The control mechanisms of initiation of meiosis in fish spermatogenesis

减数分裂是保证有性生殖的必要过程。然而，关于其启动的调节机制的详细信息尚不清楚。孕激素是一种重要的甾体激素，在男性和女性的最终成熟的调节。在雄性硬骨鱼中，已知的是，卵蛋白诱导精子形成和成熟。然而，对resistin在早期精子发生（包括减数分裂）中的作用尚不完全清楚。在这项研究中，我们研究了在日本鳗鲡精子发生过程中，resistin在减数分裂启动中的作用。十七岁？20个？- 二羟基-4-二烯-3-酮（DHP）是硬骨鱼类天然的一种睾丸激素，其受体存在于精子发生早期的精巢中。利用鳗鱼睾丸培养系统，DHP诱导精原细胞DNA合成。11-酮睾酮是精子发生的起始剂，也能促进精原细胞DNA的合成，但在减数分裂起始阶段，抗DHP抗体可抑制DNA的合成。DHP处理还诱导减数分裂特异性标记物DmcI和Spo 11的表达。此外，Spo 11和联会复合体（减数分裂前期的特异性结构）的表达也被检测到在一些生殖细胞中，细胞类型是精原干细胞在睾丸碎片与DHP培养。在卵子发生中，DHP诱导减数分裂前期使用的是新开发的鲤鱼卵巢培养。因此，我们认为DHP是精子发生和卵子发生过程中减数分裂启动的重要因子。

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.