Adhesive Specificity and the Evolution of Multicellularity

The step from unicellular to multicellular organisms was a major milestone in evolution. This was achieved by the generation of membrane-associated cell adhesion molecules. Cell adhesion is not only an essential component but sometimes even a driving force in the creation of the structural and functional complexity observed during metazoan evolution. The way multicellular organisms are morphologically organized, be it on the gross anatomical level or the microscopic histological level, results from highly regulated processes of specific cellular behaviour. These processes define how cells adhere to the substrate and to each other and how they communicate with their neighbours andwith the (micro)environment. The focus of this chapterwill be on intercellular adhesion, butwe should keep in mind that essentially the mechanisms underlying cell–cell and cell–substrate adhesion are very similar.