Journal
EUROPEAN JOURNAL OF CELL BIOLOGY
Volume 87, Issue 10, Pages 845-861Publisher
ELSEVIER GMBH, URBAN & FISCHER VERLAG
DOI: 10.1016/j.ejcb.2008.03.010
Keywords
Actin; Autowave signalling; Cell aggregation; Chemotaxis; Cyclic AMP; Development; Dictyostelium discoideum; Gradient; Reaction-diffusion wave; Self-organisation; Streaming
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Aggregating Dictyostelium discoideum amoebae periodically emit and relay cAMP, which regulates their chemotaxis and morphogenesis into a multicellular, differentiated organism. Cyclic AMP also stimulates F-actin assembly and chemotactic pseudopodium extension. We used actin-GFP expression to visualise for the first time intracellular F-actin assembly as a spatio-temporal indicator of cell reactions to cAMP, and thus the kinematics of cell communication, in aggregating streams. Every natural cAMP signal pulse induces an autowave of F-actin disassembly, which propagates from each cell's leading end to its trailing end at a linear rate, Much slower than the calculated and measured velocities of cAMP diffusion in aggregating Dictyostelium. A sequence of transient reactions follows behind the wave, including anterior F-actin assembly, chemotactic pseudopodium extension and cell advance at the cell front and, at the back, F-actin assembly, extension of a small retrograde pseudopodium (forcing a brief cell retreat) and chemotactic stimulation of the following cell, yielding a 20 s cAMP relay delay. These dynamics indicate that stream cell behaviour is mediated by a dual signalling system: a short-range cAMP pulse directed from one cell tall to an immediately following cell front and a slower, long-range wave of intracellular F-actin disassembly, each inducing the other. (C) 2008 Elsevier GmbH. All rights reserved.
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