A full skirt of flattened lamellipodia encircles a single CV-1 African green monkey kidney epithelial cell. Sporadically small, narrow finger-like surface extensions called filopodia can be seen jutting out along the periphery of the cell as well. The distinct differences in shape of these structures are directly related to the organization of the filaments present in their actin cortices. In lamellipodia, actin is arranged in a dense, highly branched meshwork of filaments, with new filaments extending out from existing filaments in a repeating pattern of Y-shaped junctions. The actin filaments present in filopodia, however, are bundled together via specialized cross-linking proteins.

The CV-1 cell featured in this video exemplifies the fact that epithelial cells are not nearly as locomotively active as fibroblasts. When placed in a culture dish, fibroblasts tend to migrate over significant distances, pulling themselves through their environment via crawling-like motions created by the cyclical expansion and contraction of surface extensions. Yet, in a similar situation, epithelial cells tend to be much more stationary, frequently choosing to stably spread out along the substratum rather than travel to new locations.

The contrasting behavior of epithelial cells and fibroblasts in culture is evocative of their primary roles in the body. In vivo, epithelial cells form contiguous sheets that cover external surfaces and line cavities, where they function as barriers. Thus, the cells naturally engage in a relatively sedentary existence. Much of the time fibroblasts in the body are rather dormant as well, but the cells, which inhabit connective tissues, are also periodically forced to rapidly migrate to new regions of the body, chiefly to aid in the recovery of wounds. Accordingly, fibroblast cells in culture are often very motile.