Simultaneous expansions of microRNAs and protein-coding genes by gene/genome duplications in early vertebrates.

Does miRNAs underlie the origin of organismal complexity in vertebrates? The current controversy is focused on whether the inventory of vertebrate miRNAs can be explained by the classical two-round genome duplications. We estimate the age distribution of vertebrate miRNA duplication events, showing the evolutionary scenario that gene/genome duplications in the early stage of vertebrates may expand the protein-encoding genes and miRNAs simultaneously. We further speculate that genetically lying behind the evolution of vertebrate complexity may be the proteome doubling and alterations of the epigenetic (including miRNA) machinery.