A Temperature-Sensitive Paralytic Mutant Defines a Primary Synaptic Calcium Channel inDrosophila

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Abstract
Neurotransmission at chemical synapses involves regulated exocytosis of neurotransmitter from the presynaptic terminal. Neurotransmitter release is thought to be triggered by calcium influx through specific classes of voltage-gated calcium channels. Here we report genetic and functional analysis implicating a specific calcium channel gene product in neurotransmitter release. We have isolated a temperature-sensitive paralytic allele of theDrosophilacalcium channel α1 subunit gene,cacophony(cac). This mutant, referred to ascacTS2, allows functional analysis of synaptic transmission after acute perturbation of a specific α1 subunit. Electrophysiological analysis at neuromuscular synapses revealed that neurotransmitter release incacTS2is markedly reduced at elevated temperatures, indicating thatcacencodes a primary α1 subunit functioning in synaptic transmission. These observations further define the molecular basis of voltage-gated calcium entry at synapses and provide a new starting point for further genetic analysis of synaptic mechanisms.