title: MRE11 and COM1/SAE2 are required for double-strand break repair and efficient chromosome pairing during meiosis of the protist Tetrahymena.
abstract: Programmed DNA double-strand breaks (DSBs) are generated during meiosis to initiate homologous recombination. Various aspects of DSB formation, signaling, and repair are accomplished or governed by Mre11, a component of the MRN/MRX complex, partially in cooperation with Com1/Sae2/CtIP. We used Tetrahymena to study evolutionarily conserved and changed functions of Mre11 and Com1. There is a difference between organisms with respect to the dependency of meiotic DSB formation on Mre11. By cytology and an electrophoresis-based assay for DSBs, we found that in Tetrahymena Mre11p is not required for the formation and ATR-dependent signaling of DSBs. Its dispensability is also reflected by wild-type-like DSB-dependent reorganization of the meiotic nucleus and by the phosphorylation of H2A.X in mre11∆ mutant. However, mre11∆ and com1∆ mutants are unable to repair DSBs, and chromosome pairing is reduced. It is concluded that, while MRE11 has no universal role in DNA damage signaling, its requirement for DSB repair is conserved between evolutionarily distant organisms. Moreover, reduced chromosome pairing in repair-deficient mutants reveals the existence of two complementing pairing processes, one by the rough parallel arrangement of chromosomes imposed by the tubular shape of the meiotic nucleus and the other by repair-dependent precise sequence matching.
authors.affiliation: Department of Chromosome Biology and Max F. Perutz Laboratories, Center for Molecular Biology, University of Vienna, Dr. Bohr Gasse 1, Vienna, Austria.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Lukaszewicz
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Howard-Till
authors.forename: Maria
authors.initials: M
authors.lastname: Novatchkova
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Mochizuki
authors.forename: Josef
authors.initials: J
authors.lastname: Loidl
mesh_terms: D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D023902:Chromosome Pairing; D003434:Crossing Over, Genetic; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics*; D045643:DNA Repair Enzymes / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008540:Meiosis; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D011995:Recombination, Genetic; D013768:Tetrahymena / Q000166:cytology / Q000235:genetics* / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D015800:Protozoan Proteins; D045643:DNA Repair Enzymes