Genetic analysis of the DNA damage response

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DNA double-strand breaks (DSBs) are potentially lethal chromosomal lesions that can trigger genome instability or cell death if they are not repaired. Eukaryotes have evolved a sophisticated network of proteins for sensing and repairing DSBs, A critical regulator of this DSB response network is ATM (ataxia-telangiectasia mutated), a large, multi-functional protein kinase that is responsible for regulating DSB repair, cell cycle checkpoint responses, as well as telomere maintenance. ATM is named for a human neurodegenerative disease associated with genome instability, immunological defects, sterility and predisposition to cancer. These diverse activities require that ATM and its essential co-factor the MRN complex collaborate to sense chromatin structures associated with DNA "ends". Their interactions somehow activate the ATM/MRN complex and localize it to foci at sites of DNA double-strand breaks (DSBs) or telomeres, the natural ends of chromosomes. Activated ATM is thought to play a dual role: both as a scaffold for assembling specific repair complexes at DNA damage sites, and as a kinase that regulates different signaling pathways by phosphorylation of specific substrates.  A major mystery in the biology of ATM is how it selectively responds to different types of chromosome "ends", discriminating between telomeres and DSBs caused by DNA damage. To address this problem, we are studying ATM-dependent DNA damage responses in Drosophila, as an animal model. We showed that loss of ATM activity causes defects that include chromosome instability, telomere defects and chromosome segregation defects during female meiosis resulting in aneuploid gametes. These results establish Drosophila as an excellent model system for studying conserved ATM functions. The present proposal outlines strategies for building on this foundation, applying complementary biochemical and genetic approaches to define and characterize novel factors that will provide new insights into molecular mechanisms underlying conserved roles of ATM in the DNA damage response.