Regulation of development in Dictyostelium discoideum: III. Carbohydrate-specific intercellular interactions in early development

Abstract

Previous studies showed that amino acid starvation and intercellular interactions are both required for differentiation of Dictyostelium discoideum during early development. The intercellular interactions have now been characterized by analysis of their sensitivity to inhibition by monosaccharides. Glucose inhibits early development by two mechanisms: (1) sparing of amino acid starvation and (2) interfering with intercellular interactions. The nonmetabolizable glucose analog α-methylglucoside inhibits intercellular interactions, as does galactose. Galactose and α-methylglucoside inhibit synergistically, suggesting the presence of two distinct but interacting sites. Two classes of cohesive sites have been identified in D. discoideum ( Beug, Katz, and Gerisch, 1973 , J. Cell Biol. , 56, 647–658). Growth phase cells exhibit only EDTA-sensitive cohesion, mediated by contact sites B; aggregation-competent cells also display contact sites A which mediate EDTA-resistant cohesion. Monosaccharides structurally related to glucose inhibit contact site B-mediated cohesion, but galactose does not. Both glucose and galactose inhibit the developmentally regulated expression of contact sites A, but neither sugar inhibits EDTA-resistant cohesion of cells which have expressed these sites. Studies in other laboratories have implicated the galactose-specific lectin discoidin I in the development of EDTA-resistant cell cohesion. We propose a model in which the two sites which mediate the intercellular interactions required for early development are the two carbohydrate-specific ligand-receptor systems, contact sites B and discoidin plus its receptor.