Identification and characterization of microRNAs in American cockroach (Periplaneta americana).

The American cockroach (Periplaneta americana), which is one of the most ancient insects in the world, is characterized by incomplete metamorphosis. So far, no one has studied the microRNA profile of P. americana and the changes in the expression of microRNAs on different developmental stages. In this study, we sequenced the small RNAs (sRNA) of four samples at four post-embryonic developmental stages. A total of 35 conserved known mature miRNAs and 134 novel mature miRNAs were identified. After differential expression analysis, we noticed there were more miRNA expressed differentially during early post-embryonic stages. We also found about one-third of known miRNAs were significantly dynamic. After a cross-species comparative analysis, we identified two miRNAs (miR-1000 and miR-932) that may be important for morphogenesis, olfactory, learning, and memory. In addition, unlike hetero-metabolous insects, miRNAs still played an important role in late post-embryonic stages in holo-metabolous insects. In conclusion, our results underline the significance of miRNA expression in post-embryonic developmental stages of the American cockroach and push forward the understanding of gene expression modulation by miRNAs in cockroach. This would also contribute to the study of gene expression regulation by miRNAs during metamorphosis development.