The Mantle Exosome and MicroRNAs of Hyriopsis cumingii Involved in Nacre Color Formation

The nacre color of shells has an effect on the pearl color in Hyriopsis cumingii and is an important indicator for its value. The nacre is part of the shell, and some studies have shown that exosomes of the mantle are involved in the formation of shells. Most of the RNA contained in exosomes are microRNAs (miRNAs); however, little information is available on the roles of exosomes and miRNAs on the formation of nacre color in mussels. In this study, exosomes of mantles were extracted from white and purple mussels. High-throughput Illumina sequencing was performed on the white and purple mussel mantle exosomes, and 7,665,167 and 10,994,115 reads were harvested. Using the standard of |log(2)(Fold change)| >= 2, and a p value <= 0.05, a total of 54 differentially expressed miRNAs were identified. The miRNAs that regulated the target genes (hcApo, HcTyr, HcTyp-1, HcMitf, HcSRCR1, and HcSRCR2) involved in shell color formation were predicted. Moreover, miR-15b negatively regulated hcApo, which plays important roles in the absorption and transport of beta-carotene in H. cumingii. These results improve our understanding of the molecular mechanisms of nacre color formation in H. cumingii.