Chemotaxis is the directional movement of cells in response to a chemical stimulus gradient. Recent studies have shown that the receptor-mediated signalling pathway and the actin cytoskeleton in motile cells exhibit the hallmarks of an excitable system and, in particular, self-organised travelling wave patterns. On page 5115, Carsten Beta and colleagues investigate whether spreading excitation waves can be initiated in the signal transduction system in Dictyostelium discoideum. The authors developed two different methods to deliver localised cAMP stimuli to confined membrane regions of differentiated chemotactic Dictyostelium cells: one using cAMP-coated microparticles and another based on path-clamp shielding of membrane patches against freely diffusing cAMP molecules in the surrounding medium. The excitability of the signal transduction system in response to cAMP receptor stimulation was probed on the basis of production of phosphatidylinositol (3,4,5)-trisphosphate (PIP3) by phosphoinositide 3-kinase (PI3K), the degradation of PIP3 by phosphoinositide 3-phosphate (PTEN) and the polymerisation of actin. The authors found that activation of the chemotactic signal transduction pathway following localised simulation of the cAMP receptor remained spatially confined to the region of membrane stimulation, with no wave-like spreading of excitation along the cell membrane. They were also able to confirm previous reports regarding the ligand-binding site of the cAMP receptor. These findings shed new light on the principles of chemotactic signal transduction.
- © 2014. Published by The Company of Biologists Ltd