(applied externally or generated by the cell) by directional assembly. The Rho
target, formin homology protein mDia1, in addition to the nucleation of actin
filament polymerization, was shown to affect microtubule dynamics both at
the plus and minus ends, and, possibly, to facilitate microtubule growth in the
direction of focal adhesions. Since microtubules interfere with myosin II-
driven contractility, the mDia1-induced changes in microtubule dynamics and
targeting may create a negative feedback loop controlling focal adhesion
Obviously, this model requires further development and refinement. The
molecular mechanism explaining the effect of force application on focal
adhesion assembly has not been elucidated. We do not yet know how
microtubules oppose cell contractility. Although bulk microtubule disruption
induces cell contraction, it has not been demonstrated that the ends of
individual microtubules can prevent contractility in their proximity; more-
over, the possible mechanism of such local relaxation is not known. Finally,
the molecular mechanism of mDia1's effects on microtubule dynamics also
should be clarified. These questions provide attractive avenues for future
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