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Presynaptic CaV2 calcium channel traffic requires CALF-1 and the α2δ subunit UNC-36

Abstract

Presynaptic voltage-gated calcium channels provide calcium for synaptic vesicle exocytosis. We show here that a green fluorescent protein–tagged α1 subunit of the Caenorhabditis elegans CaV2 channel, UNC-2, is localized to presynaptic active zones of sensory and motor neurons. Synaptic localization of CaV2 requires the α2δ subunit UNC-36 and CALF-1 (Calcium Channel Localization Factor-1), a neuronal transmembrane protein that localizes to the endoplasmic reticulum. In calf-1 mutants, UNC-2 is retained in the endoplasmic reticulum, but other active-zone components and synaptic vesicles are delivered to synapses. Acute induction of calf-1 mobilizes preexisting UNC-2 for delivery to synapses, consistent with a direct trafficking role. The α2δ subunit UNC-36 is likewise required for exit of UNC-2 from endoplasmic reticulum but has additional functions. Genetic and cell biological interactions suggest that CALF-1 couples intracellular traffic to functional maturation of CaV2 presynaptic calcium channels.

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Figure 1: GFP-tagged UNC-2 localizes to presynaptic puncta in sensory neurons and motor neurons.
Figure 2: Presynaptic GFPUNC-2 puncta are lost in calf-1(ky867) mutants.
Figure 3: calf-1 encodes a type I transmembrane protein.
Figure 4: CALF-1 acts cell-autonomously in neurons and localizes to endoplasmic reticulum.
Figure 5: Structure-function analysis of CALF-1.
Figure 6: CALF-1 and UNC-36 have related trafficking functions.
Figure 7: Acute CALF-1 expression transports UNC-2 from the cell body to the synapse.

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Acknowledgements

We thank S. Chalasani, T. Maniar and P. McGrath for their insights and advice, A. Bendesky, E. Feinberg, G. Lee, B. Lesch, M. Tsunozaki and L. Winzenread for comments on the manuscript, L. Looger for G-CaMP2.2b, K. Shen for mCherryrab-3, and the Caenorhabditis Genetic Center (CGC) and the National Bioresource Project for strains. This work was supported by the Howard Hughes Medical Institute (C.I.B.), and Y.S. was supported by the Nakajima Foundation. We dedicate this paper to Masanori Obayashi.

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Y.S. and C.I.B. designed the project, and Y.S. conducted the experiments. Y.S. and C.I.B. wrote the paper.

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Correspondence to Cornelia I Bargmann.

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Saheki, Y., Bargmann, C. Presynaptic CaV2 calcium channel traffic requires CALF-1 and the α2δ subunit UNC-36. Nat Neurosci 12, 1257–1265 (2009). https://doi.org/10.1038/nn.2383

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