30.1: Cell Migration
Cell migration is a process by which the cells move from one location to another, playing an essential role in embryological development, repair and regeneration, immune response, and metastasis. Cells migrate in response to chemical or mechanical signals generated by specific organs or tissues. The overall mechanism includes three steps - polarization, protrusion, and release. Polarization involves the formation of a distinct cell front and rear, which determines the direction of movement. Next, the cell front protrudes, forming new adhesions and generating a pulling force that moves the cell forward. At the opposite end, cell adhesions are released, allowing the rear to be pulled in the direction of migration.
Collective Cell Migration
Collective cell migration plays a key role throughout embryonic development and in maintaining adult tissues. For example, during neurulation, the migration of neural crest cells to the periphery is essential to developing the peripheral nervous system. When a group of cells migrate collectively, the cells at the front of the group, called leader cells, form the protrusions that pull the whole group forward.
These moving cell clusters can be in different forms, such as loose strands, tubes, or sheets. For example, during wound healing, sheets of epithelial cells proliferate and migrate to cover the injury site, forming scar tissue. In contrast, endothelial cells migrate collectively as strands, rather than sheets, through the newly laid extracellular matrix to develop new blood vessels. The number of cells in these moving clusters can vary greatly, from tens to thousands of cells. The distance these groups migrate also varies, ranging from a few microns to as much as a few centimeters.
Cell Migration and Cancer
Cancerous cells hijack the ability of cells to move from one location to another. Benign tumor cells lack this property and thus proliferate to form the tumor only at the primary location. However, metastatic cells can migrate away from the primary location by producing special membrane protrusions called invadopodia. These protrusions help the cancerous cells to break down the tissue barrier as they migrate and invade other tissues at a secondary location.
