Computational prediction of candidate miRNAs and their potential functions in biomineralization in pearl oyster Pinctada martensii

MicroRNAs (miRNAs) are a class of non-coding RNA molecules with presumed post-transcriptional regulatory activity in various biological processes, such as development and biomineralization. Pinctada martensii is one of the main species cultured for marine pearl production in China and Japan. In our previous research, 258 pm-miRNAs had been identified by solexa deep sequencing in P. martensii, while it is far from the number of miRNAs found in other species. In this study, based on the transcriptome database of pearl sac, we identified 30 candidate pm-miRNAs by computational prediction. Among the obtained 30 pm-miRNAs, 13 pm-miRNAs were generated from the complementary strand of protein-coding mRNAs, and 17 pm-miRNAs could not be annotated using blastx and tblastn analysis. Notably, 10 of the 30 pm-miRNAs, such as pm-miR-1b, pm-miR-205b and pm-miR-375b, were homologous with the reported pm-miRNAs, respectively. To validate the existence of the identified pm-miRNAs, eight randomly selected pm-miRNAs were tested by stem loop quantitative RT-PCR analyses using 5.8S as the internal reference gene. Target prediction between the obtained pm-miRNAs and biomineralization-related genes by microTar, miRanda and RNA22 indicated pm-miR-2386 and pm-miR-13b may be the key factors in the regulation network by regulating the formation of organic matrix or the differentiation of mineralogenic cell during shell formation. Thus, this study enriched miRNA databases of pearl oyster and provided a new way to understand biomineralization.