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The Journal of Neuroscience, January 2, 2008, 28(1):31-38; doi:10.1523/JNEUROSCI.4498-07.2008

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Cellular/Molecular
Mutations in a Drosophila ₂ Voltage-Gated Calcium Channel Subunit Reveal a Crucial Synaptic Function

Dion K. Dickman, ^* Peri T. Kurshan, ^* and Thomas L. Schwarz

F. M. Kirby Neurobiology Center, Children's Hospital and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115

Correspondence should be addressed to Thomas L. Schwarz, Children's Hospital, F. M. Kirby Neurobiology Center, Enders 208, Boston, MA 02115. Email: thomas.schwarz{at}childrens.harvard.edu

Voltage-dependent calcium channels regulate many aspects of neuronal biology, including synaptic transmission. In addition to their ₁ subunit, which encodes the essential voltage gate and selective pore, calcium channels also contain auxiliary ₂, β, and subunits. Despite progress in understanding the biophysical properties of calcium channels, the in vivo functions of these auxiliary subunits remain unclear. We have isolated mutations in the gene encoding an ₂ calcium channel subunit (d₂-3) using a forward genetic screen in Drosophila. Null mutations in this gene are embryonic lethal and can be rescued by expression in the nervous system, demonstrating that the essential function of this subunit is neuronal. The photoreceptor phenotype of d₂-3 mutants resembles that of the calcium channel ₁ mutant cacophony (cac), suggesting shared functions. We have examined in detail genotypes that survive to the third-instar stage. Electrophysiological recordings demonstrate that synaptic transmission is severely impaired in these mutants. Thus the ₂ calcium channel subunit is critical for calcium-dependent synaptic function. As such, this Drosophila isoform is the likely partner to the presynaptic calcium channel ₁ subunit encoded by the cac locus. Consistent with this hypothesis, cacGFP fluorescence at the neuromuscular junction is reduced in d₂-3 mutants. This is the first characterization of an ₂-3 mutant in any organism and indicates a necessary role for ₂-3 in presynaptic vesicle release and calcium channel expression at active zones.

Key words: calcium channel; synaptic transmission; bouton; active zone; neuromuscular junction; Drosophila

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Received June 19, 2007; revised Oct. 11, 2007; accepted Oct. 14, 2007.

Correspondence should be addressed to Thomas L. Schwarz, Children's Hospital, F. M. Kirby Neurobiology Center, Enders 208, Boston, MA 02115. Email: thomas.schwarz{at}childrens.harvard.edu

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