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Bioessays. 2013 Oct;35(10):853-61. doi: 10.1002/bies.201300059. Epub 2013 Jul 19.

Retroviruses facilitate the rapid evolution of the mammalian placenta.

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Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA.

Erratum in

  • Bioessays. 2014 Aug;36(8):807.


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.


co-option; conflict; endogenous retroviruses; evolution; evolvability; placenta; regulatory evolution

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