LAUSR

E-mail: [email protected]: http://umr168.curie.fr/en/Sykes-groupCell deformations are part of many vital processes such as division, motility orintracellular transport. They result from the continuous re-organization of the actin cytoskeleton underneath the membrane. In order to unveil how biochemical assembly can change membrane shape, we develop a minimal system based on purified components to control all the relevant parameters.We reconstruct a finely tuned actin network on cell-sized liposomes to address the respective role of membrane and actin network in membrane tubulation. The actin network is reconstituted at the outer surface of fluorescently labeled liposomes with purified proteins that allow to follow simultaneously membrane and actin dynamics. The system is tuned to generate a branched cortical network next to the membrane. We demonstrate that the actin cytoskeleton induces the formation of membrane tubes with different morphologies that are reminiscent of endocytosis and finger-like protrusions in cells: tubes are spontaneously pulled outside the liposomes and spikes grow towards liposome centers. By decreasing membrane tension via osmotic shock, we show that spike formation is promoted without affecting tubes pulling. These results suggest that these structures are two independent deformations relying on different mechanisms, both based on membrane deformation induced by cytoskeletal dynamics. This investigation highlights how membrane tubulation depends on a mechanical balance between the membrane and the actin network.