Duplication Of 20β-HSD In Zebrafish (Danio Rerio) And The Action On Oogenesis

DHP is an important Maturation-inducing hormone(MIH), triggers meiosis and gamete maturation in most teleost fish. Biosynthesis of DHP involves a cascade of steroidogenic enzymes. Among these, 20β-HSD(20β-Hydroxysteroid dehydrogenase) is a crucial enzyme that converts 17a-hydroxyprogesterone(17-HP) to DHP.Through bioinformatics analysis, we found two isoforms of 20β-HSD genes exist in the fish, and only one exist in tetrapod. In the present study, we separated two isoforms of 20β-HSD genes from zebrafish. We named the traditional one is 20β-HSD-II, the other named 20β-HSD-I. The phylogenetic analysis of 20β-HSDs in teleosts showed that 20β-HSD-I and-II clustered into different clades. On the other hand, fish 20β-HSD-I was clustered into one clade with tetrapod 20β-HSDs. Syntenic analysis indicated that fish 20β-HSD-I genes were the homologous genes of their tetrapod counterparts, but not 20β-HSD-II. So, this duplication is not a phenomenon unique toteleosts.Incomplete sequencing of the fish 20β-HSD genes, there are obvious differences in the function, but structures showed higher similarity. Transcription factor binding sites predicted show ERE and PRE binding sites exited in two isoforms of 20β-HSD genes of zebrafish. The only difference is that the number of ERE and PRE binding sites and the synthetic steroid sites SF-1.Antagonistic effect between Estrogen E2 and progestogen DHP in a certain extent. To investigate two kinds of 20β-HSD in zebrafish whether different in the process of DHP synthesis. We choose female zebrafish(Danio rerio) adults were exposed to EE2(17α-Ethynylestradiol)(0.01, 0.1 and 1μg/L) for 20 days. Histological results demonstrated that middle and high doses of EE2 gave rise to serious impacts on zebrafish oocytes which at later stage of development(MV and FV), the low dose have not obvious change. After 20 days, the oocytes in later stage of development apoptosis by low dose EE2 treatment. The ovarian degraded and ovarian occlusion in the middle and high dose group. But the oocytes in the early stage of development do not have obvious change.At the same time, we investigate the influences of EE2 on the expression regulations of 20β-HSDs of zebrafish. Quantitative RT-PCR results revealed that the expressions of 20β-HSD-II were dramatically down-regulated after EE2 exposure 6days, while the expression of 20β-HSD-I up-regulated after EE2 exposure 12 days. Thus proving that 20β-HSD-II are the rate-limiting steroidogenic genes in the biosynthesis of DHP in the zebrafish. 20β-HSD-I genes may have similar functions with tetrapod 20β-HSD, participate in the reduction of corticosterone.