Serologically distinguishable alterations in the molecular specificity of cell cohesion during morphogenesis in Dictyostelium discoideum.

Cells of the mutant strain JC-5 of the slime mold Dictyostelium discoideum exhibit at a specific, late developmental stage a temperature-sensitive morphogenetic defect associated with the loss of cell cohension. We show that at the restrictive temperature, the loss of cohesion and attendant dispersal of multicellular aggregates is associated with the disappearance or sequestration of a plasma membrane-bound moiety capable of reacting with and, hence, absorbing cohesion-blocking Fab. At the permissive temperature, the maintenance of cohesiveness past the critical stage or the recovery of lost cohesiveness is correlated with the presence or reappearance of the Fab-reactive moiety.This moiety is absent or sterically incapable of reaction with Fab preparations at an earlier developmental stage in either mutant or wild-type cells-i.e., at a time when they have just entered into multicellular aggregates. Conversely, a serologically distinguishable membrane-bound moiety present in the early mutant or wild-type cells, whose reaction with homologous Fab also precludes their cohesion, is absent or serologically unreactive in either mutant or wild-type cells that are at comparable late developmental stages. We conclude that the cohesive moiety responsible for initiation of cell aggregates is supplanted by or transformed into a serologically distinct, cohesive complex responsible for the maintenance of the aggregate's integrity through the later stages of development.