title: Novel mutations affecting axon guidance in zebrafish and a role for plexin signalling in the guidance of trigeminal and facial nerve axons.
abstract: In zebrafish embryos, the axons of the posterior trigeminal (Vp) and facial (VII) motoneurons project stereotypically to a small number of target muscles derived from the first and second branchial arches (BA1, BA2). Use of the Islet1 (Isl1)-GFP transgenic line enabled precise real-time observations of the growth cone behaviour of the Vp and VII motoneurons within BA1 and BA2. Screening for N-ethyl-N-nitrosourea-induced mutants identified seven distinct mutations affecting different steps in the axonal pathfinding of these motoneurons. The class 1 mutations caused severe defasciculation and abnormal pathfinding in both Vp and VII motor axons before they reached their target muscles in BA1. The class 2 mutations caused impaired axonal outgrowth of the Vp motoneurons at the BA1-BA2 boundary. The class 3 mutation caused impaired axonal outgrowth of the Vp motoneurons within the target muscles derived from BA1 and BA2. The class 4 mutation caused retraction of the Vp motor axons in BA1 and abnormal invasion of the VII motor axons in BA1 beyond the BA1-BA2 boundary. Time-lapse observations of the class 1 mutant, vermicelli (vmc), which has a defect in the plexin A3 (plxna3) gene, revealed that Plxna3 acts with its ligand Sema3a1 for fasciculation and correct target selection of the Vp and VII motor axons after separation from the common pathways shared with the sensory axons in BA1 and BA2, and for the proper exit and outgrowth of the axons of the primary motoneurons from the spinal cord.
authors: Laboratory for Developmental Gene Regulation, Brain Science Institute, The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
authors: Hideomi
authors: H
authors: Tanaka
authors: Ryu
authors: R
authors: Maeda
authors: Wataru
authors: W
authors: Shoji
authors: Hironori
authors: H
authors: Wada
authors: Ichiro
authors: I
authors: Masai
authors: Toshiyuki
authors: T
authors: Shiraki
authors: Megumi
authors: M
authors: Kobayashi
authors: Ryoko
authors: R
authors: Nakayama
authors: Hitoshi
authors: H
authors: Okamoto
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology*; D047108:Embryonic Development / Q000235:genetics*; D005154:Facial Nerve / Q000196:embryology*; D009046:Motor Neurons / Q000502:physiology; D009154:Mutation; D009414:Nerve Growth Factors; D011956:Receptors, Cell Surface / Q000235:genetics / Q000502:physiology*; D039961:Semaphorins / Q000502:physiology; D014276:Trigeminal Nerve / Q000196:embryology*; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics; D029961:Zebrafish Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D009414:Nerve Growth Factors; C524494:Plxna3 protein, zebrafish; D011956:Receptors, Cell Surface; D039961:Semaphorins; D029961:Zebrafish Proteins; C120876:sema3aa protein, zebrafish