Identification of Nogo-66 receptor (NgR) and homologous genes in fish.
The Nogo-66 receptor NgR has been implicated in the mediation of inhibitory effects of central nervous system (CNS) myelin on axon growth in the adult mammalian CNS. NgR binds to several myelin-associated ligands (Nogo-66, myelin associated glycoprotein, and oligodendrocyte-myelin glycoprotein), which, among other inhibitory proteins, impair axonal regeneration in the CNS of adult mammals. In contrast to mammals, severed axons readily regenerate in the fish CNS. Nevertheless, fish axons are repelled by mammalian oligodendrocytes in vitro. Therefore, the identification of fish NgR homologs is a crucial step towards understanding NgR functions in vertebrate systems competent of CNS regeneration. Here, we report the discovery of four zebrafish (Danio rerio) and five fugu (Takifugu rubripes) NgR homologs. Synteny between fish and human, comparable intron-exon structures, and phylogenetic analyses provide convincing evidence that the true fish orthologs were identified. The topology of the phylogenetic trees shows that the extra fish genes were produced by duplication events that occurred in ray-finned fishes before the divergence of the zebrafish and pufferfish lineages. Expression of zebrafish NgR homologs was detected relatively early in development and prominently in the adult brain, suggesting functions in axon growth, guidance, or plasticity.
Klinger
Michael
M
Department of Biology, University of Konstanz, Konstanz, Germany.
Taylor
John S
JS
Oertle
Thomas
T
Schwab
Martin E
ME
Stuermer
Claudia A O
CA
Diekmann
Heike
H
D000818:Animals; D001369:Axons / Q000378:metabolism; D001483:Base Sequence; D015139:Blotting, Southern; D030561:Databases, Nucleic Acid; D040461:Gene Components; D018507:Gene Expression Regulation, Developmental; D020131:Genes, Duplicate / Q000235:genetics; D008969:Molecular Sequence Data; D009185:Myelin Proteins / Q000378:metabolism*; D000070798:Nogo Proteins; D010802:Phylogeny; D021101:Radiation Hybrid Mapping; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D026801:Synteny / Q000235:genetics; D023741:Takifugu / Q000235:genetics*; D015027:Zebrafish / Q000235:genetics*; D029961:Zebrafish Proteins
D009185:Myelin Proteins; D000070798:Nogo Proteins; C000603199:RTN4 protein, human; D011956:Receptors, Cell Surface; C000592544:Rtn4a protein, zebrafish; D029961:Zebrafish Proteins