptomic analysis of HSCs during peak expansion in the fetal liver indicates that loss of hematopoietic Jag1 leads to the downregulation of critical hematopoietic factors such as GATA2, Mllt3, and HoxA7, but does not perturb Notch receptor expression. Ex vivo activation of Notch signaling in Jag1-deficient fetal HSCs partially rescues the functional defect in a transplant setting. These findings indicate a new fetal-specific niche that is based on juxtracrine hematopoietic Notch signaling and reveal Jag1 as a fetal-specific niche factor essential for HSC function.

Childhood hematopoietic stem cells constitute the permissive window for RUNX1-ETO leukemogenesis

Cancer is a very rare event at the cellular level, although it is a common disease at the body level as one third of humans die of cancer. A small subset of cells in the body harbor the cellular features that constitute a permissive window for a particular genetic change to induce cancer. The significance of a permissive window is ironically best shown by a large number of failures in generating the animal model for acute myeloid leukemia (AML) with t(8;21). Over the decades, the RUNX1-ETO fusion gene created by t(8;21) has been introduced into various types of hematopoietic cells, largely at adult stage, in mice; however, all the previous attempts failed to generate tractable AML models. In stark contrast, we recently succeeded in inducing AML with the clinical features seen in human patients by specifically introducing RUNX1-ETO in childhood hematopoietic stem cells (HSCs). This result in mice is consistent with adolescent and young adult (AYA) onset in human t(8;21) patients, and suggests that childhood HSCs constitute the permissive window for RUNX1-ETO leukemogenesis. If loss of a permissive window is induced pharmacologically, cancer cells might be selectively targeted. Such a permissive window modifier may serve as a novel therapeutic drug.

Lymphoid cell development from fetal hematopoietic progenitors and human pluripotent stem cells

Lymphoid cells encompass the adaptive immune system, including T and B cells and Natural killer T cells (NKT), and innate immune cells (ILCs), including Natural Killer (NK) cells. During adult life, these lineages are thought to derive from the differentiation of long-term hematopoietic stem cells (HSCs) residing in the bone marrow. However, during embryogenesis and fetal development, the ontogeny of lymphoid cells is both complex and multifaceted, with a large body of evidence suggesting that lymphoid lineages arise from progenitor cell populations antedating the emergence of HSCs. Recently, the application of single cell RNA-sequencing technologies and pluripotent stem cell-based developmental models has provided new insights into lymphoid ontogeny during embryogenesis. Indeed, PSC differentiation platforms have enabled de novo generation of lymphoid immune cells independently of HSCs, supporting conclusions drawn from the study of hematopoiesis in vivo. Here, we examine lymphoid development from non-HSC progenitor cells and technological advances in the differentiation of human lymphoid cells from pluripotent stem cells for clinical translation.

SOX17 is a Critical Factor in Maintaining Endothelial Function in Pulmonary Hypertension by an Exosome-Mediated Autocrine Manner

Endothelial dysfunction is considered a predominant driver for pulmonary vascular remodeling in pulmonary hypertension (PH). SOX17, a key regulator of vascular homoeostasis, has been found to harbor mutations in PH patients, which are associated with PH susceptibility. Here, this study explores whether SOX17 mediates the autocrine activity of pulmonary artery ECs to maintain endothelial function and vascular homeostasis in PH and its underlying mechanism. It is found that SOX17 expression is downregulated in the endothelium of remodeled pulmonary arteries in IPH patients and SU5416/hypoxia (Su/hypo)-induced PH mice as well as dysfunctional HPAECs. Endothelial knockdown of SOX17 accelerates the progression of Su/hypo-induced PH in mice. SOX17 overexpression in the pulmonary endothelium of mice attenuates Su/hypo-induced PH. SOX17-associated exosomes block the proliferation, apoptosis, and inflammation of HPAECs, preventing pulmonary arterial remodeling and Su/hypo-induced PH. Mechanistic analyses demonstrates that overexpressing SOX17 promotes the exosome-mediated release of miR-224-5p and miR-361-3p, which are internalized by injured HPAECs in an autocrine manner, ultimately repressing the upregulation of NR4A3 and PCSK9 genes and improving endothelial function. These results suggest that SOX17 is a key gene in maintaining endothelial function and vascular homeostasis in PH through regulating exosomal miRNAs in an autocrine manner.

