ABSTRACT
Deficiency in both ATM and the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is synthetically lethal in developing mouse embryos. Using mice that phenocopy diverse aspects of Atm deficiency, we have analyzed the genetic requirements for embryonic lethality in the absence of functional DNA-PKcs. Similar to the loss of ATM, hypomorphic mutations of Mre11 (Mre11(ATLD1)) led to synthetic lethality when juxtaposed with DNA-PKcs deficiency (Prkdc(scid)). In contrast, the more moderate DNA double-strand break response defects associated with the Nbs1(DeltaB) allele permitted viability of some Nbs1(DeltaB/DeltaB) Prkdc(scid/scid) embryos. Cell cultures from Nbs1(DeltaB/DeltaB) Prkdc(scid/scid) embryos displayed severe defects, including premature senescence, mitotic aberrations, sensitivity to ionizing radiation, altered checkpoint responses, and increased chromosome instability. The known functions of DNA-PKcs in the regulation of Artemis nuclease activity or nonhomologous end joining-mediated repair do not appear to underlie the severe genetic interaction. Our results reveal a role for DNA-PKcs in the maintenance of S/G(2)-phase chromosome stability and in the induction of cell cycle checkpoint responses.
Subject(s)
Cell Cycle Proteins/metabolism , Chromosomal Instability , DNA Repair Enzymes/metabolism , DNA-Activated Protein Kinase/physiology , DNA-Binding Proteins/metabolism , DNA-Binding Proteins/physiology , Nuclear Proteins/metabolism , Nuclear Proteins/physiology , Protein Serine-Threonine Kinases/metabolism , Tumor Suppressor Proteins/metabolism , Animals , Ataxia Telangiectasia Mutated Proteins , Cell Cycle , Cell Cycle Proteins/genetics , Cell Death , Chromosomal Proteins, Non-Histone/metabolism , DNA Breaks, Double-Stranded , DNA Repair/genetics , DNA Repair/physiology , DNA Repair Enzymes/genetics , DNA-Activated Protein Kinase/genetics , DNA-Binding Proteins/genetics , Embryo, Mammalian , Endonucleases , G2 Phase , MRE11 Homologue Protein , Mice , Mice, Transgenic , Nuclear Proteins/genetics , Protein Serine-Threonine Kinases/genetics , S Phase , Tumor Suppressor Proteins/geneticsABSTRACT
The Mre11 complex (consisting of MRE11, RAD50, and NBS1/Xrs2) is required for double-strand break (DSB) formation, processing, and checkpoint signaling during meiotic cell division in S. cerevisiae. Whereas studies of Mre11 complex mutants in S. pombe and A. thaliana indicate that the complex has other essential meiotic roles , relatively little is known regarding the functions of the complex downstream of meiotic break formation and processing or its role in meiosis in higher eukaryotes. We analyzed meiotic events in mice harboring hypomorphic Mre11 and Nbs1 mutations which, unlike null mutants, support viability . Our studies revealed defects in the temporal progression of meiotic prophase, incomplete and aberrant synapsis of homologous chromosomes, persistence of strand exchange proteins, and alterations in both the frequency and placement of MLH1 foci, a marker of crossovers. A unique sex-dependent effect on MLH1 foci and chiasmata numbers was observed: males exhibited an increase and females a decrease in recombination levels. Thus, our findings implicate the Mre11 complex in meiotic DNA repair and synapsis in mammals and indicate that the complex may contribute to the establishment of normal sex-specific differences in meiosis.