Crawling cell locomotion revisited

Abstract

Cell crawling is of primary importance for such fundamental biological processes as embryonic development, wound healing, inflammation, and cancer metastasis (1). Motion of cells along extracellular substrates or matrices requires an apparently very simple condition: a fairly small force has to be applied to the cell to move it against the friction between the cell surface and the surrounding liquid. However, under common biological circumstances, there are no external fields or factors that would generate such forces. As a result, this force must be produced by the cell itself. This represents a substantial complication as, if a force-generating device is a part of the cell body, it cannot produce the body movement on its own. Indeed, in contrast to the Baron Munchausen experience, one would fail moving him/herself by pulling his/her own hairs. One needs legs to transmit the generated force to the ground. These legs—in the cell's case, the cell-substrate adhesions—have to fulfill two apparently contradictory conditions. First, they have to transmit the force (the momentum) to the substrate and, hence, fuel the cell movement. However, they should not remain persistently stuck to the substrate, as, in such a case, they would resist the cell motion. The adhesions must emerge and then disintegrate and be recycled at different stages of the cell movement. One of the major challenges of biology and biophysics of cell motility is to understand the molecular structures a cell uses to generate and transmit force and how it removes and recycles these structures after their functions are completed and they become an obstacle to cell movement. The study by Ofer et al. in PNAS (2) suggests and substantiates experimentally an elegant and simple mechanism for the latter process.