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Originally published as Genetics Published Articles Ahead of Print on December 6, 2006.
Genetics, Vol. 175, 567-584, February 2007, Copyright © 2007
doi:10.1534/genetics.106.065219
Onset of the DNA Replication Checkpoint in the Early Drosophila Embryo
Justin Crest*,1,
Nathan Oxnard*,
Jun-Yuan Ji
and
Gerold Schubiger*
* Department of Biology, University of Washington, Seattle, Washington 98195-1800 and Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts 02129
1 Corresponding author: MCD Biology Department, University of California, Santa Cruz, CA 95064.
E-mail: jcrest{at}ucsc.edu
The Drosophila embryo is a promising model for isolating gene products that coordinate S phase and mitosis. We have reported before that increasing maternal Cyclin B dosage to up to six copies (six cycB) increases Cdk1–Cyclin B (CycB) levels and activity in the embryo, delays nuclear migration at cycle 10, and produces abnormal nuclei at cycle 14. Here we show that the level of CycB in the embryo inversely correlates with the ability to lengthen interphase as the embryo transits from preblastoderm to blastoderm stages and defines the onset of a checkpoint that regulates mitosis when DNA replication is blocked with aphidicolin. A screen for modifiers of the six cycB phenotypes identified 10 new suppressor deficiencies. In addition, heterozygote dRPA2 (a DNA replication gene) mutants suppressed only the abnormal nuclear phenotype at cycle 14. Reduction of dRPA2 also restored interphase duration and checkpoint efficacy to control levels. We propose that lowered dRPA2 levels activate Grp/Chk1 to counteract excess Cdk1–CycB activity and restore interphase duration and the ability to block mitosis in response to aphidicolin. Our results suggest an antagonistic interaction between DNA replication checkpoint activation and Cdk1–CycB activity during the transition from preblastoderm to blastoderm cycles.
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Genetics 2007 175: NP.
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