Contact-mediated triggering of lamella formation by Dictyostelium amoebae on solid surfaces

Amoebae of the slime mould Dictyostelium discoideum form broad ultrathin cytoplasmic lamellae by a centripetal contractile process soon after they have spread on certain solid surfaces. We have investigated the surface requirements for initial triggering of this contact-mediated signalling system. The lamellar response is not normally evoked by glass, but is seen on glass covalently derivatized with paraffinic chains, as well as on glass covalently derivatized with amine groups and on glass bearing adsorbed polylysine. We have recorded the frequency of the lamellar response on these surfaces as a function of ionic strength and pH, and have measured the electrostatic potentials of the surfaces by the streaming potential method. Using these data we have concluded that the general trigger for the lamellar response is not a 'simple' physical or chemical property of the substrata: it is not dependent on specific chemical groups, degree of hydrophobicity, electrostatic potential, or charge density, taken as isolated factors. It seems likely that triggering is dependent on the overall energetics of cell-substratum interaction.