Project description:Cellular binary fate decisions require the progeny to silence genes associated with the alternative fate. The major subsets of alpha:beta T cells have been extensively studied as a model system for fate decisions. While the transcription factor RUNX3 is required for the initiation of Cd4 silencing in CD8 T cell progenitors, it is not required to maintain the silencing of Cd4 and other helper T lineage genes. The other runt domain containing protein, RUNX1, silences Cd4 in an earlier T cell progenitor, but this silencing is reversed whereas the gene silencing after RUNX3 expression is not reverse. Therefore, we hypothesized that RUNX3 and not RUNX1 recruits other factors that maintains the silencing of helper T lineage genes in CD8 T cells. To this end, we performed a proteomics screen of RUNX1 and RUNX3 to determine candidate silencing factors.
Project description:The classical tenet of hematopoiesis posits well-accepted lineage trees that arise from progressively restricted oligopotent and unipotent progenitor populations. However, because fate in hematopoiesis has mostly been studied in the context of transplantation, it is unclear whether these lineage branches and such proposed oligopotent progenitors exist in an unperturbed hematopoietic system. Here, we utilize endogenous transposon tagging to trace the fate of thousands of progenitors and stem cells over time to re-evaluate these dogmas. Our results describe a novel clonal roadmap where the megakaryocyte lineage arises independently of lymphoid and myeloid/erythroid fates. Our data also demonstrate that true oligopotency is largely restricted to the multipotent progenitor (MPP) compartment. Analysis of thousands of stem cell and progenitor transcriptomes demonstrates that lineage determination starts at the MPP stage and identifies a functional hierarchy within this population that drives hematopoiesis. Finally, our results demonstrate that long-term hematopoietic stem cells behave physiologically as megakaryocyte lineage progenitors. Our data provide evidence for a substantially revised hematopoietic roadmap, and highlights unique properties of MPPs and HSCs in situ.
