# PARP-2 catalytic activity drives replication-ICL repair in an allele-specific manner during germline development

## TL;DR

This study shows that the protein PARP-2 is crucial for DNA repair and genome stability in C. elegans, especially during germline development.

## Contribution

The study reveals that PARP-2 has a dual role in DNA repair and stress response regulation, with its catalytic activity being essential for genome stability.

## Key findings

- PARP-2 is essential for replication-coupled DNA repair and nucleolar signaling in C. elegans germline development.
- A catalytic-dead PARP-2 mutant causes more severe defects than the null allele, indicating its role in restraining stress responses.
- PARP-2 is enriched at fragile genomic loci, suggesting a constitutive surveillance role in maintaining genome stability.

## Abstract

Maintaining genome integrity in the germline is critical for fertility and organismal survival. Here, we identify C. elegans PARP-2 as an essential and non-redundant regulator of replication-coupled DNA repair. PARP-2 localizes to chromatin during germline development and is also present in the nucleolus; replication stress is associated with changes in its nucleolar distribution, linking fork perturbation to nucleolar signaling and ribosomal homeostasis. Loss of PARP-2 leads to embryonic lethality, larval arrest, and hypersensitivity to replication-blocking and crosslinking agents, accompanied by accumulation of recombination intermediates. Strikingly, a catalytic-dead mutant (E509K) causes even more severe defects than the null allele, including hyperactivation of DNA damage pathways and elevated apoptosis, revealing that PARP-2 enzymatic activity not only executes repair but also restrains excessive stress responses. Chromatin profiling further shows enrichment of PARP-2 at promoter-proximal, fragile loci, suggesting a constitutive surveillance role. Together, these findings establish PARP-2 as a multifunctional genome guardian that integrates catalytic and structural roles to maintain genome stability and nucleolar function, with implications for understanding PARP-associated disease mutations.

The ability to faithfully pass on genetic information is essential for fertility and survival. In this study, we show that the protein PARP-2 plays a central role in protecting the genome of the roundworm C. elegans. PARP-2 normally works during DNA replication, helping to repair problems that arise when the replication machinery stalls. We find that PARP-2 not only binds to chromatin in developing germ cells but is also present in the nucleolus, and that DNA replication stress is accompanied by changes in its nucleolar association. Animals that lack PARP-2 die early or stop growing, and they are very sensitive to DNA-damaging agents. Surprisingly, worms carrying a version of PARP-2 that has lost its enzymatic activity suffer even worse defects, including excessive activation of DNA damage responses and cell death. This shows that PARP-2 has a dual role: it helps repair DNA but also prevents stress pathways from overreacting. We also discovered that PARP-2 is often found near fragile regions of the genome, suggesting it constantly monitors genome stability.