The Microtubule Network

The cross-talk between microtubule (+) end tips and cortical actin is an important aspect of the maintenance of cell polarity. It is often difficult to monitor it in cells cultured in classical conditions. The highly reproducible response of the actin cytoskeleton to the topology of adhesive micro-patterns greatly facilitates the analysis of how cortical actin activity influences microtubule plus end dynamics. This is described in Thery et al (PNAS 2006).

MT plus ends trajectories visualized by recording EB1-GFP fluorescence in time-lapse microscopy were tracked, demonstrating that when microtubules reach the cell periphery they adopt different behavior depending on the cortical actin activity.

• On adhesive areas where lamellipodia protrude due to actin polymerization, microtubules stop growing when entering this region and pause for some time.

• By contrast, on non-adhesive area where actin filaments form contractile bundles or stress fibers, microtubules keep growing along these actin bundles until they reach a cell adhesion site where they pause.

The example of EB1 Microtubule trajectories on Crossbow shaped micropattern

Immuno-labeling of tubulin on fixed cells confirmed that the density of the MT array was lower in the sectors facing  non-adhesive edges than toward the adhesive edges. 

                    fibronectin micropattern                                  actin stress fibers                              Microtubules seen by IF on fixed cell     

The use of micro-patterns should be an invaluable and powerful approach to analyze the self-centering properties of the centrosome-microtubules network as well as microtubule-dependent endomembrane distribution.