Genetic analysis of the role of reactive oxygen and Hsp70 in the response to anoxia in Drosophila
Dioxygen is required by all aerobic organisms. Too much or too little oxygen results in cell and/or tissue damage, and eventually death. Hypoxia-reoxygenation imposes severe oxidative stress with wide-ranging implications in biology and medicine. In contrast to most mammals, insects exhibit extraordinary tolerance to low levels of oxygen and even to anoxia. Anoxia is a potent anesthetic, causing immediate coma (catalepsy) in insects. Numerous studies have described the phenomenon of tolerance to anoxia (and hypoxia) observed in 'Drosophila melanogaster'. However, no mechanistic explanation for such resistance has been offered. This thesis presents a biological and genetic investigation of the role of reactive oxygen metabolism in the response of ' Drosophila' to anoxia. At the biological level, the impact of reactive oxygen metabolism on recovery from anoxia has been examined through the use of fly strains mutant and transgenic for various antioxidant enzymes. ROS may act as effectors for recovery from anoxia and the major site of their action may involve the neuromuscular tissue. At the genetic level, the expression pattern of specific genes encoding antioxidant enzymes and Hsp70 in response to anoxia has been examined. Genes encoding SOD1, SOD2, and CAT are not up-regulated during anoxic stress, whereas Hsp70 is induced during recovery from anoxia. The biological role of Hsp70 induction by anoxia remains unknown. At the genome-wide level, 'Drosophila' DNA microarray and differential display methodologies have been utilized to identify genes differentially expressed during normoxia, anoxia, and post-anoxia recovery. The results show that DNA microarrays are an efficient tool to identify other genes which may participate in the mechanism(s) underlying the resistance of 'Drosophila' to anoxia. This study provides the first evidence for the role of ROS metabolism in recovery from anoxia in 'Drosophila', and for the correlated involvement of Hsp70 and other newly identified genes in this process. Further characterization of these genes may lead to a clearer understanding of the genetic basis of the capacity of 'Drosophila' to endure and recover from extended periods of total oxygen deprivation. These findings may ultimately provide practical insights into understanding ischemic tissue damage in human medicine.