Preservation of genomic integrity in the nematode Caenorhabditis elegans

Preservation of genomic integrity is an important task in the life of an organism. This thesis explores the role the MRE-11/RAD-50 complex plays in promoting genomic stability in the nematode Caenorhabditis elegans . While study of the function of the Mre11/Rad50 complex in simple eukaryotes and in vitro systems has established multiple roles for the complex in the preservation of genomic integrity, study of the in vivo function of the vertebrate Mre11/Rad50 complex has been hampered due to inviability of vertebrate cells that lack either Mre11 or Rad50. However, examination of a number of in vivo roles of the metazoan complex was possible in C. elegans because homozygous mutants were viable.; C. elegans mre-11 plays a crucial role in meiotic recombination, and several experimental approaches have provided strong evidence that this requirement may involve a role in meiotic double-strand break initiation. In addition, mre-11 and rad-50 mutants exhibit a profound sensitivity to ionizing radiation as evidenced by a reduction in progeny survivorship and the induction of chromosomal defects. However, the complex is dispensable for the DNA damage checkpoint that functions in late pachytene of the C. elegans germline. In fact, a significant increase in apoptotic bodies is produced by ionizing radiation treatment.; Although homozygous C. elegans mre-11 and rad-50 mutants are viable, MRE-11 and RAD-50 do play an essential role in the maintenance of reproductive capacity in C. elegans. A marked drop in both viability and fecundity occurs in successive generations of homozyougs mre-11 and rad-50 mutants. This progressive loss of reproductive capacity may stem from a role in DNA repair in premeiotic nuclei. RAD-51 plays a crucial role in the repair of DNA damage by homologous recombination. The accumulation of non-meiotic RAD-51 foci in rad-50 mutants is consistent with a role in removing spontaneous DNA damage that occurs during replication. Furthermore, the ability to form RAD-51 foci yet inability to complete the DNA repair process also supports the postulate that the MRE-11/RAD-50 complex plays a structural role in the repair of DNA double-strand breaks, perhaps by stabilizing a favorable physical association between the damaged chromosome and a potential repair partner.