Comparative Analysis of Cardiac microRNAs: Insights into the Molecular Evolution of the Vertebrate Heart

MicroRNAs (miRNAs) are known to play important roles in cardiac development. Heart is the first organ to form in the embryo and all subsequent events in the life of an organism depend on its function. Notably, heart has acquired distinct morphological complexity during vertebrate evolution. Here we characterized and compared the global expression of heart miRNAs in representative species of vertebrate groups aiming to bring insights on the molecular basis of heart evolution. Using next-generation sequencing we profiled miRNOmes of fish Oreochromis niloticus, lizard Tropidurus torquatus and frog Xenopus laevis. Further raw miRNA expression data from zebrafish, salmon, X. tropicalis, chicken, zebra finch, platypus, opossum, mouse, rhesus and human was also compiled and analyzed using bioinformatics. We discovered 32 miRNAs, including previously described cardiac miRNAs (miR-1, -21, -125, -133, -143, -145, -199, -499) with conserved expression to all 13 species analyzed, indicating highly constrained regulatory pathways within vertebrates. Preliminary Gene Ontology enrichment analysis in the human genome revealed that such evolutionary conserved miRNAs have functions in heart development and contraction rate, key traits for the variable morphological complexity observed from fish to mammals. Also, miR-129 and miR-216, without previous association to heart development, were expressed and found to contain many conserved target sites in the 3’UTR of tbx, bmp4, and nkx2.5 genes, related to cardiac cell fate and patterning during heart morphogenesis. Ongoing functional experiments can provide further evidence of bona-fide interactions between these selected miRNAs and putative targets, helping to elucidate the molecular basis of vertebrate heart development.