Most swimming cells utilize distinct organelles, such as flagella or cilia, to propel themselves through their environment. The cells that comprise epithelia and other animal tissues, however, locomote via repeated extension and contraction of their actin cortices. Actin is located throughout animal cells, but the protein is most abundant in the cortex, a peripheral layer located just underneath the plasma membrane. The filaments of actin that comprise the cortex are organized into a three-dimensional network cross-linked by alpha-actinin, filamin, and other specialized proteins.

Vacuole formation and behavior can be observed in several different human osteosarcoma cells. In animal cells, the membrane-bound sacs primarily function in the temporary storage and transport of materials. The vacuoles observable in the video materialize at the peripheries of cells via endocytic means and then travel toward the center of the cells. The eventual disappearance of the vacuoles signifies the breakdown of their membranes so that their contents (presumably culture medium) can be utilized by the cells.

During the playback of this time-lapse sequence of U2OS cells, the tendency of cultured epithelial cells to fasten together into colonies can be observed. This organization is suggestive of the behavior of epithelial cells in vivo, where they form tight junctions with one another to produce contiguous epithelial sheets. A monolayer of human osteosarcoma cells has formed by the end of video, which is similar in many regards to the epithelial sheets formed in the body.