title: Netrin UNC-6 and the regulation of branching and extension of motoneuron axons from the ventral nerve cord of Caenorhabditis elegans.
abstract: In the Caenorhabditis elegans embryo, some ventral midline motoneurons extend a process circumferentially to the dorsal midline and a process longitudinally along ventral nerve cord interneurons. Circumferential migrations are guided by netrin UNC-6, which repels motoneuron axons dorsally. Although the motoneuron cell bodies and the longitudinal axons are positioned along UNC-6-expressing interneurons in the ventral nerve cord, the circumferential processes extend only from the motoneuron cell bodies and from defined locations along some longitudinal axons. This implies a mechanism regulates motoneuron branching of UNC-6-responsive processes. We show that expression of unc-6DeltaC, which encodes UNC-6 without domain C, partially rescues circumferential migration defects in unc-6 null animals. This activity depends on the netrin receptors UNC-5 and UNC-40. These results indicate that UNC-6DeltaC can provide the circumferential guidance functions of UNC-6. Furthermore, we show that expression of unc-6DeltaC causes motoneuron branching and the extension of processes from abnormal positions along the ventral nerve cord. This activity is also UNC-5- and UNC-40-dependent. We propose that local interactions mediated by domain C regulate motoneuron branching and responsiveness to the UNC-6 cue.
authors.affiliation: Department of Pathology, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854-5635, USA.
authors.forename: Y S
authors.initials: YS
authors.lastname: Lim
authors.forename: S
authors.initials: S
authors.lastname: Mallapur
authors.forename: G
authors.initials: G
authors.lastname: Kao
authors.forename: X C
authors.initials: XC
authors.lastname: Ren
authors.forename: W G
authors.initials: WG
authors.lastname: Wadsworth
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001369:Axons / Q000502:physiology; D017173:Caenorhabditis elegans / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins; D002478:Cells, Cultured; D017952:Ganglia, Invertebrate / Q000502:physiology; D015801:Helminth Proteins / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology / Q000648:ultrastructure; D009419:Nerve Tissue Proteins / Q000502:physiology; D000075385:Netrins; D010641:Phenotype
chemical_list: D029742:Caenorhabditis elegans Proteins; D015801:Helminth Proteins; D009419:Nerve Tissue Proteins; D000075385:Netrins; C078146:UNC-6 protein, C elegans