Multiple waves of fetal-derived immune cells constitute adult immune system

It has been over three decades since Drs. Herzenberg and Herzenberg proposed the layered immune system hypothesis, suggesting that different types of stem cells with distinct hematopoietic potential produce specific immune cells. This layering of immune system development is now supported by recent studies showing the presence of fetal-derived immune cells that function in adults. It has been shown that various immune cells arise at different embryonic ages via multiple waves of hematopoiesis from special endothelial cells (ECs), referred to as hemogenic ECs. However, it remains unknown whether these fetal-derived immune cells are produced by hematopoietic stem cells (HSCs) during the fetal to neonatal period. To address this question, many advanced tools have been used, including lineage-tracing mouse models, cellular barcoding techniques, clonal assays, and transplantation assays at the single-cell level. In this review, we will review the history of the search for the origins of HSCs, B-1a progenitors, and mast cells in the mouse embryo. HSCs can produce both B-1a and mast cells within a very limited time window, and this ability declines after embryonic day (E) 14.5. Furthermore, the latest data have revealed that HSC-independent adaptive immune cells exist in adult mice, which implies more complicated developmental pathways of immune cells. We propose revised road maps of immune cell development.

Pathogenic human variant that dislocates GATA2 zinc fingers disrupts hematopoietic gene expression and signaling networks

Although certain human genetic variants are conspicuously loss of function, decoding the impact of many variants is challenging. Previously, we described a patient with leukemia predisposition syndrome (GATA2 deficiency) with a germline GATA2 variant that inserts 9 amino acids between the 2 zinc fingers (9aa-Ins). Here, we conducted mechanistic analyses using genomic technologies and a genetic rescue system with Gata2 enhancer-mutant hematopoietic progenitor cells to compare how GATA2 and 9aa-Ins function genome-wide. Despite nuclear localization, 9aa-Ins was severely defective in occupying and remodeling chromatin and regulating transcription. Variation of the inter-zinc finger spacer length revealed that insertions were more deleterious to activation than repression. GATA2 deficiency generated a lineage-diverting gene expression program and a hematopoiesis-disrupting signaling network in progenitors with reduced granulocyte-macrophage colony-stimulating factor (GM-CSF) and elevated IL-6 signaling. As insufficient GM-CSF signaling caused pulmonary alveolar proteinosis and excessive IL-6 signaling promoted bone marrow failure and GATA2 deficiency patient phenotypes, these results provide insight into mechanisms underlying GATA2-linked pathologies.

E2F1 Mediates SOX17 Deficiency-Induced Pulmonary Hypertension

Rationale

Rare genetic variants and genetic variation at loci in an enhancer in SRY-Box Transcription Factor 17 (SOX17) are identified in patients with idiopathic pulmonary arterial hypertension (PAH) and PAH with congenital heart disease. However, the exact role of genetic variants or mutation in SOX17 in PAH pathogenesis has not been reported.

Objectives

To investigate the role of SOX17 deficiency in pulmonary hypertension (PH) development.

Methods

Human lung tissue and endothelial cells (ECs) from IPAH patients were used to determine the expression of SOX17. Tie2Cre-mediated and EC-specific deletion of Sox17 mice were assessed for PH development. Single-cell RNA sequencing analysis, human lung ECs, and smooth muscle cell culture were performed to determine the role and mechanisms of SOX17 deficiency. A pharmacological approach was used in Sox17 deficiency mice for therapeutic implication.

Measurement and Main Results

SOX17 expression was downregulated in the lungs and pulmonary ECs of IPAH patients. Mice with Tie2Cre mediated Sox17 knockdown and EC-specific Sox17 deletion developed spontaneously mild PH. Loss of endothelial Sox17 in EC exacerbated hypoxia-induced PH in mice. Loss of SOX17 in lung ECs induced endothelial dysfunctions including upregulation of cell cycle programming, proliferative and anti-apoptotic phenotypes, augmentation of paracrine effect on pulmonary arterial smooth muscle cells, impaired cellular junction, and BMP signaling. E2F Transcription Factor 1 (E2F1) signaling was shown to mediate the SOX17 deficiency-induced EC dysfunction and PH development.

Conclusions

Our study demonstrated that endothelial SOX17 deficiency induces PH through E2F1 and targeting E2F1 signaling represents a promising approach in PAH patients.

