Chromatin-to-nucleoprotamine transition is controlled by the histone H2B variant TH2B [ChIP-Seq]
The conversion of male germ cell chromatin to a nucleoprotamine structure is fundamental to the life cycle yet the underlying molecular details remain obscure. Here we show that an essential step is the genome-wide incorporation of TH2B, a histone H2B variant of hitherto unknown function. Using mouse models in which TH2B is depleted or C-terminally modified we show that TH2B directs the final transformation of dissociating nucleosomes into protamine-packed structures. Depletion of TH2B induces compensatory mechanisms that permit histone removal by up-regulating H2B and programming nucleosome instability through targeted histone modifications, including lysine crotonylation and arginine methylation. Furthermore, after fertilization, TH2B re-assembles onto the male genome during protamine-to-histone exchange. Thus, TH2B is a unique histone variant, which plays a key role in the histone-to-protamine packing of the male genome and guides genome-wide chromatin transitions that both precede and follow transmission of the male genome to the egg. Overall design: Examination of TH2B binding on chromatin in meiotic (spermatocytes) and post-meiotic (round spermatids) male germ cells from adult Th2b+/tag mice (TH2B C-terminally fused to three consecutive affinity tags: His, Flag and Ha). Examination of TH2B (wild type) binding on chromatin in male germ cells from adult wt mice.