When most vertebrate cells in culture prepare for mitosis, they retract their lamellipodia and other surface extensions to assume a spherical form, as demonstrated by many of the A-549 human epithelial cells imaged to produce this time-lapse sequence. Following the mitotic process, the surfaces of the new daughter cells seem to bubble wildly as if they were suddenly placed under high heat and were being boiled alive. The bubble-like mounds they exhibit, however, are called blebs and are actually remnants of the rounded form the cells lose soon after division as they begin to settle on the substratum.

After cell division, daughter A-549 cells do not often migrate in their own directions. This is because contact strongly inhibits the migratory behavior of epithelial cells. Connective strands of material can be clearly observed between many of the daughter cells formed during the high speed playback of this time-lapse sequence. In a few instances, the strands break and the cells are able to move apart. More frequently, however, the strands successfully keep the cells together long enough that stronger cell-cell junctions are formed. The margins of the tightly adjoined epithelial cells seem to mellifluously meld together.

The surface extensions of the epithelial cells appear to roll in and out like waves on a beach. The broad lamellipodia are primarily utilized for locomotion. As they extend out over the culture medium, they form close points of contact with the substratum, which remain stationary as traction forces enable the cell to pull itself along in a manner suggestive of crawling. As the cell progresses, posterior adhesions are usually released, but occasionally remain intact. In the latter instance, fragments of material connected to the culture surface may be abandoned by the cell, as occurs when one of the A-549 cells migrates out of the field of view along the left-hand side. Small, finger-like projections called filopodia are also produced by the epithelial cells and can be utilized for locomotion or to obtain information about the cell’s environment.