The cytoskeleton of an epithelial cell is converted to a fibroblast-like morphology upon contact with a fibroblast. So say Edward Bonder (Rutgers University, Newark, NJ) and colleagues, who present what they hope will be the beginning of a lengthy study of the interactions between heterotypic cell types.
The main conclusion so far, says Bonder, is that “even though you have nontypical contacts there is still recognition,” leading to a structural transformation. Such heterotypic contacts occur frequently during development, such as when fibroblast-like neural crest cells migrate over the epithelial layer of the neural tube, or when fibroblasts directly contact an overlying epithelium before laying down an intervening barrier of basal lamina.
The intial cytoskeletal organization is very different in fibroblasts and epithelial cells. Fibroblasts have actin-filament bundles pointed out to the cell's leading edge and protruding into lamellae, whereas epithelial cells have an arc of actin running parallel to the leading edge. Upon contact of the two cell types, little change is seen in the fibroblast, but the epithelial cell converts to a more fibroblast-like organization.
Despite expressing different cadherins, the two cell types appear to form adhesion complexes that contain β-catenin. The transient association is terminated when the fibroblast wheels on its axis and marches off in another direction. Although such interactions may serve primarily to keep two tissue layers separate, they may also be essential to cement that separation by inducing the formation of more permanent barriers such as the basal lamina. ▪