Neural crest cell locomotion induced by antibodies to β1 integrins A tool for studying the roles of substratum molecular avidity and density in migration

Migration of neural crest cells depends on direct, transient interactions between fibronectin molecules and their corresponding Arg-Gly-Asp integrin receptors. We have previously suggested that the moderate-activity interaction between integrin receptors and fibronectin may be critical for the transient association of the cells with their substratum. In order to test this hypothesis, we have examined the in vitro locomotory behavior of neural crest cells on substrata of differing apparent avidities for integrin receptors. As substrata, we used a variety of monoclonal and polyclonal antibodies to the integrin beta 1 subunit that were characterized for their respective relative apparent avidities for the receptor. Neural crest cells were able to migrate on these antibodies and exhibited an organization of substratum-adhesion sites and of cytoskeletal elements virtually identical to that observed on fibronectin, indicating that they can at least partially mimic the migration-promoting activity of fibronectin. However, the number of migrating cells as well as their morphology and their speed of locomotion varied significantly with both the concentration of the antibody substratum and its relative avidity for the receptor. Thus, on high-avidity monoclonal antibodies and on polyclonal divalent antibodies at high concentrations only a limited number of cells escaped from the neural tube, and the rate of their migration was reduced compared to that on fibronectin (23 +/- 5 microns h-1 versus 65 +/- 10 microns h-1). In addition, cells were unusually flattened and cohesive. Time-lapse videomicroscopy revealed that, on high-avidity substrata, neural crest cells were able to extend cell processes that adhered to the substratum, but showed a dramatically reduced capability of breaking pre-existing substratum contacts. In contrast, the same antibodies at low concentrations produced neural crest cell migration at rates very similar to those on fibronectin at the same concentrations. Low-avidity monoclonal antibodies and polyclonal monovalent antibodies at all concentrations tested permitted extensive migration of neural crest cells, which exhibited the same morphology and locomotory behavior as on fibronectin. These results indicate that both the avidity of receptors for the substratum and the number of receptors bound to the substratum are critical in regulating the locomotory behavior of neural crest cells in vitro, and therefore might help to regulate the directionality of migration and final localization pattern of neural crest cells in vivo.