title: Calcium channels link the muscle-derived synapse organizer laminin β2 to Bassoon and CAST/Erc2 to organize presynaptic active zones.
abstract: Synapse formation requires the organization of presynaptic active zones, the synaptic vesicle release sites, in precise apposition to postsynaptic neurotransmitter receptor clusters; however, the molecular mechanisms responsible for these processes remain unclear. Here, we show that P/Q-type and N-type voltage-dependent calcium channels (VDCCs) play essential roles as scaffolding proteins in the organization of presynaptic active zones. The neuromuscular junction of double knock-out mice for P/Q- and N-type VDCCs displayed a normal size but had significantly reduced numbers of active zones and docked vesicles and featured an attenuation of the active-zone proteins Bassoon, Piccolo, and CAST/Erc2. Consistent with this phenotype, direct interactions of the VDCC β1b or β4 subunits and the active zone-specific proteins Bassoon or CAST/Erc2 were confirmed by immunoprecipitation. A decrease in the number of active zones caused by a loss of presynaptic VDCCs resembled the pathological conditions observed in the autoimmune neuromuscular disorder Lambert-Eaton myasthenic syndrome. At the synaptic cleft of double knock-out mice, we also observed a decrease of the synaptic organizer laminin β2 protein, an extracellular ligand of P/Q- and N-type VDCCs. However, the transcription level of laminin β2 did not decrease in double knock-out mice, suggesting that the synaptic accumulation of laminin β2 protein required its interaction with presynaptic VDCCs. These results suggest that presynaptic VDCCs link the target-derived synapse organizer laminin β2 to active-zone proteins and function as scaffolding proteins to anchor active-zone proteins to the presynaptic membrane.
authors.affiliation: Department of Anatomy and Cell Biology and Kansas Intellectual and Developmental Disabilities Research Center, University of Kansas Medical School, Kansas City, Kansas 66160, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.forename: Sara E
authors.initials: SE
authors.lastname: Billings
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishimune
mesh_terms: D000818:Animals; D020864:Calcium Channels, N-Type / Q000235:genetics / Q000502:physiology*; D020865:Calcium Channels, P-Type / Q000235:genetics / Q000502:physiology*; D020907:Calcium Channels, Q-Type / Q000235:genetics / Q000502:physiology*; D002452:Cell Count; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004576:Electromyography; D004622:Embryo, Mammalian; D007797:Laminin / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009046:Motor Neurons / Q000166:cytology / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000378:metabolism*; D010791:Phrenic Nerve / Q000378:metabolism / Q000648:ultrastructure; D021122:Protein Subunits / Q000378:metabolism; D013116:Spinal Cord / Q000166:cytology / Q000378:metabolism; D013569:Synapses / Q000378:metabolism*
chemical_list: D020864:Calcium Channels, N-Type; D020865:Calcium Channels, P-Type; D020907:Calcium Channels, Q-Type; D003598:Cytoskeletal Proteins; D007797:Laminin; D009419:Nerve Tissue Proteins; D021122:Protein Subunits; C498441:Bsn protein, mouse; C500963:Cacna1b protein, mouse; C505599:Erc2 protein, mouse; C058783:laminin beta2