Identification of 17β-HSDs gene family and their expression patterns in gonadal development of Sinonovacula constricta
17 β-hydroxy steroid dehydrogenases(17β-HSDs)are the oxidoreductases in the last step of sex steroid hormone synthesis process,and play important roles in animal gonadal development and reproductive regulation.In this study,on the basis of the genome data of the razor clam Sinonovacula constricta,17β-HSD genes were cloned and identified,and their chromosome distributions,phylogenetic relationships and gene expression patterns in dif-ferent tissues and under different gonadal developmental stages were analyzed.The results showed that 17β-HSD6,17β-HSD10,17β-HSD12 and 17β-HSD14 genes of S.constricta were located on four different chromosomes,and the encoded proteins all contained the conserved SDR superfamily domains.The four 17β-HSD proteins were clearly differentiated and clustered into four independent branches in the phylogenetic trees.The results of qRT-PCR showed that 17β-HSD genes were all expressed in testes tissues,and possessed higher expression levels in gon-ads and hepatopancreas.During the gonadal development of S.constricta,17β-HSD6 gene was expressed higher in testis and ovary at the spawning stage.The expression levels of 17β-HSD10,17β-HSD12 and 17β-HSD14 genes showed a trend of increasing first and then decreasing during the development cycle of testis and ovary,which were all expressed higher at the mature stage.At the mature stage,17β-HSD10 gene was expressed significantly higher in testis than in ovary(p<0.05),while the expression levels of 17β-HSD1 2 and 17β-HSD14 genes were all signific-antly higher in ovary than in testis(p<0.05).Therefore,17β-HSD6 gene might not be involved in regulating gon-adal development process,while the expressions of 17β-HSD10,17β-HSD12 and 17β-HSD14 genes were closely re-lated to the gonadal development,suggesting that they might affect the gonadal development by regulating the syn-thesis and metabolism of sex steroid hormones in S.constricta.These findings laid theoretical foundations for fur-ther study on mechanism of 17β-HSD genes in regulating gonadal development and reproductive endocrine of mol-lusks.