MTL5在调控精子发生减数分裂进程中的作用和机制

减数分裂I前期依次经历细线期、偶线期、粗线期和双线期，其中任何阶段发生障碍都会导致减数分裂停滞和无精子症发生。我们发现睾丸特异表达的金属硫样蛋白MTL5在偶线期定位于细胞质，粗线期定位于细胞核，其敲除小鼠精母细胞不能进入粗线期；MTL5与MuvB转录调节复合物成员LIN9互作，缺失了与LIN9结合位点的Mtl5突变小鼠精母细胞中截短的MTL5蛋白仍然表达但不能进入细胞核，减数分裂亦不能进入粗线期。因此我们推测在精子发生过程中，MTL5必需从细胞质进入细胞核，再以转录调控的方式调节减数分裂进程。在本项目中，我们将1）进一步明确Mtl5敲除导致减数分裂停滞的确切时间，2）研究其何时及如何入核，3）找寻受其调控并在减数分裂进程中起关键作用的基因，4）检测MTL5及其相关基因在无精子症患者中的突变；以期揭示MTL5调控减数分裂进程的分子机制，为相关无精子症的分子诊断和干预提供分子标靶。

The prophase of meiosis I includes leptotene, zygotene, pachytene, and diplotene, and disturbance at any stage will lead to meiotic arrest and azoospermia. In our previous research, we found that MTL5, a testis-specific metallothionein-like protein, was transferred from the cytoplasm to nucleus during zygotene to pachytene stage. Meiosis cannot proceed to pachytene stage in Mtl5 knockout mice. Furthermore, we showed that MTL5 can interact with LIN9, a member of the MuvB transcriptional regulation complex. The truncated MTL5 protein of Mtl5 mutant mice lacking the binding site for LIN9 is still expressed but cannot enter the nucleus in spermatocytes. Meiosis of the Mtl5 mutant mice can also not proceed to the pachytene stage. Based on these findings, we hypothesize that MTL5 may transcriptionally regulate the process during the transition of zygotene to pachytene stage through its nucleus entrance. To test this hypothesis, we will further clarify the exact phenotype when Mtl5 knockout, to study when and how it enters the nucleus, to find out the target genes that are regulated by MTL5 and play key roles in meiosis, and also to assess the mutations of MTL5 and its related genes in azoospermia patients. This study will reveal the molecular regulating mechanism of MTL5 during meiosis and may provide molecular targets for diagnosis and treatment of associated azoospermia.