title: Enhanced neurotransmitter release is associated with reduction of neuronal branching in a Drosophila mutant overexpressing frequenin.
abstract: Frequenin is a Drosophila Ca2+ binding protein whose overexpression causes a chronic facilitation of transmitter release at the larval neuromuscular junction and multiple firing of action potentials. These functional abnormalities are similar to those found in other hyperexcitable mutants (Shaker, ether-a-gogo, Hyperkinetic) which, in turn, exhibit increased branching at the motor nerve endings. We report here that mutants which overexpress frequenin have motor nerve terminals with reduced number and length of branches as well as number of synaptic boutons. Similar defects are observed in transgenic flies which have additional copies of the frequenin gene indicating that the phenotype can be adscribed to the overexpression of the protein. The ultrastructure of boutons, however, appears indistinguishable from wild type. In addition, we show here that frequenin overexpression leads also to a down regulation of Shaker proteins expression. The contrast between the observations in frequenin and the other hyperexcitable mutants indicates that nerve terminal morphology and enhanced transmitter release do not have a direct causal relationship.
authors.affiliation: Laboratoire de Neurobiologie Cellulaire et Moléculaire, CNRS, Gif-sur-Yvette, France. angaut@hermes.cnrs-gif.fr
authors.forename: D
authors.initials: D
authors.lastname: Angaut-Petit
authors.forename: P
authors.initials: P
authors.lastname: Toth
authors.forename: O
authors.initials: O
authors.lastname: Rogero
authors.forename: L
authors.initials: L
authors.lastname: Faille
authors.forename: F J
authors.initials: FJ
authors.lastname: Tejedor
authors.forename: A
authors.initials: A
authors.lastname: Ferrús
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D048429:Cell Size; D029721:Drosophila Proteins; D004331:Drosophila melanogaster; D004591:Electrophoresis, Polyacrylamide Gel; D007150:Immunohistochemistry; D007814:Larva; D018613:Microscopy, Confocal; D009154:Mutation / Q000235:genetics / Q000502:physiology*; D009411:Nerve Endings; D009419:Nerve Tissue Proteins / Q000096:biosynthesis* / Q000235:genetics; D009474:Neurons / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D018377:Neurotransmitter Agents / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000502:physiology / Q000648:ultrastructure
chemical_list: D002135:Calcium-Binding Proteins; D029721:Drosophila Proteins; C082454:Frq protein, Drosophila; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents