Baton pass hypothesis: successive incorporation of unconserved endogenous retroviral genes for placentation during mammalian evolution. (7th September 2015)

• Record Type: Journal Article
• Authors: Imakawa, Kazuhiko; Nakagawa, So; Miyazawa, Takayuki
• Is Part Of: Genes to cells. Volume 20:Number 10(2015:Oct.)
• Page Start: 771
• Page End: 788
• Publication Date: 2015-09-07
• Subjects: Cytogenetics -- Periodicals; Cells -- Mechanical properties -- Periodicals; Molecular genetics -- Periodicals; Genes -- Periodicals; Molecular biology -- Periodicals; Cytology -- Periodicals; Biomechanics -- Periodicals; 571.6
• DOI: 10.1111/gtc.12278
• Languages: English
• ISSNs: 1356-9597

Abstract

<abstract abstract-type="main" id="gtc12278-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p>It is well accepted that numerous RNAs derived from endogenous retroviruses (<italic>ERV</italic>s) are expressed in mammalian reproductive structures, particularly in the uterus, trophoblast, and placenta. Syncytin 1 and syncytin 2 in humans and syncytin A and syncytin B in mice are membrane proteins originating from <italic>Env</italic> genes of <italic>ERV</italic>s. These ERVs are involved in the fusion of trophoblast cells, resulting in multinucleated syncytiotrophoblast formation. Evidence accumulated indicates that syncytin‐like fusogenic proteins are expressed in the placenta of rabbits, dogs/cats, ruminant ungulates, tenrecs, and opossums. The <italic>syncytin</italic> genes so far characterized are known to be endogenized to the host genome only within the past 12–80 million years, more recently than the appearance of mammalian placentas, estimated to be 160–180 million years ago. We speculate that <italic>ERV</italic>s including <italic>syncytin</italic>‐like gene variants integrated into mammalian genomes in a locus‐specific manner have replaced the genes previously responsible for cell fusion. We therefore propose the 'baton pass' hypothesis, in which multiple successive <italic>ERV</italic> variants 'take over' cell‐fusion roles, resulting in increased trophoblast cell fusion, morphological variations in placental structures, and enhanced reproductive success in placental mammals.</p> </abstract>