DNA damage primes hematopoietic stem cells for megakaryopoiesis

Hematopoietic stem cells (HSCs) reside in the bone marrow (BM), can self-renew, and generate all blood cells. Most hematopoietic lineages arise through successive, increasingly lineage-committed progenitors. In contrast, megakaryocytes (MKs), hyperploid cells that generate platelets essential to hemostasis, can derive rapidly and directly from HSCs, subpopulations of which are primed for MK differentiation. The underlying mechanism is unknown however. Here we show that DNA damage and subsequent arrest in the G2 phase of the cell cycle rapidly induce MK commitment in HSCs, but not in progenitors, through an initially predominantly post-transcriptional mechanism. Cycling HSCs show extensive replication-induced DNA damage associated with uracil misincorporation in vivo and in vitro. Consistent with this notion, thymidine attenuated DNA damage, rescued HSC maintenance and reduced the generation of CD41+ MK-committed HSCs in vitro. Similarly, overexpression of the dUTP-scavenging enzyme, dUTPase, enhanced in vitro maintenance of HSCs. Replication stress-induced MK priming, at least in part caused by uracil misincorporation, is therefore a barrier to HSC maintenance and expansion. DNA damage-induced MK priming may allow rapid generation of a lineage essential to immediate organismal survival, while simultaneously removing damaged HSCs and potentially avoiding malignant transformation of self-renewing stem cells We performed scRNAseq of HSC cultured for 48hrs in RO-3066 or DMSO vehicle.