LMO2 is required for TAL1 DNA binding activity and initiation of definitive haematopoiesis at the haemangioblast stage

Gastrulation-stage gene expression in Nipbl+/- mouse embryos foreshadows the development of syndromic birth defects

In animal models, Nipbl deficiency phenocopies gene expression changes and birth defects seen in Cornelia de Lange syndrome, the most common cause of which is Nipbl haploinsufficiency. Previous studies in Nipbl+/- mice suggested that heart development is abnormal as soon as cardiogenic tissue is formed. To investigate this, we performed single-cell RNA sequencing on wild-type and Nipbl+/- mouse embryos at gastrulation and early cardiac crescent stages. Nipbl+/- embryos had fewer mesoderm cells than wild-type and altered proportions of mesodermal cell subpopulations. These findings were associated with underexpression of genes implicated in driving specific mesodermal lineages. In addition, Nanog was found to be overexpressed in all germ layers, and many gene expression changes observed in Nipbl+/- embryos could be attributed to Nanog overexpression. These findings establish a link between Nipbl deficiency, Nanog overexpression, and gene expression dysregulation/lineage misallocation, which ultimately manifest as birth defects in Nipbl+/- animals and Cornelia de Lange syndrome.

Orphan Nuclear Receptor Family 4A (NR4A) Members NR4A2 and NR4A3 Selectively Modulate Elements of the Monocyte Response to Buffered Hypercapnia

Hypercapnia occurs when the partial pressure of carbon dioxide (CO2) in the blood exceeds 45 mmHg. Hypercapnia is associated with several lung pathologies and is transcriptionally linked to suppression of immune and inflammatory signalling through poorly understood mechanisms. Here we propose Orphan Nuclear Receptor Family 4A (NR4A) family members NR4A2 and NR4A3 as potential transcriptional regulators of the cellular response to hypercapnia in monocytes. Using a THP-1 monocyte model, we investigated the sensitivity of NR4A family members to CO2 and the impact of depleting NR4A2 and NR4A3 on the monocyte response to buffered hypercapnia (10% CO2) using RNA-sequencing. We observed that NR4A2 and NR4A3 are CO2-sensitive transcription factors and that depletion of NR4A2 and NR4A3 led to reduced CO2-sensitivity of mitochondrial and heat shock protein (Hsp)-related genes, respectively. Several CO2-sensitive genes were, however, refractory to depletion of NR4A2 and NR4A3, indicating that NR4As regulate certain elements of the cellular response to buffered hypercapnia but that other transcription factors also contribute. Bioinformatic analysis of conserved CO2-sensitive genes implicated several novel putative CO2-sensitive transcription factors, of which the ETS Proto-Oncogene 1 Transcription Factor (ETS-1) was validated to show increased nuclear expression in buffered hypercapnia. These data give significant insights into the understanding of immune responses in patients experiencing hypercapnia.

Gastrulation-stage gene expression in Nipbl +/- mouse embryos foreshadows the development of syndromic birth defects

In animal models, Nipbl-deficiency phenocopies gene expression changes and birth defects seen in Cornelia de Lange Syndrome (CdLS), the most common cause of which is Nipbl-haploinsufficiency. Previous studies in Nipbl+/- mice suggested that heart development is abnormal as soon as cardiogenic tissue is formed. To investigate this, we performed single-cell RNA-sequencing on wildtype (WT) and Nipbl+/- mouse embryos at gastrulation and early cardiac crescent stages. Nipbl+/- embryos had fewer mesoderm cells than WT and altered proportions of mesodermal cell subpopulations. These findings were associated with underexpression of genes implicated in driving specific mesodermal lineages. In addition, Nanog was found to be overexpressed in all germ layers, and many gene expression changes observed in Nipbl+/- embryos could be attributed to Nanog overexpression. These findings establish a link between Nipbl-deficiency, Nanog overexpression, and gene expression dysregulation/lineage misallocation, which ultimately manifest as birth defects in Nipbl+/- animals and CdLS.

