Cell-Substratum Adhesion in Embryonic Chick Central Nervous System Is a 170,000-mol-wt Neural-specific Polypeptide Mediated by

Embryonal chick neural retina cells release into the culture medium a complex of proteins and glycosaminoglycans, termed adherons, that promote cell to substratum adhesion. A monoclonal antibody (C1H3) blocks adheron-mediated cell to substratum adhesion and specifically binds to a 170,000-mol-wt protein present in retinal adherons (Cole, G. J., and L. Glaser, 1984, J. Biol. Chem., 259:4031-4034). The 170,000-mol-wt protein also can be identified in embryonic chick brain and peripheral nervous tissue. In the neural retina, C1H3 also binds to a second antigen with a molecular weight of 140,000 that is absent in the brain. Embryonic brain, therefore, provides a source for the immunopurification of the 170,000-molwt protein. Brain adherons also contain the 170,000-mol-wt protein, and cell to substratum adhesion mediated by these adherons is blocked by the C1H3 monoclonal antibody. The 170,000-mol-wt protein in the brain is therefore functionally identical to that in the retina. To demonstrate that adheron-mediated cell to substratum adhesion is caused by cell binding to the 170,000-mol-wt protein, we showed that (a) protease digestion, but not glycosaminoglycan hydrolase digestion of adherons, blocked their ability to bind cells to substratum; (b) the immunopurified 170,000-mol-wt protein blocks adheron-mediated cell to substratum adhesion; and (c) cells can bind to immunopurified 170,000-mol-wt protein bound to glass surfaces. Adhesive interactions between cell types in the developing nervous system are likely to be dependent on several distinct processes. A primary mode of interaction occurs between neurons and is in part mediated by the neural cell adhesion molecule, N-CAM (1).' Molecules participating in neuronneuron interactions that are immunochemically or functionally related to N-CAM have also been described in the nervous system (2-4). Grumet et al. (5) have recently identified a molecule distinct from N-CAM that participates in adhesion between neurons and gila. In addition to these types of cellcell adhesion, extracellular molecules have been implicated in cell adhesion processes. Macromolecules that comprise the extracellular matrix provide a substratum that permits the adhesion and migration of developing cells, and thus probably play a key role in development. Extracellular molecules that are possible candidates in cell-substratum adhesion have been identified in cultured muscle cells (6, 7) and fibroblast-like cells (8, 9). Characteristic of these molecules is their release from the cells into the culture medium, and their promotion of cell-substratum adhesion when used to coat plastic culture dishes. Extracellular macromolecules that are released by nonneural cells and permit cell-substratum adhesion of neural cells have also been described (I0). In addition, a complex of proteins and glycosaminoglycans, termed adherons, 2 has been isolated from the culture medium of embryonic chick neural retina cells and has specifically been shown to mediate cellsubstratum adhesion of these neural cells (11). Neural retinal cells adhere specifically to plastic dishes coated with retinal ' Abbreviations used in this paper: buffer A, 8 g NaC1, 0.2 g KCI, 0.2 g KH:PO4, 0.15 g Na2HPO4/liter (pH 7.4); DME, Dulbecco's minimal essential medium; EBSS, Earle's balanced salt solution; NCAM, neural cell adhesion molecule; NP-40, Nonidet P-40. 2 The term adheron is used operationally to describe particulate material prepared by the method of Schubert et al. (11). It is not meant to imply that this material represents a defined macromolecular aggregate of constant composition. THE JOURNAL OF CI~LL BIOLOGY • VOLUME 99 NOVEMBER 1984 1605-1612 © The Rockefeller University Press 0021-9525/84/11/1605/08 $1.0