Postsynaptic actin regulates active zone spacing and glutamate receptor apposition at the Drosophila neuromuscular junction

Mol Cell Neurosci. 2014 Jul:61:241-54. doi: 10.1016/j.mcn.2014.07.005. Epub 2014 Jul 24.

Abstract

Synaptic communication requires precise alignment of presynaptic active zones with postsynaptic receptors to enable rapid and efficient neurotransmitter release. How transsynaptic signaling between connected partners organizes this synaptic apparatus is poorly understood. To further define the mechanisms that mediate synapse assembly, we carried out a chemical mutagenesis screen in Drosophila to identify mutants defective in the alignment of active zones with postsynaptic glutamate receptor fields at the larval neuromuscular junction. From this screen we identified a mutation in Actin 57B that disrupted synaptic morphology and presynaptic active zone organization. Actin 57B, one of six actin genes in Drosophila, is expressed within the postsynaptic bodywall musculature. The isolated allele, act(E84K), harbors a point mutation in a highly conserved glutamate residue in subdomain 1 that binds members of the Calponin Homology protein family, including spectrin. Homozygous act(E84K) mutants show impaired alignment and spacing of presynaptic active zones, as well as defects in apposition of active zones to postsynaptic glutamate receptor fields. act(E84K) mutants have disrupted postsynaptic actin networks surrounding presynaptic boutons, with the formation of aberrant actin swirls previously observed following disruption of postsynaptic spectrin. Consistent with a disruption of the postsynaptic actin cytoskeleton, spectrin, adducin and the PSD-95 homolog Discs-Large are all mislocalized in act(E84K) mutants. Genetic interactions between act(E84K) and neurexin mutants suggest that the postsynaptic actin cytoskeleton may function together with the Neurexin-Neuroligin transsynaptic signaling complex to mediate normal synapse development and presynaptic active zone organization.

Keywords: Actin; Cytoskeleton; NMJ; Neurexin; Spectrin; Synapse.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Actins / genetics
  • Actins / metabolism*
  • Age Factors
  • Animals
  • Animals, Genetically Modified
  • Calcium-Binding Proteins / metabolism
  • Calponins
  • Drosophila
  • Drosophila Proteins / genetics
  • Drosophila Proteins / metabolism*
  • Gene Expression Regulation / genetics
  • Glutamic Acid / metabolism
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Horseradish Peroxidase / metabolism
  • Larva
  • Microfilament Proteins / metabolism
  • Microscopy, Electron, Transmission
  • Models, Molecular
  • Mutation / drug effects
  • Mutation / genetics
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism
  • Neuromuscular Junction / genetics*
  • Neuromuscular Junction / metabolism*
  • Neuromuscular Junction / ultrastructure
  • Patch-Clamp Techniques
  • Receptors, Glutamate / genetics
  • Receptors, Glutamate / metabolism*
  • Synaptic Potentials / genetics

Substances

  • Actins
  • Calcium-Binding Proteins
  • Drosophila Proteins
  • Microfilament Proteins
  • Nerve Tissue Proteins
  • Receptors, Glutamate
  • glutamate receptor III, Drosophila
  • postsynaptic density proteins
  • Green Fluorescent Proteins
  • Glutamic Acid
  • Horseradish Peroxidase