Sox17 mediates adult arterial endothelial cell adaptation to hemodynamics

Sox17 is a critical regulator of arterial identity during early embryonic vascular development. However, its role in adult endothelial cells (ECs) are not fully understood. Sox17 is highly expressed in arterial ECs but not in venous ECs throughout embryonic development to adulthood suggesting that it may play a functional role in adult arteries. Here, we investigated Sox17 mediated phenotypical changes in adult ECs. To precisely control the temporal expression level of Sox17, we designed a tetracycline-inducible lentiviral gene expression system to express Sox17 selectively in cultured venous ECs. We confirmed that Sox17-induced ECs exhibit a gene profile favoring arterial and tip cell identity. Furthermore, in comparison to control ECs, Sox17-activated ECs under shear leads to greater expression of arterial markers and suppression of venous identity. These data suggest that Sox17 enables greater hemodynamic adaptability of ECs in response to fluid shear stress. Here, we also demonstrate key morphogenic behaviors of Sox17-mediated ECs. In both vasculogenic and angiogenic 3D fibrin gel studies, Sox17-mediated ECs prefer to form cohesive vessels with one another while interfering the vessel formation of the control ECs. Sox17-mediated ECs elicit hyper-sprouting behavior in the presence of pericytes but not fibroblasts, suggesting Sox17 mediated sprouting frequency is dependent on supporting cell type. Using a microfluidic chip, we also show that Sox17-mediated ECs maintain thinner diameter vessels that do not widen under interstitial flow like the control ECs. Taken together, these data showed that Sox17 mediated EC gene expression and phenotypical changes are highly modulated in the context of biomechanical stimuli, suggesting Sox17 plays a role in regulating the arterial ECs adaptability under arterial hemodynamics as well as tip cells behavior during angiogenesis and vasculogenesis. The results from this study may be valuable in improving vein graft adaptation to arterial hemodynamics and bioengineering microvasculature for tissue engineering applications.

Surfing on the waves of the human γδ T cell ontogenic sea

While γδ T cells are present virtually in all vertebrates, there is a remarkable lack of conservation of the TRG and TRD loci underlying the generation of the γδ T cell receptor (TCR), which is associated with the generation of species-specific γδ T cells. A prominent example is the human phosphoantigen-reactive Vγ9Vδ2 T cell subset that is absent in mice. Murine γδ thymocyte cells were among the first immune cells identified to follow a wave-based layered development during embryonic and early life, and since this initial observation, in-depth insight has been obtained in their thymic ontogeny. By contrast, less is known about the development of human γδ T cells, especially regarding the generation of γδ thymocyte waves. Here, after providing an overview of thymic γδ wave generation in several vertebrate classes, we review the evidence for γδ waves in the human fetal thymus, where single-cell technologies have allowed the breakdown of human γδ thymocytes into functional waves with important TCR associations. Finally, we discuss the possible mechanisms contributing to the generation of waves of γδ thymocytes and their possible significance in the periphery.

The Role of SOX Transcription Factors in Ageing and Age-Related Diseases

The quest for eternal youth and immortality is as old as humankind. Ageing is an inevitable physiological process accompanied by many functional declines that are driving factors for age-related diseases. Stem cell exhaustion is one of the major hallmarks of ageing. The SOX transcription factors play well-known roles in self-renewal and differentiation of both embryonic and adult stem cells. As a consequence of ageing, the repertoire of adult stem cells present in various organs steadily declines, and their dysfunction/death could lead to reduced regenerative potential and development of age-related diseases. Thus, restoring the function of aged stem cells, inducing their regenerative potential, and slowing down the ageing process are critical for improving the health span and, consequently, the lifespan of humans. Reprograming factors, including SOX family members, emerge as crucial players in rejuvenation. This review focuses on the roles of SOX transcription factors in stem cell exhaustion and age-related diseases, including neurodegenerative diseases, visual deterioration, chronic obstructive pulmonary disease, osteoporosis, and age-related cancers. A better understanding of the molecular mechanisms of ageing and the roles of SOX transcription factors in this process could open new avenues for developing novel strategies that will delay ageing and prevent age-related diseases.

Loss-of-function mutations of SOX17 lead to YAP/TEAD activation-dependent malignant transformation in endometrial cancer

Aberrant hyperactivation of the Hippo pathway effector YAP/TEAD complex causes tissue overgrowth and tumorigenesis in various cancers, including endometrial cancer (EC). The transcription factor SOX17 (SRY [sex-determining region Y]-box 17) is frequently mutated in EC; however, SOX17 mutations are rare in other cancer types. The molecular mechanisms underlying SOX17 mutation-induced EC tumorigenesis remain poorly understood. Here, we demonstrate that SOX17 serves as a tumor suppressor to restrict the proliferation, migration, invasion, and anchorage-independent growth of EC cells, partly by suppressing the transcriptional outputs of the Hippo-YAP/TEAD pathway. SOX17 binds to TEAD transcription factors through its HMG domain and attenuates the DNA-binding ability of TEAD. SOX17 loss by inactivating mutations leads to the malignant transformation of EC cells, which can be reversed by small-molecule inhibitors of YAP/TEAD or cabozantinib, an FDA-approved drug targeting the YAP/TEAD transcriptional target AXL. Our findings reveal novel molecular mechanisms underlying Hippo-YAP/TEAD pathway-driven EC tumorigenesis, and suggest potential therapeutic strategies targeting the Hippo-YAP/TEAD pathway in SOX17-mutated EC.

SOX17-positive rete testis epithelium is required for Sertoli valve formation and normal spermiogenesis in the male mouse

Seminiferous tubules (STs) in the mammalian testes are connected to the rete testis (RT) via a Sertoli valve (SV). Spermatozoa produced in the STs are released into the tubular luminal fluid and passively transported through the SV into the RT. However, the physiological functions of the RT and SV remain unclear. Here, we identified the expression of Sox17 in RT epithelia. The SV valve was disrupted before puberty in RT-specific Sox17 conditional knockout (Sox17-cKO) male mice. This induced a backflow of RT fluid into the STs, which caused aberrant detachment of immature spermatids. RT of Sox17-cKO mice had reduced expression levels of various growth factor genes, which presumably support SV formation. When transplanted next to the Sox17⁺ RT, Sertoli cells of Sox17-cKO mice reconstructed the SV and supported proper spermiogenesis in the STs. This study highlights the novel and unexpected modulatory roles of the RT in SV valve formation and spermatogenesis in mouse testes, as a downstream action of Sox17.

Temporal molecular program of human hematopoietic stem and progenitor cells after birth

Hematopoietic stem and progenitor cells (HSPCs) give rise to the blood system and maintain hematopoiesis throughout the human lifespan. Here, we report a transcriptional census of human bone-marrow-derived HSPCs from the neonate, infant, child, adult, and aging stages, showing two subpopulations of multipotent progenitors separated by CD52 expression. From birth to the adult stage, stem and multipotent progenitors shared similar transcriptional alterations, and erythroid potential was enhanced after the infant stage. By integrating transcriptome, chromatin accessibility, and functional data, we further showed that aging hematopoietic stem cells (HSCs) exhibited a bias toward megakaryocytic differentiation. Finally, in comparison with the HSCs from the cord blood, neonate bone-marrow-derived HSCs were more quiescent and had higher long-term regeneration capability and durable self-renewal. Taken together, this work provides an integral transcriptome landscape of HSPCs and identifies their dynamics in post-natal steady-state hemopoiesis, thereby helping explore hematopoiesis in development and diseases.

Early microbial exposure shapes adult immunity by altering CD8+ T cell development

Microbial exposure during development can elicit long-lasting effects on the health of an individual. However, how microbial exposure in early life leads to permanent changes in the immune system is unknown. Here, we show that the microbial environment alters the set point for immune susceptibility by altering the developmental architecture of the CD8+ T cell compartment. In particular, early microbial exposure results in the preferential expansion of highly responsive fetal-derived CD8+ T cells that persist into adulthood and provide the host with enhanced immune protection against intracellular pathogens. Interestingly, microbial education of fetal-derived CD8+ T cells occurs during thymic development rather than in the periphery and involves the acquisition of a more effector-like epigenetic program. Collectively, our results provide a conceptual framework for understanding how microbial colonization in early life leads to lifelong changes in the immune system.

Genes in pediatric pulmonary arterial hypertension and the most promising BMPR2 gene therapy

Pulmonary arterial hypertension (PAH) is a rare but progressive and lethal vascular disease of diverse etiologies, mainly caused by proliferation of endothelial cells, smooth muscle cells in the pulmonary artery, and fibroblasts, which ultimately leads to right-heart hypertrophy and cardiac failure. Recent genetic studies of childhood-onset PAH report that there is a greater genetic burden in children than in adults. Since the first-identified pathogenic gene of PAH, BMPR2, which encodes bone morphogenetic protein receptor 2, a receptor in the transforming growth factor-β superfamily, was discovered, novel causal genes have been identified and substantially sharpened our insights into the molecular genetics of childhood-onset PAH. Currently, some newly identified deleterious genetic variants in additional genes implicated in childhood-onset PAH, such as potassium channels (KCNK3) and transcription factors (TBX4 and SOX17), have been reported and have greatly updated our understanding of the disease mechanism. In this review, we summarized and discussed the advances of genetic variants underlying childhood-onset PAH susceptibility and potential mechanism, and the most promising BMPR2 gene therapy and gene delivery approaches to treat childhood-onset PAH in the future.

