Aging impairs double-strand break repair by homologous recombination inDrosophilagerm cells

Abstract

SummaryAging is characterized by genome instability, which contributes to cancer formation and cell lethality leading to organismal decline. The high levels of DNA double‐strand breaks (DSBs) observed in old cells and premature aging syndromes are likely a primary source of genome instability, but the underlying cause of their formation is still unclear. DSBs might result from higher levels of damage or repair defects emerging with advancing age, but repair pathways in old organisms are still poorly understood. Here, we show that premeiotic germline cells of young and old flies have distinct differences in their ability to repair DSBs by the error‐free pathway homologous recombination (HR). Repair of DSBs induced by either ionizing radiation (IR) or the endonuclease I‐SceI is markedly defective in older flies. This correlates with a remarkable reduction in HR repair measured with the DR ‐white DSB repair reporter assay. Strikingly, most of this repair defect is already present at 8 days of age. Finally, HR defects correlate with increased expression of early HR components and increased recruitment of Rad51 to damage in older organisms. Thus, we propose that the defect in the HR pathway for germ cells in older flies occurs following Rad51 recruitment. These data reveal that DSB repair defects arise early in the aging process and suggest that HR deficiencies are a leading cause of genome instability in germ cells of older animals.

Quantitative insights into age-associated DNA-repair inefficiency in single cells

“…The relative usage and efficiency of different DSB repair mechanisms depend on factors including cellcycle stage, ploidy, and cell type 15,16,17,18 . Previous studies have detected changes in repair pathway usage between chronologically old and young tissues, that could indicate age-related changes in repair efficiency 19,20 . However, how the repair efficiency of specific DSB repair pathways longitudinally changes in mitotically aging single cells remains unexplored.…”

Actin’ between phase separated domains for heterochromatin repair

“…Additionally, chromatin movement across nuclear domains is not uncommon and an important challenge is to establish the relevance of transient nuclear filaments and motors in nuclear dynamics for different functions. Heterochromatin silencing 135,136 , HR repair [137][138][139][140] , nuclear periphery 141 , and actin/myosin components 142 deteriorate with age, suggesting these declines as a contributor to repair defects and genome instability observed in older organisms [143][144][145][146] (reviewed in 33,46 ). Thus, understanding heterochromatin repair mechanisms is expected to open new opportunities for addressing human disease, and the tools are now in place for exciting new discoveries in the near future.…”

Live cell imaging of nuclear actin filaments and heterochromatic repair foci in Drosophila and mouse cells

“…Understanding these spatial and temporal dynamics requires the ability to visualize repair components, heterochromatin domains, and nuclear F-actin by live cell imaging. Repair sites can be detected by fluorescent tagging of repair components that form cytologically visible foci upon recruitment to DSBs [18,20,[34][35][36][37][38][39][40][41][42]. For example, Mdc1 (Drosophila Mu2) associates with the phosphorylated form of the histone variant H2Av [23,43,44] (γH2Av, corresponding to mammalian DSB mark γH2AX [40,45,46]), and mediates the recruitment of other HR proteins [47][48][49][50].…”