Positive selection linked with generation of novel mammalian dentition patterns

Abstract

A diverse group of genes are involved in the tooth development of mammals. Several studies, focusedmainly onmice and rats, have provided a detailed depiction of the processes coordinating tooth formation and shape. Here we surveyed 236 tooth-Associated genes in39mammaliangenomesandtestedfor signatures of selectiontoassesspatternsofmolecular adaptation in genes regulating mammalian dentition. Of the 236 genes, 31 (~13.1%) showed strong signatures of positive selection that may be responsible for the phenotypic diversity observed inmammalian dentition.Mammalian-specific tooth-Associated genes had acceleratedmutation rates compared with older genes found across all vertebrates. More recently evolved genes had fewer interactions (either genetic or physical),were associated with fewer GeneOntology terms and had faster evolutionary rates compared with older genes. The introns of these positively selected genes also exhibited accelerated evolutionary rates, whichmay reflect additional adaptive pressure in the intronic regions that are associatedwith regulatory processes that influence tooth-gene networks. The positively selected geneswere mainly involved in processes likemineralization and structural organization of tooth specific tissues such as enamel and dentin. Of the 236 analyzed genes, 12mammalian-specific genes (younger genes) provided insights on diversification ofmammalian teeth as they have higher evolutionary rates and exhibit different expression profiles compared with older genes. Our results suggest that the evolution and development ofmammalian dentition occurred in part through positive selection acting on genes that previously had other functions.