Most of the field of view is free from cells at the beginning of this time-lapse sequence. A single MDBK epithelial cell can be seen freely migrating across the surface of the imaging chamber, while other cells are organized into small colonies. The path taken by the traveling cell is meandering, the lamellipodia along its leading edge seeming to crop up in an erratic fashion and pulling the cell along in zigzags. When it reaches the top of the field of view, the MDBK cells takes a U-turn and begins to migrate in the opposite direction.

In culture, MDBK cells and other epithelial lines tend to form groups that over time come together to produce sheets similar to the epithelial sheets formed in the body. This tendency is clearly demonstrated by the MDBK cells featured in this video. The wayward migratory behavior of the previously mentioned cell becomes impinged upon by small colonies of surrounding cells that slowly close in on it, as if they were jealous of the cell’s independence. By the end of the time-lapse sequence an almost contiguous monolayer has formed.

Most of the protrusive activity around the periphery of animal cells halts along the margins they share with neighboring cells. Yet, this does not mean that cells in a colony or a sheet are not dynamic entities. As evidenced by the MDBK cells in the time-lapse sequence, cells continue to undergo significant changes in shape and location even when they are closely packed together. The activity of cells in such a group can also produce large-scale movements.