G2 arrest primes hematopoietic stem cells for megakaryopoiesis.

In contrast to most hematopoietic lineages, megakaryocytes (MKs) can derive rapidly and directly from hematopoietic stem cells (HSCs). The underlying mechanism is unclear, however. Here, we show that DNA damage induces MK markers in HSCs and that G2 arrest, an integral part of the DNA damage response, suffices for MK priming followed by irreversible MK differentiation in HSCs, but not in progenitors.

DNA damage primes hematopoietic stem cells for direct megakaryopoiesis.

Hematopoietic stem cells (HSCs) reside in the bone marrow (BM), can self-renew, and generate all cells of the hematopoietic system. 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.

BRDT is an essential epigenetic regulator for proper chromatin organization, silencing of sex chromosomes and crossover formation in male meiosis.

The double bromodomain and extra-terminal domain (BET) proteins are critical epigenetic readers that bind to acetylated histones in chromatin and regulate transcriptional activity and modulate changes in chromatin structure and organization. The testis-specific BET member, BRDT, is essential for the normal progression of spermatogenesis as mutations in the Brdt gene result in complete male sterility. Although BRDT is expressed in both spermatocytes and spermatids, loss of the first bromodomain of BRDT leads to severe defects in spermiogenesis without overtly compromising meiosis.