A mutation that depresses cGMP phosphodiesterase activity in Dictyostelium affects cell motility through an altered chemotactic signal.

The streamer F (StmF) mutant of Dictyostelium discoideum is defective in cGMP-phosphodiesterase activity. In early aggregation territories, when individual cells chemotax toward aggregation centers prior to streaming, the average periodicity of surging of StmF cells is half that of wild-type cells. In addition, in the period between surges, which has been interpreted to include the peak and back of the wave, StmF cells abnormally remain nonmotile and retain their elongate shape. In contrast, in the period between surges wild-type cells form pseudopods randomly around their cell perimeter and take on an amorphous shape. Using a newly developed protocol for vitally staining and tracking individual mutant cells in unstained wild-type aggregation territories and individual wild-type cells in unstained StmF aggregation territories, we have found that mutant cells behave normally (i.e., like their predominant wild-type neighbors) in the deduced back of waves generated by wild-type cells. Conversely, wild-type cells behave aberrantly (i.e., like their predominant StmF neighbors) in the deduced back of waves generated by mutant cells. These results suggest that the defective behavior of StmF cells in early StmF aggregation territories is not due to a single cell defect in responsiveness, but, rather, is due either to the genesis of an aberrant cAMP wave or to the accumulation of a molecule which interferes with normal behavior in the back of the wave.