Our long-term objective is to understand how programmed cell death and DNA repair guide development and maintenance of the nervous system. This ROl focuses a specific form of DNA repair called Non-Homologous End Joining (NHEJ), which is required for proper development of the CNS. Enzymes involved in NHEJ and other DNA repairs serve critical roles in genomic stability and neuronal survival in neurodegenerative disorders such as Alzheimer's and ALS. In the developing brain, programmed cell death is regulated process acting in concert with neurogenesis and differentiation. Knockout mice deficient NHEJ or other DNA repair processes typically have increased apoptosis in the embryonic CNS and perinatal lethality. We will utilize NHEJ deficient mice in combination with cellular and molecular approaches to study the impact of genomic instability on neuronal survival and differentiation. To accomplish this broad goal, we have four Specific aims. The first proposes to compare the molecular phenotypes of neural progenitors and postmitotic neurons in the cerebral cortex of normal and NHEJ-deficient mouse embryos. We will monitor cell death and examine the expression of cell cycle and other molecular markers. We will also generate CNS-specific conditional knockouts of NHEJ genes using cre-recombinase technology to evaluate whether failed NHEJ in neural progenitors and neurons is responsible for the differences in apoptosis. The second aim will determine if NHEJ deficient embryonic CNS cultures exhibit increased apoptotic responses to hypoxia, free radical damage, or excitotoxic injury. The third aim will examine whether NHEJ deficiency and accumulated DNA breaks coupled with hypoxia or excitotoxic injury activate p53 and downstream apoptotic effects such as mitochondrial dysfunction. We will generate compound knockout mice lacking NHEJ genes and either p53 or Bax to test this hypothesis. Our fourth aim will extend these studies to ask whether exogenous growth factors or free radical scavengers can delay or prevents downstream apoptotic signaling in NHEJ deficient mice.