Model for the evolution of the resistin and resistin-like genes.

Abstract

<p><i>Retn</i> and <i>Retnl</i> genes are indicated by the red arrows, with the arrow pointing in the direction of transcription. Other genes are shown in yellow (locus of origin) or blue (location of inserted <i>Retnl</i> gene). Curved arrows indicated gene duplications that were either a transposition (to generate <i>Retnl</i>) or tandem, on the rodent and primate lineages. X’s indicate inactivating mutations in the primate and artiodactyl genes that generate pseudogenes. (A). In the ancestor to mammals, <i>Retn</i> was located in the locus of origin. (B). On an early mammalian lineage, prior to the placental mammal-marsupial divergence, a copy of <i>Retn</i> was transposed to a new genomic location to generate the <i>Retnl</i> gene. The transposition likely allowed <i>Retnl</i> to acquire a novel expression pattern. (C). <i>Retn</i> and <i>Retnl</i> genes have different fates on divergent mammalian lineages. While <i>Retn</i> remained as a single copy intact gene on different mammalian lineages, <i>Retnl</i> had different fates, raising the possibility that it acquired lineage-specific functions. <i>Retnl</i> remained as a single copy gene in perissodactyls, duplicated intact (potentially functional) copies in rodents, duplicated and generated a pseudogene in primates, or was inactivated in artiodactyls.</p