Single cell migration : take a look at the rear

Orateur : Martial BALLAND (Laboratoire Interdisciplinaire de Physique, Université Grenoble Alpes)

A key step for cells to initiate migration is the breaking of symmetry leading to a front-rear polarity. RhoGTPase-mediated cytoskeleton reorganization and their associated cellular traction forces play a crucial role in acquiring and maintaining this polarity. In order to unravel the underlying force-motion relation during the initiation of cellular migration we here report an approach where we combine soft substrate micropatterning and traction force microscopy (TFM). This enables us to follow the dynamic force modulation while cells migrate on thin adhesive 1D micro patterned lines that mimic a 3D fibrillar matrix migration assay. Studied were performed on two distinct cell types (NIH 3T3 and RPE-1) that both exhibit mesenchymal migration modes. Both cell lines display an elongated shape and can spontaneously undergo a transition from a symmetric protrusive activity to the formation of an asymmetric polarized structure. This crucial step, occurring at the very beginning of cellular migration, relies on local actin reinforcement at the perspective rear that finally determines the direction of migration. Subsequently, the cell can retract its rear to initiate locomotion during which we strikingly observe a dramatic drop in cell-substrate mechanical interaction. We thus hypothesize that to undergo migration, an anisotropic distribution of actin induces an asymmetry in cellular forces distribution that ultimately leads to the initiation of migration. In order to test this hypothesis we employed optogenetics to locally control the activity of RhoA, a major regulator of cell contractility. Herein, local RhoA photoactivation can mimic the breaking of symmetry due to a locally induced actin reinforcement as observed in spontaneous cell migration. In this way, cytoskeleton rearrangement and force redistribution in the perspective back of the cell are crucial events occurring prior to the initiation of movement. Subsequently, maintaining a decreased level of contractility upon rear retraction determines migration persistence time. Our study therefore depicts how mechanical traction forces are spatio-temporally coordinated with morphological events during the initiation and maintenance of front-rear polarization.

Télécharger dans mon agenda