Identification of sex-biased miRNA involved in sex differentiation and spermatogenesis in yellow catfish by comparative transcriptome analysis

In this study, three small RNA libraries constructed from gonad tissues of XX female, XY male and YY super-male yellow catfish were sequenced by Solexa high-throughput sequencing technology to investigate the expression pattern of sex-biased microRNA. The sequencing data generated a total of 384 conserved miRNAs and 113 potential novel miRNAs, among which 23, 30 and 14 miRNAs were specifically detected in XX ovary, XY testis, and YY testis, respectively. Interestingly, more abundant piRNAs were found in ovary compared to testis in yellow catfish, which phenomenon is also observed in other fish species but opposite in mammalians. We detected a number of microRNAs differentially expressed between ovary and testis, such as miR-21, miR-462, miR-430 and -200 family. When compared the transcriptome between XY and YY testis, we observed relative lower expression of miR-141 and miR-429 in YY testis. Histological analysis indicated that YY super-males have more spermatids and less spermatocytes in spermatogenic cyst than XY males under the same age and culturing conditions. The expression level of miR-141 and 429 coincides with the progression of spermatogenesis both in yellow catfish and human. At last, The expression pattern of nine arbitrarily selected miRNAs detected by quantitative RT-PCR was consistent with the Solexa sequencing results. Our study provides a comprehensive miRNA transcriptome analysis for gonad of yellow catfish with different sex genotypes, and identifies a number of sex-biased miRNAs that are potentially involved in sex differentiation and spermatogenesis. Overall design: Examination of small RNA expression profilings in yellow catfish gonads of three sex genotypes