Convergent Co-option of the Retroviral gag Gene during the Early Evolution of Mammals

Abstract

Retroviruses occasionally can infect host germ lines, forming endogenous retroviruses. Vertebrates, in turn, recruited retroviral genes for their own biological functions, a process formally known as co-option or exaptation. To date, co-opted retroviral gag genes have rarely been reported. In this study, we identified two co-opted retroviral gag genes, designated wucaishi1 ( wcs1 ) and wucaishi2 ( wcs2 ), in mammals. The co-option of wcs1 and wcs2 occurred before the origin of modern placentals and before the origin of modern marsupials, respectively. Our study indicates that retroviral gag gene co-option might have occurred more frequently than previously thought during the evolutionary course of vertebrates.