Cellular search migrations in normal development and carcinogenesis.

This review describes the large group of morphogenetic processes designated as search migrations. Search migrations typically include two stages: i) search, when a group of cells or of the cytoplasmic processes migrate over the cell-free spaces, and ii) choice, the stage when migrating cells reach specific loci where they stop and undergo specific differentiations induced by local factors such as cell-cell contacts and humoral agents. Migrating cells that do not meet their targets usually undergo apoptosis. Numerous examples of search migrations range from gastrulation to formation of axon-muscle connections. Critical stages of carcinogenesis such as acquisition of cell ability for invasion may be regarded as the genetic aberration of normal search migration: cancer cells perform an endless search but cannot make final choice.