In order to maintain genomic integrity, DNA must be replicated without damaging the genetic code. This can be especially difficult under stressful conditions where additional barriers to replication may arise. Additionally, challenging repetitive sequences, such as those in telomeric DNA, provide endogenous barriers to replication. In humans, SMARCAL1 helps maintain genomic integrity by restarting stalled replication forks. This is a critical function, and defects in SMARCAL1 have been implicated in the rare disease Schimke Immuno-osseous Dysplasia. We used CRISPR to generate knockout alleles of the C. elegans SMARCAL1 ortholog,
smrc-1. We found that these mutants show a decreased brood size and laid fewer eggs than wild type and also show increased germline apoptosis, phenotypes that are dependent on the activity of the DNA damage checkpoint. To further investigate the role of SMRC-1 in DNA damage repair, we subjected
smrc-1 mutants to hydroxyurea (HU) and camptothecin (CPT), which can inhibit replication fork progression, as well as ionizing radiation (IR) which causes double stranded breaks. We found that
smrc-1 mutants are sensitive to hydroxyurea (HU) and tagged SMRC-1 proteins relocalize from the nucleoplasm to chromatin-associated foci following HU exposure. Consistent with a role for SMRC-1 at stalled replication forks,
smrc-1 mutants enhance the genomic instability phenotype of
dog-1, showing increased mutations in a region that forms G-quadruplexes.
smrc-1 mutants also exhibit a mortal germline (MRT) phenotype that we attribute to a buildup of mutations over generations. Interestingly, absence of SMRC-1 function enhances the MRT phenotype in the telomere mutant,
trt-1, implicating SMRC-1 as a major determinant of telomere integrity. SMRC-1 protein co-immunoprecipiates with the H3K9 methyltransferase, MET-2 and double mutants show enhanced sterility. These studies introduce the exciting possibility that replication fork repair is coupled with the protection of repetitive sequences by methylation.