Coordinated regulatory feedback between estradiol and miR-17-92 cluster in ovaries of Japanese flounder Paralichthys olivaceus

Endogenous microRNAs (miRNAs), often distributed in clusters, can enable the subtle and precise regulation in gene expression via a variety of ways and different regions. In this study, multiple regulatory patterns for the estrogenic cyp19a1a and hsd17b12a genes by miR-17-92 cluster (miR-17, miR-18a, miR-19a, miR-20a, miR-19b and miR-92a) were investigated in ovaries of Japanese flounder (Paralichthys olivaceus), the important marine cultured fish in North Asia with sexual dimorphism in growth and sex reversal scenario. Through dual-luciferase reporter assay, the regulation of P. olivaceus estrogenic genes by miR-17-92 cluster could be the combined multieffect between 3 '-UTR and 5 '-ends targeting. For cyp19a1a, miR-17/20a induced its expression by binding to the promoter but simultaneously inhibited cyp19a1a through 3 '-UTR targeting, while miR-92a activated cyp19a1a by binding to the promoter, which made the overall up-regulation of cyp19a1a more significant. For hsd17b12a, the binding of miR-17/20a and miR-92a to the promoter and the binding of miR-18a to 3 '-UTR all inhibited its expression, which ultimately reduced the hsd17b12a level. Both in vitro and in vivo experiments in P. olivaceus ovaries confirmed these canonical and non-canonical regulatory patterns of miR-17-92 cluster, which coordinately reduced the estradiol (E2) level. Moreover, E2 could act as a repressor of miR-17-92 cluster, which may form a regulatory feedback loop whereby E2 regulates estrogenic process through miR-17-92 cluster. These results contributed to a deeper understanding of the miR-17-92 cluster function in teleosts and provided more insights into the molecular mechanism of fish reproductive regulation.