miR-17 is involved in Japanese Flounder (Paralichthys olivaceus) development by targeting the Cdc42 mRNA.

The expression patterns of 197 miRNAs during Japanese flounder metamorphic development were recently analyzed. miR-17 was differentially expressed during the metamorphic period of the Japanese flounder; however, the role of miR-17 in Japanese flounder development has remained elusive to date. Bioinformatics analysis showed that Cdc42 was a putative target of miR-17. Cdc42 is a gene related to cell adhesion, migration, polarity, cytokinesis, growth, actin cytoskeleton, microtubule dynamics and transcription factor activity; thus, Cdc42 may contribute to metamorphic development. In our study, overexpression of miR-17 in FEC cells suppressed Cdc42 expression. The luciferase reporter assay confirmed that Cdc42 was the target of miR-17. The Cdc42 cDNA from the Japanese flounder was cloned and characterized for the first time. The expression of miR-17 was found to be negatively correlated with Cdc42 mRNA expression during temporal development and in the tissues of adult Japanese flounders. These results indicated that the decrease in miR-17 contributed to the up-regulation of Cdc42 during Japanese flounder metamorphosis. Cdc42 gene expression was down-regulated by thyroid hormone during Japanese flounder metamorphosis, whereas miR-17 was significantly up-regulated by thyroid hormone during these stages. These results indicated that miR-17 was a negative regulator of Cdc42.