title: Comm function in commissural axon guidance: cell-autonomous sorting of Robo in vivo.
abstract: 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.
authors.affiliation: Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Dr. Bohr-Gasse 3-5, A-1030 Vienna, Austria.
authors.forename: Krystyna
authors.initials: K
authors.lastname: Keleman
authors.forename: Carlos
authors.initials: C
authors.lastname: Ribeiro
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Dickson
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001369:Axons / Q000502:physiology*; D019556:COS Cells; D002450:Cell Communication / Q000502:physiology*; D002522:Chlorocebus aethiops; D004330:Drosophila; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004625:Embryo, Nonmammalian; D056827:Endosomal Sorting Complexes Required for Transport; D018507:Gene Expression Regulation, Developmental; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007150:Immunohistochemistry / Q000379:methods; D066298:In Vitro Techniques; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D018613:Microscopy, Confocal / Q000379:methods; D008954:Models, Biological; D000075702:Nedd4 Ubiquitin Protein Ligases; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009474:Neurons / Q000502:physiology*; D051761:Paired Box Transcription Factors; D017434:Protein Structure, Tertiary / Q000235:genetics; D011971:Receptors, Immunologic / Q000378:metabolism*; D013194:Staining and Labeling / Q000379:methods; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014162:Transfection / Q000379:methods; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D000097905:Roundabout Proteins
chemical_list: D029721:Drosophila Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D049452:Green Fluorescent Proteins; D008565:Membrane Proteins; D000075702:Nedd4 Ubiquitin Protein Ligases; D009419:Nerve Tissue Proteins; D051761:Paired Box Transcription Factors; D011971:Receptors, Immunologic; D014157:Transcription Factors; D044767:Ubiquitin-Protein Ligases; D000097905:Roundabout Proteins; C073863:Poxn protein, Drosophila; C110665:comm protein, Drosophila