title: The essential function of the MRN complex in the resolution of endogenous replication intermediates.
abstract: The MRN complex (Mre11/Rad50/Nbs1) is important in double-strand break (DSB) recognition, end resection, replication fork stabilization, and ATM and ATR activation. Complete deletion of MRN is incompatible with cell and organism life, presumably due to replication-born DSBs; however, the underlying mechanism remains unknown. We devised a noninvasive high-content assay, termed high-content microscopy-assisted cell-cycle phenotyping (hiMAC), to investigate the fate of cells lacking Nbs1. Surprisingly, deletion of Nbs1 does not kill cells during replication. The primary lesions in Nbs1-deleted cells are replication intermediates that result from defective resolution rather than fork destabilization. These lesions are converted to DSBs in the subsequent G2 phase, which subsequently activate Chk1, delay G2 progression, and lead to chromosome instability. Nbs1-deleted cells establish a DSB equilibrium that permits cell cycling but activates p53, causing G1 and G2 arrest, and cell death. Thus, we identify a physiological role of Nbs1 in the resolution of stalled replication forks.
authors.affiliation: Leibniz Institute for Age Research - Fritz Lipmann Institute (FLI), Jena 07745, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Bruhn
authors.affiliation: Leibniz Institute for Age Research - Fritz Lipmann Institute (FLI), Jena 07745, Germany.
authors.forename: Zhong-Wei
authors.initials: ZW
authors.lastname: Zhou
authors.affiliation: Leibniz Institute for Age Research - Fritz Lipmann Institute (FLI), Jena 07745, Germany.
authors.forename: Haiyan
authors.initials: H
authors.lastname: Ai
authors.affiliation: Leibniz Institute for Age Research - Fritz Lipmann Institute (FLI), Jena 07745, Germany; Faculty of Biology and Pharmacy, Friedrich Schiller University Jena, Jena 07743, Germany. Electronic address: zqwang@fli-leibniz.de.
authors.forename: Zhao-Qi
authors.initials: ZQ
authors.lastname: Wang
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D017766:Acid Anhydride Hydrolases; D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D053903:DNA Breaks, Double-Stranded; D045643:DNA Repair Enzymes / Q000378:metabolism; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000378:metabolism; D016195:G2 Phase; D017353:Gene Deletion; D000076228:MRE11 Homologue Protein; D051379:Mice; D008856:Microscopy, Fluorescence / Q000379:methods; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C512689:Mre11a protein, mouse; C466108:Nijmegen breakage syndrome 1 protein, mouse; D009687:Nuclear Proteins; D011494:Protein Kinases; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C495198:Rad50 protein, mouse; D045643:DNA Repair Enzymes