Molecular cloning and tissue expression of a cDNA encoding IP1--a P0-like glycoprotein of trout CNS myelin

A full-length cDNA encoding a major structural glycoprotein of trout CNS myelin (IP1) was cloned and sequenced. The deduced amino acid sequence exhibited a significant structural homology with the P0 proteins of rat PNS and shark CNS. Sequence conservation was strongest in the extracellular domain, and it included the position of the two cysteine residues required for stabilization of an immunoglobulin-like secondary structure as well as those of the single N-glycosylation acceptor site. The cytoplasmic domain was shorter by 38 amino acids than those of rat and shark P0 and except for a high proportion of basic amino acids did not show any appreciable sequence homology. A single mRNA species of 2 kb was identified by northern blotting, which was expressed in brain tissue but not in liver. By in situ hybridization a selective labeling of myelinating glial cells in the trout CNS and PNS was revealed. The developmental appearance of the IP1 transcript closely coincided with a period of active myelin deposition in most regions of the trout brain.