KAP1 controls endogenous retroviruses in embryonic stem cells

Almost half of the mammalian genome is derived from virus-like entities called retroelements, many of them the result of the incorporation of endogenous retroviruses. Didier Trono and colleagues use a combination of genetic, functional and biochemical analyses to demonstrate that KRAB-associated protein 1 (KAP1)-mediated epigenetic regulation is involved in the early embryonic silencing of intracisternal A particles (IAPs), a still active and highly polymorphic subset of endogenous retroviruses. This work establishes a role for the KAP1 co-repressor in the control of endogenous retroelements during early embryonic development.