ABSTRACT
Checkpoints monitor the state of DNA and can delay or arrest the cell cycle at multiple points including G1-S transition, progress through S phase and G2-M transition. Regulation of progress through mitosis, specifically at the metaphase-anaphase transition, occurs after exposure to ionizing radiation (IR) in Drosophila and budding yeast, but has not been conclusively demonstrated in mammals. Here we report that regulation of metaphase-anaphase transition in Drosophila depends on the magnitude of radiation dose and time in the cell cycle at which radiation is applied, which may explain the apparent differences among experimental systems and offer an explanation as to why this regulation has not been seen in mammalian cells. We further document that mutants in Drosophila Chk1 (Grapes) that are capable of delaying the progress through mitosis in response to IR are incapable of delaying progress through mitosis when DNA synthesis is blocked by mutations in an essential replication factor encoded by double park (Drosophila Cdt1). We conclude that DNA damage and replication checkpoints operating in the same cell cycle at the same developmental stage in Drosophila can exhibit differential requirements for the Chk1 homolog. The converse situation exists in fission yeast where loss of Chk1 is more detrimental to the DNA damage checkpoint than to the DNA replication checkpoint. It remains to be seen which of these two different uses of Chk1 homologs are conserved in mammals. Finally, our results demonstrate that Drosophila provides a unique opportunity to study the regulation of the entry into, and progress through, mitosis by DNA structure checkpoints in metazoa.
Subject(s)
DNA Replication , DNA/biosynthesis , Drosophila/metabolism , Mitosis/physiology , Protein Kinases/metabolism , Anaphase/physiology , Anaphase/radiation effects , Animals , Cell Cycle/physiology , Cell Cycle/radiation effects , Checkpoint Kinase 1 , DNA/radiation effects , DNA Damage/radiation effects , DNA Replication/radiation effects , Dose-Response Relationship, Radiation , Drosophila/embryology , Drosophila/radiation effects , Gastrin-Releasing Peptide/genetics , Gastrin-Releasing Peptide/metabolism , Gastrin-Releasing Peptide/radiation effects , Metaphase/physiology , Metaphase/radiation effects , Mitosis/radiation effects , Mutation , Protein Kinases/radiation effects , Saccharomyces cerevisiae/enzymology , Saccharomyces cerevisiae/metabolism , Saccharomyces cerevisiae/radiation effects , Time FactorsABSTRACT
PURPOSE: To investigate the long-term effects of X-irradiation on different aspects of gastrointestinal function in the non-human primate (Macaca mulatta). MATERIALS AND METHODS: Animals were exposed to X-radiation (5 or 6 Gy) or not (sham) and gastrointestinal function was investigated 4-6 years after exposure. Basal and agonist-stimulated short circuit current (Isc) responses were measured in isolated jejunum. Intestinal tissue was taken for histological analysis as well as for determination of mucosal marker enzyme activities and gastrointestinal regulatory peptide levels. Vasoactive intestinal peptide receptor characteristics were determined as well as VIP-stimulated Isc responses. GI peptides were also measured in plasma. RESULTS: Few differences were seen in basal electrical parameters or tissue morphology but there was a tendency for reduced basolateral membrane enzyme activity. VIP-stimulated Isc responses were reduced in irradiated animals as were VIP-stimulated adenylate cyclase responses. Plasma and tissue (ileal and colonic muscle layers) gastrin releasing peptide levels were increased in irradiated animals. In contrast circulating gastrin levels were lower. CONCLUSIONS: Late effects of total-body irradiation on GI function in monkeys showed altered circulating and tissue levels of some GI peptides. In addition the biological effects of vasoactive intestinal peptide were modified.
