title: Drawing a fine line on endogenous retroelement activity.
abstract: Endogenous retroelements (EREs) are essential motors of evolution yet require careful control to prevent genomic catastrophes, notably during the vulnerable phases of epigenetic reprogramming that occur immediately after fertilization and in germ cells. Accordingly, a variety of mechanisms restrict these mobile genetic units. Previous studies have revealed the importance of KRAB-containing zinc finger proteins (KRAB-ZFPs) and their cofactor, KAP1, in the early embryonic silencing of endogenous retroviruses and so-called SVAs, but the implication of this transcriptional repression system in the control of LINE-1, the only known active autonomous retrotransposon in the human genome, was thought to be marginal. Two recent studies straighten the record by revealing that the KRAB/KAP system is key to the control of L1 in embryonic stem (ES) cells, and go further in demonstrating that DNA methylation and KRAB/KAP1-induced repression contribute to this process in an evolutionally dynamic fashion. These results shed light on the delicate equilibrium between higher vertebrates and endogenous retroelements, which are not just genetic invaders calling for strict control but rather a constantly renewed and nicely exploitable source of evolutionary potential.
authors.affiliation: School of Life Sciences; École Polytechnique Fédérale de Lausanne (EPFL) ; Lausanne, Switzerland.
authors.forename: Nathaly
authors.initials: N
authors.lastname: Castro-Diaz
authors.affiliation: School of Life Sciences; École Polytechnique Fédérale de Lausanne (EPFL) ; Lausanne, Switzerland.
authors.forename: Marc
authors.initials: M
authors.lastname: Friedli
authors.affiliation: School of Life Sciences; École Polytechnique Fédérale de Lausanne (EPFL) ; Lausanne, Switzerland.
authors.forename: Didier
authors.initials: D
authors.lastname: Trono
keywords: ERE; KAP1; KRAB-ZFPs or KRAB-ZNFs; LINE-1 or L1; embryonic stem cells; endogenous retroelements; genome evolution; retrotransposition