Figure 1. Embryos in utero suspend development and survive in hypoxia.

A. Nomarsky images of embryos in the uterus of a gravid adult C. elegans prior to and immediately after being exposed to 1000 ppm O₂ for 24 h. Both pictures are of the same animal, and no embryos were fertilized or laid during exposure to hypoxia. v, vulva; sp, spermatheca of anterior gonad arm. Bar is 50 μm. B. Survival of embryos to adulthood after exposure to 1000 ppm O₂ for 24 h. Dissected 2-cell embryos (n=40) were removed from the adult and exposed directly to hypoxia. Embryos in utero were laid by gravid adults exposed to hypoxia after return to normoxia (n=10 adults, 145 embryos). *, p<0.05. C. Viability of embryos exposed to 1000 ppm O₂ for 24 h in utero. Gravid adult animals of each genotype were allowed to lay eggs exposed to hypoxia in utero upon return room air. The average number of embryos laid was 15.8±4.8 for N2 (n=18 adults), 9.4±3.6 for san-1(ok1580) (n=16 adults) and 10.7±3.8 for hif-1(ia04) (n=20 adults). The fraction of the embryos that hatched and developed successfully to L4/young adult was scored. Data are from two independent experiments. Error bars are standard deviation of the mean. *, p<0.05 compared to N2 controls; ns, not significant.