Teaser

Gene expression changes during gastrulation of Nipbl-deficient mice shed light on early origins of structural birth defects.

Identifying a novel role for the master regulator Tal1 in the Endothelial to Hematopoietic Transition

Progress in the generation of Hematopoietic Stem and Progenitor Cells (HSPCs) in vitro and ex vivo has been built on the knowledge of developmental hematopoiesis, underscoring the importance of understanding this process. HSPCs emerge within the embryonic vasculature through an Endothelial-to-Hematopoietic Transition (EHT). The transcriptional regulator Tal1 exerts essential functions in the earliest stages of blood development, but is considered dispensable for the EHT. Nevertheless, Tal1 is expressed with its binding partner Lmo2 and it homologous Lyl1 in endothelial and transitioning cells at the time of EHT. Here, we investigated the function of these genes using a mouse embryonic-stem cell (mESC)-based differentiation system to model hematopoietic development. We showed for the first time that the expression of TAL1 in endothelial cells is crucial to ensure the efficiency of the EHT process and a sustained hematopoietic output. Our findings uncover an important function of Tal1 during the EHT, thus filling the current gap in the knowledge of the role of this master gene throughout the whole process of hematopoietic development.

Hematopoietic stem cells characteristics: from isolation to transplantation

Abstract:

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

Mapping Human Pluripotent Stem Cell-derived Erythroid Differentiation by Single-cell Transcriptome Analysis

There is an imbalance between the supply and demand of functional red blood cells (RBCs) in clinical applications. This imbalance can be addressed by regenerating RBCs using several in vitro methods. Induced pluripotent stem cells (iPSCs) can handle the low supply of cord blood and the ethical issues in embryonic stem cell research and provide a promising strategy to eliminate immune rejection. However, no complete single-cell level differentiation pathway exists for the iPSC-derived RBC differentiation system. In this study, we used iPSC line BC1 to establish a RBCs regeneration system. The 10× genomics single-cell transcriptome platform was used to map the cell lineage and differentiation trajectories on day 14 of the regeneration system. We observed that iPSCs differentiation was not synchronized during embryoid body (EB) culture. The cells (day 14) mainly consisted of mesodermal and various blood cells, similar to the yolk sac hematopoiesis. We identified six cell classifications and characterized the regulatory transcription factors (TFs) networks and cell-cell contacts underlying the system. iPSCs undergo two transformations during the differentiation trajectory, accompanied by the dynamic expression of cell adhesion molecules and estrogen-responsive genes. We identified different stages of erythroid cells, such as burst-forming unit erythroid (BFU-E) and orthochromatic erythroblasts (ortho-E), and found that the regulation of TFs (e.g., TFDP1 and FOXO3) is erythroid-stage specific. Immune erythroid cells were identified in our system. This study provides systematic theoretical guidance for optimizing the iPSCs-derived RBCs differentiation system, and this system is a useful model for simulating in vivo hematopoietic development and differentiation.

FGF primes angioblast formation by inducing ETV2 and LMO2 via FGFR1/BRAF/MEK/ERK

It is critical to specify a signal that directly drives the transition that occurs between cell states. However, such inferences are often confounded by indirect intercellular communications or secondary transcriptomic changes due to primary transcription factors. Although FGF is known for its importance during mesoderm-to-endothelium differentiation, its specific role and signaling mechanisms are still unclear due to the confounding factors referenced above. Here, we attempted to minimize the secondary artifacts by manipulating FGF and its downstream mediators with a short incubation time before sampling and protein-synthesis blockage in a low-density angioblastic/endothelial differentiation system. In less than 8 h, FGF started the conversion of KDRlow/PDGFRAlow nascent mesoderm into KDRhigh/PDGFRAlow angioblasts, and the priming by FGF was necessary to endow endothelial formation 72 h later. Further, the angioblastic conversion was mediated by the FGFR1/BRAF/MEK/ERK pathway in mesodermal cells. Finally, two transcription factors, ETV2 and LMO2, were the early direct functional responders downstream of the FGF pathway, and ETV2 alone was enough to complement the absence of FGF. FGF's selective role in mediating the first-step, angioblastic conversion from mesoderm-to-endothelium thus allows for refined control over acquiring and manipulating angioblasts. The noise-minimized differentiation/analysis platform presented here is well-suited for studies on the signaling switches of other mesodermal-lineage fates as well.

