Role of micro RNA on the Expression of Luteinizing Hormone-Human Chorionic Gonadotropin Receptor Messenger Ribonucleic Acid in rat ovary

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MicroRNAs (miRNAs) are small non-coding RNAs that interact with mRNAs and trigger either translation repression or RNA cleavage of target genes. In this study, we investigated whether miRNA is involved in down-regulation of the LH receptor (LHR) in the ovary. A miRNA microarray was carried out to analyze the overall miRNA expression profile while LHR mRNA was down-regulated, and found that 23 miRNAs were highly expressed during this period. Combining these results with data from the bioinformative database, the clustering analysis led us to focus on miR-136* for further analysis. In both in vivo and in vitro studies, miR-136* levels were found to increase 6 hr after hCG administration while LHR mRNA levels were down-regulated. To confirm that miR-136* binds to LHR mRNA, we cloned the 3'-end of LHR mRNA from 2570 to 2895 into reporter vector which contained a Renilla luciferase coding region upstream of the cloning site. When the miR-136* inhibitor was co-transfected with the reporter vector in granulosa cells, the luciferase activity was de-repressed, revealing that miR-136* definitely bound to the 3'-end of LHR mRNA. From these data, we conclude that miR-136* participates in the mechanism of down-regulation of LHR mRNA, whereby miR-136* forms base pairs with LHR mRNA.