title: Involvement of Slit-Robo signaling in the development of the posterior commissure and concomitant swimming behavior in Xenopus laevis.
abstract: BACKGROUND
  During vertebrate development, the central nervous system (CNS) has stereotyped neuronal tracts (scaffolds) that include longitudinal and commissural axonal bundles, such as the medial longitudinal fascicle or the posterior commissure (PC). As these early tracts appear to guide later-developing neurons, they are thought to provide the basic framework of vertebrate neuronal circuitry. The proper construction of these neuronal circuits is thought to be a crucial step for eliciting coordinated behaviors, as these circuits transmit sensory information to the integrative center, which produces motor commands for the effective apparatus. However, the developmental plan underlying some commissures and the evolutionary transitions they have undergone remain to be elucidated. Little is known about the role of axon guidance molecules in the elicitation of early-hatched larval behavior as well.
  
  
  RESULTS
  Here, we report the developmentally regulated expression pattern of axon-guidance molecules Slit2 ligand and Robo2 receptor in Xenopus laevis and show that treatment of X. laevis larvae with a slit2- or robo2-morpholino resulted in abnormal swimming behavior. We also observed an abnormal morphology of the PC, which is part of the early axonal scaffold.
  
  
  CONCLUSIONS
  Our present findings suggest that expression patterns of Slit2 and Robo2 are conserved in tetrapods, and that their signaling contributes to the construction of the PC in Xenopus. Given that the PC also includes several types of neurons stemming from various parts of the CNS, it may represent a candidate prerequisite neuronal tract in the construction of subsequent complex neuronal circuits that trigger coordinated behavior.
authors.affiliation: Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan.
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Tosa
authors.affiliation: Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan.
authors.forename: Kiyohito
authors.initials: K
authors.lastname: Tsukano
authors.affiliation: Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Itoyama
authors.affiliation: Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan.
authors.forename: Mai
authors.initials: M
authors.lastname: Fukagawa
authors.affiliation: Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan.
authors.forename: Yukako
authors.initials: Y
authors.lastname: Nii
authors.affiliation: Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan.
authors.forename: Ryota
authors.initials: R
authors.lastname: Ishikawa
authors.affiliation: Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526 Japan.
authors.forename: Ken-Ichi T
authors.initials: KT
authors.lastname: Suzuki
authors.affiliation: Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan.
authors.forename: Makiko
authors.initials: M
authors.lastname: Fukui
authors.affiliation: Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194 Japan.
authors.forename: Masahumi
authors.initials: M
authors.lastname: Kawaguchi
authors.affiliation: Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577 Japan.
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Murakami