School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.
State Key Laboratory of Molecular Biology, Shanghai Key Laboratory of Molecular Andrology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 200031, Shanghai, China.
Cell Death Differ. 2019 Nov;26(11):2194-2207. doi: 10.1038/s41418-019-0283-z. Epub 2019 Feb 13.
Lethal (3) malignant brain tumor like 2 (L3MBTL2) is a member of the MBT-domain proteins, which are involved in transcriptional repression and implicated in chromatin compaction. Our previous study has shown that L3MBTL2 is highly expressed in the testis, but its role in spermatogenesis remains unclear. In the present study, we found that L3MBTL2 was most highly expressed in pachytene spermatocytes within the testis. Germ cell-specific ablation of L3mbtl2 in the testis led to increased abnormal spermatozoa, progressive decrease of sperm counts and premature testicular failure in mice. RNA-sequencing analysis on L3mbtl2 deficient testes confirmed that L3MBTL2 was a transcriptional repressor but failed to reveal any significant changes in spermatogenesis-associated genes. Interestingly, L3mbtl2 deficiency resulted in increased γH2AX deposition in the leptotene spermatocytes, subsequent inappropriate retention of γH2AX on autosomes, and defective crossing-over and synapsis during the pachytene stage of meiosis I, and more germ cell apoptosis and degeneration in aging mice. L3MBTL2 interacted with the histone ubiquitin ligase RNF8. Inhibition of L3MBTL2 reduced nuclear RNF8 and ubH2A levels in GC2 cells. L3mbtl2 deficiency led to decreases in the levels of the RNF8 and ubH2A pathway and in histone acetylation in elongating spermatids, and in protamine 1 deposition and chromatin condensation in sperm. These results suggest that L3MBTL2 plays important roles in chromatin remodeling during meiosis and spermiogenesis.
致死性（3）恶性脑肿瘤样 2（L3MBTL2）是 MBT 结构域蛋白家族的成员，该蛋白家族参与转录抑制，并与染色质紧缩有关。我们之前的研究表明，L3MBTL2在睾丸中高度表达，但它在精子发生中的作用尚不清楚。在本研究中，我们发现 L3MBTL2 在睾丸的粗线期精母细胞中表达最高。睾丸中 L3mbtl2 的生殖细胞特异性缺失导致小鼠出现异常精子增多、精子计数逐渐减少和睾丸早衰。对 L3mbtl2 缺失睾丸的 RNA 测序分析证实，L3MBTL2 是一种转录抑制物，但未能揭示与精子发生相关的基因有任何显著变化。有趣的是，L3mbtl2 缺失导致细线期精母细胞中 γH2AX 沉积增加，随后在有丝分裂 I 的粗线期，γH2AX 不适当保留在常染色体上，以及交叉和联会出现缺陷，在衰老小鼠中，更多的生殖细胞凋亡和退化。L3MBTL2 与组蛋白泛素连接酶 RNF8 相互作用。L3MBTL2 的抑制减少了 GC2 细胞中的核 RNF8 和 ubH2A 水平。L3mbtl2 缺失导致延伸精母细胞中 RNF8 和 ubH2A 途径以及组蛋白乙酰化水平降低，同时导致精子中鱼精蛋白 1 沉积和染色质浓缩减少。这些结果表明，L3MBTL2 在减数分裂和精子发生过程中的染色质重塑中发挥重要作用。
