CHEMOTAXIS Complementary Roles for Guanylyl Cyclase and cGMP

Dictyostelium respond with directed migration to secreted adenosine 3',5'-monophosphate (cAMP). Although they migrate to static gradients, they respond more strongly to waves (where there is a change in cAMP concentration over time). Guanosine 3',5'-monophosphate (cGMP) stimulates formation of myosin filaments as part of the Dictyostelium chemotactic response to cAMP. Using a system in which Dictyostelium were initially exposed to a spatiotemporal gradient of cAMP and then to a static gradient, Veltman and Van Haastert investigated chemotactic responses of Dictyostelium expressing two mutant forms of green fluorescent protein-labeled soluble guanylyl cyclase (sGC), an enzyme that produces cGMP). One mutation (sGCcat) eliminated cGMP production, and the other (sGCN) eliminated sGC localization to the leading edge of migrating cells. Dictyostelium expressing sGCN responded well to the spatiotemporal gradient but moved at rates comparable to those lacking GC when exposed to the static gradient. In contrast, cells expressing sGCcat responded poorly to the spatiotemporal gradient but well to the static gradient. Further analysis revealed that cells expressing sGCcat failed to show localization of myosin to the posterior cortex during chemotaxis and, unlike migrating cells expressing wild-type sGC, continued to extend pseudopodia in the back of the cell. Cells expressing sGCN had appropriate myosin localization but lost orientation of the leading edge. Thus, the authors propose that cGMP and sGC play complementary roles during Dictyostelium chemotaxis, with the rapidly diffusing cGMP playing the key role in temporal sensing and the very slowly diffusing sGC critically involved in spatial sensing.

D. M. Veltman, P. J. M. Van Haastert, Guanylyl cyclase protein and cGMP product independently control front and back of chemotaxing Dictyostelium cells. Mol. Biol. Cell 17, 3921-3929 (2006). [Abstract] [Full Text]