NULL MUTATIONS OF THE DICTYOSTELIUM CYCLIC-NUCLEOTIDE PHOSPHODIESTERASE GENE BLOCK CHEMOTACTIC CELL-MOVEMENT IN DEVELOPING AGGREGATES

Extracellular cAMP is a critical messenger in the multicellular develo pment of the cellular slime mold Dictyostelium discoideum. The levels of cAMP are controlled by a cyclic nucleotide phosphodiesterase (PDE) that is secreted by the cells. The PDE gene (pdsA) is controlled by th ree promoters that permit expression during vegetative growth, during aggregation, and in prestalk cells of the older structures. Targeted d isruption of the gene aborts development, and complementation with a m odified pdsA restores development. Two distinct promoters must be used for full complementation, and an inhibitory domain of the PDE must be removed. We took advantage of newly isolated PDE-null cells and the n atural chimerism of the organism to ask whether the absence of PDE aff ected individual cell behavior. PDE-null cells aggregated with isogeni c wild-type cells in chimeric mixtures, but could not move in a coordi nated manner in mounds. The wildtype cells move inward toward the cent er of the mound, leaving many of the PDE-null cells at the periphery o f the aggregate. During the later stages of development, PDE-null cell s in the chimera segregate to regions which correspond to the prestalk region and the rear of the slug. Participation in the prespore/spore population returns with the restoration of a modified pdsA to the null cells. (C) 1997 Academic Press.