Comm function in commissural axon guidance: cell-autonomous sorting of Robo in vivo

Nat Neurosci. 2005 Feb;8(2):156-63. doi: 10.1038/nn1388. Epub 2005 Jan 16.


Commissureless (Comm) controls axon guidance across the Drosophila melanogaster midline by regulating surface levels of Robo, the receptor for the midline repellent Slit. Two different models have been proposed for how Comm regulates Robo: a 'sorting' model and a 'clearance' model, both based on studies using heterologous cells in vitro. Here, we test these two models in vivo. We establish a genetic rescue assay for Comm, and use this assay to show that midline crossing does not require the presence of Comm in midline cells, as proposed by the clearance model. Moreover, by monitoring the trafficking of a Robo-green fluorescent protein (GFP) fusion in living embryos, we demonstrate that Comm prevents the delivery of Robo-GFP to the growth cone, as predicted by the sorting model. It has also been suggested that Comm must be ubiquitinated by the Nedd4 ubiquitin ligase. We show here, however, that ubiquitination of Comm is not required for its function in vitro or in vivo, and that Nedd4 is unlikely to function in axon guidance at the midline.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Animals, Genetically Modified
  • Axons / physiology*
  • COS Cells
  • Cell Communication / physiology*
  • Chlorocebus aethiops
  • Drosophila
  • Drosophila Proteins / chemistry
  • Drosophila Proteins / genetics
  • Drosophila Proteins / metabolism
  • Drosophila Proteins / physiology*
  • Embryo, Nonmammalian
  • Endosomal Sorting Complexes Required for Transport
  • Gene Expression Regulation, Developmental
  • Green Fluorescent Proteins / metabolism
  • Immunohistochemistry / methods
  • In Vitro Techniques
  • Membrane Proteins / chemistry
  • Membrane Proteins / physiology*
  • Microscopy, Confocal / methods
  • Models, Biological
  • Nedd4 Ubiquitin Protein Ligases
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism
  • Neurons / physiology*
  • Paired Box Transcription Factors
  • Protein Structure, Tertiary / genetics
  • Receptors, Immunologic / metabolism*
  • Staining and Labeling / methods
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • Transfection / methods
  • Ubiquitin-Protein Ligases / metabolism


  • Drosophila Proteins
  • Endosomal Sorting Complexes Required for Transport
  • Membrane Proteins
  • Nerve Tissue Proteins
  • Paired Box Transcription Factors
  • Poxn protein, Drosophila
  • Receptors, Immunologic
  • Transcription Factors
  • comm protein, Drosophila
  • roundabout protein
  • Green Fluorescent Proteins
  • Nedd4 Ubiquitin Protein Ligases
  • Ubiquitin-Protein Ligases