MicroRNA, Pm-miR-2305, Participates in Nacre Formation by Targeting Pearlin in Pearl Oyster Pinctada martensii

MicroRNAs (miRNAs) are noncoding RNA molecules that function as negative regulators of target genes. In our previous research, 258 pm-miRNAs were identified in Pinctada martensii by Solexa deep sequencing. Pm-miR-2305 was one of the identified pm-miRNAs with a potential function in biomineralization. In the present study, the precursor of pm-miR-2305 was predicted with 96 bp, containing a characteristic hairpin structure. Stem-loop qRT-PCR analysis indicated that pm-miR-2305 was constitutively expressed in all the tissues (adductor muscle, gill, mantle, hepatopancreas, foot, and gonad) of P. martensii and was highly expressed in the foot. After the over-expression of pm-miR-2305 in the mantle by mimics injection into the muscle of P. martensii, nacre demonstrated disorderly growth, as detected by scanning electron microscopy. Dual luciferase reporter gene assay indicated that pm-miR-2305 mimics could significantly inhibit the luciferase activity of the reporter containing the 3'UTR of the pearlin gene. Western blot analysis demonstrated that the protein expression of pearlin was down-regulated in the mantle tissue after the over-expression of pm-miR-2305. Therefore, our data showed that pm-miR-2305 participated in nacre formation by targeting pearlin in P. martensii.