Ubc9 Mediates SUMO2/3 Modification to Regulate Meiosis in Male Mice

Objective: SUMOylation is a crucial protein modification that regulates various physiological and pathological processes. Ubc9 serves as a key ubiquitin-conjugating enzyme in the process of SUMOylation. However, the role of Ubc9 has yet to be elucidated during spermatogenesis in mammals. Methods: We analyzed the expression profile of Ubc9 in spermatogenesis via quantitative polymerase chain reaction, Western blotting, and meiotic chromosome spread assays. Stra8-EGFPCre mice were used to construct a germ cell-specific conditional Ubc9 knockout mouse model to explore the effects of Ubc9 on male fertility and testicular development. Histological and immunofluorescence staining were performed to observe the development of germ cells and the synaptonemal complex. Moreover, proteomics analysis of the testes was used to detect changes in the control and Ubc9-deficient mice at postnatal day 8. Results: Our results revealed that Ubc9 was highly expressed in the early stage of meiosis. Ubc9 was extensively distributed in the nucleus during meiosis I. Conditional Ubc9 knockout mice with Stra8-EGFPCre resulted in atrophy and reduced volume and mass of testes and complete loss of male fertility. Histological and immunofluorescence staining of testes revealed that the number of germ cells was significantly reduced in the seminiferous tubules in conditional Ubc9 knockout mice at postnatal day 9. Meiotic chromosome spread assays revealed that the synaptonemal complex was abnormally developed and arrested in meiosis I. Moreover, immunofluorescence staining with SUMO1 and SUMO2/3 revealed that Ubc9 regulated the development of the synaptonemal complex mainly via SUMO2/3 rather than SUMO1. The results of the proteomics analysis revealed that the levels of proteins related to the synaptonemal complex, including SYCE1, SYCE2, TEX12, SYCP1, DMC1, and Hormad1, were markedly decreased with Ubc9 deficiency. Conclusions: Taken together, our study demonstrated that Ubc9 influenced the development of the synaptonemal complex during meiosis I and is essential for male fertility in mammals.