The migratory behavior of avian embryonic cells does not require phosphorylation of the fibronectin-receptor complex

When locomotory embryonic cells become stationary, they acquire new substratum-adhesion properties. In particular, the distribution of fibronectin receptors shifts from diffuse and highly mobile on the cell membrane to immobilized in close association with fibronectin molecules and cytoskeletal elements in focal contacts. Receptor phosphorylation has been proposed as a possible regulator of the interaction between the receptor and its intracellular and extracellular ligands. In the present study, we have compared the phosphorylation state of the fibronectin receptor in motile neural crest and somitic cells, in stationary somitic cells, and in Rous-sarcoma virus transformed-chick embryo fibroblasts, using immunoprecipitation following metabolic labeling. While no receptor phosphorylation was detected in motile embryonic cells, the beta subunit of the receptor was phosphorylated in stationary cells. This subunit was also highly phosphorylated in Rous-sarcoma virus-transformed chicken cells. These results suggest that phosphorylation of the fibronectin receptor cannot account for its distribution in the cell membrane and for the nature of the interactions between this receptor and its ligands in embryonic cells.