A presynaptic homeostatic signaling system composed of the Eph receptor, ephexin, Cdc42, and CaV2.1 calcium channels

Neuron. 2009 Feb 26;61(4):556-69. doi: 10.1016/j.neuron.2008.12.028.


The molecular mechanisms underlying the homeostatic modulation of presynaptic neurotransmitter release remain largely unknown. In a screen, we isolated mutations in Drosophila ephexin (Rho-type guanine nucleotide exchange factor) that disrupt the homeostatic enhancement of presynaptic release following impairment of postsynaptic glutamate receptor function at the Drosophila neuromuscular junction. We show that Ephexin is sufficient presynaptically for synaptic homeostasis and localizes in puncta throughout the nerve terminal. However, ephexin mutations do not alter other aspects of neuromuscular development, including morphology or active zone number. We then show that, during synaptic homeostasis, Ephexin functions primarily with Cdc42 in a signaling system that converges upon the presynaptic CaV2.1 calcium channel. Finally, we show that Ephexin binds the Drosophila Eph receptor (Eph) and Eph mutants disrupt synaptic homeostasis. Based on these data, we propose that Ephexin/Cdc42 couples synaptic Eph signaling to the modulation of presynaptic CaV2.1 channels during the homeostatic enhancement of presynaptic release.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Calcium Channels, N-Type / genetics
  • Calcium Channels, N-Type / physiology*
  • Drosophila / physiology*
  • Drosophila Proteins / genetics*
  • Drosophila Proteins / physiology*
  • Electrophysiology
  • Guanine Nucleotide Exchange Factors / genetics*
  • Guanine Nucleotide Exchange Factors / physiology*
  • Homeostasis / genetics
  • Homeostasis / physiology*
  • Immunohistochemistry
  • Molecular Sequence Data
  • Muscles / innervation
  • Muscles / physiology
  • Mutation / genetics
  • Mutation / physiology
  • Neurotransmitter Agents / metabolism
  • Receptor, EphA1 / genetics
  • Receptor, EphA1 / physiology*
  • Receptors, Glutamate / physiology
  • Receptors, Presynaptic / genetics
  • Receptors, Presynaptic / physiology*
  • Signal Transduction / genetics
  • Signal Transduction / physiology*
  • Synaptic Transmission / physiology
  • cdc42 GTP-Binding Protein / genetics
  • cdc42 GTP-Binding Protein / physiology*


  • Calcium Channels, N-Type
  • Drosophila Proteins
  • Exn protein, Drosophila
  • Guanine Nucleotide Exchange Factors
  • Neurotransmitter Agents
  • Receptors, Glutamate
  • Receptors, Presynaptic
  • voltage-dependent calcium channel (P-Q type)
  • Receptor, EphA1
  • cdc42 GTP-Binding Protein