Molecular cloning of gonadotropin genes and their regulation of expression.

与其他脊椎动物一样，鱼类的生殖活动是由一个由脑-垂体-性腺轴组成的内分泌系统调节的。过去认为鱼类只有一种类型的垂体促性腺激素（GTH），但最近在鲑鱼中发现了两种类型的GTH。鲤科鱼类已被作为鱼类生殖内分泌学研究的模式种，但对鲤科鱼类GTH合成调控的研究尚不充分。为了研究垂体中GTH合成或GTH基因表达的调控机制，需要特异性的cDNA探针。我去年从金鱼的垂体中克隆了GTH亚基（I和II）的cDNA，获得了针对金鱼GTH的特异性探针。今年，我通过northern blot分析检测了性腺成熟过程中GTH基因的表达。在鲑鱼中，GTHI在性腺发育早期占主导地位，GTHII在性腺成熟阶段占主导地位，而在金鱼中，GTHI和GTHII的表达随着性腺成熟的进展而增加。结果可能反映了鲑科鱼和金鱼产卵周期的不同模式；鲑鱼在产卵期只产卵一次，而金鱼则要产卵好几次。我还研究了水温对GTH基因表达的影响。GTHI在低温下表达量较高，GTHII在中等温度下表达量较高。这些结果提示水温参与了金鱼GTH基因差异表达的调控。

As in other vertebrates, reproductive activities in fish is regulated by an endocrine system, consisting of brain-pituitary-gonad axis. It had been thought that fish had only single type of pituitarty gonadotropin (GTH), but recently two types of GTH were identified in salmon.Althogh cyprinid species have been used as model species for the study of reproductive endocrinology of fish, it is not well studied on the regulation of GTH synthesis in these species.For the study of regulatory mechanism of GTH synthesis or GTH gene expression in the pituitary, specific cDNA probes are necessities. I cloned cDNA of GTH subunits (I and II) from the pituitary of goldfish last year and obtained specific probes for goldfish GTH.This year, I examined GTH gene expression during gonadal maturation by Norhtern blot analysis. Unlike salmonids in which GTHI dominates during eary stage of gonadal development and GTHII in maturational stage, expression of both GTHI and II showed an increase with the progression of gonadal maturation in goldfish. The results may reflect different patterns of spawning cycle between salmonids and goldfish ; salmonids spawn once during their spawning period, whereas goldfish spawns several times.I also examined effects of water temperature on GTH gene expression. Expression of GTHI was higher at low temperature and that of GTHII at moderate temperature. These results suggest that water temperature is involved in the regulation of differential expression in goldfish GTH genes.