Mechanism of meiosis initiation in spermatogonia

减数分裂启动的机制尚不清楚。我们的研究表明，在精原细胞的第7代精原细胞中存在减数分裂启动的检查点，并提出了FSH和催乳素浓度比调节减数分裂启动的假说。由于减数分裂的启动需要支持细胞在卵泡刺激素的刺激下产生一定的因子(S)来避开细胞凋亡并作用于精原细胞，因此我们筛选了纽特睾丸来源的基因芯片，并将其鉴定为促卵泡刺激素上调的克隆之一。结果表明，Ig型NRG在Sertoli细胞中表达，CRD型mRNA在Sertoli和生殖细胞中均有表达。FSH刺激Ig-型基因的表达，但不刺激CRD型基因的表达。将NRG功能区EGF样区的重组蛋白加入到睾丸器官培养中，可刺激精原细胞的增殖，发现NRG在小鼠睾丸中有表达，在支持细胞中的表达水平随着发育的进展而降低，而在支持细胞和生殖细胞中的表达水平均升高。在仅有A型精原细胞的情况下，从6dpp开始在睾丸器官培养中加入NRG1和3的重组蛋白，以促进精原细胞的增殖和初级精母细胞特异的SPO11mRNA的表达。FSH可刺激NRGs基因的表达。这些结果表明，NRGs作为作用于精原细胞的重要因素，在减数分裂的启动过程中起着关键作用。

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.