The control of cell adhesion in a morphogenetic system.

A new general type of morphogenetic process has been revealed by experiments on the phenomenon of non-coalescence between different strain types {alpha and delta) in the sponge Ephydatia fluviatilis. The question investigated was whether any process of cell adhesion was responsible for the phenomenon. Preliminary results suggested that the cells might show specific adhesion but further results indicated that a more complex system existed. Each strain produces a soluble factor that increases the adhesiveness of homologous cells but decreases that of cells of heterologous strains. The adhesion of cells, even in the presence of these factors, is non-specific but the factors specifically control adhesion and determine its quantitative value. The adsorption of the factors to the cells was tested for with inconclusive results. Heterologous factors may irreversibly alter a cell's adhesiveness. It is shown that this system, particularly by reason of its negative effect on adhesiveness, (a) accounts adequately for the phenomenon of non-coalescence, (b) provides a model system for many forms of morphogenesis and (c) allows many apparently contradictory results obtained by other workers to be reconciled.