GGNBP2 regulates histone ubiquitination and methylation in spermatogenesis

Gametogenetin binding protein 2 (GGNBP2) was indispensable in normal spermatids for transformation into mature spermatozoa in mice, and when Gametogenetin binding protein 2 is bound to BRCC36 and RAD51, the complex participates in repairing DNA double-strand breaks (DSB) during the meiotic progression of spermatocytes. Ggnbp2 knockout resulted in the up-regulation of H2A_K119ubi and down-regulation of H2B_K120ubi in GC-2 cells (mouse spermatogonia-derived cell line) and postnatal day 18 testis lysate. Our results also demonstrated that Gametogenetin binding protein 2 inducedASXL1 to activate the deubiquitinating enzyme BAP1 in deubiquitinating H2A, while Gametogenetin binding protein 2 knockout disrupted the interaction between ASXL1 and BAP1, resulting in BAP1 localization change. Furthermore, the Gametogenetin binding protein 2 deletion reduced H2B ubiquitination by affecting E2 enzymes and E3 ligase binding. Gametogenetin binding protein 2 regulated H2A and H2B ubiquitination levels and controlled H3_K27 and H3_K79 methylation by PRC2 subunits and histone H3K79 methyltransferase. Altogether, our results suggest that Ggnbp2 knockout increased DNA damage response by promoting H2A ubiquitination and H3_K27trimethylation (H3_K27me3) and reduced nucleosome stability by decreasing H2B ubiquitination and H3K79 dimethylation (H3_K79me2), revealing new mechanisms of epigenetic phenomenon during spermatogenesis. Gametogenetin binding protein 2 seems critical in regulating histone modification and chromatin structure in spermatogenesis.

配子发生素结合蛋白2（Gametogenetin binding protein 2，GGNBP2）在小鼠正常精子细胞向成熟精子的转化过程中不可或缺；当该蛋白与BRCC36、RAD51结合后，所形成的复合物可参与精母细胞减数分裂进程中的DNA双链断裂（DNA double-strand breaks，DSB）修复。敲除Ggnbp2会导致GC-2细胞（小鼠精原细胞来源细胞系）及出生后18日龄小鼠睾丸裂解物中H2A_K119ubi水平上调，同时使H2B_K120ubi水平下调。本研究结果同时显示，配子发生素结合蛋白2可通过诱导ASXL1激活去泛素化酶BAP1，以介导H2A的去泛素化修饰；而敲除该蛋白会破坏ASXL1与BAP1的相互作用，进而导致BAP1的定位发生改变。此外，敲除配子发生素结合蛋白2可通过影响E2酶与E3连接酶的结合，降低H2B的泛素化水平。配子发生素结合蛋白2可调控H2A与H2B的泛素化水平，并通过PRC2复合物亚基及组蛋白H3K79甲基转移酶，调控H3_K27与H3_K79的甲基化修饰。综上，本研究结果表明，敲除Ggnbp2可通过促进H2A泛素化及H3_K27三甲基化（H3_K27me3）增强DNA损伤应答，并通过降低H2B泛素化及H3_K79二甲基化（H3_K79me2）削弱核小体稳定性，从而揭示了精子发生过程中表观遗传现象的全新调控机制。配子发生素结合蛋白2在精子发生过程中调控组蛋白修饰与染色质结构的过程中发挥关键作用。