CELL-ADHESION MOLECULES - MORPHOGENETIC MOLECULES

Cell adhesion is a peculiar way of communication between cells playing a fundamental role in pattern formation of pluricellular beings. It controls the shape, the movement and the growth of cells and cell collectives. Cell adhesion is mediated by extracellular matrix and cell surface glycoproteins such as the cell adhesion molecules (CAM). CAM expression is modulated during development according to very precise spatial and temporal sequences affecting almost all the cells of the organism. A definite group of cells at a definite time expresses a panel of CAM which distinguishes it from the other groups of cells. If a morphogenetic role has been proposed for these molecules, until recently their function and precise role during embryogenesis and histogenesis were only putative. The isolation of DNAs coding for these CAM led to a breakthrough in the studies of these molecules. The gene transfer that became possible from there allowed to demonstrate the homophilic adhesion of the CAM. It showed also that the expression of Ca2+ dependent CAM (cadherin) is a major step of the reversible epithelial-mesenchymal transformation, which is a fundamental process appearing recurrently during development. Furthermore it appeared that CAM are among the molecules responsible for cell-sorting out in vitro. They govern cell collective formation and define borders between these collectives. Cell adhesion molecules govern the compartimentalization that occurs in the embryo during development.