title: Tenascin-R as a repellent guidance molecule for developing optic axons in zebrafish.
abstract: To investigate the role of tenascin-R in nervous system development, we studied axon pathfinding in the developing optic system of zebrafish. Zebrafish tenascin-R has the same domain structure as tenascin-R in amniotes. Amino acid sequence identity with human tenascin-R is 60%. In 3-d-old larvae, tenascin-R mRNA is expressed in scattered cells throughout the periventricular cell layer of the diencephalon and tectum. Tenascin-R immunoreactivity is not detectable in the optic nerve, optic tract, or tectal optic neuropil but immediately borders the optic tract caudally. Reducing expression of tenascin-R in 3-d-old larvae in vivo by injecting morpholinos into fertilized eggs led to excessive branching of the optic tract in 86% of all injected larvae compared with 20-37% in controls. Branches were almost exclusively caudal, where tenascin-R immunoreactivity normally borders the optic tract, suggesting a role for tenascin-R in guiding optic axons in the ventral diencephalon by a contact-repellent mechanism.
authors.affiliation: Zentrum für Molekulare Neurobiologie Hamburg, Universität Hamburg, D-20246 Hamburg, Germany. tcbecker@zmnh.unihamburg.de
authors.forename: Catherina G
authors.initials: CG
authors.lastname: Becker
authors.forename: Jörn
authors.initials: J
authors.lastname: Schweitzer
authors.forename: Julia
authors.initials: J
authors.lastname: Feldner
authors.forename: Thomas
authors.initials: T
authors.lastname: Becker
authors.forename: Melitta
authors.initials: M
authors.lastname: Schachner
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D001921:Brain / Q000378:metabolism; D003001:Cloning, Molecular; D004027:Diencephalon / Q000166:cytology / Q000254:growth & development; D005456:Fluorescent Dyes; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000502:physiology; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007814:Larva; D015336:Molecular Probe Techniques; D008969:Molecular Sequence Data; D009025:Morpholines / Q000737:chemistry; D015341:Nucleic Acid Probes / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D009900:Optic Nerve / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D017386:Sequence Homology, Amino Acid; D019063:Tenascin / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D014795:Visual Pathways / Q000166:cytology / Q000187:drug effects; D015027:Zebrafish
chemical_list: D005456:Fluorescent Dyes; D009025:Morpholines; D015341:Nucleic Acid Probes; D012333:RNA, Messenger; D019063:Tenascin; C074638:tenascin R