Distribution of fibronectin during the morphogenesis of the truncus.

The distribution of fibronectin during morphogenesis of the truncus has been studied in chick embryo hearts between days 4 and 10 of incubation. Fibronectin appears as a natural marker for some truncal cells and permits the visualization of the different processes of cell rearrangement which result in truncal morphogenesis. The mesenchymal cells involved in formation of the aorto-pulmonary septum and in formation of the arterial tunica media are intensely fluorescent for fibronectin. These cells present fibrillar deposits of fibronectin associated with their surfaces. Very little staining for fibronectin is observed in association with the anlage of the semilunar valves. Prospective adventitial cells are negative for fibronectin. The close association between the fluorescence and the surface of the cells involved in formation of the aorto-pulmonary septum and the arterial tunica media suggests that fibronectin may be implicated in the formation of both structures. The intensity and amount of the fluorescence staining decreases as morphogenesis of the truncus is completed. The decrease in fibronectin staining is suggested to be related to changes in cell phenotypic expression.