Hematopoietic stem cells: self-renewal and expansion

: Hematopoietic stem cells (HSCs) are a unique population of cells with the remarkable ability to replenish themselves through self-renewal and to give rise to differentiated cell lineages. Though having been discovered more than 50 years ago, and having been widely used in bone marrow transplantation to treat blood disorders including leukemia, expansion of HSCs remains an unmet task, thus affecting its more effective usage in clinical practice.

PURPOSE OF REVIEW

The purpose of this review article is to summarize past efforts in ex-vivo HSC expansion and to compare recent advances in expanding murine and human HSCs by targeting the N-methyladenosine (mA) pathway.

RECENT FINDINGS

Unlike past many efforts that mainly target single or limited pathways and often lead to lineage bias or expansion of progenitor cells or limited long-term HSCs (LT-HSCs), the blocking the degradation of mA pathway has an advantage of stabilizing hundreds of key factors required for maintaining HSCs, thus resulting in expansion of functional LT-HSCs.

SUMMARY

The new approach of targeting the mA pathway has a promising application in clinical HSC-based transplantation.

Lineage Decision-Making within Normal Haematopoietic and Leukemic Stem Cells

To produce the wide range of blood and immune cell types, haematopoietic stem cells can “choose” directly from the entire spectrum of blood cell fate-options. Affiliation to a single cell lineage can occur at the level of the haematopoietic stem cell and these cells are therefore a mixture of some pluripotent cells and many cells with lineage signatures. Even so, haematopoietic stem cells and their progeny that have chosen a particular fate can still “change their mind” and adopt a different developmental pathway. Many of the leukaemias arise in haematopoietic stem cells with the bulk of the often partially differentiated leukaemia cells belonging to just one cell type. We argue that the reason for this is that an oncogenic insult to the genome “hard wires” leukaemia stem cells, either through development or at some stage, to one cell lineage. Unlike normal haematopoietic stem cells, oncogene-transformed leukaemia stem cells and their progeny are unable to adopt an alternative pathway.

Inducible Forward Programming of Human Pluripotent Stem Cells to Hemato-endothelial Progenitor Cells with Hematopoietic Progenitor Potential

Induced pluripotent stem cells (iPSCs) offer a promising platform to model early embryonic developmental processes, to create disease models that can be evaluated by drug screens as well as proof-of-concept experiments for regenerative medicine. However, generation of iPSC-derived hemato-endothelial and hematopoietic progenitor cells for these applications is challenging due to variable and limited cell numbers, which necessitates enormous up-scaling or development of demanding protocols. Here, we unravel the function of key transcriptional regulators SCL, LMO2, GATA2, and ETV2 (SLGE) on early hemato-endothelial specification and establish a fully inducible and stepwise hemato-endothelial forward programming system based on SLGE-regulated overexpression. Regulated induction of SLGE in stable SLGE-iPSC lines drives very efficient generation of large numbers of hemato-endothelial progenitor cells (CD144⁺/CD73^–), which produce hematopoietic progenitor cells (CD45⁺/CD34⁺/CD38^–/CD45RA⁻/CD90⁺/CD49f⁺) through a gradual process of endothelial-to-hematopoietic transition (EHT).

