title: Divergent evolution of the vertebrate polysialyltransferase Stx and Pst genes revealed by fish-to-mammal comparison.
abstract: Polysialic acid (PSA) is a developmentally regulated carbohydrate attached to the neural cell adhesion molecule (NCAM). PSA is involved in dynamic processes like cell migration, neurite outgrowth and neuronal plasticity. In mammals, polysialylation of NCAM is catalyzed independently by two polysialyltransferases, STX (ST8Sia II) and PST (ST8Sia IV), with STX mainly acting during early development and PST at later stages and into adulthood. Here, we functionally characterize zebrafish Stx and Pst homolog genes during fish development and evaluate their catalytic affinity for NCAM in vitro. Both genes have the typical gene architecture and share conserved synteny with their mammalian homologues. Expression analysis, gene-targeted knockdown experiments and in vitro catalytic assays indicate that zebrafish Stx is the principal--if not unique--polysialyltransferase performing NCAM-PSA modifications in both developing and adult fish. The knockdown of Stx exclusively affects PSA synthesis, producing defects in axonal growth and guidance. Zebrafish Pst is in principle capable of synthesizing PSA, however, our data argue against a fundamental function of the enzyme during development. Our findings reveal an important divergence of Stx and Pst enzymes in vertebrates, which is also characterized by a differential gene loss and rapid evolution of Pst genes within the bony-fish class.
authors.affiliation: Zoologisches Institut I, Lehrstuhl für Zell-und Neurobiologie, Universität Karlsruhe (TH), Haid-und-Neu-Strasse 9, D-76131 Karlsruhe, Germany.
authors.forename: Monika
authors.initials: M
authors.lastname: Marx
authors.forename: Eric
authors.initials: E
authors.lastname: Rivera-Milla
authors.forename: Katharina
authors.initials: K
authors.lastname: Stummeyer
authors.forename: Rita
authors.initials: R
authors.lastname: Gerardy-Schahn
authors.forename: Martin
authors.initials: M
authors.lastname: Bastmeyer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001369:Axons / Q000378:metabolism; D005075:Biological Evolution; D018507:Gene Expression Regulation, Developmental; D008322:Mammals; D008969:Molecular Sequence Data; D019006:Neural Cell Adhesion Molecules / Q000502:physiology*; D009841:Oligonucleotides / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D012794:Sialic Acids / Q000378:metabolism; D012799:Sialyltransferases / Q000378:metabolism / Q000502:physiology*; D013045:Species Specificity; D015027:Zebrafish
chemical_list: D019006:Neural Cell Adhesion Molecules; D009841:Oligonucleotides; D012794:Sialic Acids; C021319:polysialic acid; C046778:CMP-N-acetylneuraminate-poly-alpha-2,8-sialosyl sialyltransferase; D012799:Sialyltransferases; C515117:ST8SIA4 protein, human