title: Retroviruses facilitate the rapid evolution of the mammalian placenta.
abstract: The mammalian placenta exhibits elevated expression of endogenous retroviruses (ERVs), but the evolutionary significance of this feature remains unclear. I propose that ERV-mediated regulatory evolution was, and continues to be, an important mechanism underlying the evolution of placental development. Many recent studies have focused on the co-option of ERV-derived genes for specific functional adaptations in the placenta. However, the co-option of ERV-derived regulatory elements could potentially lead to the incorporation of entire gene regulatory networks, which, I argue, would facilitate relatively rapid developmental evolution of the placenta. I suggest a model in which an ancient retroviral infection led to the establishment of the ancestral placental developmental gene network through the co-option of ERV-derived regulatory elements. Consequently, placental development would require elevated tolerance to ERV activity. This in turn would expose a continuous stream of novel ERV mutations that may have catalyzed the developmental diversification of the mammalian placenta.
authors.affiliation: Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: Edward B
authors.initials: EB
authors.lastname: Chuong
mesh_terms: D000818:Animals; D020077:Endogenous Retroviruses / Q000235:genetics*; D004742:Enhancer Elements, Genetic; D019143:Evolution, Molecular; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D008322:Mammals / Q000235:genetics; D009154:Mutation; D010920:Placenta / Q000502:physiology*; D011247:Pregnancy; D012045:Regulatory Sequences, Nucleic Acid; D020079:Terminal Repeat Sequences; D014327:Trophoblasts / Q000502:physiology
keywords: co-option; conflict; endogenous retroviruses; evolution; evolvability; placenta; regulatory evolution