Cell cycle progression and cell division are sensitive to hypoxia in Drosophila melanogaster embryos

We and others recently demonstrated that Drosophila melanogaster embryos arrest development and embryonic cells cease dividing when they are deprived of O-2. To further characterize the behavior of these embryos in response to O-2 deprivation and to define the O-2-sensitive checkpoints in the cell cycle, embryos undergoing nuclear cycles 3-13 were subjected to O-2 deprivation and examined by confocal microscopy under control, hypoxic, and reoxygenation conditions. In vivo, real-time analysis of embryos carrying green fluorescent protein-kinesin demonstrated that cells arrest at two major points of the cell cycle, either at the interphase (before DNA duplication) or at metaphase, depending on the cell cycle phase at which O-2 deprivation was induced. Immunoblot analysis of embryos whose cell divisions are synchronized by inducible String (cdc25 homolog) demonstrated that cyclin B was degraded during low O-2 conditions in interphase-arrested embryos but not in those arrested in metaphase. Embryos resumed cell cycle activity within similar to 20 min of reoxygenation, with very little apparent change in cell cycle kinetics. We conclude that there are specific points during the embryonic cell cycle that are sensitive to the O-2 level in D. melanogaster. Given the fact that O-2 deprivation also influences the growth and development of other species, we suggest that similar hypoxia-sensitive cell cycle checkpoints may also exist in mammalian cells.