Synaptic Calcium-Channel Function inDrosophila: Analysis and Transformation Rescue of Temperature-Sensitive Paralytic and Lethal Mutations ofCacophony

Abstract

Voltage-gated calcium channels play a key role in chemical synaptic transmission by providing the calcium trigger for regulated neurotransmitter release. Genes encoding the primary structural subunit, α1, as well as accessory subunits of presynaptic calcium channels have now been identified in a variety of organisms. Thecacophony (cac)gene inDrosophila, also known asnightblind A, encodes a voltage-gated calcium-channel α1 subunit homologous to vertebrate α1 subunits implicated in neurotransmitter release. A recent genetic screen in our laboratory isolatedcacTS2, a conditionalcacmutant exhibiting rapid paralysis at elevated temperatures. This mutant has allowed synaptic electrophysiology after acute perturbation of a specific calcium-channel gene product, demonstrating thatcacencodes a primary calcium channel functioning in neurotransmitter release. Here we report the molecular lesion incacTS2, a missense mutation within a calcium-dependent regulatory domain of the α1 subunit, as well as phenotypic rescue of temperature-sensitive and lethalcacmutations by transgenic expression of a wild-typecaccDNA. Notably, rescue of rapid, calcium-triggered neurotransmitter release was achieved by neural expression of a single cDNA containing a subset of alternative exons and lacking any conserved synaptic-protein interaction sequence. Possible implications of these findings are discussed in the context of structure–function studies of synaptic calcium channels, as well as alternative splicing and mRNA editing of thecactranscript.