title: Ncam1a and Ncam1b: two carriers of polysialic acid with different functions in the developing zebrafish nervous system.
abstract: Polysialic acid (polySia) is mainly described as a glycan modification of the neural cell adhesion molecule NCAM1. PolySia-NCAM1 has multiple functions during the development of vertebrate nervous systems including axon extension and fasciculation. Phylogenetic analyses reveal the presence of two related gene clusters, NCAM1 and NCAM2, in tetrapods and fishes. Within the ncam1 cluster, teleost fishes express ncam1a (ncam) and ncam1b (pcam) as duplicated paralogs which arose from a second round of ray-finned fish-specific genome duplication. Tetrapods, in contrast, express a single NCAM1 gene. Using the zebrafish model, we identify Ncam1b as a novel major carrier of polySia in the nervous system. PolySia-Ncam1a is expressed predominantly in rostral regions of the developing nervous system, whereas polySia-Ncam1b prevails caudally. We show that ncam1a and ncam1b have different expression domains which only partially overlap. Furthermore, Ncam1a and Ncam1b and their polySia modifications serve different functions in axon guidance. Formation of the posterior commissure at the forebrain/midbrain junction requires polySia-Ncam1a on the axons for proper fasciculation, whereas Ncam1b, expressed by midbrain cell bodies, serves as an instructive guidance cue for the dorso-medially directed growth of axons. Spinal motor axons, on the other hand, depend on axonally expressed Ncam1b for correct growth toward their target region. Collectively, these findings suggest that the genome duplication in the teleost lineage has provided the basis for a functional diversification of polySia carriers in the nervous system.
authors: Zoologisches Institut, Abteilung für Zell- und Neurobiologie, Karlsruhe Institute of Technology (KIT), Haid und Neu-Strasse 9, Karlsruhe, Germany.
authors: Melanie
authors: M
authors: Langhauser
authors: Jana
authors: J
authors: Ustinova
authors: Eric
authors: E
authors: Rivera-Milla
authors: Darja
authors: D
authors: Ivannikov
authors: Carmen
authors: C
authors: Seidl
authors: Christin
authors: C
authors: Slomka
authors: Jukka
authors: J
authors: Finne
authors: Yoshihiro
authors: Y
authors: Yoshihara
authors: Martin
authors: M
authors: Bastmeyer
authors: Joachim
authors: J
authors: Bentrop
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism; D001921:Brain / Q000196:embryology* / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D019143:Evolution, Molecular; D020440:Gene Duplication; D008636:Mesencephalon / Q000196:embryology / Q000378:metabolism; D005810:Multigene Family; D009420:Nervous System / Q000196:embryology* / Q000378:metabolism; D019006:Neural Cell Adhesion Molecules / Q000378:metabolism*; D016548:Prosencephalon / Q000196:embryology / Q000378:metabolism; D012794:Sialic Acids / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism; D015027:Zebrafish / Q000196:embryology* / Q000378:metabolism; D029961:Zebrafish Proteins / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D019006:Neural Cell Adhesion Molecules; D012794:Sialic Acids; D029961:Zebrafish Proteins; C435270:ncam1a protein, zebrafish; C021319:polysialic acid