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. Author manuscript; available in PMC: 2014 May 13.
Published in final edited form as: Cell. 2009 Feb 6;136(3):566–566.e1. doi: 10.1016/j.cell.2009.01.011

SnapShot: Microtubule Regulators II

Karen Lyle 1, Praveen Kumar 1, Torsten Wittmann 1
PMCID: PMC4019436  NIHMSID: NIHMS575583  PMID: 19203588

Dynamic remodeling of the microtubule cytoskeleton is essential for many cell processes including division, migration and differentiation. Microtubules are dynamic polymers of α/β-tubulin dimers and transition stochastically between phases of growth (polymerization) and shortening (depolymerization). Intracellular microtubule organization is controlled by the activity and distribution of nucleation sites, proteins that directly influence polymerization dynamics, proteins that cut or bundle existing microtubules, and proteins that indirectly stabilize microtubules. Classical microtubule-associated proteins are mainly found in neuronal cells. Tau and MAP1B is specific for axons and MAP2 is predominantly localized to dendrites. These proteins bind along the length of microtubules and protect neurite microtubule arrays from depolymerization. Although many microtubule-associated proteins bundle microtubules when overexpressed in cells, true bundling activity has only been demonstrated for few protein families. Homotetrameric motor proteins of the kinesin-5 family slide antiparallel microtubules, and are required for spindle formation and spindle pole separation. MAP65-related proteins have been shown to promote antiparallel microtubule bundling, and yeast Ase1 is required for spindle midzone formation. MAP65 proteins are particularly numerous in plants. Together with additional plant-specific proteins such as WVD2, MAP65 proteins are involved in the formation of cortical microtubule bundles in plant cells. In addition to direct regulation of polymerization dynamics, microtubules can be stabilized by interactions with other intracellular structures. For example, CLASPs and spectraplakins mediate microtubule interactions with actin cables and adhesion sites. Because microtubules are the primary component of the mitotic spindle and essential for accurate chromosome segregation during cell division, it is not surprising that a number of microtubule-regulatory proteins function predominantly during spindle assembly. Many mitosis-specific microtubule stabilizers such as TPX2, NuMA, RHAMM, and HURP are segregated into the nucleus during interphase and are activated in a Ran·GTP dependent manner around mitotic chromatin. Tektins are a group of highly specialized microtubule-stabilizing proteins necessary for the assembly of cilia and flagella in all eukaryotic cells. The specific functions of many other microtubule-associated and/or stabilizing proteins are poorly understood. Microtubule-based motor proteins that have no documented effects on microtubule dynamics are not included in this table.

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Acknowledgements

T.W. is supported by NIH R01GM079139. K.L. is supported by NIH/NIDCR training grant 5T32DE007306.

Abbreviations

APC

adenomatous polyposis coli protein

CLAMP

Calponin-homology and microtubule-associated protein

CLASP

CLIP-associated protein

HURP

hepatoma-upregulated protein

Lis

lissencephaly

MURF

muscle-specific ring finger

NuMA

nuclear-mitotic apparatus protein

NuSAP

nucleolar spindle-associated protein

RHAMM

receptor of hyaluronan-mediated motility

STOP

stable-tubules only protein

TACC

transforming acidic coiled-coil

TPX2

targeting protein for Xklp2

VAP

VAMP-associated protein

VHL

vonHippel-Lindau syndrome protein

WVD

wave-dampened.

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