THE ROLE OF CYCLIC-GMP IN REGULATING MYOSIN DURING CHEMOTAXIS OF DITYOSTELIUM - EVIDENCE FROM A MUTANT LACKING THE NORMAL CYCLIC-GMP RESPONSE TO CYCLIC-AMP

Evidence has previously been reported that, during chemotaxis of the c ellular slime mould Dictyostelium discoideum, cyclic GMP regulates the association of myosin II with the cytoskeleton and that this regulati on is effected by inhibiting myosin II heavy chain phosphorylation (Li u and Newell, J.Cell Sci., 90, 123-129, 1988; 98, 483-490, 1991). Here we provide further evidence in support of this hypothesis using a mut ant (KI-10) that is defective in chemotaxis and lacks the normal cycli c AMP-induced cyclic GMP response. We found that the cyclic AMP-induce d cytoskeletal actin response was similar to that of the parental stra in in this mutant (although showing a slight displacement in the dose- response curve) but the cytoskeletal myosin II heavy chain response wa s abolished. Moreover, the mutant showed no phosphorylation of myosin II heavy chain in response to cyclic AMP. Compared to the parental str ain XP55, the mutant cells contained approximately 40% more protein an d their doubling time was 30% longer. These differences could be due t o differences in the efficiency of cell division, a process in which t he proper regulation of myosin function is essential and in which cycl ic GMP may therefore play a role.