Induction of stage-specific cell cohesion in D. discoideum by a plasma-membrane-associated moiety reactive with wheat germ agglutinin

Dictyostelium discoideum strain JC-5 is a temperature-sensitive, cohesion-defective mutant. At the restrictive temperature, aggregates are formed and develop normally to a specific late stage, but then disperse to a lawn of noncohesive cells. The defect stems from the inability of the mutant at the restrictive temperature to accumulate or retain an adequate level of a newly arisen, plasma-membrane-associated cohesive moiety during the later stages of morphogenesis. We now report that the noncohesive mutant cells can be induced to cohere at a level of greater than 99% by addition of a fraction reactive with wheat germ agglutinin and isolated from the plasma membranes of late-stage, cohesive mutant or wild-type cells. Furthermore, the cohesivities of late-stage, cohesive mutant or wild-type cells can be significantly enhanced by the same preparations but early-stage cohesive cells remain unaffected. The cohesion-inducing activity can be recovered from two regions of a one-dimensional polyacrylamide gel electropherogram following elution and renaturation. The first is associated with a single silver-staining band (apparent molecular weight 95,000). It appears de novo at a postaggregative stage, and accumulates in a thermostable fashion in the wild-type and in a thermosensitive fashion in the mutants, concurrent with the loss of cohesivity. The second is associated with a complex of silver-staining bands (apparent molecular weights 40,000-50,000). The activity of the eluate reactive with wheat germ agglutinate is destroyed within 5 min at 100 degrees C.