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A more recent version of this article appeared on April 1, 2009
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Submitted on September 9, 2008
Revised on January 12, 2009
Accepted on January 30, 2009
Cell Biology and Metabolism Program, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
Monitoring Editor: Yixian Zheng
The proper execution of premeiotic S phase is essential to both the maintenance of genomic integrity and accurate chromosome segregation during the meiotic divisions. However, the regulation of premeiotic S phase remains poorly defined in metazoa. Here we identify the p21Cip1/p27Kip1/p57Kip2–like Cyclin-dependent kinase inhibitor (CKI) Dacapo (Dap) as a key regulator of premeiotic S phase and genomic stability during Drosophila oogenesis. In dap-/- females, ovarian cysts enter the meiotic cycle with high levels of Cyclin E/Cdk2 activity and accumulate DNA damage during the premeiotic S phase. High Cyclin E/Cdk2 activity inhibits the accumulation of the replication-licensing factor Doubleparked/Cdt1 (Dup/Cdt1). Accordingly, we find that dap-/- ovarian cysts have low levels of Dup/Cdt1. Moreover, mutations in dup/cdt1 dominantly enhance the dap-/- DNA damage phenotype. Importantly, the DNA damage observed in dap-/- ovarian cysts is independent of the DNA double-strands breaks that initiate meiotic recombination. Taken together, our data suggest that the CKI Dap promotes the licensing of DNA replication origins for the premeiotic S phase by restricting Cdk activity in the early meiotic cycle. Finally, we report that dap-/- ovarian cysts frequently undergo an extra mitotic division before meiotic entry, indicating that Dap influences the timing of the mitotic/meiotic transition.