title: Squeezing axons out of the gray matter: a role for slit and semaphorin proteins from midline and ventral spinal cord.
abstract: Commissural axons cross the nervous system midline and then turn to grow alongside it, neither recrossing nor projecting back into ventral regions. In Drosophila, the midline repellent Slit prevents recrossing: axons cross once because they are initially unresponsive to Slit, becoming responsive only upon crossing. We show that commissural axons in mammals similarly acquire responsiveness to a midline repellent activity upon crossing. Remarkably, they also become responsive to a repellent activity from ventral spinal cord, helping explain why they never reenter that region. Several Slit and Semaphorin proteins, expressed in midline and/or ventral tissues, mimic these repellent activities, and midline guidance defects are observed in mice lacking neuropilin-2, a Semaphorin receptor. Thus, Slit and Semaphorin repellents from midline and nonmidline tissues may help prevent crossing axons from reentering gray matter, squeezing them into surrounding fiber tracts.
authors.affiliation: Department of Anatomy, Howard Hughes Medical Institute, University of California, San Francisco 94143, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Zou
authors.forename: E
authors.initials: E
authors.lastname: Stoeckli
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.forename: M
authors.initials: M
authors.lastname: Tessier-Lavigne
mesh_terms: D000818:Animals; D001369:Axons; D002450:Cell Communication; D029721:Drosophila Proteins; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D009024:Morphogenesis; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009434:Neural Pathways / Q000166:cytology / Q000196:embryology*; D039942:Neuropilin-1; D051381:Rats; D013116:Spinal Cord / Q000166:cytology / Q000196:embryology*; D000098552:Slit Homolog 2 Protein
chemical_list: D029721:Drosophila Proteins; D036341:Intercellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins; C066819:sli protein, Drosophila; D039942:Neuropilin-1; D000098552:Slit Homolog 2 Protein