Centre de Génétique et de Physiologie Moléculaire et Cellulaire, CNRS UMR5534, Université Claude Bernard Lyon 1, Villeurbanne, France.
PLoS Genet. 2013;9(2):e1003285. doi: 10.1371/journal.pgen.1003285. Epub 2013 Feb 7.
The differentiation of post-meiotic spermatids in animals is characterized by a unique reorganization of their nuclear architecture and chromatin composition. In many species, the formation of sperm nuclei involves the massive replacement of nucleosomes with protamines, followed by a phase of extreme nuclear compaction. At fertilization, the reconstitution of a nucleosome-based paternal chromatin after the removal of protamines requires the deposition of maternally provided histones before the first round of DNA replication. This process exclusively uses the histone H3 variant H3.3 and constitutes a unique case of genome-wide replication-independent (RI) de novo chromatin assembly. We had previously shown that the histone H3.3 chaperone HIRA plays a central role for paternal chromatin assembly in Drosophila. Although several conserved HIRA-interacting proteins have been identified from yeast to human, their conservation in Drosophila, as well as their actual implication in this highly peculiar RI nucleosome assembly process, is an open question. Here, we show that Yemanuclein (YEM), the Drosophila member of the Hpc2/Ubinuclein family, is essential for histone deposition in the male pronucleus. yem loss of function alleles affect male pronucleus formation in a way remarkably similar to Hira mutants and abolish RI paternal chromatin assembly. In addition, we demonstrate that HIRA and YEM proteins interact and are mutually dependent for their targeting to the decondensing male pronucleus. Finally, we show that the alternative ATRX/XNP-dependent H3.3 deposition pathway is not involved in paternal chromatin assembly, thus underlining the specific implication of the HIRA/YEM complex for this essential step of zygote formation.
动物减数分裂后精母细胞的分化以其独特的核架构和染色质组成的重排为特征。在许多物种中，精子核的形成涉及大量核小体被鱼精蛋白取代，随后是极度核浓缩的阶段。在受精时，在去除鱼精蛋白后，组蛋白重新构建基于核小体的父本染色质需要在第一轮 DNA 复制之前沉积母体提供的组蛋白。这个过程专门使用组蛋白 H3 变体 H3.3，构成了一个独特的全基因组复制独立（RI）从头组装染色质的例子。我们之前已经表明，组蛋白 H3.3 伴侣 HIRA 在果蝇中对父本染色质组装起着核心作用。尽管从酵母到人类已经鉴定出几种保守的 HIRA 相互作用蛋白，但它们在果蝇中的保守性，以及它们在这个高度特殊的 RI 核小体组装过程中的实际作用，仍然是一个悬而未决的问题。在这里，我们表明，果蝇 Hpc2/Ubinuclein 家族的成员 Yemanuclein (YEM) 对于雄性原核中组蛋白的沉积是必不可少的。yem 功能丧失等位基因以与 Hira 突变体非常相似的方式影响雄性原核的形成，并消除 RI 父本染色质的组装。此外，我们证明 HIRA 和 YEM 蛋白相互作用并相互依赖于它们靶向去浓缩的雄性原核。最后，我们表明替代的 ATRX/XNP 依赖的 H3.3 沉积途径不参与父本染色质组装，从而突出了 HIRA/YEM 复合物在合子形成这一关键步骤中的特定作用。
