Comparative microRNAome analysis of the testis and ovary of the Chinese giant salamander.

MicroRNAs (miRNAs) are 18-24 nucleotides non-coding RNAs that regulate gene expression by post-transcriptional suppression of mRNA. The Chinese giant salamander (CGS, Andrias davidianus), which is an endangered species, has become one of the important models of animal evolution; however, no miRNA studies on this species have been conducted. In this study, two small RNA libraries of CGS ovary and testis were constructed using deep sequencing technology. A bioinformatics pipeline was developed to distinguish miRNA sequences from other classes of small RNAs represented in the sequencing data. We found that many miRNAs and other small RNAs such as piRNA and tsRNA were abundant in CGS tissue. A total of 757 and 756 unique miRNAs were annotated as miRNA candidates in the ovary and testis respectively. We identified 145 miRNAs in CGS ovary and 155 miRNAs in CGS testis that were homologous to those in Xenopus laevis ovary and testis respectively. Forty-five miRNAs were more highly expressed in ovary than in testis and 21 miRNAs were more highly expressed in testis than in ovary. The expression profiles of the selected miRNAs (miR-451, miR-10c, miR-101, miR-202, miR-7a and miR-499) had their own different roles in other eight tissues and different development stages of testis and ovary, suggesting that these miRNAs play vital regulatory roles in sexual differentiation, gametogenesis and development in CGS. To our knowledge, this is the first study to reveal miRNA profiles that are related to male and female CGS gonads and provide insights into sex differences in miRNA expression in CGS.