title: Regulation of meiotic progression by the meiosis-specific checkpoint kinase Mek1 in fission yeast.
abstract: During the eukaryotic cell cycle, accurate transmission of genetic information to progeny is ensured by the operation of cell cycle checkpoints. Checkpoints are regulatory mechanisms that block cell cycle progression when key cellular processes are defective or chromosomes are damaged. During meiosis, genetic recombination between homologous chromosomes is essential for proper chromosome segregation at the first meiotic division. In response to incomplete recombination, the pachytene checkpoint (also known as the meiotic recombination checkpoint) arrests or delays meiotic cell cycle progression, thus preventing the formation of defective gametes. Here, we describe a role for a meiosis-specific kinase, Mek1, in the meiotic recombination checkpoint in fission yeast. Mek1 belongs to the Cds1/Rad53/Chk2 family of kinases containing forkhead-associated domains, which participate in a number of checkpoint responses from yeast to mammals. We show that defects in meiotic recombination generated by the lack of the fission yeast Meu13 protein lead to a delay in entry into meiosis I owing to inhibitory phosphorylation of the cyclin-dependent kinase Cdc2 on tyrosine 15. Mutation of mek1(+) alleviates this checkpoint-induced delay, resulting in the formation of largely inviable meiotic products. Experiments involving ectopic overexpression of the mek1(+) gene indicate that Mek1 inhibits the Cdc25 phosphatase, which is responsible for dephosphorylation of Cdc2 on tyrosine 15. Furthermore, the meiotic recombination checkpoint is impaired in a cdc25 phosphorylation site mutant. Thus, we provide the first evidence of a connection between an effector kinase of the meiotic recombination checkpoint and a crucial cell cycle regulator and present a model for the operation of this meiotic checkpoint in fission yeast.
authors.affiliation: Centro de Investigación del Cáncer, CSIC/University of Salamanca, Campus Unamuno, 37007 Salamanca, Spain.
authors.forename: Livia
authors.initials: L
authors.lastname: Pérez-Hidalgo
authors.forename: Sergio
authors.initials: S
authors.lastname: Moreno
authors.forename: Pedro A
authors.initials: PA
authors.lastname: San-Segundo
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D001483:Base Sequence / Q000235:genetics; D016203:CDC2 Protein Kinase / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D015966:Gene Expression Regulation, Fungal / Q000235:genetics; D018816:Genes, cdc / Q000502:physiology*; D048369:MAP Kinase Kinase 1; D008540:Meiosis / Q000235:genetics*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000302:isolation & purification*; D008954:Models, Biological; D010766:Phosphorylation; D010770:Phosphotransferases / Q000235:genetics / Q000302:isolation & purification*; D012568:Schizosaccharomyces / Q000201:enzymology* / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D020687:cdc25 Phosphatases / Q000235:genetics / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D018076:DNA, Complementary; C433032:Meu13 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; D010770:Phosphotransferases; C119549:Mek1 protein, S pombe; D016203:CDC2 Protein Kinase; C469447:cdc2 protein, S pombe; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D020687:cdc25 Phosphatases