Double-Strand Breaks in Heterochromatin Move Outside of a Dynamic HP1a Domain to Complete Recombinational Repair

SummaryDouble-strand breaks (DSBs) in heterochromatic repetitive DNAs pose significant threats to genome integrity, but information about how such lesions are processed and repaired is sparse. We observe dramatic expansion and dynamic protrusions of the heterochromatin domain in response to ionizing radiation (IR) in Drosophila cells. We also find that heterochromatic DSBs are repaired by homologous recombination (HR) but with striking differences from euchromatin. Proteins involved in early HR events (resection) are rapidly recruited to DSBs within heterochromatin. In contrast, Rad51, which mediates strand invasion, only associates with DSBs that relocalize outside of the domain. Heterochromatin expansion and relocalization of foci require checkpoint and resection proteins. Finally, the Smc5/6 complex is enriched in heterochromatin and is required to exclude Rad51 from the domain and prevent abnormal recombination. We propose that the spatial and temporal control of DSB repair in heterochromatin safeguards genome stability by preventing aberrant exchanges between repeats.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (235 K)Download as PowerPoint slideHighlights► DSB detection and processing occur very efficiently in heterochromatin after IR ► Heterochromatic DSBs move outside the expanding HP1a domain to complete HR repair ► HP1a expansion and DSB relocalization require checkpoint and resection proteins ► Smc5/6 prevent Rad51 foci formation and aberrant recombination within the HP1a domain