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Inducible and robust hemato-endothelial forward programming of human iPSCs

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Efficient, scalable generation of hemato-endothelial progenitor cells

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Production of HPCs with HSC-like immunophenotype and multi-lineage potential

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Whole transcriptome screen for potential regulators of definitive hematopoiesis

LMO2 gene deletions significantly worsen the prognosis of Wilms’ tumor development in patients with WAGR syndrome

WAGR syndrome (OMIM #194072) is a rare genetic disorder that consists of development of Wilms’ tumor (nephroblastoma), aniridia, genitourinary anomalies and intellectual disability (mental retardation). It is associated with WAGR-region deletions in the 11p13 chromosome region. Our previous study of congenital aniridia patients revealed a noticeable number of aniridia patients with WAGR-region deletions but without Wilms’ tumor in their medical history. We assessed the involvement of other neighboring genes from affected chromosome regions in the patients with and without Wilms’ tumor. Reliable confidence was obtained for the LMO2 gene, which is significantly more often deleted in patients with nephroblastoma. Thus, our study presents genetic evidence that the development of Wilms tumors in WAGR syndrome patients should be attributed to the deletion of WT1 and LMO2 rather than WT1 only.

Epigenetic dysregulation of ZEB1 is involved in LMO2-promoted T-cell acute lymphoblastic leukaemia leukaemogenesis

T-cell acute lymphoblastic leukaemia (T-ALL) is a hematological malignancy caused by the accumulation of genomic lesions that affect the development of T-cells. ZEB1, a member of zinc finger-homeodomain family transcription factor, exhibits crucial function in promoting T-cell differentiation and potentially acts as a tumor suppressor in T-ALL. However, the molecular mechanism by which ZEB1 regulates T-ALL leukaemogenesis remains obscure. Here, we showed that oncogenic LIM only 2 (LMO2) could recruit Sap18 and HDAC1 to assemble an epigenetic regulatory complex, thus inducing histone deacetylation in ZEB1 promoter and chromatin remodeling to achieve transcriptional repression. Furthermore, downregulation of ZEB1 by LMO2 complex results in an increased leukaemia stem cell (LSC) phenotype as well as unsensitivity in response to methotrexate (MTX) chemotherapy in T-ALL cells. Importantly, we demonstrated that Trichostatin A (TSA, a HDAC inhibitor) addition significantly attenuates MTX unsensitivity caused by dysfunction of LMO2/ZEB1 signaling. In conclusion, these findings have identified a molecular mechanism underlying LMO2/ZEB1-mediated leukaemogenesis, paving a way for treating T-ALL with a new strategy of epigenetic inhibitors.

Identification of Novel Hemangioblast Genes in the Early Chick Embryo

During early vertebrate embryogenesis, both hematopoietic and endothelial lineages derive from a common progenitor known as the hemangioblast. Hemangioblasts derive from mesodermal cells that migrate from the posterior primitive streak into the extraembryonic yolk sac. In addition to primitive hematopoietic cells, recent evidence revealed that yolk sac hemangioblasts also give rise to tissue-resident macrophages and to definitive hematopoietic stem/progenitor cells. In our previous work, we used a novel hemangioblast-specific reporter to isolate the population of chick yolk sac hemangioblasts and characterize its gene expression profile using microarrays. Here we report the microarray profile analysis and the identification of upregulated genes not yet described in hemangioblasts. These include the solute carrier transporters SLC15A1 and SCL32A1, the cytoskeletal protein RhoGap6, the serine protease CTSG, the transmembrane receptor MRC1, the transcription factors LHX8, CITED4 and PITX1, and the previously uncharacterized gene DIA1R. Expression analysis by in situ hybridization showed that chick DIA1R is expressed not only in yolk sac hemangioblasts but also in particular intraembryonic populations of hemogenic endothelial cells, suggesting a potential role in the hemangioblast-derived hemogenic lineage. Future research into the function of these newly identified genes may reveal novel important regulators of hemangioblast development.