Prostate Cancer Stem Cells: The Role of CD133

Prostate cancer stem cells (PCSCs), possessing self-renewal properties and resistance to anticancer treatment, are possibly the leading cause of distant metastasis and treatment failure in prostate cancer (PC). CD133 is one of the most well-known and valuable cell surface markers of cancer stem cells (CSCs) in many cancers, including PC. In this article, we focus on reviewing the role of CD133 in PCSC. Any other main stem cell biomarkers in PCSC reported from key publications, as well as about vital research progress of CD133 in CSCs of different cancers, will be selectively reviewed to help us inform the main topic.

Lessons from early life: understanding development to expand stem cells and treat cancers

Haematopoietic stem cell (HSC) self-renewal is a process that is essential for the development and homeostasis of the blood system. Self-renewal expansion divisions, which create two daughter HSCs from a single parent HSC, can be harnessed to create large numbers of HSCs for a wide range of cell and gene therapies, but the same process is also a driver of the abnormal expansion of HSCs in diseases such as cancer. Although HSCs are first produced during early embryonic development, the key stage and location where they undergo maximal expansion is in the foetal liver, making this tissue a rich source of data for deciphering the molecules driving HSC self-renewal. Another equally interesting stage occurs post-birth, several weeks after HSCs have migrated to the bone marrow, when HSCs undergo a developmental switch and adopt a more dormant state. Characterising these transition points during development is key, both for understanding the evolution of haematological malignancies and for developing methods to promote HSC expansion. In this Spotlight article, we provide an overview of some of the key insights that studying HSC development have brought to the fields of HSC expansion and translational medicine, many of which set the stage for the next big breakthroughs in the field.

Differential regulation of alternate promoter regions in Sox17 during endodermal and vascular endothelial development

Sox17 gene expression is essential for both endothelial and endodermal cell differentiation. To better understand the genetic basis for the expression of multiple Sox17 mRNA forms, we identified and performed CRISPR/Cas9 mutagenesis of two evolutionarily conserved promoter regions (CRs). The deletion of the upstream and endothelial cell-specific CR1 caused only a modest increase in lympho-vasculogenesis likely via reduced Notch signaling downstream of SOX17. In contrast, the deletion of the downstream CR2 region, which functions in both endothelial and endodermal cells, impairs both vascular and endodermal development causing death by embryonic day 12.5. Analyses of 3D chromatin looping, transcription factor binding, histone modification, and chromatin accessibility data at the Sox17 locus and surrounding region further support differential regulation of the two promoters during the development.

Engineering chimeric antigen receptor neutrophils from human pluripotent stem cells for targeted cancer immunotherapy

Neutrophils, the most abundant white blood cells in circulation, are closely related to cancer development and progression. Healthy primary neutrophils present potent cytotoxicity against various cancer cell lines through direct contact and via generation of reactive oxygen species. However, due to their short half-life and resistance to genetic modification, neutrophils have not yet been engineered with chimeric antigen receptors (CARs) to enhance their antitumor cytotoxicity for targeted immunotherapy. Here, we genetically engineered human pluripotent stem cells with synthetic CARs and differentiated them into functional neutrophils by implementing a chemically defined platform. The resulting CAR neutrophils present superior and specific cytotoxicity against tumor cells both in vitro and in vivo. Collectively, we established a robust platform for massive production of CAR neutrophils, paving the way to myeloid cell-based therapeutic strategies that would boost current cancer-treatment approaches.

Neutrophils are important innate immune cells that mediate both protumor and antitumor activities. Chang et al. genetically engineer human pluripotent stem cells to produce chimeric antigen receptor (CAR) neutrophils that display superior antitumor activities and improve survival in an in situ glioblastoma xenograft model.

A SOX17-PDGFB signaling axis regulates aortic root development

Developmental etiologies causing complex congenital aortic root abnormalities are unknown. Here we show that deletion of Sox17 in aortic root endothelium in mice causes underdeveloped aortic root leading to a bicuspid aortic valve due to the absence of non-coronary leaflet and mispositioned left coronary ostium. The respective defects are associated with reduced proliferation of non-coronary leaflet mesenchyme and aortic root smooth muscle derived from the second heart field cardiomyocytes. Mechanistically, SOX17 occupies a Pdgfb transcriptional enhancer to promote its transcription and Sox17 deletion inhibits the endothelial Pdgfb transcription and PDGFB growth signaling to the non-coronary leaflet mesenchyme. Restoration of PDGFB in aortic root endothelium rescues the non-coronary leaflet and left coronary ostium defects in Sox17 nulls. These data support a SOX17-PDGFB axis underlying aortic root development that is critical for aortic valve and coronary ostium patterning, thereby informing a potential shared disease mechanism for concurrent anomalous aortic valve and coronary arteries.

