M Biarnes, MP Valignat, O Theodoly. Collaboration with F Gallet, S Hennon (Univ Paris 7)

A wide variety of cells migrate directionally in response to chemical or mechanical cues, however the exact mechanisms involved in cue detection and translation into directed movement are still debatable.

Figure 4 : Lymphocytes tails (or uropods) are the steering device of lymphocytes. A- Confocal microscopy image of a T lymphocyte (green-membrane, blue-nucleus) with a 12 µm diameter magnetic bead (red) attached to its tail. B,C- The magnetic bead allowed us to actuate cells’ tail with magnetic tweezers (B) and to pilot the cell on a targeted path, here a series  of horizontal (blue) and vertical (red) steps (C).

We have recently shown that cells’ tails, called uropods, act as microscopic wind vanes that transmit detection of flow direction into cell steering via the on-going machinery of polarity maintenance, without need for novel internal guidance signalling triggered by flow. Contrary to chemotaxis, which implies active regulation of cue-dependant signalling, upstream flow mechanotaxis of lymphocytes may only rely on a passive self-steering mechanism.

Figure 5 : A wind vane self-steering system. The actuation of the cell’s tail direction by flow is similar to a wind vane actuation by a breeze. The direction of the tail direction coupled to the ongoing maintenance of cell polarity induces cell turning. This mechanism is reminiscent of mechanical self-steering system used on sailing boats.