Ratchetaxis in channels: cells move directionally by pushing walls asymmetrically

Cell motility is essential in a variety of biological phenomena ranging from early development to organ homeostasis and diseases. This phenomenon was so far mainly studied and characterized on flat surfaces in vitro whereas this situation is rarely seen in vivo. Recently, cell motion in 3D microfabricated channels was reported to be possible, and it was shown that confined cells push on walls. However, rules setting cell directions in this context were not characterized yet. Here, we show by using assays that ratchetaxis operates in 3D ratchets on fibroblasts and on epithelial cancerous cells. Open ratchets rectify cell motion, whereas closed ratchets impose a direct cell migration along channels set by the cell orientation at the channel entry point. We also show that nuclei are pressed at constrictions zones through mechanisms involving dynamic asymmetries of focal contacts, stress fibers, and intermediate filaments. Interestingly, cells do not pass these constricting zones when defective in the keratin fusion implicated in squamous cancer. By combining ratchetaxis with chemical gradients, we finally report that cells are sensitive to local asymmetries in confinement and that topological and chemical cues may be encoded differently by cells. Altogether our ratchet channels could mimic small blood vessels where cells are confined: cells would probe local asymmetries which would determine their entry into tissues and direction. Our results could shed light on invasions mechanisms in cancer.