The control mechanisms of initiation of meiosis in fish spermatogenesis

减数分裂是保证有性生殖不可缺少的过程。然而，关于其启动的管理机制的详细资料尚不清楚。黄体酮是调节雄性和雌性最终成熟的重要类固醇。在雄性硬骨鱼中，已知黄体酮诱导精子受精和成熟。然而，黄体酮在包括减数分裂在内的早期精子发生中的作用尚不完全清楚。本研究探讨了黄体酮在日本鳗鲡精子发生过程中减数分裂起始的作用。17吗?, 20吗?硬骨鱼天然黄体酮-二羟基-4-孕酮-3-酮（DHP）及其受体存在于精子发生早期的睾丸中。利用鳗鲡睾丸培养系统，DHP诱导精原细胞DNA合成。11-酮睾酮是精子发生的启动剂，也刺激了精原细胞的DNA合成，但这种DNA合成在减数分裂开始阶段被抗dhp抗体阻止。DHP处理还能诱导减数分裂特异性标记的表达；DmcI和Spo11。此外，在一些细胞类型为精原干细胞的睾丸碎片中，也检测到Spo11和突触复合物（减数分裂前期的特异性结构）的表达。在卵发生过程中，DHP利用新开发的鲤鱼卵巢培养物诱导减数分裂前期。因此，我们从这些结果中得出结论，DHP，一种黄体酮是精子发生和卵子发生中减数分裂起始的重要因素。

Meiosis is indispensable process for ensuring the sexual reproduction. However, detailed information on the regulational mechanisms of its initiation is not clear. Progestin is an important steroid for regulation of final maturation in male and female. In male teleosts, it is known that progestin induces spermiation and maturation. However, the function of progestin in early spermatogenesis including meiosis is not completely known. In this study, we examined the functions of progestin on initiation of meiosis in spermatogenesis of the Japanese eel. 17?, 20? -dihydroxy-4-pregnen-3-one (DHP), a natural progestin in teleost, and its receptor was presented in the testis of early stage of spermatogenesis. Using eel testicular culture systems, DHP induced the DNA synthesis of spermatogonia. 11-Ketotestosterone, which is initiator of spermatogenesis, also stimulated the DNA synthesis of spermatogonia, but this DNA synthesis prevented by anti-DHP antibody treatment at the phase of initiation of meiosis. DHP treatment also induced the expression of meiosis specific marker; DmcI and Spo11. Furthermore, the expression of Spo11 and synaptonemal complexes (specific construct of meiotic prophase) were also detected in some germ cells, which cell type is spermatogonial stem cell in testicular fragments cultured with DHP. In oogenesis, DHP induced meiotic prophase using ovarian culture of common carp which is newly developed for this analysis. We therefore concluded from these results that DHP, a progestin is essential factor for initiation of meiosis in both spermatogenesis and oogenesis.