Chemically-defined generation of human hemogenic endothelium and definitive hematopoietic progenitor cells

Human hematopoietic stem cells (HSCs), which arise from aorta-gonad-mesonephros (AGM), are widely used to treat blood diseases and cancers. However, a technique for their robust generation in vitro is still missing. Here we show temporal manipulation of Wnt signaling is sufficient and essential to induce AGM-like hematopoiesis from human pluripotent stem cells. TGFβ inhibition at the stage of aorta-like SOX17⁺CD235a^- hemogenic endothelium yielded AGM-like hematopoietic progenitors, which closely resembled primary cord blood HSCs at the transcriptional level and contained diverse lineage-primed progenitor populations via single cell RNA-sequencing analysis. Notably, the resulting definitive cells presented lymphoid and myeloid potential in vitro; and could home to a definitive hematopoietic site in zebrafish and rescue bloodless zebrafish after transplantation. Engraftment and multilineage repopulating activities were also observed in mouse recipients. Together, our work provided a chemically-defined and feeder-free culture platform for scalable generation of AGM-like hematopoietic progenitor cells, leading to enhanced production of functional blood and immune cells for various therapeutic applications.

The Opportunity of Proteomics to Advance the Understanding of Intra- and Extracellular Regulation of Malignant Hematopoiesis

Fetal and adult hematopoiesis are regulated by largely distinct sets of cell-intrinsic gene regulatory networks as well as extracellular cues in their respective microenvironment. These ontogeny-specific programs drive hematopoietic stem and progenitor cells (HSPCs) in fetus and adult to divergent susceptibility to initiation and progression of hematological malignancies, such as leukemia. Elucidating how leukemogenic hits disturb the intra- and extracellular programs in HSPCs along ontogeny will provide a better understanding of the causes for age-associated differences in malignant hematopoiesis and facilitate the improvement of strategies for prevention and treatment of pediatric and adult acute leukemia. Here, we review current knowledge of the intrinsic and extrinsic programs regulating normal and malignant hematopoiesis, with a particular focus on the differences between infant and adult acute leukemia. We discuss the recent advances in mass spectrometry-based proteomics and its opportunity for resolving the interplay of cell-intrinsic and niche-associated factors in regulating malignant hematopoiesis.

Hematopoietic stem cells temporally transition to thrombopoietin dependence in the fetal liver

Tissue stem cells temporally change intrinsic mechanisms to meet physiological demands. However, little is known whether and how stem cells rely on distinct extrinsic maintenance mechanisms over time. Here, we found that hematopoietic stem cells (HSCs) temporally transition to depend on thrombopoietin (TPO), a key extrinsic factor, from E16.5 onward in the developing liver. Deletion of Tpo reduced mTOR activity, induced differentiation gene expression, and preferentially depleted metabolically active HSCs. Ectopic activation of the JAK2 or MAPK pathway did not rescue HSCs in Tpo^-/- mice. Enforced activation of the mTOR pathway by conditionally deleting Tsc1 significantly rescued HSCs and their gene expression in Tpo^-/- mice. Lin28b intrinsically promoted mTOR activation in HSCs, and its expression diminished over time. Conditional deletion of Lin28b further reduced mTOR activity and strongly exacerbated HSC depletion in Tpo^-/- mice. Therefore, HSCs temporally transition from intrinsic LIN28B-dependent to extrinsic TPO-dependent maintenance in the developing liver.

Disruption of thymic central tolerance by infection with murine roseolovirus induces autoimmune gastritis

Infections with herpesviruses, including human roseoloviruses, have been proposed to cause autoimmune disease, but defining a causal relationship and mechanism has been difficult due to the ubiquitous nature of infection and development of autoimmunity long after acute infection. Murine roseolovirus (MRV) is highly related to human roseoloviruses. Herein we show that neonatal MRV infection induced autoimmune gastritis (AIG) in adult mice in the absence of ongoing infection. MRV-induced AIG was dependent on replication during the neonatal period and was CD4+ T cell and IL-17 dependent. Moreover, neonatal MRV infection was associated with development of a wide array of autoantibodies in adult mice. Finally, neonatal MRV infection reduced medullary thymic epithelial cell numbers, thymic dendritic cell numbers, and thymic expression of AIRE and tissue-restricted antigens, in addition to increasing thymocyte apoptosis at the stage of negative selection. These findings strongly suggest that infection with a roseolovirus early in life results in disruption of central tolerance and development of autoimmune disease.

