Mutator Phenotype ofCaenorhabditis elegansDNA Damage Checkpoint Mutants

Abstract

DNA damage response proteins identify sites of DNA damage and signal to downstream effectors that orchestrate either apoptosis or arrest of the cell cycle and DNA repair. The C. elegans DNA damage response mutants mrt-2, hus-1, and clk-2(mn159) displayed 8-to 15-fold increases in the frequency of spontaneous mutation in their germlines. Many of these mutations were small-to medium-sized deletions, some of which had unusual sequences at their breakpoints such as purine-rich tracts or direct or inverted repeats. Although DNA-damage-induced apoptosis is abrogated in the mrt-2, hus-1, and clk-2 mutant backgrounds, lack of the apoptotic branch of the DNA damage response pathway in cep-1/p53, ced-3, and ced-4 mutants did not result in a Mutator phenotype. Thus, DNA damage checkpoint proteins suppress the frequency of mutation by ensuring that spontaneous DNA damage is accurately repaired in C. elegans germ cells. Although DNA damage response defects that predispose humans to cancer are known to result in large-scale chromosome aberrations, our results suggest that small-to medium-sized deletions may also play roles in the development of cancer.

Genome Integrity Is Regulated by theCaenorhabditis elegansRad51D Homologrfs-1

“…This assay was developed by Harris et al (2006) to quantify the Mutator phenotypes of mrt-2 and clk-2. Both extragenic and intragenic suppressors can be obtained, thus the spontaneous rate of reversion of this locus is higher than many others.…”

“…unc-58(e665) reversion assay: rfs-1; unc-58(e665) and unc-58(e665) homozygotes were grown as described previously (Harris et al 2006). Approximately 100 10-cm plates per genotype were scored by eye for the presence of non-Unc or weak Unc revertants.…”

“…Approximately 100 10-cm plates per genotype were scored by eye for the presence of non-Unc or weak Unc revertants. Calculations of haploid genomes tested and reversion frequency were performed as described (Harris et al 2006).…”

The Caenorhabditis elegans Rad17 Homolog HPR-17 Is Required for Telomere Replication

“…It is also possible that the unraveling of chromatin or telomere-binding proteins at the T-loop, which resembles a recombination intermediate, might be sufficient to trigger a DNA damage response. In this context, deficiency for the 9-1-1 complex subunit mrt-2 has been shown to result in aberrant homologous recombination events (Harris et al 2006). In addition, mrt-2 suppresses chromosome rearrangements that flank G-rich DNA tracts, which may resemble the G-rich strand of telomeric DNA in their ability to form noncanonical G quadruplex structures (Harris et al 2006).…”

“…In this context, deficiency for the 9-1-1 complex subunit mrt-2 has been shown to result in aberrant homologous recombination events (Harris et al 2006). In addition, mrt-2 suppresses chromosome rearrangements that flank G-rich DNA tracts, which may resemble the G-rich strand of telomeric DNA in their ability to form noncanonical G quadruplex structures (Harris et al 2006). Once bound to telomeric DNA, the 9-1-1 complex may facilitate the recruitment of telomerase to chromosome ends, perhaps by modulating processing of the chromosome terminus or by acting to tether telomerase during telomere repeat addition (Francia et al 2006;Verdun and Karlseder 2006), as might be expected for a protein complex homologous to the PCNA polymerase clamp.…”