Project description:Despite our growing understanding of embryonic immune development, rare early megakaryocytes (MKs) remain relatively understudied. Here we used single-cell RNA sequencing of human MKs from embryonic yolk sac (YS) and fetal liver (FL) to characterize the transcriptome, cellular heterogeneity, and developmental trajectories of early megakaryopoiesis. In the YS and FL, we found heterogeneous MK subpopulations with distinct developmental routes and patterns of gene expression that could reflect early functional specialization. Intriguingly, we identified a subpopulation of CD42b+CD14+ MKs in vivo that exhibit high expression of genes associated with immune responses and can also be derived from human embryonic stem cells (hESCs) in vitro. Furthermore, we identified THBS1 as an early marker for MK-biased embryonic endothelial cells. Overall, we provide important insights and invaluable resources for dissection of the molecular and cellular programs underlying early human megakaryopoiesis.
Project description:We newly identified prospectively-isolatable unipotent megakaryocyte progenitor population (MegP) as the major source of megakaryocytes, which emerges directly from early stage of hematopoiesis bypassing megakaryocyte-erythroid lineage bifurcation and contributes to physiological and pathological human megakaryopoiesis. To explore gene expression signature of hematopoietic stem/progenitor populrations miroarry-based whole transcriptome analysis was performed. As a result, gene expression signature of MegP clearly reflected its differentiation potential.
Project description:Background: Recent advances in single-cell techniques have provided the opportunity to finely dissect cellular heterogeneity within populations previously defined by âbulkâ assays and to uncover rare cell types. In human hematopoiesis, megakaryocytes and erythroid cells differentiate from a shared precursor, the megakaryocyte-erythroid progenitor (MEP), which remains poorly defined.Results: To clarify the cellular pathway in erythro-megakaryocyte differentiation, we correlated the surface immunophenotype, transcriptional profile and differentiation potential of individual MEP cells. Highly purified, single MEP cells (n=681) were analyzed using index fluorescence-activated cell sorting with parallel targeted transcriptional profiling of the same cells performed using a specifically designed panel of 87 genes. Differentiation potential was tested in novel, single-cell differentiation assays. Our results demonstrated that immunophenotypic MEP in fact comprise three distinct subpopulations: (1) âPre-MEPâ, enriched for erythroid/megakaryocyte progenitors but with residual myeloid differentiation capacity (2) âE-MEPâ, strongly biased towards erythroid differentiation, and (3) âMK-MEPâ, a previously undescribed, rare population of cells that are bipotent but primarily generate megakaryocytic progeny. Therefore, conventionally-defined MEP are in fact a mixed population: a minority give rise to mixed-lineage colonies while the majority of cells are transcriptionally-primed to generate exclusively single-lineage output. Conclusions: Our study clarifies the cellular hierarchy in human megakaryocyte/erythroid lineage commitment and highlights the importance of using a combination of single-cell approaches to dissect cellular heterogeneity and identify rare cell types within a population. We present a novel immunophenotyping strategy that enables the prospective identification of specific intermediate progenitor populations in erythro-megakaryopoiesis, allowing for in-depth study of disorders including inherited cytopenias, myeloproliferative disorders and erythromegakaryocytic leukemias. Multiplex RT-PCR gene expression profiling of 807 human megakaryocyte-erythroid progenitor cells (MEP) isolated from three healthy donors by apheresis following G-CSF treatment. Cells were excluded if more than 70 assays did not result in amplification or displayed Ct higer than 13 for B2M or higher than 15 for GAPDH. Furthermore cells with a mean non-dropout Ct value greater than 20 were removed. This resulted in a dataset of 681 cells, which were subsequently normalised to the mean of B2M and GAPDH expression.
Project description:Mutations in transcription factor Growth Factor Independence 1B (GFI1B) cause inherited bleedings with varying intensity possibly caused by different effects on the transcriptional function of GFI1B. We studied transcriptomic changes of normal and GFI1BT174N,H181Y,R184P,Q287* mutants in megakaryoblast MEG01 cells using RNA-sequencing. Compared to normal GFI1B each variant affected different gene modules with limited overlap between variants. Remarkably, GFI1BQ287* specifically activated a myeloid-associated gene module. Based on this finding we studied megakaryocyte differentiation using normal and GFI1BQ287* patient-derived induced pluripotent stem cells (IPSC) followed by single cell RNA-sequencing. This revealed a 45-fold decrease in the megakaryocyte/myeloid cell ratio in the GFI1BQ287* versus control condition. Moreover, myeloid specific genes were expressed within GFI1BQ287* but not normal megakaryocytes. Finally, we studied how megakaryocyte development was affected by inhibiting binding of GFI1B to Lysine Specific Demethylase 1 (LSD1), an interaction required for megakaryocyte development. Treatment of both MEG01 cells and normal IPSC-derived developing megakaryocytes with the small-molecule inhibitor GSK-LSD1 resulted in profound activation of myeloid gene programs within megakaryocytes, while the IPSC-derived megakaryocyte/myeloid ratio dropped two-fold. We conclude that GFI1B and LSD1 suppress myeloid differentiation allowing for proper megakaryocyte development. LSD1 inhibitor and GFI1BQ287*-mediated perturbation of this function causes myeloid skewing during megakaryocyte development.
Project description:Background: Recent advances in single-cell techniques have provided the opportunity to finely dissect cellular heterogeneity within populations previously defined by “bulk” assays and to uncover rare cell types. In human hematopoiesis, megakaryocytes and erythroid cells differentiate from a shared precursor, the megakaryocyte-erythroid progenitor (MEP), which remains poorly defined.Results: To clarify the cellular pathway in erythro-megakaryocyte differentiation, we correlated the surface immunophenotype, transcriptional profile and differentiation potential of individual MEP cells. Highly purified, single MEP cells (n=681) were analyzed using index fluorescence-activated cell sorting with parallel targeted transcriptional profiling of the same cells performed using a specifically designed panel of 87 genes. Differentiation potential was tested in novel, single-cell differentiation assays. Our results demonstrated that immunophenotypic MEP in fact comprise three distinct subpopulations: (1) “Pre-MEP”, enriched for erythroid/megakaryocyte progenitors but with residual myeloid differentiation capacity (2) “E-MEP”, strongly biased towards erythroid differentiation, and (3) “MK-MEP”, a previously undescribed, rare population of cells that are bipotent but primarily generate megakaryocytic progeny. Therefore, conventionally-defined MEP are in fact a mixed population: a minority give rise to mixed-lineage colonies while the majority of cells are transcriptionally-primed to generate exclusively single-lineage output. Conclusions: Our study clarifies the cellular hierarchy in human megakaryocyte/erythroid lineage commitment and highlights the importance of using a combination of single-cell approaches to dissect cellular heterogeneity and identify rare cell types within a population. We present a novel immunophenotyping strategy that enables the prospective identification of specific intermediate progenitor populations in erythro-megakaryopoiesis, allowing for in-depth study of disorders including inherited cytopenias, myeloproliferative disorders and erythromegakaryocytic leukemias.