Bromodomain-dependent stage-specific male genome programming by Brdt [ChIP-Seq]

Male germ cell differentiation is a highly regulated multistep process initiated by the commitment of progenitor cells into meiosis and characterized by major chromatin reorganizations in haploid spermatids. We report here that a single member of the double bromodomain BET factors, Brdt, is a master regulator of both meiotic divisions and post-meiotic genome repackaging. Upon its activation at the onset of meiosis, Brdt drives and determines the developmental timing of a testis-specific gene expression program. In meiotic cells, Brdt initiates a genuine histone acetylation-guided programming of the genome by activating essential meiotic genes and repressing a “progenitor cells” gene expression program, while “priming” a post-meiotic gene group for further activation. At post-meiotic stages, a global chromatin hyperacetylation gives the signal for Brdt’s first bromodomain to direct the genome-wide replacement of histones by transition proteins. Brdt is therefore a unique and essential regulator of male germ cell differentiation, which, by using various domains in a developmentally controlled manner, first drives a specific spermatogenic gene expression program, and later controls the tight packaging of the male genome. Overall design: Examination of Brdt binding on chromatin in meiotic (spermatocytes) and post-meiotic (round spermatids) male germ cells from adult wild type mice and mice with a deletion of Brdt BD1 (first bromodomain).

雄性生殖细胞分化是受严格调控的多阶段过程，起始于祖细胞向减数分裂的定向分化，并以单倍体精子细胞中的大规模染色质重塑为核心特征。本研究报道，双溴结构域BET因子（double bromodomain BET factors）家族的单个成员Brdt，同时是减数分裂过程及减数分裂后基因组重塑的关键调控因子。在减数分裂起始时被激活后，Brdt可驱动并调控睾丸特异性基因表达程序的发育时序。在减数分裂细胞中，Brdt通过激活核心减数分裂基因并抑制「祖细胞」基因表达程序，启动以组蛋白乙酰化为导向的精准基因组编程，同时为后续激活预「预置」减数分裂后基因簇。在减数分裂后阶段，全基因组染色质高度乙酰化会发出信号，使Brdt的第一个溴结构域（first bromodomain）介导组蛋白在全基因组范围内被过渡蛋白替代。因此，Brdt是雄性生殖细胞分化过程中独特且必需的调控因子：它以发育时序依赖的方式利用不同结构域，首先驱动特异性生精基因表达程序，随后调控雄性基因组的紧密包装。实验设计：检测成年野生型小鼠与Brdt BD1（first bromodomain）敲除小鼠的减数分裂期（精母细胞）及减数分裂后（圆形精子细胞）雄性生殖细胞中染色质上的Brdt结合情况。