Mechanism of meiosis initiation in spermatogonia

减数分裂开始的机制尚不清楚。我们发现在newt睾丸精原细胞的7^< >代中存在减数分裂起始检查点，并提出了减数分裂起始受卵泡刺激素和催乳素浓度比调节的假设。人们认为，减数分裂的开始需要支持细胞在FSH的刺激下产生一些规避细胞凋亡并作用于精原细胞的因子。因此，我们筛选了来自蝾螈睾丸的cDNA芯片，并鉴定出神经调节蛋白（NRG）是fsh上调的克隆之一。结果表明，igg型NRG在支持细胞中表达，而crd型mRNA在支持细胞和生殖细胞中均有表达。FSH对ig型mRNA的表达刺激较大，而对crd型mRNA的表达刺激较小。将NRG的功能结构域egf样结构域的重组蛋白加入到睾丸器官培养中，可刺激精原细胞增殖。结果发现NRG mRNA在小鼠睾丸中有表达；NRG1 mRNA在支持细胞中的表达水平随着发育的进行而降低，而nrg3 mRNA在支持细胞和生殖细胞中的表达水平均升高。当仅存在a型精原细胞时，在6dpp的睾丸器官培养中加入NRG1和3的重组蛋白，可促进精原细胞增殖和原代精原细胞特异性SPO11 mRNA的表达。FSH刺激NRGs mRNA的表达。这些结果表明NRGs作为作用于精原细胞的重要因子在减数分裂起始中起着关键作用。

The mechanism underlying meiosis initiation has yet to be clarified. We have shown that there is a checkpoint of meiosis initiation in the 7^<th> generation of spermatogonia in newt testis and presented a hypothesis that meiosis initiation is regulated by the concentration ratio of FSH and prolactin. It was thought that meiosis initiation requires Sertoli cells, upon stimulation by FSH, produce some factor(s) that circumvent apoptosis and act on spermatogonia.Hence we screened cDNA microarray derived from newt testis and identified neuregulin (NRG) as one of the FSH-upregulated clones. It was revealed that Ig-type NRG is expressed in Sertoli cells, while CRD-type mRNA is expressed in both Sertoli and germ cells. FSH stimulates the expression of Ig-type mRNA highly, but not that of CRD-type. When recombinant protein of the EGF-like domain which is a functional domain of NRG is added to organ culture of the testis, it stimulated the spermatogonial proliferation.Then we found that NRG mRNA is expressed in mouse testis; NRG1 mRNA level expressed in Sertoli cells decreases as development proceeds, while NRG 3 mRNA level expressed both in Sertoli and germ cells increases. Recombinant proteins of NRG1 and 3 were added to organ culture of testis from 6dpp when only A-type spermatogonia are present, resulting in promotion of spermatogonial proliferation and expression of SPO11 mRNA that is specific to primary spermatocytes. FSH stimulated the expression of NRGs mRNA. These results indicate that NRGs play a pivotal role in meiosis initiation as important factors to act on spermatogonia.