Defects in chromosome synapsis and/or meiotic recombination activate a surveillance mechanism that blocks meiotic cell cycle progression to prevent anomalous chromosome segregation and formation of aberrant gametes. unrepaired DNA double-strand breaks accumulate, leading also to activation of the meiotic recombination checkpoint (Lydall and mutants are useful genetic tools to elicit the meiotic recombination checkpoint response, and they are widely used to investigate this meiotic surveillance mechanism. Mutations in components of this checkpoint alleviate the meiotic arrest or delay of and but lead to the formation of largely inviable spores. Meiotic defects, such as incomplete synapsis or accumulation of meiotic recombination intermediates, are initially detected by the checkpoint sensors, including the Mec1/Ddc2 and the 9-1-1 complexes (Lydall vegetative cells (Amon itself. The Sum1 repressor, which also binds to a subset of the same sites in vegetative cells, decreases during midmeiosis but is stabilized SCH 900776 enzyme inhibitor in checkpoint-arrested cells. It has been proposed that competition between Ndt80 and Sum1 for binding to MSEs controls middle gene expression (Chu and Herskowitz, 1998 ; Lindgren gene, encoding the budding yeast polo-like kinase (PLK), is a crucial member of the set of genes under Ndt80 control (Sourirajan and Lichten, 2008 ). PLKs carry out a vast variety of cellular functions in a range of organisms from yeast to mammals during both mitotic and meiotic cell cycles (Barr mutant but does not suppress the spore viability defects. We demonstrate that high doses of Cdc5 do not alter the Swe1-dependent checkpoint response but do lead to premature induction of Ndt80 production, which depends on Cdc5. We also provide molecular evidence indicating that, unlike DNA-damaged vegetative cells, bypass of meiotic delay by overexpression does not result from enhanced checkpoint adaptation. We SCH 900776 enzyme inhibitor propose that regulation of Ndt80 by Cdc5 is SCH 900776 enzyme inhibitor important for the meiotic recombination checkpoint response. RESULTS Overexpression of partially suppresses meiotic delay Previous studies described a role for the nucleolar-enriched Pch2 and Sir2 proteins in the meiotic recombination checkpoint (San-Segundo and Roeder, 1999 , SCH 900776 enzyme inhibitor 2000 ). The nucleolus also plays an important functional role in the regulation of other cell cycle eventsfor example, the Cdc14-dependent exit from mitosis regulated by the Cdc14 early anaphase release (FEAR) and mitosis exit network (MEN) pathways (Jaspersen from BA554C12.1 high-copy plasmids (Jaspersen mutant. As shown in Figure 1A, only overexpression of the polo-like kinase gene reproducibly conferred a significant bypass of the arrest, leading to increased dityrosine fluorescence and higher sporulation efficiency compared with the mutant containing empty vector. Open in a separate window FIGURE 1: overexpression partially suppresses the checkpoint-dependent meiotic delay of but does not improve spore viability. (A) Overexpression of mutant. Dityrosine fluorescence after 3 d on a sporulation plate is shown as an indicator for the formation of mature asci. The sporulation efficiency, assessed by microscopic counting of asci, is also presented. Strains are BR2495 (wild type) and MY63 (meiotic arrest by overexpression. Time course of meiotic nuclear divisions; the percentage of cells SCH 900776 enzyme inhibitor containing more than two nuclei is represented. Strains and plasmids used are wild type (DP396/pRS426), wild type + (DP396/pJC29), + (DP386/pJC29), + (DP386/pSS127), and (DP386/pRS426). (C) overexpression partially alleviates the meiotic delay of the mutant. Strains are wild type (BR1919-2N/pRS426), (DP456/pRS426), and (DP456/pJC29). (D) overexpression does not suppress the spore viability defect of and (DP396/pJC29), (DP386/pRS426), (DP386/pJC29), (DP393/pRS426), and (DP393/pJC29). The total number of spores scored for each strain is indicated (n). To confirm this initial observation, we followed the kinetics of meiotic progression. As expected, the mutant displayed a quite robust meiotic arrest, undergoing meiotic divisions very inefficiently and only after prolonged incubation under sporulation conditions (Figure 1B).