Molecular mechanisms of germ cell differntiation before and during meiosis

为了阐明配子体发生过程中参与生殖细胞分化的分子机制，必须识别和表征生殖细胞分化过程中参与控制这些特化的有丝分裂和减数分裂细胞周期的基因。鳗鱼睾丸完全受激素诱导，为研究精子发生的调控机制提供了强有力的实验模型。为了了解精子发生的控制机制，我们分离了几种细胞周期相关基因cdna，并研究了细胞周期相关基因产物与鳗鱼睾丸配子体发生的关系。激素诱导精子发生后，细胞周期蛋白E2、A2、B （B1、B2、B3）在精原细胞中依次表达。Dmc1和细胞周期蛋白A1在生精细胞减数分裂过程中依次表达。虽然Bl和B2在生精细胞中从精原细胞到精母细胞都有表达，但cyclin B3在生精细胞到精原细胞过程中表达有限。激素启动后精子发生过程中b型细胞周期蛋白表达模式和MPF活性的差异表明，每种b型细胞周期蛋白在鳗鱼精子发生过程中发挥着不同的作用，细胞周期蛋白B3特异性参与精子原细胞增殖（有丝分裂），而不参与减数分裂。为了阐明e型细胞周期蛋白在精子发生过程中的作用，我们在精子发生前通过电穿孔将e型细胞周期蛋白导入睾丸碎片，研究了e型细胞周期蛋白对体外精子发生的影响。以这种方式引入e型细胞周期蛋白导致在体外开始精子发生，而不需要激素诱导精子发生。精子发生的开始伴随着B型精原细胞的大量增殖。而不受A型精原细胞自我更新增殖的影响，提示激素诱导生精后，cyclin E2表达的增加在生精细胞从干细胞更新向主动生精的分化过程中起重要作用。少

To clarify the molecular mechanisms involved in germ cell differentiation during gametogenesis, the genes involved in controlling these specialized mitotic and meiotic cell cycles of germ cell differentiation must be identified and characterized. The eel testis provides powerful experimental models for investigating the regulatory mechanisms of spermatogenesis, because this model is completely regulated by hormonal induction. To understand the control mechanisms of spermatogenesis, we isolated several kinds of cell-cycle related gene cDNAs, and investigated the relationships between cell cycle-related gene products and gametogenesis in eel testes. After the hormonal induction of spermatogenesis, cyclin E2, A2, and B (B1, B2, B3) are expressed in spermatogonia sequentially. Dmc1 and cyclin A1 become expressed in spermatogenic cells sequentially during meiosis. Although Bl and B2 are expressed in spermatogenic cells from spermatogonia to spermatcytes, cyclin B3 expression is limited duri … More ng spermatogenesis to spermatogonia. The differences in the expression patterns and MPF activities among the B-type cyclins during spermatogenesis after hormonal initiation suggests that each B-type cyclin plays a distinct role in eel spermatogenesis, and that cyclin B3 is specifically involved in spermatogonial proliferation (mitosis), but not meiosis. To clarify the role of E-type cyclins during die initiation of spermatogenesis, we examined the effects of E-type cyclins on spermatogenesis in vitro by introducing E-type cyclins by means of electroporation into testis fragments before the induction of spermatogenesis. The introduction of E-type cyclins in this manner resulted in the initiation of spermatogenesis in vitro, without the need for hormonal induction of spermatogenesis. The initiation of spermatogenesis was accompanied by massive proliferation of type B spermatogonia. but not by self-renewal proliferation of type A spermatogonia, suggesting that an increase in cyclin E2 expression after the hormonal induction of spermatogenesis plays an important role in the shift of spermatogenic cell differentiation from stem cell renewal to active spermatogenesis. Less