Previous studies suggested that microRNAs (miRNAs) participate in almost all cellular processes and the continuous
development of miRNA-mediated posttranscriptional regulation might have facilitated the development of complex
organisms. Especially, the microRNA-22 (miR-22) family has been recently extensively reported. Here, we accessed
the evolution of miR-22 structure, regulation, and targets, and this indicated that miR-22 plays key roles in more complex
organisms. We demonstrated that the miR-22 family arose approximate 600 million years ago from the latest common ancestor
of bilaterians. Moreover, a survey of genomic contexts and the secondary structure of the miR-22 family revealed
that it originated de novo from a relatively conserved intron region, and the mature sequence of the miR-22 family
evolved by seed pairing with highly conserved 3' "U" and 5' "G" boundaries. Furthermore, a complete picture of the evolution
of the regulatory networks associated with miR-22 was obtained from the analysis of experimentally identified, as
well as computationally predicted, functional targets of miR-22.
Keywords: Evolution, microRNA, miR-22, origin, phylogeny, taxonomy.
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