Temperature-dependent modulation of chromosome segregation in msh4 mutants of budding yeast.
BACKGROUND
In many organisms, homologous chromosomes rely upon recombination-mediated linkages, termed crossovers, to promote their accurate segregation at meiosis I. In budding yeast, the evolutionarily conserved mismatch-repair paralogues, Msh4 and Msh5, promote crossover formation in conjunction with several other proteins, collectively termed the Synapsis Initiation Complex (SIC) proteins or 'ZMM's (Zip1-Zip2-Zip3-Zip4-Spo16, Msh4-Msh5, Mer3). zmm mutants show decreased levels of crossovers and increased chromosome missegregation, which is thought to cause decreased spore viability.


RESULTS
In contrast to other ZMM mutants, msh4 and msh5 mutants show improved spore viability and chromosome segregation in response to elevated temperature (23 degrees C versus 33 degrees C). Crossover frequencies in the population of viable spores in msh4 and msh5 mutants are similar at both temperatures, suggesting that temperature-mediated chromosome segregation does not occur by increasing crossover frequencies. Furthermore, meiotic progression defects at elevated temperature do not select for a subpopulation of cells with improved segregation. Instead, another ZMM protein, Zip1, is important for the temperature-dependent improvement in spore viability.


CONCLUSIONS
Our data demonstrate interactions between genetic (zmm status) and environmental factors in determining chromosome segregation.
Chan
Andrew Chi-Ho
AC
MRC Genome Damage and Stability Centre, University of Sussex, Falmer, United Kingdom.
Borts
Rhona H
RH
Hoffmann
Eva
E
D020090:Chromosome Segregation; D002875:Chromosomes / Q000648:ultrastructure*; D003434:Crossing Over, Genetic; D004268:DNA-Binding Proteins / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D008540:Meiosis; D008957:Models, Genetic; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*; D004718:Saccharomycetales / Q000235:genetics*; D013172:Spores, Fungal / Q000378:metabolism; D013696:Temperature
D004268:DNA-Binding Proteins; C091158:MSH4 protein, S cerevisiae; C094801:MSH5 protein, S cerevisiae; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; C090118:Zip1 protein, S cerevisiae