DNA double-strand breaks induce H2Ax phosphorylation domains in a contact-dependent manner

Efficient repair of DNA double-strand breaks (DSBs) requires a coordinated DNA Damage Response (DDR), which includes phosphorylation of histone H2Ax, forming gamma H2Ax. This histone modification spreads beyond the DSB into neighboring chromatin, generating a DDR platform that protects against end disassociation and degradation, minimizing chromosomal rearrangements. However, mechanisms that determine the breadth and intensity of gamma H2Ax domains remain unclear. Here, we show that chromosomal contacts of a DSB site are the primary determinants for gamma H2Ax landscapes. DSBs that disrupt a topological border permit extension of gamma H2Ax domains into both adjacent compartments. In contrast, DSBs near a border produce highly asymmetric DDR platforms, with gamma H2Ax nearly absent from one broken end. Collectively, our findings lend insights into a basic DNA repair mechanism and how the precise location of a DSB may influence genome integrity. Formation of gamma H2Ax serves as a checkpoint for double-strand break (DSB) repair pathways. Here the authors reveal via integrated chromatin analysis that gamma H2Ax domains are established by chromosomal contacts with the DSB site.