Synthetic lethality between PAXX and XLF in mammalian development.

Abstract : PAXX was identified recently as a novel nonhomologous end-joining DNA repair factor in human cells. To characterize its physiological roles, we generated Paxx-deficient mice. Like Xlf −/− mice, Paxx −/− mice are viable, grow normally , and are fertile but show mild radiosensitivity. Strikingly, while Paxx loss is epistatic with Ku80, Lig4, and Atm deficiency, Paxx/Xlf double-knockout mice display embryonic lethality associated with genomic instability , cell death in the central nervous system, and an almost complete block in lymphogenesis, phenotypes that closely resemble those of Xrcc4 −/− and Lig4 −/− mice. Thus, combined loss of Paxx and Xlf is synthetic-lethal in mammals.