Cell Adhesion as a Basis of Pattern in Embryonic Development

Abstract

Synopsis. The development of the modern methodologies of cell biology in the fifties and sixties and of molecular biology in the seventies and eighties has led to a reductionist view of embryonic development that centers on the cell and the gene as the functional units of development. The functional units in most inductive and morphogenetic processes in the embryo are not single cells, however, but rather are collectives of interacting cells that give rise to the tissues and organs. Can these methodological developments reconcile a molecular analysis with the fact that form arises epigenetically from the increasing number of embryonic cells during development? To answer this question one must link genetic regulation to mechanochemical processes that coordinate cell division, cell move? ment and cell death. Recent studies of cell adhesion suggest that one such link is provided by cell adhesion molecules (CAMs) that mediate cell-cell binding. These studies suggest that CAMs are involved in defining cell collectives and their borders as they interact during inductive events in morphogenesis. Although CAMs cannot be considered the cause of induction, they play key roles among the complex causal chains of inductive interactions involving hormones and growth factors, extracellular matrix components and cellular receptors. We provide here a brief summary of modern developments in the field centered about the function of CAMs in morphogenesis and using recent experimental results in the developing feather as a paradigmatic example.