A Zygotic Checkpoint for Unrepaired Lesions.

DNA demethylation, a process involving DNA repair, is critical for reprogramming of the paternal genome during the oocyte-to-zygote transition. A new study by Ladstätter and Tachibana-Konwalski shows that a Chk1-mediated zygotic checkpoint monitors the cohesin-dependent repair of DNA lesions arising from DNA demethylation, which prevents zygotes carrying unrepaired lesions from entering mitosis.