Characterization of evolutionarily conserved microRNAs in amphioxus

Amphioxus is an extant species closest to the ancestry of vertebrates. Observation of microRNA (miRNA) distribution of amphioxus would lend some hints for evolutionary research of vertebrates. In this study, using the publicly available scaffold data of the Florida amphioxus (Branchiostoma floridae) genome, we screened and characterized homologs of miRNAs that had been identified in other species. In total, 68 pieces of such homologs were obtained and classified into 33 families. Most of these miRNAs were distributed as clusters in genome. Inter-species comparison showed that many miRNAs, which had been thought as vertebrate- or mammal-specific before, were also present in amphioxus, while some miRNAs that had been considered as protostome-specific before also existed in amphioxus. Compared with ciona, amphioxus had an apparent miRNA gene expansion, but phylogenetic analysis showed that the duplicated miRNAs or clusters of amphioxus had a higher homology level than those duplicated ones in vertebrates.