Center for Reproductive Medicine, Peking University Third Hospital, Beijing, 100191, China.
Key Laboratory of Assisted Reproduction, Ministry of Education, Beijing, 100191, China.
Cell Mol Life Sci. 2019 Jun;76(11):2217-2229. doi: 10.1007/s00018-019-03038-z. Epub 2019 Apr 12.
As the female gamete, meiotic oocytes provide not only half of the genome but also almost all stores for fertilization and early embryonic development. Because de novo mRNA transcription is absent in oocyte meiosis, protein-level regulations, especially the ubiquitin proteasome system, are more crucial. As the largest family of ubiquitin E3 ligases, Skp1-Cullin-F-box complexes recognize their substrates via F-box proteins with substrate-selected specificity. However, the variety of F-box proteins and their unknown substrates hinder our understanding of their functions. In this report, we find that Fbxo30, a new member of F-box proteins, is enriched in mouse oocytes, and its expression level declines substantially after the metaphase of the first meiosis (MI). Notably, depletion of Fbxo30 causes significant chromosome compaction accompanied by chromosome segregation failure and arrest at the MI stage, and this arrest is not caused by over-activation of spindle assembly checkpoint. Using immunoprecipitation and mass spectrometric analysis, we identify stem-loop-binding protein (SLBP) as a novel substrate of Fbxo30. SLBP overexpression caused by Fbxo30 depletion results in a remarkable overload of histone H3 on chromosomes that excessively condenses chromosomes and inhibits chromosome segregation. Our finding uncovers an unidentified pathway-controlling chromosome segregation and cell progress.
作为雌性配子，减数分裂卵母细胞不仅提供了基因组的一半，还提供了受精和早期胚胎发育所需的几乎所有物质储备。由于卵母细胞减数分裂中不存在从头转录的 mRNA，因此蛋白质水平的调控，特别是泛素蛋白酶体系统，更为关键。Skp1-Cullin-F-box 复合物作为最大的泛素 E3 连接酶家族，通过具有底物选择性特异性的 F-box 蛋白识别其底物。然而，F-box 蛋白的多样性及其未知的底物阻碍了我们对其功能的理解。在本报告中，我们发现 Fbxo30 是 F-box 蛋白的一个新成员，在小鼠卵母细胞中富集，并且其表达水平在第一次减数分裂中期（MI）后显著下降。值得注意的是，Fbxo30 的耗竭导致染色体明显紧缩，伴有染色体分离失败和 MI 阶段停滞，这种停滞不是由纺锤体组装检查点的过度激活引起的。通过免疫沉淀和质谱分析，我们确定了茎环结合蛋白（SLBP）是 Fbxo30 的一个新底物。Fbxo30 耗竭导致 SLBP 的过度表达，从而导致染色体上组蛋白 H3 的显著过载，过度浓缩染色体并抑制染色体分离。我们的发现揭示了一条未被识别的控制染色体分离和细胞进程的途径。
