Influence of Quorum Sensing and cell-Substrate Adhesion on Amoeboid Migration

Orateur : Jean-Paul RIEU (Laboratoire de Physique de la Matière Condensée et Nanostructures, Université Claude Bernard, Lyon)

Amoeboid movement is a crawling type of movement accomplished in a coordinated way by extension of cell protrusion (pseudopods), flowing of the cytosol inside them and retraction of the tail (uropod). Periodic contractions of the cortical acto-myosin layer are essential for this movement but the involvment of adhesion complexes is absolutely unclear. Adhesion could be unspecific. It was shown that cell-substrate adhesion depends on the chemical nature of the surface (Décavé, Bruckert et al. 2002) but motility was not studied. Mammalian mesenchymal cells present an optimal migration reached at intermediate adhesion (Di Milla et al., 1993). In case of amoeboid movement, little is known about the relation between cell-substrate adhesion and migration rate. By trying to tackle this problem, we found that cell migration depends greatly on various other environmental such as diffusible signal molecules transmitted by the surrounding aqueous medium. Many cells communicate through the production of these diffusible molecules that accumulate and once a critical concentration has been reached, can activate or repress a number of target genes in a process termed quorum sensing (QS). However, little is known about the effect of QS on cell migration. In order to investigate the relation between cell migration, adhesion and QS, we have studied the mean squared displacements (MSD) and detachment strength of Dictyostelium cells on various substrates and as a function of cell density and of the conditioning of the surrounding medium. We have developed a method for studying cellular adhesion with a microfluidic device with parallel non-connected tapered channels of variable width. This analysis revealed a high heterogeneity within a given cell population, and the necessity to use large data sets and automated tracking procedures to draw reliable conclusions on cell motion. The main finding is the presence of a QS factor regulating the migration of Dictyostelium cells in the vegetative state. The higher the cell density, the faster are the cells. Cell migration is uncorrelated with cell adhesion as measured by the detachment assay.

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