Scenarios of the evolutionary implications of canonical miRNA functionality absence inMnemiopsis leidyi. a, Ctenophora (represented by M. leidyi) branching earlier than Porifera (represented by A. queenslandica). In this scenario, miRNA functionality likely emerged after the branching of Ctenophora. b, Porifera branching prior to Ctenophora. In this scenario, miRNA functionality coevolved with the Metazoa and was lost from Mnemiopsis leidyi, along with the biogenesis proteins Drosha and Pasha. Also shown are the closest outgroups to the Metazoa with sequenced genomes (i.e., S. arctica, C. owczarzaki, S. rosetta, and M. brevicollis); see Methods for details on the identification of miRNA pathway proteins in these species.
Maxwell et al. BMC Genomics 2012 13:714 doi:10.1186/1471-2164-13-714