Identification of common ovarian and testicular miRNAs among cultured fish species

Abstract

MicroRNAs (miRNAs) are important post-transcriptional regulators of gene expression in a wide variety of physiological processes. In cul-tured fish, it has been shown that miRNAs play a role in the reproductive system, where gonad-specific miRNAs are involved. In order to identify common aquacultured markers for early sex-development and to improve reproduction of farmed fish, we compared our zebrafish data with published data of sex-specific gonadal miRNAs to four farmed fish species (i.e., Atlantic cod, catfish, Nile tilapia and European sea bass) together with available data for transgenic zebrafish. In our fish facilities, AB zebrafish were kept at standard husbandry conditions until adulthood when ovaries and testes were dissected. miRNAs were isolated and specific RNA libraries were prepared and sequenced by Illumina technology (50 bp 1 x 50 bp, v4, HiSeq). About 16 million clean reads were obtained from gonadal samples. After determining differentially expressed miRNAs in ovary versus testis, we found 18 significantly upregulated miRNAs specific for ovaries and 25 for testes. Comparing our data with transgenic zebrafish miRNAs, we found one common differentially expressed miRNA specific for each sex: dre-miR-146b-5p in the ovary and dre-miR-212-5p in the testis. FISH analysis revealed the expression of miR146 in the germ cells but not in supporting cells of the ovaries. Significantly expressed miRNAs (normalized reads >100) from the five teleost fish species showed 31 common miRNAs in the gonads, in which five miRNAs were specific for ovaries and other five for testes. Although fur 135research is needed, these common and sex-specific miRNAs in several cultured fish species reveal potential miRNA biomarkers for early development and sex differentiation. Functional studies will demonstrate the molecular mechanism behind these miRNAs and their role in sex differentiation