Molecular mechanism of promotive regulation of vitellogenin synthesis and spermatogenesis by GnRH neuron in scallop

1.用BrdU掺入法定量检测扇贝性成熟过程中生殖细胞的有丝分裂活性。生殖细胞的增殖模式可分为两个阶段：第一阶段，卵原细胞和精原细胞在生长期缓慢增殖;第二阶段，卵原细胞发育成卵母细胞，精原细胞开始快速增殖，经过成熟期和产卵期。生殖细胞的增殖可能在I期和II期的不同endocine控制下进行。mGnRH样肽（mGnRH-like peptide）是两种类型GnRH之一，它存在于扇贝中枢神经系统的神经元中，并通过血细胞转运到性腺，促进精原细胞的II期增殖。促性腺激素释放激素诱导的增殖是通过促性腺激素释放激素受体介导的，随后通过性腺中的雌激素细胞中的雌激素合成介导的。因此，GnRH刺激性腺中雌激素的合成和释放，从而激活精原细胞的有丝分裂.卵母细胞生长的基础上的卵黄蛋白原（Vtg）的合成和积累在第二阶段进行控制的GnRH神经元在中枢神经系统。与雄性相同类型的GnRH刺激卵巢中的雌激素细胞，合成的雌激素促进类似卵泡细胞的辅助细胞中Vtg基因的转录。另一方面，另一种新发现的促性腺激素释放激素样神经肽VPF（vitellogenesis promoting factor）能促进Vtg mRNA翻译成Vtg蛋白。通过雌激素受体（ER）介导的Vtg基因表达。在扇贝等3种贝类中均检测到雌激素受体cDNA，且雌激素受体基因均受雌激素自身配体的诱导，提示雌激素信号可能通过自身调节机制放大，并有效地转导到辅助细胞中，实现卵黄蛋白原基因的高表达，从而促进卵黄蛋白原蛋白的合成和卵母细胞的生长。

1. Mitotic activity of gonial cell of scallop was quantitatively detected using BrdU incorporation through sexual maturation. It was suggested that the pattern of proliferation of gonial cells can be divided into two phases: phase I; oogonia and spermatogonia slowly proliferate through the growing stage: phase II; oogonia develop into oocytes and spermatogonia begin to proliferate rapidly through the mature and spawning stages. The proliferation of gonial cells is likely under the different endocine controls in phase I and II. The spermatogonial proliferation at phase II was promoted by a mGnRH-like peptide, one of two types of GnRH, which were identified in the neuron of CNS of scallop and transported to the gonad via hemocytes. The GnRH-induced proliferation was mediated through GnRH receptor and subsequently through estrogen synthesis in the estrogenic cell in the gonad. Therefore, it seems that GnRH stimulates estrogen synthesis and release in the gonad, resulting in activation of mitosis of spermatogonia.2. Oocyte growth based on vitellogenin (Vtg) synthesis and accumulation at phase II was progressively controlled by GnRH neuron in CNS. The same type of GnRH as in male stimulated estrogenic cell in the ovary and the synthesized estrogen promoted Vtg gene transcription in the auxiliary cell which is similar to a follicle cell. On the other hand, another type of GnRH-like neuro peptide, whish has been newly identified as VPF (vitellogenesis promoting factor), promoted Vtg protein translation from Vtg mRNA. Vtg gene expression mediated through an estrogen receptor (ER). ER cDNAs were identified in three kinds of bivalves including scallop and the genes were induced by their own ligand, estrogen, suggesting that estrogen signaling is likely amplified by auto-regulation mechanism and effectively transduced into the auxiliary cell to achieve a high vitellogenin gene expression, resulting in vitellogenin protein synthesis and oocyte growth.