Fibronectin and integrins in development.

Extracellular matrix glycoprotein fibronectin and integrins, transmembrane receptors for extracellular matrix proteins, have been implicated in morphogenesis, cytodifferentiation and organogenesis. During development, embryonic cells move on or through fibronectin-rich matrices, which support migration and contain the guidance cues that direct the cells along their migratory pathways. Integrins are involved in different aspects of the movement, including recognition of the pathway, transient attachment to the substrate and cytoskeleton rearrangement in the moving cells as well as organization of the matrix during migratory pathway formation. Differentiated tissues exhibit a characteristic and often rather limited set of integrins. On the contrary, during development, tissue repertoire of integrins changes, and integrins that are absent from the adult differentiated tissue may appear transiently and be expressed only during certain developmental stages. These periods of transient expression coincide with cell movement, differentiation and maturation of cells and can be correlated with changes of environment, i.e. neighboring cells, composition and structure of the extracellular matrix. In this article we discuss the recent data on the roles of fibronectin-integrin interactions in directed cell migration in embryos and on the distribution and possible functions of integrins in developing tissues.