ADrosophilaTemperature-Sensitive Seizure Mutant in Phosphoglycerate Kinase Disrupts ATP Generation and Alters Synaptic Function

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Abstract
A novel paralytic mutant,nubian, was identified in a behavioral screen for conditional temperature-sensitive seizure mutants inDrosophila melanogaster. nubianmutants display reduced lifespan, abnormal motor behavior, altered synaptic structure, and defective neurotransmitter release. Thenubianmutant disrupts phosphoglycerate kinase (PGK), an enzyme required for ATP generation in the terminal stage of the glycolytic pathway. Consistent with altered ATP generation innubiananimals, brain extracts show a threefold reduction in resting ATP levels compared with controls. Microarray analysis ofnubianmutants reveals altered transcription of genes implicated in glucose and lipid metabolism. Disruption of ATP generation innubiananimals is accompanied by temperature-dependent defects in neuronal activity, with initial seizure activity, followed by an activity-dependent loss of synaptic transmission.nubianmutants also display structural defects at the synapse, with larger varicosity size but normal varicosity number, indicating that these synaptic parameters are regulated independently. Both exocytotic (NSF) and endocytotic (dynamin) ATPase/GTPase activity are required for normal synaptic transmission. Biochemical and physiological analyses indicate that synaptic defects innubiananimals are secondary to defective endocytosis, suggesting that endocytotic pathways may be generally more sensitive to altered ATP levels than those used for exocytosis. Alterations in ATP metabolism likely disrupt similar pathways in humans, because PGK deficiency is associated with mental retardation, seizures, and exercise intolerance. Given the behavioral similarities between disruptions of PGK function inDrosophilaand humans, the analysis ofnubiananimals may reveal conserved neuronal responses associated with altered ATP generation within the brain.