Structure of the axonal surface recognition molecule neurofascin and its relationship to a neural subgroup of the immunoglobulin superfamily.

Abstract

Abstract. The chick axon-associated surface glycoprotein neurofascin is implicated in axonal growth and fasciculation as revealed by antibody perturbation experiments. Here we report the complete cDNA sequence of neurofascin. It is composed of four structural elements: At the NH2 terminus neurofascin contains six Ig-like motifs of the C2 subeategory followed by four fibronectin type III (FNl/I)-related repeats. Between the FNIII-like repeats and the plasma membrane spanning region neurofasein contains a domain 75-amino acid residues-long rich in proline, alanine and threonine which might be the target of extensive O-linked glycosylation. A transmembrane segment is followed by a 113-amino acid residues-long cytoplasmic domain. Sequence comparisons indicate that neurofascin is most closely related to chick Nr-CAM and forms with L1 (Ng-CAM) and Nr-CAM a subgroup within the vertebrate Ig superfamily.Sequencing of several overlapping cDNA probes reveals interesting heterogeneities throughout the neurofascin polypeptide. Genomic Southern blots analyzed with neurofasein cDNA clones suggest that neurofascin is encoded by a single gene and its premRNA might be therefore alternatively spliced. Northern blot analysis with domain specific probes showed that neurofascin mRNAs of about 8.5 kb are expressed throughout development in embryonic brain but not in liver.Isolation of neurofasein by immunoaffinity chromatography results in several molecular mass components. To analyze their origin the amino-terminal sequences of several neurofascin components were determined. The NH2-terminal sequences of the 185, 160, and 110-135 kD components are all the same as the NH2 termini predicted by the eDNA sequence, whereas the other neurofascin components start with a sequence found in a putative alternatively spliced segment between the Ig-and FNIII-like part indicating that they are derived by proteolytic cleavage. A combination of enzymatic and chemical deglycosylation procedures and the analysis of peanut lectin binding reveals O-and N-linked carbohydrates on neurofascin components which might generate additional heterogeneity.

A Neuronal Form of the Cell Adhesion Molecule L1 Contains a Tyrosine-Based Signal Required for Sorting to the Axonal Growth Cone

“…Homologs of mammalian L1 in chick (NgCAM/8D9/G4) and zebrafish (L1.1 and L1.2) contain the YRSLE sequence, but it is absent in Drosophila (neuroglian) (Tongiorgi et al, 1995;Hortsch, 1996). In addition, it is conserved in two other members of the L1 subfamily, neurofascin and NrCAM (Kayyem et al, 1992;Volkmer et al, 1992), implying an important function for this sequence.…”

Regulation of axonal growth in the vertebrate nervous system by interactions between glycoproteins belonging to two subgroups of the immunoglobulin superfamily.

“…splicing are known for neurofascin and Nr-CAM, whereas only two cytoplasmic isoforms of L1 and Ng-CAM have been described Volkmer et al, 1992;Miura et al, 1991).…”

“…So far, Nr-CAM and neurofascin have only been found in the chick. goon et al, 1991;Grumet et al, 1991;Volkmer et al, 1992). Axonin-1/TAG-1 and Fll/F3 also exist as secreted forms, probably derived from an intracellular pool rather than released from the cell surface (Ruegg et al, 1989).…”

The irregular chiasm C-roughest locus of Drosophila, which affects axonal projections and programmed cell death, encodes a novel immunoglobulin-like protein.

“…and extracellular matrix proteins, as well as the identification of factors, diffusible and localized, growth promoting and inhibitory, that have been shown by a number of criteria to be involved in axonal navigation or growth (Rathjen et al 1987;Furley et al 1990;Bums et al 1991;Pourqui6 et al 1992b;Volkmer et al 1992). Some of these studies have uncovered the intriguing evolutionary conservation of the basic molecular and cellular mechanisms underlying growth cone guidance and recognition by showing that many proteins implicated in such processes share structural similarities in both vertebrates and invertebrates and often belong to the same superfamilies of genes (Dodd and Jessel 1988;Harrelson and Goodman 1988;Grenningloh et al 1990;Hortsch and Goodman 1991;Jessel 1988;Rathjen and Jessell 1991;Reichardt and Tomaselli 1991;Takeichi 1991;Walsh and Doherty 1991).…”