Histone acetylation-mediated chromatin compaction during mouse spermatogenesis.

One of the most dramatic chromatin remodelling events takes place during mammalian spermatogenesis involving massive incorporation of somatic and testis-specific histone variants, as well as generalized histone modifications before their replacement by new DNA packaging proteins. Our data suggest that the induced histone acetylation occurring after meiosis may direct the first steps of genome compaction. Indeed, a double bromodomain-containing protein expressed in postmeiotic cells, Brdt, shows the extraordinary capacity to specifically condense acetylated chromatin in vivo and in vitro. In elongating spermatids, Brdt widely co-localizes with acetylated histones before accumulating in condensed chromatin domains. These domains preferentially maintain their acetylation status until late spermatogenesis. Based on these data, we propose that Brdt mediates a general histone acetylation-induced chromatin compaction and also maintains differential acetylation of specific regions, and is therefore involved in organizing the spermatozoon's genome.