English: GFP-Polo localization to mitotic kinetochores and centrosomes increases in response to hypoxia. A syncytial embryo with GFP-Polo and red fluorescently labeled histone (His2AvD-tDimer [37]) completes one cycle of mitosis; a subset of this oocyte is shown in Figure 5B. CO2 gas was turned on after 6:15, and the cell arrested in metaphase of that cell cycle. After 11:30, the gas was turned off, and the embryo resumed mitotic cycling thereafter, reaching metaphase of the next mitotic cycle approximately 25 minutes later. The second cell cycle in this video is prolonged because the onset of hypoxia is much faster than the return to normoxia, as CO2 is quickly pumped into the gas chamber. However, removal of the chamber caused a loss of microscope focus and stage positioning, so to be able to best monitor the oocyte throughout imaging we simply opened the cover to allow ambient air to return by diffusion.