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

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.