Identification and comparative analysis of the ovary and testis microRNAome of mud crab Scylla paramamosain

The role of microRNA (miRNA) in reproductive regulation is attracting increasingly more attention. In this study, we obtained 9,643,114 and 15,498,999 raw reads from the ovary and testis library of important farmed mud crab Scylla paramamosain, respectively. After data mining, a total of 4,096,464 and 11,737,973 mappable small RNA sequences remained for analysis. By mapping to the reference genome and expressed sequence tag (EST) of Daphnia pulex and other crabs, a total of 1,417 miRNAs were identified. On the basis of 1,417 miRNAs, 514 (36.3%) unique miRNAs coexpressed in the gonad of female and male libraries, and 336 (23.7%) and 567 (40%) expressed preferentially in female and male libraries, respectively. Analysis of library sequencing data resulted in the identification of 108 miRNAs (out of 1,417; 7.6%) that showed significant differential expression between the two samples. Of these, 13 miRNAs were expressed only in the testis, two miRNAs were expressed only in the ovary, and 93 miRNAs were coexpressed: 57 (61.3%) were upregulated (ovary/testis) and 36 (38.7%) were downregulated (ovary/testis). To confirm the expression patterns of the predicted miRNAs, we randomly selected 14 candidate miRNAs from 108 differentially expressed miRNAs and performed stem-loop real time quantitative PCR (RT-qPCR) assays in five ovary developing stages. Five miRNAs showed similar expression patterns in almost every stage as those revealed by identification of differentially expressed genes (IDEG6) analysis. The above five miRNAs were predicted to match the 3-untranslated region of the published S. paramamosain gene. Four out of five miRNA had a regulation effect on many genes, especially the genes related to gonadal development.