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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.

Pubmed ID: 10409513


  • Zallen JA
  • Kirch SA
  • Bargmann CI


Development (Cambridge, England)

Publication Data

August 8, 1999

Associated Grants


Mesh Terms

  • Animals
  • Animals, Genetically Modified
  • Axons
  • Body Patterning
  • Caenorhabditis elegans
  • Chemotaxis
  • Female
  • Genes, Reporter
  • Green Fluorescent Proteins
  • Interneurons
  • Luminescent Proteins
  • Motor Neurons
  • Mutagenesis
  • Nerve Tissue Proteins
  • Neurons
  • Neurons, Afferent
  • Receptors, Immunologic