title: Meiotic crossover control by concerted action of Rad51-Dmc1 in homolog template bias and robust homeostatic regulation.
abstract: During meiosis, repair of programmed DNA double-strand breaks (DSBs) by recombination promotes pairing of homologous chromosomes and their connection by crossovers. Two DNA strand-exchange proteins, Rad51 and Dmc1, are required for meiotic recombination in many organisms. Studies in budding yeast imply that Rad51 acts to regulate Dmc1's strand exchange activity, while its own exchange activity is inhibited. However, in a dmc1 mutant, elimination of inhibitory factor, Hed1, activates Rad51's strand exchange activity and results in high levels of recombination without participation of Dmc1. Here we show that Rad51-mediated meiotic recombination is not subject to regulatory processes associated with high-fidelity chromosome segregation. These include homolog bias, a process that directs strand exchange between homologs rather than sister chromatids. Furthermore, activation of Rad51 does not effectively substitute for Dmc1's chromosome pairing activity, nor does it ensure formation of the obligate crossovers required for accurate homolog segregation. We further show that Dmc1's dominance in promoting strand exchange between homologs involves repression of Rad51's strand-exchange activity. This function of Dmc1 is independent of Hed1, but requires the meiotic kinase, Mek1. Hed1 makes a relatively minor contribution to homolog bias, but nonetheless this is important for normal morphogenesis of synaptonemal complexes and efficient crossing-over especially when DSB numbers are decreased. Super-resolution microscopy shows that Dmc1 also acts to organize discrete complexes of a Mek1 partner protein, Red1, into clusters along lateral elements of synaptonemal complexes; this activity may also contribute to homolog bias. Finally, we show that when interhomolog bias is defective, recombination is buffered by two feedback processes, one that increases the fraction of events that yields crossovers, and a second that we propose involves additional DSB formation in response to defective homolog interactions. Thus, robust crossover homeostasis is conferred by integrated regulation at initiation, strand-exchange and maturation steps of meiotic recombination.
authors.affiliation: Howard Hughes Medical Institute and Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, United States of America ; Genetics Graduate Group, University of California, Davis, Davis, California, United States of America.
authors.forename: Jessica P
authors.initials: JP
authors.lastname: Lao
authors.affiliation: Committee on Genetics, University of Chicago, Cummings Life Science Center, Chicago, Illinois, United States of America ; Department of Radiation and Cellular Oncology, University of Chicago, Cummings Life Science Center, Chicago, Illinois, United States of America.
authors.forename: Veronica
authors.initials: V
authors.lastname: Cloud
authors.affiliation: Howard Hughes Medical Institute and Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, United States of America.
authors.forename: Chu-Chun
authors.initials: CC
authors.lastname: Huang
authors.affiliation: Department of Radiation and Cellular Oncology, University of Chicago, Cummings Life Science Center, Chicago, Illinois, United States of America.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Grubb
authors.affiliation: Weil Graduate School of Medical Sciences of Cornell University, New York, New York, United States of America ; Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors.forename: Drew
authors.initials: D
authors.lastname: Thacker
authors.affiliation: Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States of America.
authors.forename: Chih-Ying
authors.initials: CY
authors.lastname: Lee
authors.affiliation: Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States of America ; Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Dresser
authors.affiliation: Howard Hughes Medical Institute and Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, California, United States of America ; Genetics Graduate Group, University of California, Davis, Davis, California, United States of America ; Department of Molecular & Cellular Biology, University of California, Davis, Davis, California, United States of America ; Department of Cell Biology & Human Anatomy, University of California, Davis, Davis, California, United States of America.
authors.forename: Neil
authors.initials: N
authors.lastname: Hunter
authors.affiliation: Committee on Genetics, University of Chicago, Cummings Life Science Center, Chicago, Illinois, United States of America ; Department of Radiation and Cellular Oncology, University of Chicago, Cummings Life Science Center, Chicago, Illinois, United States of America ; Department of Molecular Genetics and Cell Biology, University of Chicago, Cummings Life Science Center, Chicago, Illinois, United States of America.
authors.forename: Douglas K
authors.initials: DK
authors.lastname: Bishop
mesh_terms: D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D002842:Chromatids / Q000235:genetics; D023902:Chromosome Pairing / Q000235:genetics; D020090:Chromosome Segregation / Q000235:genetics; D003434:Crossing Over, Genetic; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D006706:Homeostasis; D059765:Homologous Recombination / Q000235:genetics; D008540:Meiosis / Q000235:genetics*; D051135:Rad51 Recombinase / Q000235:genetics* / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism; D013573:Synaptonemal Complex / Q000235:genetics
chemical_list: D018797:Cell Cycle Proteins; C513033:DMC1 protein, S cerevisiae; D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D051135:Rad51 Recombinase