MicroRNAs and metazoan phylogeny: big trees from little genes
MicroRNAs and metazoan phylogeny: big trees from little genes
Understanding the evolution of a clade, from either a morphologic or genomic perspective, first and foremost requires a correct phylogenetic tree topology. This allows for the polarization of traits so that synapomorphies (innovations) can be distinguished from plesiomorphies and homoplasies. Metazoan phylogeny was originally formulated on the basis of morphological similarity, and in some areas of the tree was robustly supported by molecular analyses, whereas in others was strongly repudiated by molecular analyses. Nonetheless, some areas of the tree still remain largely unknown, despite decades, if not centuries, of research. This lack of consensus may be largely due to apomorphic body plans combined with apomorphic sequences. Here, the chapter proposes that microRNAs may represent a new dataset that can unequivocally resolve many relationships in metazoan phylogeny, ranging from the interrelationships among genera to the interrelationships among phyla. miRNAs, small non-coding regulatory genes, shows three properties that make them excellent candidates for phylogenetic markers: 1) new microRNA families are continually being incorporated into metazoan genomes through time; 2) they show very low homoplasy, with only rare instances of secondary loss, and only rare instances of substitutions occurring in the mature gene sequence; and 3) are almost impossible to evolve convergently. Because of these three properties, this chapter proposes that miRNAs are a novel type of data that can be applied to virtually any area of the metazoan tree, to test among competing hypotheses or to forge new ones, and to help finally resolve the correct topology of the metazoan tree.
Keywords: microRNA, Metazoa, evolution, methodology, Lophotrochozoa
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