title: Null mutation in shaking-B eliminates electrical, but not chemical, synapses in the Drosophila giant fiber system: a structural study.
abstract: Mutations in the Drosophila shaking-B gene perturb synaptic transmission and dye coupling in the giant fiber escape system. The GAL4 upstream activation sequence system was used to express a neuronal-synaptobrevin-green fluorescent protein (nsyb-GFP) construct in the giant fibers (GFs); nsyb-GFP was localized where the GFs contact the peripherally synapsing interneurons (PSIs) and the tergotrochanteral motorneurons (TTMns). Antibody to Shaking-B protein stained plaquelike structures in the same regions of the GFs, although not all plaques colocalized with nsyb-GFP. Electron microscopy showed that the GF-TTMn and GF-PSI contacts contained many chemical synaptic release sites. These sites were interposed with extensive regions of close membrane apposition (3.25 nm +/- 0.12 separation), with faint cross striations and a single-layered array of 41-nm vesicles on the GF side of the apposition. These contacts appeared similar to rectifying electrical synapses in the crayfish and were eliminated in shaking-B2 mutants. At mutant GF-TTMn and GF-PSI contacts, chemical synapses and small regions of close membrane apposition, more similar to vertebrate gap junctions, were not affected. Gap junctions with more vertebratelike separation of membranes (1.41 nm +/- 0.08) were abundant between peripheral perineurial glial processes; these were unaffected in the mutants.
authors.affiliation: Institute of Neurobiology, University of Puerto Rico Medical Sciences Campus, San Juan 00901, USA. jmblagbu@crayfish.upr.clu.edu
authors.forename: J M
authors.initials: JM
authors.lastname: Blagburn
authors.forename: H
authors.initials: H
authors.lastname: Alexopoulos
authors.forename: J A
authors.initials: JA
authors.lastname: Davies
authors.forename: J P
authors.initials: JP
authors.lastname: Bacon
mesh_terms: D000483:Alleles; D000818:Animals; D017630:Connexins / Q000096:biosynthesis* / Q000502:physiology*; D004330:Drosophila / Q000502:physiology*; D029721:Drosophila Proteins; D004594:Electrophysiology; D017629:Gap Junctions / Q000502:physiology / Q000648:ultrastructure; D049452:Green Fluorescent Proteins; D007150:Immunohistochemistry; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008854:Microscopy, Electron; D009046:Motor Neurons / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D009154:Mutation / Q000502:physiology*; D009412:Nerve Fibers / Q000378:metabolism* / Q000502:physiology* / Q000648:ultrastructure; D009419:Nerve Tissue Proteins / Q000096:biosynthesis* / Q000378:metabolism / Q000502:physiology*; D050683:R-SNARE Proteins; D013569:Synapses / Q000378:metabolism* / Q000502:physiology*