Genome-wide identification and characterization of teleost-specific microRNAs within zebrafish

The molecular genetic basis of teleost phenotypic diversity remains poorly understood, despite the increasing availability of genome and transcriptome data. Changes in gene expression, resulting from regulatory mutations, contribute to many or even most phenotypic innovations. In this study, we performed comparative genomic analyses to identify 44 Conserved Teleost-Specific MicroRNAs (CTSMs). An analysis of the sequences of CTSMs demonstrated that their sequence variability is significantly higher than that of Evolutionarily Conserved microRNAs (ECs - microRNAs conserved throughout vertebrates), and that this difference primarily results from variation in the loop regions. We computationally predicted target genes for CTSMs and found that the targets of CTSMs show significantly lower SNP density compared with targets of ECs as well as non-targets of CTSMs. The temporal expression profile of targets of CTSMs obtained from RNA-seq data revealed that the targets of CTSMs are specifically enriched in early-stage embryos and exhibit a broader expression spectrum. Finally, functional enrichment analysis (GO and KEGG) indicated that the targets of CTSMs play diverse functional roles, with a significantly enriched category being the "immune response". Our study provides the first systematic identification and characterization of conserved teleost-specific microRNAs and their targets and presents valuable foundation for a better understanding the genomic basis for the diversification of teleosts.