Aprotein more often linked to effects on the actin cytoskeleton has been implicated in the polar stabilization of microtubules. Gregg Gundersen (Columbia University, New York, NY) and colleagues show that mDia1 and mDia2, two formins related to fly Diaphanous and budding yeast Bni1, can induce the formation of stable detyrosinated microtubules that may help polarize cells.
Gundersen had earlier found that the Rho-GTPase induces the formation of stable microtubules, so he set out to find the relevant Rho effector. He tested a series ofRho mutants that had varying abilities to interact with different effectors and to induce stable microtubules. The one effector whose Rho interactions correlated perfectly with stable microtubule induction was mDia.
Expression of mDia2 induced formation of stable capped microtubules, and mDia2 cosedimented with taxol-stabilized microtubules. Gundersen suspects that Dia is not itself capping microtubules, but is a scaffold for other capping proteins. Once capped, stable microtubules are gradually detyrosinated, and this modification, says Gundersen, may bias transport to the leading edge of the cell. ▪