Fibronectin has a dual role in locomotion and anchorage of primary chick fibroblasts and can promote entry into the division cycle.

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Abstract
Fibronectin (FN), which is already known to be a natural factor for fibroblast spreading on substrata, was shown to be essential for 2 distinct types of adhesion with different biological functions in chick heart fibroblasts, i.e., adhesion directed toward locomotion and toward stationary anchorage for growth. Manipulation of culture conditions and the use of antisera of differing specificities demonstrated that both exogenous and cell-derived FN are important in each process. The organization of the fibronectin-containing matrix differs between the 2 states. Immunoelectron microscopy with a colloidal gold marker reveals the presence of small membrane-associated plaques of fibronectin in motile cells with associated submembranous specialization. A fibrillar matrix containing fibronectin is dominant in nonmotile, growing fibroblasts. The development of focal adhesions for stationary anchorage can be dramatically enhanced by addition of cell-derived FN at an appropriate stage, and this promotes entry into the growth cycle. New macromolecular synthesis in addition to FN is necessary for focal adhesion development but not for locomotion.