Differential adhesion in model systems.

During embryonic development, cells or groups of cells migrate from their locations of origin to assume their correct anatomical positions. Intercellular adhesion plays an active and instructive role in orchestrating this process. Precisely how adhesion provides spatial positioning information is a subject of intense interest. In the 1960s, Steinberg proposed the differential adhesion hypothesis (DAH) to explain how differences in the intensity of cell adhesion could give rise to predictable spatial interactions between different cell types. The DAH is grounded in the same set of physical principles governing the interaction of immiscible fluids and thus provides a rigorous conceptual framework connecting the chemistry of cell adhesion to the physics underlying cell and tissue segregation. Testing the DAH required the development of methods to measure intercellular cohesion and of assays to accurately assess relative spatial position between cells. The DAH has been experimentally verified and computationally simulated. Moreover, evidence concerning the role of differential adhesion in a number of morphodynamic events is accumulating. It is clear that differential adhesion is a major driving force in various aspects of embryonic development, but recent studies have also advanced the concept that other factors, such as cortical tension and elasticity, may also be involved in fine tuning, or even driving the process. It is likely that an interplay between adhesion and these other factors co-operate to generate the forces required for tissue self-organization.