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Accelerated actin filament polymerization from microtubule plus ends

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Science  20 May 2016:
Vol. 352, Issue 6288, pp. 1004-1009
DOI: 10.1126/science.aaf1709

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Making the fast faster still

Coordination between actin and microtubule cytoskeleton dynamics is critical during cell migration, phagocytosis, cytokinesis, and embryogenesis. However, the basis for cross-regulation of cytoskeleton dynamics is unclear. Henty-Ridilla et al. found that a component of the microtubule cytoskeleton accelerates actin filament elongation and protects the growing actin filament end (see the Perspective by Rottner). Thus, growing microtubules appear to be able to directly control the actin assembly machinery and actin filament dynamics.

Science, this issue p. 1004; see also p. 894

Abstract

Microtubules (MTs) govern actin network remodeling in a wide range of biological processes, yet the mechanisms underlying this cytoskeletal cross-talk have remained obscure. We used single-molecule fluorescence microscopy to show that the MT plus-end–associated protein CLIP-170 binds tightly to formins to accelerate actin filament elongation. Furthermore, we observed mDia1 dimers and CLIP-170 dimers cotracking growing filament ends for several minutes. CLIP-170–mDia1 complexes promoted actin polymerization ~18 times faster than free–barbed-end growth while simultaneously enhancing protection from capping proteins. We used a MT-actin dynamics co-reconstitution system to observe CLIP-170–mDia1 complexes being recruited to growing MT ends by EB1. The complexes triggered rapid growth of actin filaments that remained attached to the MT surface. These activities of CLIP-170 were required in primary neurons for normal dendritic morphology. Thus, our results reveal a cellular mechanism whereby growing MT plus ends direct rapid actin assembly.

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