The use of environmental stress, such as microtubule-depolymerizing agents or DNA damage, was instrumental for understanding cell cycle arrest and checkpoints. Previously, we showed that severe oxygen deprivation (anoxia) induces a state of suspended animation in which cell cycle progression is reversibly arrested at interphase, late prophase, and metaphase in blastomeres. The spindle checkpoint genes are required for metaphase arrest; the mechanisms regulating anoxia-induced prophase arrest are not known. Live cell imaging of
tbg-1::GFP;
pie-1::GFP::H2B animals, to monitor cell cycle progression, shows that an immediate response to anoxia is chromosome association with the inner nuclear membrane (chromosome docking) in prophase blastomeres. In these blastomeres nuclear envelope breakdown and the transition from prophase to prometaphase is arrested. The phenomenon of chromosome docking is also observed in the oocytes of hermaphrodites exposed to anoxia, aged hermaphrodites and
fog-2 mutants, but not other stresses such as starvation and heat shock, suggesting that chromosome docking is a characteristic of quiescent cells. To determine if chromosome docking is a response to reduced ATP we exposed animals to sodium azide and find that chromosome docking is induced in blastomeres and oocytes; however, unlike anoxic animals this affects their viability which suggests anoxia-induced cell cycle arrest is not a function of mitochondrial dysfunction. To identify genetic mechanisms required for prophase arrest we used RNAi to screen a subset of nuclear membrane associated and kinetochore genes. This screen identified
npp-16, a non-essential component of the nuclear pore complex, as being required for anoxia-induced prophase arrest. The
npp-16(
ok1839) embryos exposed to anoxia have a reduction in the number of prophase blastomeres, an increase in abnormal nuclei, and a decrease in embryonic viability relative to control. Live cell imaging indicates that blastomeres of
npp-16(
ok1839);
tbg-1::GFP;
pie-1::GFP::H2B embryos exposed to anoxia do not arrest at prophase resulting in abnormal nuclei. Experiments are underway to test the hypothesis that anoxia induces a prophase checkpoint involving
npp-16 and understand the role a nucleoporin may have in arrested cells. Since oxygen deprivation plays a central role in resistance of solid tumor cells to radiation and chemotherapy treatments, these studies could elucidate how oxygen deprivation influences cell division and reveal mechanisms involved with a less understood cell cycle arrest position during mitosis-prophase arrest.