Cyclin B-Cdk activity stimulates meiotic re-replication in budding yeast.
Randy Strich (1), Michael Mallory (1), Michal Jarnik (1), Katrina Cooper (2)
(1) Cell & Developmental Biology, Fox Chase Cancer Center, 333 Cottman Ave, Philadelphia, PA, 19111, USA;
(2) Dept. of Biochemistry, Drexel College of Medicine, Philadelphia, PA
Haploidization of gametes during meiosis requires a single round of pre-meiotic DNA replication (meiS) followed by two successive nuclear divisions. This study demonstrates that ectopic activation of cyclin B-cyclin dependent kinase in budding yeast recruits up to 30% of meiotic cells to execute 1-3 additional rounds of meiS. Re-replication occurs prior to the meiotic nuclear divisions indicating that this process is different than the post-meiotic mitoses observed in other fungi. The cells with over-replicated DNA produced asci containing up to 20 spores that were viable, haploid, and demonstrated Mendellian marker segregation. Genetic tests indicated that these cells executed the meiosis I reductional division and possessed a spindle checkpoint. However, re-replication was not regulated by Sic1p, an inhibitor of replication initiation. Finally, interfering with normal synaptonemal complex formation or recombination increased the efficiency of re-replication. These studies indicate that the block to re-replication is very different in meiotic and mitotic cells and suggest a negative role for the recombination machinery in allowing re-replication. Moreover, the production of haploids, regardless of the genome content, suggests that the cell counts replication cycles, not chromosomes, in determining the number of nuclear divisions to execute.
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