title: Origins and evolution of microRNA genes in Drosophila species.
abstract: MicroRNAs (miRs) regulate gene expression at the posttranscriptional level. To obtain some insights into the origins and evolutionary patterns of miR genes, we have identified miR genes in the genomes of 12 Drosophila species by bioinformatics approaches and examined their evolutionary changes. The results showed that the extant and ancestral Drosophila species had more than 100 miR genes and frequent gains and losses of miR genes have occurred during evolution. Although many miR genes appear to have originated from random hairpin structures in intronic or intergenic regions, duplication of miR genes has also contributed to the generation of new miR genes. Estimating the rate of nucleotide substitution of miR genes, we have found that newly arisen miR genes have a substitution rate similar to that of synonymous nucleotide sites in protein-coding genes and evolve almost neutrally. This suggests that most new miR genes have not acquired any important function and would become inactive. By contrast, old miR genes show a substitution rate much lower than the synonymous rate. Moreover, paired and unpaired nucleotide sites of miR genes tend to remain unchanged during evolution. Therefore, once miR genes acquired their functions, they appear to have evolved very slowly, maintaining essentially the same structures for a long time.
authors.affiliation: Institute of Molecular Evolutionary Genetics and Department of Biology, Pennsylvania State University, University Park, USA. mun12@psu.edu
authors.forename: Masafumi
authors.initials: M
authors.lastname: Nozawa
authors.forename: Sayaka
authors.initials: S
authors.lastname: Miura
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Nei
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001483:Base Sequence; D002874:Chromosome Mapping; D004251:DNA Transposable Elements / Q000235:genetics; D004330:Drosophila / Q000145:classification / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics; D004331:Drosophila melanogaster / Q000235:genetics; D019143:Evolution, Molecular; D020440:Gene Duplication; D015321:Gene Rearrangement; D017344:Genes, Insect; D035683:MicroRNAs / Q000737:chemistry / Q000235:genetics*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D005810:Multigene Family; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D022661:RNA, Untranslated / Q000235:genetics; D013045:Species Specificity
chemical_list: D004251:DNA Transposable Elements; D029721:Drosophila Proteins; D035683:MicroRNAs; D022661:RNA, Untranslated