Journal
JOURNAL OF CELL SCIENCE
Volume 117, Issue 14, Pages 2925-2935Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jcs.01143
Keywords
chemotaxis; PtdIns(3,4,5)P-3; self-organization; patches; pseudopod
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The leading edge of Dictyostelium cells in chemoattractant gradients can be visualized using green fluorescent protein (GFP) tagged to the pleckstrin-homology (PH) domain of cytosolic regulator of adenylyl cyclase (CRAC), which presumable binds phosphatidylinositol-(3,4,5)triphosphate [PtdIns(3,4,5)P-3]. Uniform cyclic AMP (cAMP) concentrations induce persistent translocation of PHCrae-GFP from the cytosol to multiple patches, which are similar to the single patch of PHCrac-GFP at the leading edge in a cAMP gradient. We show that cAMP determines the probability of patch formation (half-maximal effect at 0.5 nM cAMP) but not the size, lifetime or intensity of patches, indicating that patches are self-organizing structures. A pseudopod is extended from the area of the cell with a PHCrac-GFP patch at about 10 seconds after patch formation. Cells treated with the F-actin inhibitor latrunculin A are round without pseudopodia; uniform cAMP still induces localized patches of PHCrac-GFP. Inhibition of phosphoinositide-3-kinase (PI3K) activity with LY294002 inhibits PHCrac-GFP patches and inhibits chemotaxis towards nanomolar cAMP but has no effect at higher cAMP concentrations. Thus, very low CAMP concentrations induce self-organizing PHCrac-GFP patches that serve as a spatial cue for pseudopod formation, which enhances the sensitivity and amplitude of chemotactic movement.
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