Nut interactome in round/elongating spermatids

NUT, nuclear protein in testis is the universal fusion partner of BRD4 in the highly aggressive NUT Midline Carcinoma (NMC), but its physiological function was unknown. Here we show that Nut is exclusively expressed in post-meiotic spermatogenic cells, at the time of genome-wide histone hyperacetylation. Inactivation of Nut induces a spermatogenesis arrest at the histone-to-protamine replacement stage, leading to male infertility. Subsequent molecular investigations show that Nut sustains global histone H4 hyperacetylation in post-meiotic cells. Additionally, Nut mediates a p300/CBP-dependent gene expression program and, by enhancing acetylation of H4 at both K5 and K8 sites, provides binding sites for the first bromodomain of Brdt, which drives histone removal. Nut’s major function is therefore to use the ubiquitous HATs p300/CBP to direct a cell-type specific histone hyperacetylation. Its ectopic activity in NMC recreates a forced p300-induced histone hyperacetylation / bromodomain binding loop that normally operates in post-meiotic spermatogenic cells.