Mechanisms of amoeboid chemotaxis: An evaluation of the cortical expansion model

Abstract

In this work we evaluate the cortical expansion model for amoeboid chemotaxis with regard to new information about molecular events in the cytoskeleton following chemotactic stimulation of Dictyostelium amoebae. A rapid upshift in the concentration of chemoattractant can be used to synchronize the motile behavior of a large population of cells. This synchrony presents an opportunity to study the biochemical basis of morphological changes such as pseudopod extension that are required for amoeboid chemotaxis. Changes in the composition and activity of the cytoskeleton following stimulation can be measured with precision and correlated with important morphological changes. Such studies demonstrate that activation of actin nucleation is one of the first and most crucial events in the actin cytoskeleton following stimulation. This activation is followed by incorporation of specific actin cross-linking proteins into the cytoskeleton, which are implicated in the extension of pseudopods and filopods. These results, as well as those from studies with mutants deficient in myosin, indicate that cortical expansion, driven by focal actin polymerization, cross-linking and gel osmotic swelling, is an important force for pseudopod extension. It is concluded that whereas three forces, frontal sliding, tail contraction, and cortical expansion may cooperate to produce amoeboid movement, the cortical expansion model offers the simplest explanation of how focal stimulation with a chemoattractant causes polarized pseudopod extension.

Involvement of aquaporin-4 in astroglial cell migration and glial scar formation

“…The importance of water fluxes across the plasma membrane in causing localized swelling of lamellipodia has been discussed extensively in the early literature on cell migration (Condeelis et al, 1990;Oster and Perelson, 1987). However, the idea that these water fluxes are primarily mediated by aquaporins is new (Saadoun et al, 2005).…”

Genetic deletion of ABP-120 alters the three-dimensional organization of actin filaments in Dictyostelium pseudopods.

“…ABP-120 becomes incorporated into the cytoskeleton in two peaks that occur with the same kinetics as the second and third peaks of actin incorporation into the cytoskeleton suggesting that ABP-120 plays a role in the cross-linking of filaments into the cytoskeleton at these times Condeelis et al, 1990). In ABP-120-containing cells, pseudopod extension occurs in response to stimulation with cAMP during the second and third peaks of actin incorporation into the cytoskeleton.…”

Ca2+ chemotaxis inDictyostelium discoideum

“…In the first 30 seconds, the cringe includes a dramatic decrease in velocity, rounding up, blebbing, the relocalization of myosin from the cytoplasm to cortex and a spike in F-actin concentration (Hall et al, 1988;Yumura and Fukui, 1985;Condeelis et al, 1990;Wessels et al, 1989;Postma et al, 2003). When 10 mM Ca 2+ solution was added to cells translocating in 40 mM K + solution, there was a similar immediate decrease in velocity from 11.9±1.9 m/min to 6.8±1.0 m/min (n20), but cells did not round up.…”