Dual chemotaxis signalling regulates Dictyostelium development: intercellular cyclic AMP pulses and intracellular F-actin disassembly waves induce each other.
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 20s 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 tail to an immediately following cell front and a slower, long-range wave of intracellular F-actin disassembly, each inducing the other.
Department of Biology-Chemistry, University of Bremen, Leobener Str., NW2, D-28359 Bremen, Germany. jfgrutsch@yahoo.com
Michael G
MG
Vicker
James F
JF
Grutsch
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002449:Cell Aggregation / Q000502:physiology; D002633:Chemotaxis / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism*; D004023:Dictyostelium / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D018613:Microscopy, Confocal; D015398:Signal Transduction
D000199:Actins; D000242:Cyclic AMP