Maugars Gersende, Schmitz Monika
Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, Umeå, Sweden.
Mol Reprod Dev. 2008 Feb;75(2):403-13. doi: 10.1002/mrd.20767.
Atlantic salmon males may mature already as small parr in freshwater. Sexual maturation in teleosts as in vertebrates is characterized by the activation of the brain-pituitary-gonad axis. The endocrine regulation of early puberty is still not well understood. In the present study, one-summer-old male Atlantic salmon parr were sampled regularly from December several months prior to the beginning of spermatogenesis until spawning in October. Pituitary expression levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) beta subunit genes were analyzed in parallel with testis expression of FSH receptor (FSHR) and LH receptor (LHR) genes by RT-PCR and plasma 11-ketostestosterone (11-KT) was measured. Expression levels of FSHbeta, low during winter and spring started to increase prior to the onset of gonadal growth at the end of May while LHbeta mRNA levels were hardly detectable. Both gonadotropin receptor genes were expressed in immature testis with FSHR transcripts being more abundant (8-fold). FSHR transcript levels increased in parallel to FSHbeta levels from early spermatogenesis onwards, while LHR mRNA started to increase prior to any large changes in LHbeta expression. Both transcript levels of LHbeta and LHR were highest during spermiation. Plasma 11-KT increased at the beginning of spermatogenesis reaching highest levels at spermiogenesis suggesting a possible role of FSH in inducing 11-KT production during early spermatogenesis while LH stimulates via its specific receptor 11-KT production at spermiogenesis. The commitment into sexual maturation appears to be dependant on both the presence of FSHR in immature testis and the increase of FSH expression.
大西洋鲑雄鱼在淡水中作为小幼鲑时就可能成熟。硬骨鱼的性成熟与脊椎动物一样，其特征是脑-垂体-性腺轴的激活。早期青春期的内分泌调节仍未得到很好的理解。在本研究中，从精子发生开始前几个月的12月到10月产卵期间，定期采集一岁大的雄性大西洋鲑幼鲑样本。通过逆转录聚合酶链反应（RT-PCR）分析促卵泡激素（FSH）和促黄体生成素（LH）β亚基基因的垂体表达水平，并与FSH受体（FSHR）和LH受体（LHR）基因的睾丸表达水平进行平行分析，同时测量血浆11-酮睾酮（11-KT）。FSHβ的表达水平在冬季和春季较低，在5月底性腺生长开始前开始升高，而LHβ的mRNA水平几乎检测不到。两种促性腺激素受体基因在未成熟睾丸中均有表达，其中FSHR转录本更为丰富（8倍）。从精子发生早期开始，FSHR转录本水平与FSHβ水平平行升高，而LHR mRNA在LHβ表达发生任何大的变化之前就开始增加。LHβ和LHR的转录本水平在精子形成期均最高。血浆11-KT在精子发生开始时升高，在精子形成期达到最高水平，这表明FSH可能在精子发生早期诱导11-KT产生中发挥作用，而LH在精子形成期通过其特异性受体刺激11-KT产生。性成熟的开始似乎既取决于未成熟睾丸中FSHR的存在，也取决于FSH表达的增加。
