Comparative expression analysis of let-7 microRNAs during ovary development in Megalobrama amblycephala

As a critical regulator of gene expression, let-7 family miRNAs have been reported to be involved in multiple physiological processes. In this study, in order to elucidate the putative regulatory effect of let-7 miRNAs during fish gonadal development and to identify which member is crucial for this regulation, the expression of ten members including let-7a/b/c/d/e/f/g/h/i/j were quantified in ovary, pituitary, and brain tissues during the different ovarian developmental stages of blunt snout bream Megalobrama amblycephala. According to the data from analysis of expression patterns, let-7a showed the highest expression value in almost all the tested ovaries, pituitaries, and brains, with let-7b and let-7d moderately expressed, following by other let-7 miRNAs. In terms of the differential expression levels of ten let-7 miRNAs at each developmental stage, the results showed that let-7a/b/d/f/h expression gradually increased during the ovary development from stage I to V and dropped significantly at the phase VI in ovary tissues. However, the expression of let-7a/b/e/f in pituitary increased during the ovary development from stage I to IV and declined at stage V. Among all the let-7 miRNAs, let-7a/b/d had the highest expression and their expression patterns were consistent with the gonad development of M. amblycephala. Furthermore, the mostly predicted target genes of let-7 miRNAs are significantly enriched in signaling pathways closely related to gonadal development through KEGG enrichment analysis. These results indicate that let-7 miRNA members, especially let-7a/b/d, may play important roles in the regulation of ovary development in M. amblycephala through negatively regulating expression of their target genes.