Project description:A classical view of blood cell development is that multipotent haematopoietic stem and progenitor cells (HSPCs) become lineage-restricted at defined stages. The Lin–c-kit+Sca1+Flt3+ stage, termed lymphoid-primed multipotent progenitors (LMPPs), have lost megakaryocyte and erythroid potential but are heterogeneous in their fate. Through single cell RNA-sequencing, we identify heterogeneous expression of Dach1 and associated genes in this fraction where it co-expressed with myeloid/stem genes but inversely correlated with lymphoid genes. Through generation of Dach1-GFP reporter mice, we identify a transcriptionally and functionally unique Dach1– subpopulation within LMPPs with lymphoid potential but devoid of myeloid potential. We term these ‘lymphoid-primed progenitors’, or LPPs. These findings define the earliest branch point of lymphoid development in haematopoiesis and a means for their prospective isolation.
Project description:A classical view of blood cell development is that multipotent haematopoietic stem and progenitor cells (HSPCs) become lineage-restricted at defined stages. The Lin–c-kit+Sca1+Flt3+ stage, termed lymphoid-primed multipotent progenitors (LMPPs), have lost megakaryocyte and erythroid potential but are heterogeneous in their fate. Through single cell RNA-sequencing, we identify heterogeneous expression of Dach1 and associated genes in this fraction where it co-expressed with myeloid/stem genes but inversely correlated with lymphoid genes. Through generation of Dach1-GFP reporter mice, we identify a transcriptionally and functionally unique Dach1– subpopulation within LMPPs with lymphoid potential but devoid of myeloid potential. We term these ‘lymphoid-primed progenitors’, or LPPs. These findings define the earliest branch point of lymphoid development in haematopoiesis and a means for their prospective isolation.
Project description:Chromatin accessibility was assessed by ATAC-Seq in lymphoid-primed multipotent progenitors (LMPPs) from human foetal livers (FLs) and mouse wild-type FLs as well as FLs from mouse embryos that express the oncofusion Mll-AF4 in the definitive blood system. The aim of this study was to establish whether overall chromatin accessibility at key haematopoietic sites and loci that have been linked to leukaemia are differentially accessible in human vs mouse LMPPs and whether this is altered by the expression of the Mll-AF4 oncofusion.
Project description:Tcf1 is necessary for optimal T lineage development. Tcf1 deficient progenitors fail to initiate the T lineage program in vitro and development is severely defective in vivo. We used microarrays to assess the overal global gene expression differences from Tcf1 wildtype and deficient lymphoid biased progenitors cultures on Notch-ligand expressing stroma to determine if Tcf1 deficient progenitors are able to intiate the T lineage specification program. Abstract of manuscript: The thymus imposes the T cell fate on incoming multipotent progenitors, but the molecular mechanisms are poorly understood. We show that transcription factor Tcf1 initiates T-lineage-specific gene expression. Tcf1 is downstream of Notch1 signaling and expressed in early T-cell progenitors. Progenitors deficient for Tcf1 are unable to initiate normal T-lineage specification. Conversely, ectopic expression of Tcf1 in hematopoietic progenitors is sufficient to induce expression of T-lineage specific genes in vitro. Thus, our study identifies Tcf1 as critically involved in the establishment T cell identity. Tcf1 wildtype and deficient bone marrow lymphoid primed progenitors (LMPPs, Lineage marker- Sca+kit+Flt3high) were harvested in triplicate and seeded onto OP9-DL4 expressing stroma for 4 days upon which highly pure lineage negative and Thy1+CD25+ T cells were cell sorted for expression analysis. The lineage negative populations represent three seperate mice from each genotype and the Thy1+CD25+T lineage population represents two replicates from the Tcf1 wildtype group. No Thy1+CD25+ T lineage cells develop from Tcf1 deficient progentiors.
Project description:Declining immune function with age is associated with reduced lymphoid output of hematopoietic stem cells (HSCs). Currently, there is poor understanding of the dynamic changes with age in the heterogeneous multipotent hematopoietic progenitor cell compartment, which regulates output of differentiated lymphoid cells. In this study, we observed progressive and specific loss of lymphoid-primed multipotent progenitor cells (LMPP/MPP4) as young animals began to age. Single cell RNA-seq revealed a concomitant increase in cycling of these progenitors with loss of a lymphoid priming signature. To interrogate functional multipotency of single cells, we developed a novel, feeder-free in vitro assay to concurrently assess lymphoid and myeloid potential. This assay revealed altered clonal composition of the LMPP/MPP4 compartment with aging, where progenitors with B cell and macrophage-restricted potential are lost while functionally multipotent progenitors are preserved. These results pinpoint an age and cellular compartment to focus further interrogation of the drivers of lymphoid cell loss with aging.