title: Evolutionary conservation of key structures and binding functions of neural cell adhesion molecules.
abstract: The neural cell adhesion molecule N-CAM is a sialic acid-rich, cell surface glycoprotein that mediates cell adhesion by a homophilic mechanism. Its binding function has been implicated in both morphogenesis and histogenesis; during development it changes in amount at the cell surface and perinatally it undergoes a decrease in sialic acid content (embryonic--adult conversion) with an increase in binding efficacy. In the present study, salient aspects of the structure and the mutual binding specificities of N-CAMs from a variety of vertebrate species were examined to determine whether (N-CAM)-mediated adhesion mechanisms have been conserved during evolution. N-CAM immunoreactivity was detected in a series of polypeptides of characteristic molecular weight extracted from brain tissues of all vertebrate species tested, including mammals, birds, reptiles, amphibia, and bony and cartilaginous fish. Adhesion mediated by N-CAM occurred across species lines as indicated by the co-aggregation of chicken and mouse neural cells. By using a quantitative membrane vesicle aggregation assay, the efficacy of cross-species brain membrane vesicle adhesion in various pairings (chicken-mouse, chicken-frog, mouse-frog) was found to be similar to the efficacy of intra-species adhesion. Effective cross-species aggregation of brain membrane vesicles also occurred in embryonic-embryonic, adult-adult, and embryonic-adult pairings. In a control experiment, embryonic chicken liver membrane vesicles (which do not contain N-CAM) did not co-aggregate with embryonic chicken brain membrane vesicles. Cross-species co-aggregation could be inhibited by Fab' fragments of antibodies of N-CAM and was most effectively inhibited in the presence of mixtures made from the Fab' fragments of specific antibodies prepared against the N-CAMs from each of the animal species constituting a co-aggregating pair. These results suggest that, in accord with the proposed role of N-CAM as a regulator of morphogenesis, both the specificity of the binding region of the molecule and its basic chemical structure have been highly conserved during evolution.
mesh_terms: D000818:Animals; D000954:Antigens, Surface / Q000276:immunology; D005075:Biological Evolution; D001921:Brain / Q000196:embryology / Q000378:metabolism*; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules; D002462:Cell Membrane / Q000378:metabolism; D002645:Chickens; D000939:Epitopes / Q000276:immunology; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007814:Larva / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D013045:Species Specificity; D014982:Xenopus laevis
chemical_list: D000954:Antigens, Surface; D015815:Cell Adhesion Molecules; D000939:Epitopes; D007140:Immunoglobulin Fab Fragments