Deficiency of either of the two homologs of poly(ADP-ribose) glycohydrolase (PARG), PARG-1 and PARG-2, in Caenorhabditis elegans leads to hypersensitivity to ionizing radiation (IR). In the germ cells of parg-2 mutant worms, the dissipation of recombinase RAD-51 foci was slower than in wild-type (WT) cells, suggesting defects in DNA double-strand break (DSB) repair via homologous recombination (HR). Nevertheless, RPA-1, the large subunit of replication protein A, accumulated faster in parg-2 worms and disappeared earlier than in WT worms. This accelerated RPA-1 accumulation may result from the enhanced expression of exonuclease-1 (EXO-1) after IR treatment. Accordingly, an exo-1 mutation reduced IR sensitivity and accumulation of RPA-1 in parg-2 worms. A mutation of polq-1, encoding for a key factor in the alternative end-joining (Alt-EJ) pathway, suppressed the IR hypersensitivity phenotype of parg-2 worms and normalized the kinetics of RAD-51 dissipation. This indicates that error-prone Alt-EJ may mediate DSB repair in parg-2 worms, causing hypersensitivity to IR. In summary, PARG-2 deficiency in C. elegans causes hyperactive DSB end resection likely through EXO-1 overproduction. DSBs with long single-stranded DNA ends in parg-2 worms are thought to be repaired by Alt-EJ instead of HR, causing genomic instability.
Bibliographical noteFunding Information:
The WT Bristol N2, parg‐1(gk120), parg‐2(ok980) , and cpIs53 [mex‐5p::GFP‐C1::PLC(delta)‐PH::tbb‐2 3'UTR+unc‐119 (+)] strains were acquired from the C. elegans Genetics Center (St Paul, MN, USA), which is funded by the NIH Office of Research Infrastructure Programs (P40 OD010440). We thank Shohei Mitani (Tokyo Women's Medical University School of Medicine) for providing the exo‐1(tm1842) and polq‐1(tm2572) mutants. We are grateful to Jae Won Jung (East Carolina University) for technical assistance with an X‐irradiator and Seong Min Yoon (Yonsei University) for help with genetic crosses of worms. This work was supported by the National Research Foundation of Korea (the Basic Science Research program, 2016R1D1A1B03934743 to H‐SK) and the Brain Korea 21 (BK21 PLUS) Program, awarded to WB.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology