Genes required for axon pathfinding and extension in the C. elegans nerve ring.
Over half of the neurons in Caenorhabditis elegans send axons to the nerve ring, a large neuropil in the head of the animal. Genetic screens in animals that express the green fluorescent protein in a subset of sensory neurons identified eight new sax genes that affect the morphology of nerve ring axons. sax-3/robo mutations disrupt axon guidance in the nerve ring, while sax-5, sax-9 and unc-44 disrupt both axon guidance and axon extension. Axon extension and guidance proceed normally in sax-1, sax-2, sax-6, sax-7 and sax-8 mutants, but these animals exhibit later defects in the maintenance of nerve ring structure. The functions of existing guidance genes in nerve ring development were also examined, revealing that SAX-3/Robo acts in parallel to the VAB-1/Eph receptor and the UNC-6/netrin, UNC-40/DCC guidance systems for ventral guidance of axons in the amphid commissure, a major route of axon entry into the nerve ring. In addition, SAX-3/Robo and the VAB-1/Eph receptor both function to prevent aberrant axon crossing at the ventral midline. Together, these genes define pathways required for axon growth, guidance and maintenance during nervous system development.
Zallen
J A
JA
Programs in Developmental Biology, Neuroscience and Genetics, Howard Hughes Medical Institute, Department of Anatomy, University of California, San Francisco, California 94143-0452, USA.
Kirch
S A
SA
Bargmann
C I
CI
D000818:Animals; D030801:Animals, Genetically Modified; D001369:Axons / Q000502:physiology*; D019521:Body Patterning; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000254:growth & development*; D002633:Chemotaxis; D005260:Female; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D007395:Interneurons / Q000502:physiology; D008164:Luminescent Proteins / Q000032:analysis / Q000235:genetics; D009046:Motor Neurons / Q000502:physiology; D016296:Mutagenesis; D009419:Nerve Tissue Proteins; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D011971:Receptors, Immunologic / Q000235:genetics / Q000502:physiology*; D000097905:Roundabout Proteins
D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D009419:Nerve Tissue Proteins; D011971:Receptors, Immunologic; D000097905:Roundabout Proteins