Clonal analysis of lineage fate in unperturbed hematopoiesis

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.