Imaging the time course of DNA damage response at a nonrepetitive endogenous locus.

DNA double-strand breaks (DSBs) are among the most genotoxic lesions. Investigating the cellular dynamics of repair factors during DSB repair requires methodologies that preserve both spatial and temporal information. Here, we describe a method for tracking repair progression over time at any desired genomic locus by combining DSB induction on the seconds timescale (very fast CRISPR) and genomic labeling using local genome denaturation (genome oligopaint via local denaturation fluorescence in situ hybridization [GOLDFISH]). Through protocol optimization to retain repair signatures such as γH2AX, p53-binding protein 1 (53BP1), and BRCA1, we show that the kinetics of DSB foci formation at nonrepetitive endogenous loci can be measured with minutes time resolution.