Genetic interaction between DNA polymerase beta and DNA-PKcs in embryogenesis and neurogenesis.

DNA polymerase beta (Polbeta) has been implicated in base excision repair. Polbeta knockout mice exhibit apoptosis in postmitotic neuronal cells and die at birth. Also, mice deficient in nonhomologous end-joining (NHEJ), a major pathway for DNA double-strand break repair, cause massive neuronal apoptosis. Severe combined immunodeficiency (SCID) mice have a mutation in the gene encoding DNA-dependent protein kinase catalytic subunit (DNA-PKcs), the component of NHEJ, and exhibit defective lymphogenesis. To study the interaction between Polbeta and DNA-PKcs, we generated mice doubly deficient in Polbeta and DNA-PKcs. Polbeta(-/-)DNA-PKcs(scid/scid) embryos displayed greater developmental delay, more extensive neuronal apoptosis, and earlier lethality than Polbeta(-/-) and DNA-PKcs(scid/scid) embryos. Furthermore, to study the involvement of p53 in the phenotype, we generated Polbeta(-/-)DNA-PKcs(scid/scid)p53(-/-) triple-mutant mice. The mutants did not exhibit apoptosis but were lethal with defective neurulation at midgestation. These results suggest a genetic interaction between Polbeta and DNA-PKcs in embryogenesis and neurogenesis.