C. elegans mre-11 is required for meiotic recombination and DNA repair but is dispensable for the meiotic G₂ DNA damage checkpoint

Abstract

We investigated the roles of Caenorhabditis elegans MRE-11 in multiple cellular processes required to maintain genome integrity. Although yeast Mre11 is known to promote genome stability through several diverse pathways, inviability of vertebrate cells that lack Mre11 has hindered elucidation of the in vivo roles of this conserved protein in metazoan biology. Worms homozygous for an mre-11 null mutation are viable, allowing us to demonstrate in vivo requirements for MRE-11 in meiotic recombination and DNA repair. In mre-11 mutants, meiotic crossovers are not detected, and oocyte chromosomes lack chiasmata but appear otherwise intact. ␥-irradiation of mre-11 mutant germ cells during meiotic prophase eliminates progeny survivorship and induces chromosome fragmentation and other cytologically visible abnormalities, indicating a defect in repair of radiation-induced chromosome damage. Whereas mre-11 mutant germ cells are repair-deficient, they retain function of the meiotic G 2 DNA damage checkpoint that triggers germ cell apoptosis in response to ionizing radiation. Although mre-11/mre-11 animals derived from heterozygous parents are viable and produce many embryos, there is a marked drop both in the number and survivorship of embryos produced by succeeding generations. This progressive loss of fecundity and viability indicates that MRE-11 performs a function essential for maintaining reproductive capacity in the species.

Genome-wide RNAi identifies p53-dependent and -independent regulators of germ cell apoptosis in C. elegans

“…For example, we identified only two of the more than 12 DNA damage response genes previously shown to induce germ cell apoptosis upon RNAi-mediated knockdown. 9,10,25,26 However, many of these genes needed to be fed for several generations at high dsRNA concentrations for the apoptosis phenotype to become evident. We also failed to identify in our screen daz-1 and the ste13/ME31B/RCK/p54 homologue cgh-1; both genes have been shown to induce germ cell apoptosis through as yet unknown mechanisms upon inactivation.…”

Germ Cell Apoptosis and DNA Damage Responses

“…It is not known whether the C. elegans CtIP, which is required for the repair of SPO-11 generated DNA double-strand breaks, has such a role in the worm (Penkner et al 2007 ) . The MRE-11 nuclease is required for ATL-1 loading (Garcia-Muse and Boulton 2005 ) but DNA damage checkpoint response defects have not been reported in the mre-11 worm mutant (Chin and Villeneuve 2001 ) . A DNA damage-speci fi c clamp loader, comprised of Rad17 in a complex with the four smallest RFC (Replication Factor C) subunits, recruits a PCNA (proliferating cell nuclear antigen)-like complex referred to as "9-1-1" complex to the dsDNAssDNA transition at resected DNA ends.…”

Death and more: DNA damage response pathways in the nematode C. elegans

“…56 However, the fact that mre-11 mutants show increased, rather than decreased germ cell apoptosis argues that in C. elegans, the DNA damage checkpoint is still functional in mre-11 mutants. 57 Another crucial component of the C. elegans meiotic recombination machinery is a germline-specific member of the MutS protein family, MSH-5. 58 Crossing over and chiasma formation events depend on msh-5 gene (msh¼mismatch repair gene) function: in msh-5 mutants, both events are severely reduced or eliminated.…”