Slc20a1b is essential for hematopoietic stem/progenitor cell expansion in zebrafish

Hematopoietic stem and progenitor cells (HSPCs) are able to self-renew and can give rise to all blood lineages throughout their lifetime, yet the mechanisms regulating HSPC development have yet to be discovered. In this study, we characterized a hematopoiesis defective zebrafish mutant line named smu07, which was obtained from our previous forward genetic screening, and found the HSPC expansion deficiency in the mutant. Positional cloning identified that slc20a1b, which encodes a sodium phosphate cotransporter, contributed to the smu07 blood phenotype. Further analysis demonstrated that mutation of slc20a1b affects HSPC expansion through cell cycle arrest at G2/M phases in a cell-autonomous manner. Our study shows that slc20a1b is a vital regulator for HSPC proliferation in zebrafish early hematopoiesis and provides valuable insights into HSPC development.

Transcriptional reprogramming in neonatal hematopoietic stem and progenitor cells

Hematopoietic stem cells (HSCs) and lineage-committed hematopoietic progenitor cells (HPCs) undergo profound shifts in gene expression during the neonatal and juvenile stages of life. Temporal changes in HSC/HPC gene expression underlie concomitant changes in self-renewal capacity, lineage biases, and hematopoietic output. Moreover, they can modify disease phenotypes. For example, childhood leukemias have distinct driver mutation profiles relative to adult leukemias, and they may arise from distinct cells of origin. The putative relationship between neonatal HSC/HPC ontogeny and childhood blood disorders highlights the importance of understanding how, at a mechanistic level, HSCs transition from fetal to adult transcriptional states. In this perspective piece, we summarize recent work indicating that the transition is uncoordinated and imprecisely timed. We discuss implications of these findings, including mechanisms that might enable neonatal HSCs and HPCs to acquire adultlike properties over a drawn-out period, in lieu of precise gene regulatory networks. The transition from fetal to adult transcriptional programs coincides with a pulse of type I interferon signaling that activates many genes associated with the adultlike state. This pulse may sensitize HSCs/HPCs to mutations that drive leukemogenesis shortly after birth. If we can understand how developmental switches modulate HSC and HPC fate after birth-both under normal circumstances and in the setting of disease-causing mutations-we can potentially reprogram these switches to treat or prevent childhood leukemias.

The Fetal-to-Adult Hematopoietic Stem Cell Transition and its Role in Childhood Hematopoietic Malignancies

As with most organ systems that undergo continuous generation and maturation during the transition from fetal to adult life, the hematopoietic and immune systems also experience dynamic changes. Such changes lead to many unique features in blood cell function and immune responses in early childhood. The blood cells and immune cells in neonates are a mixture of fetal and adult origin due to the co-existence of both fetal and adult types of hematopoietic stem cells (HSCs) and progenitor cells (HPCs). Fetal blood and immune cells gradually diminish during maturation of the infant and are almost completely replaced by adult types of cells by 3 to 4 weeks after birth in mice. Such features in early childhood are associated with unique features of hematopoietic and immune diseases, such as leukemia, at these developmental stages. Therefore, understanding the cellular and molecular mechanisms by which hematopoietic and immune changes occur throughout ontogeny will provide useful information for the study and treatment of pediatric blood and immune diseases. In this review, we summarize the most recent studies on hematopoietic initiation during early embryonic development, the expansion of both fetal and adult types of HSCs and HPCs in the fetal liver and fetal bone marrow stages, and the shift from fetal to adult hematopoiesis/immunity during neonatal/infant development. We also discuss the contributions of fetal types of HSCs/HPCs to childhood leukemias.

Autophagy is dispensable for the maintenance of hematopoietic stem cells in neonates

Hematopoietic stem cells (HSCs) undergo self-renewal or differentiation to sustain lifelong hematopoiesis. HSCs are preserved in quiescence with low mitochondrial activity. Recent studies indicate that autophagy contributes to HSC quiescence through suppressing mitochondrial metabolism. However, it remains unclear whether autophagy is involved in the regulation of neonatal HSCs, which proliferate actively. In this study, we clarified the role of autophagy in neonatal HSCs using 2 types of autophagy-related gene 7 (Atg7)-conditional knockout mice: Mx1-Cre inducible system and Vav-Cre system. Atg7-deficient HSCs exhibited excess cell divisions with enhanced mitochondrial metabolism, leading to bone marrow failure at adult stage. However, Atg7 deficiency minimally affected hematopoiesis and metabolic state in HSCs at neonatal stage. In addition, Atg7-deficient neonatal HSCs exhibited long-term reconstructing activity, equivalent to wild-type neonatal HSCs. Taken together, autophagy is dispensable for stem cell function and hematopoietic homeostasis in neonates and provide a novel aspect into the role of autophagy in the HSC regulation.

