Chemotaxis Dictyostelium response

Heterogeneity in the kinetic states of signaling molecules was also found in ligand binding reactions in chemotaxing Dictyostelium cells [45]. Dictyostelium cells exhibit chemotaxis in response to cyclic adenosine 3, 5 -monophosphate (cAMP). Dictyostelium cells move randomly in the absence of a cAMP concentration gradient. In the presence of a gradient, however, movement is... 

Electrotactic migration is not (at least not exclusively) mediated by chemotaxis. When chemical gradients in an electric field are disrupted with a continuous flow of culture medium perpendicular to the electric field vector, cells respond just as well to the electric field (20). G-protein coupled receptor signaling is essential for chemotaxis of many types of cells (22). Dictyostelium discoidum cells with a Gfl subunit null mutation lose their chem-otactic response while maintaining motility (23). Nevertheless, G(3 null mutants still respond to applied electric fields by directional migration, albeit less robustly than wild-type cells (20, 24). Therefore, electrotaxis and chemotaxis can be decoupled. 

Intracellular free calcium responses during chemotaxis of Dictyostelium cells. J. CellSci. 109,2673-2678. 

Chemotaxis to extracellular cAMP vwll be the focus of this section because it is the best characterized chemotactic response in Dictyostelium, but chemotaxis at other times of the Dictyostelium life cycle relies on the same principles and uses closely related pathways which are based on the same or homologous molecules. This is illustrated by the observation that ablation of the single gene coding for the alpha subunit of the het-erotrimeric G-protein working dovmstream of the membrane receptors completely abolishes chemotaxis [172, 244] in Dictyostelium. 

At the onset of development, Dictyostelium cells start to produce and respond to the small molecular chemoattractant cAMP [146]. The details of the inner workings of the oscillatory cAMP-signaling network are not directly relevant to the description of the chemotactic response and will only be touched on briefly. In a field of cells, periodic cAMP waves emerge which coordinate the formation of centers towards which the cells move by chemotaxis. On the level of an individual cell, the... 

The Dictyostelium phosphoinositide 3-kinases have a domain organization similar to mammalian Class I phosphoinositide 3-kinases. They have an N-terminal domain that does not show much conservation, followed by a Ras-binding domain, a C2 domain, and a bipartite kinase domain. The involvement of phosphoinositide 3-kinases in polarized cellular responses suggested that their subcellular localization during chemotaxis might be important. Deletion analysis revealed that the N-terminal domain alone is required and sufficient for cAMP-induced... 

This section will focus on receptor tyrosine kinase-mediated chemotac-tic responses of mesenchymal cells. G-protein-coupled receptor-mediated chemotaxis mechanisms were discussed above in the Dictyostelium section. 

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