Anoxia tolerant DNA replication is supported by ATR kinase in the annual killifish Austrofundulus limnaeus

Hypoxia and anoxia suppress cell proliferation due to an increase in replication stress and activation of DNA damage checkpoints. Embryos of the annual killifish Austrofundulus limnaeus tolerate prolonged anoxia, indicating improved genomic stability under oxygen starvation. We investigated the cell cycle regulation of the anoxia tolerant killifish embryonic cell line PSU-AL-WS40NE during anoxia. Live-cell imaging confirms continued proliferation of WS40NE cells for the first 24 h of anoxia with minimal cell death. Fluorescence imaging shows that cells accumulate in G1 after the first day in anoxia with a rapid entry into S phase upon reoxygenation. Pharmacological inhibition shows a reliance on ataxia telangiectasia and Rad3 related (ATR) signaling, suggesting that increased γH2AX levels are driven by replication stress instead of DNA damage. This conclusion is supported by a lack of induction of a G2 checkpoint, suggesting minimal DNA damage during anoxic exposure. Maintaining cellular proliferation during anoxia and accumulating cells in the G1 phase for extended anoxic exposure is likely one way that embryos of the killifish can survive prolonged anoxia, which provides insight into mechanisms that enable cells to proliferate under metabolic stress.