SOX17 Antagonizes the WNT Signaling Pathway and is Epigenetically Inactivated in Clear-Cell Renal Cell Carcinoma

Background

SRY-box containing gene 17 (SOX17) was reported to be a candidate tumor suppressor gene in multiple tumors. Little is known about its role in clear-cell renal cell carcinoma (ccRCC). This study aims to identify the epigenetic regulation and tumor-suppressive function of SOX17 in ccRCC.

Patients and Methods

Fifty-five human ccRCC tissue samples, ten adjacent non-malignant kidney tissue samples, 20 paired paraffin section tissues and seven RCC cell lines were obtained. Immunohistochemistry (IHC) and real-time PCR were used to examine the expression of the target genes at the mRNA and protein levels. The methylation of SOX17 was analyzed using methylation-specific PCR (MSP) and bisulfite genomic sequencing (BGS) assay. The functions of SOX17 were examined by using CCK8, colony formation, wound healing assay and Matrigel invasion assays. Luciferase assay was used to analyze the function of SOX17 in the WNT signaling pathway.

Results

We investigated the SOX17 expression in ccRCC tissues and adjacent non-malignant kidney tissues using PCR and IHC. The expression of SOX17 was lower in ccRCC tissues. Next, we analyzed the DNA promoter methylation of SOX17 in 55 human ccRCC tissues, 10 adjacent non-malignant kidney tissues and RCC cell lines using MSP. DNA methylation of the SOX17 promoter region occurred in 60% of ccRCC tissues and 10% of adjacent non-malignant kidney tissues. In vitro experiments showed that SOX17 suppressed the proliferation of RCC cells. Furthermore, SOX17 inhibited the migration of RCC cells as shown in the wound healing and migration assays. In addition, we found that SOX17 overexpression affected the WNT signaling pathway by downregulating c-myc and cyclinD1.

Conclusion

In summary, our study showed that SOX17 is downregulated in ccRCC and the loss of SOX17 expression is regulated via epigenetic mechanisms in ccRCC. In addition, SOX17 negatively regulates the WNT signaling pathway and function as a tumor suppressor in ccRCC.

Defining the Emerging Blood System During Development at Single-Cell Resolution

Developmental hematopoiesis differs from adult and is far less described. In the developing embryo, waves of lineage-restricted blood precede the ultimate emergence of definitive hematopoietic stem cells (dHSCs) capable of maintaining hematopoiesis throughout life. During the last two decades, the advent of single-cell genomics has provided tools to circumvent previously impeding characteristics of embryonic hematopoiesis, such as cell heterogeneity and rare cell states, allowing for definition of lineage trajectories, cellular hierarchies, and cell-type specification. The field has rapidly advanced from microfluidic platforms and targeted gene expression analysis, to high throughput unbiased single-cell transcriptomic profiling, single-cell chromatin analysis, and cell tracing-offering a plethora of tools to resolve important questions within hematopoietic development. Here, we describe how these technologies have been implemented to address a wide range of aspects of embryonic hematopoiesis ranging from the gene regulatory network of dHSC formation via endothelial to hematopoietic transition (EHT) and how EHT can be recapitulated in vitro, to hematopoietic trajectories and cell fate decisions. Together, these studies have important relevance for regenerative medicine and for our understanding of genetic blood disorders and childhood leukemias.

Lithium Directs Embryonic Stem Cell Differentiation Into Hemangioblast-Like Cells

Definitive hematopoietic stem cells (HSCs) derive from specialized regions of the endothelium known as the hemogenic endothelium (HE) during embryonic developmental processes. This knowledge opens up new possibilities for designing new strategies to obtain HSCs in vitro from pluripotent stem cells (PSCs). Previous advances in this field show that the Wnt/β-catenin signaling pathway plays a crucial role in PSC-derived HSC formation. In this work, lithium, a GSK3 inhibitor, is identified as an element capable of stabilizing β-catenin and inducing embryonic stem cells (ESCs) differentiation in hemangioblast-like cells, highly consistent with the role of Wnt agonists on ESC differentiation. ESCs treated with 10 mm lithium express CD31+, SCA-1+, Nkx2-5+, CD34+, and FLK1+ cells characteristic of the hemangioblast cells that precede HE development. However, 10 mm Li treated cells remain arrested in a hemangioblast-like phase, which switched into the expression of HE markers after stimulation with maturation medium. The ability of lithium-treated ESCs to further derive into HE is confirmed after defined maturation, resulting in a rapid increase in cells positive for the HE markers RUNX1 and SOX17. The results represent a novel strategy for generating HSC precursors in vitro as a multipotent source of stem cells for blood disease therapies.