Identification and Characterization of microRNAs and Their Predicted Functions in Biomineralization in the Pearl Oyster (Pinctada fucata)

The biological process of pearl formation is an ongoing research topic, and a number of genes associated with this process have been identified. However, the involvement of microRNAs (miRNAs) in biomineralization in the pearl oyster, Pinctada fucata, is not well understood. In order to investigate the divergence and function of miRNAs in P. fucata, we performed a transcriptome analysis of small RNA libraries prepared from adductor muscle, gill, ovary, and mantle tissues. We identified 186 known and 42 novel miRNAs in these tissues. Clustering analysis showed that the expression patterns of miRNAs were similar among the somatic tissues, but they differed significantly between the somatic and ovary tissues. To validate the existence of the identified miRNAs, nine known and three novel miRNAs were verified by stem-loop qRT-PCR using U6 snRNA as an internal reference. The expression abundance and target prediction between miRNAs and biomineralization-related genes indicated that miR-1990c-3p, miR-876, miR-9a-3p, and novel-3 may be key factors in the regulatory network that act by controlling the formation of matrix proteins or the differentiation of mineralogenic cells during shell formation in mantle tissue. Our findings serve to further clarify the processes underlying biomineralization in P. fucata.