The effects of chromatin regulators on somatic DNA double-strand break repair

DNA double-strand breaks (DSBs) occur frequently in mitotically-dividing cells and require appropriate repair. DSB are repaired by two conserved mechanisms in eukaryotes: non-homologous end-joining and homologous recombination. These pathways compete to repair a DSB, and proper modulation of the non-homologous end-joining and homologous recombination pathways is critical to ensure cell survival, maintain genome integrity, and prevent carcinogenesis. Recent evidence indicates that the chromatin context can influence DSB repair, yet many aspects remain unclear.;Candidate chromatin regulator genes affecting somatic DSB repair in Drosophile melanogaster were identified using ionizing radiation challenge. Animals heterozygous for chromatin regulator gene mutations were exposed to 30Gy irradiation and the survival phenotypes were determined.;The ESC/E(Z) and Gypsy insulator complexes are involved in chromatin structure maintenance in Drosophila, and mutations in either complex conferred radiation resistance. I went on to show that somatic DSBs are repaired more frequently by homologous recombination in a heterozygous ESC/E(Z) or Gypsy complex mutant background as evidenced by elevated gene conversion from the homolog following a P element induced DSB. Furthermore, when an ESC/E(Z) complex mutation was combined with a Gypsy complex mutation, double heterozygote mutants displayed a synergistic increase in gene conversion using the homolog.;Heterozygosity of the osa2 allele of eyelid conferred hypersensitivity to ionizing radiation. These animals also showed a markedly reduced capacity to repair somatic DSBs by homologous recombination using the homolog and exhibited unstable genomes.;This research advances the current understanding of how chromatin regulators influence DSB repair pathway choice in the soma of eukaryotic organisms.;Keywords. Drososphila melanogaster, DNA repair, double-strand breaks, homologous recombination, gene conversion, non-homologous end-joining, chromatin, Polycomb Group, Trithorax Group, Gypsy Insulator, chromatin organization, SWI/SNF, Brahma, Eyelid, suppressor of Hairy wing, modifier of mdg4...