Cell–cell interactions via cell adhesion are the basis for the evolution of all multicellular organisms. The first experiments to understand cell adhesion were performed at the beginning of the last century by Wilson (1907), who dissociated sponges and allowed them to fuse and to reconstitute. Fifty years later, Townes and Holtfreter (1955) demonstrated that dissociated cells from amphibian embryos adhere to form random aggregates of their origin, with ectoderm forming an outer surface layer, endoderm forming a compact central ball, and mesoderm producing a loose array of cells. In 1963, Roger Sperry (1963) proposed that different cells bear distinct cell surface proteins that serve as markers or tags. One of these markers, the Neural Cell Adhesion Molecule (NCAM) was first described in 1974 by Elizabeth Bock (Jacque et al. 1974) and designated as D2 antigen. Three years later, the group of Edelman (Thiery et al. 1977) approved...