Identification and characterization of skin color microRNAs in Koi carp (Cyprinus carpio L.) by Illumina sequencing.

Background: MicroRNAs (miRNAs) are endogenous, small (21-25 nucleotide), non-coding RNAs that play important roles in numerous biological processes. Koi carp exhibit diverse color patterns, making it an ideal subject for studying the genetics of pigmentation. However, the influence of miRNAs on skin color regulation and variation in Koi carp is poorly understood.

Results: Herein, we performed small RNA (sRNA) analysis of the three main skin colors in Koi carp by Illumina sequencing. The results revealed 330, 397, and 335 conserved miRNAs (belonging to 81 families) and 340, 353, and 351 candidate miRNAs in black, red, and white libraries, respectively. A total of 164 differentially expressed miRNAs (DEMs) and 14 overlapping DEMs were identified, including miR-196a, miR-125b, miR-202, miR-205-5p, miR-200b, and etc. Target prediction and functional analysis of color-related miRNAs such as miR-200b, miR-206, and miR-196a highlighted putative target genes, including Mitf, Mc1r, Foxd3, and Sox10 that are potentially related to pigmentation. Determination of reference miRNAs for relative quantification showed that let-7a was the most abundant single reference gene, and let-7a and miR-26b was the most abundant combination.

Conclusions: The findings provide novel insight into the molecular mechanisms determining skin color differentiation in Koi carp, and serve as a valuable reference for future studies on tissue-specific miRNA abundance in Koi carp.