Presynaptic calcium channel localization and calcium-dependent synaptic vesicle exocytosis regulated by the Fuseless protein.
A systematic forward genetic Drosophila screen for electroretinogram mutants lacking synaptic transients identified the fuseless (fusl) gene, which encodes a predicted eight-pass transmembrane protein in the presynaptic membrane. Null fusl mutants display >75% reduction in evoked synaptic transmission but, conversely, an approximately threefold increase in the frequency and amplitude of spontaneous synaptic vesicle fusion events. These neurotransmission defects are rescued by a wild-type fusl transgene targeted only to the presynaptic cell, demonstrating a strictly presynaptic requirement for Fusl function. Defects in FM dye turnover at the synapse show a severely impaired exo-endo synaptic vesicle cycling pool. Consistently, ultrastructural analyses reveal accumulated vesicles arrested in clustered and docked pools at presynaptic active zones. In the absence of Fusl, calcium-dependent neurotransmitter release is dramatically compromised and there is little enhancement of synaptic efficacy with elevated external Ca(2+) concentrations. These defects are causally linked with severe loss of the Cacophony voltage-gated Ca(2+) channels, which fail to localize normally at presynaptic active zone domains in the absence of Fusl. These data indicate that Fusl regulates assembly of the presynaptic active zone Ca(2+) channel domains required for efficient coupling of the Ca(2+) influx and synaptic vesicle exocytosis during neurotransmission.
Long
A Ashleigh
AA
Department of Biological Sciences, Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, Tennessee 37235-1634, USA.
Kim
Eunju
E
Leung
Hung-Tat
HT
Woodruff
Elvin
E
An
Lingling
L
Doerge
R W
RW
Pak
William L
WL
Broadie
Kendal
K
D000818:Animals; D030801:Animals, Genetically Modified; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D004330:Drosophila; D029721:Drosophila Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D004596:Electroretinography / Q000379:methods; D004625:Embryo, Nonmammalian; D005074:Evoked Potentials, Visual / Q000502:physiology; D005089:Exocytosis / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology; D046228:Microarray Analysis; D009154:Mutation / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000502:physiology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D018408:Patch-Clamp Techniques / Q000379:methods; D010775:Photic Stimulation / Q000379:methods; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure; D034622:RNA Interference / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology; D013572:Synaptic Vesicles / Q000502:physiology*; D014785:Vision, Ocular / Q000235:genetics; D014795:Visual Pathways / Q000033:anatomy & histology / Q000378:metabolism
D015220:Calcium Channels; D029721:Drosophila Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D049452:Green Fluorescent Proteins; D002118:Calcium