SnapShot: Microtubule Regulators II Karen Lyle, Praveen Kumar, and Torsten Wittmann Department of Cell and Tissue Biology, University of California, San Francisco, CA 94143, USA Representative Proteins Protein Family Biochemical Function H. sapiens D. melanogaster C. elegans A. thaliana S. cerevisiae S. pombe MAP1 stabilizes neuronal microtubules MAP1A, futsch MAP1B, MAP1S MAP2/Tau inhibit depolymerization, increase *Tau, MAP2, Tau PTL-1 Mhp1 Classical microtubule rigidity MAP4 Microtubule- Associated Proteins Kinesin-5 crosslinks and slides antiparallel Eg5 Klp61F BMK-1 AtKRP125c Kip1, Cin8 Cut7 (BimC) microtubules MAP65 promotes antiparallel microtubule PRC1 Feo (fascetto) SPD-1 AtMAP65-1, Ase1 Ase1 bundling 2, 3, 4, 5, 6, Proteins 7, 8, PLE Bundling Microtubule- WVD2 bundles microtubules WVD2, WDL APC mediates interactions with cortical *APC, APC2 dAPC1, dAPC2 APR-1 (Kar9) cytoskeleton, promotes net growth Bud6 cortical capture of astral Bud6 microtubules CLASPs mediate interactions with cell CLASP1, Orbit/MAST CLS-2 CLASP Stu1 Peg1 cortex, kinetochores, and Golgi CLASP2 Interactions Spectraplakins link microtubules to the actin MACF1/ shot (short stop) VAB-10 cytoskeleton ACF7, through Cell Cortex through *MACF2/ Microtubule Stabilization Microtubule BPAG1 Kinesin-7 captures microtubules at CENP-E cmet Kip2 Tea2 kinetochores Astrin crosslinks microtubules Spag5 HURP wraps tubulin sleeves around *DLGAP5 microtubules NuMA stabilizes spindle pole microtubules NUMA Mud (mushroom ■Mitosis/spindle assembly body defect) ■Tissue-specifi c microtubule organization ■Microtubule cell cortex interactions NuSAP stabilizes microtubules near NuSAP ■Plant-specifi c protein families chromosomes *Mutation or overexpression linked to disease RHAMM stabilizes microtubules at spindle RHAMM poles TACC proteins stabilize microtubules at spindle *TACC-1, D-TACC TAC-1 Alp7 mitosis-specifi c Functions mitosis-specifi poles TACC-2, TACC-3 Microtubule-Stabilizing Proteins with Proteins Microtubule-Stabilizing TPX2 stabilizes spindle pole microtubules TPX2 TPXL-1 AtTPX2 CLAMP stabilizes microtubules CLAMP Doublecortin stabilizes microtubules during *DCX ZYG-8 neuronal migration Formins stabilize microtubules by Dia1, Dia2, Dia (diaphanous) Bni1 decreasing disassembly INF1 Lis1 stabilizes microtubules during *LIS1 Lis-1 LIS-1 neuronal migration MAP6/STOP protect microtubules from cold- E-STOP, induced disassembly N-STOP, SL21 MAP70 stabilizes microtubules AtMAP70 MURF stabilize microtubules in striated MURF-2, proteins muscle MURF-3 Tektins crosslink and stabilize axoneme Tektin-1, 2, Tektin-A, C, tektin microtubules in cilia and fl agella 3, 4, 5 CG3085, CG32820 VAPs stabilize presynaptic microtubules VAPB DVAP33-A VPR-1 Other Microtubule-Stabilizing Proteins Other Microtubule-Stabilizing VHL stabilizes microtubules *VHL D-VHL VHL-1 YB-1 promotes microtubule assembly YB-1 yps (ypsilon schachtel) 566 Cell 136, February 6, 2009 ©2009 Elsevier Inc. DOI 10.1016/j.cell.2009.01.011 See online version for legend and references. SnapShot: Microtubule Regulators II Karen Lyle, Praveen Kumar, and Torsten Wittmann Department of Cell and Tissue Biology, University of California, San Francisco, CA 94143, USA Dynamic remodeling of the microtubule cytoskeleton is essential for many cellular processes including cell division, migration, and differentiation. Microtubules are dynamic polymers of α/β-tubulin dimers and transition stochastically between phases of growth (polymerization) and shortening (depolymerization). The transition from microtubule growth to shortening is referred to as catastrophe, and the transition from microtubule shortening to growth is called rescue. Intracellular microtubule orga- nization is controlled by the activity and distribution of nucleation sites and by the activity of microtubule-regulatory proteins. Such proteins include those that directly influence polymerization dynamics, that cut or bundle existing microtubules, or that stabilize microtubules indirectly. Classical microtubule-associated proteins are mainly found in neurons. The tau and MAP1B microtubule-associated proteins are specific for axons; 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 a few protein families. These include homotetrameric motor proteins of the kinesin-5 family, which help antiparallel microtubules to slide and are required for spindle formation and spindle pole separation. MAP65-related proteins promote antiparallel microtubule bundling, and yeast Ase1 is required for spindle midzone formation. MAP65 proteins are particularly numerous in plants. Together with additional plant-spe- cific 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 act predominantly during spindle assembly. Many mitosis-specific microtubule stabiliz- ers, such as TPX2, NuMA, RHAMM, and HURP, are segregated into the nucleus during interphase and are activated in a RanGTP-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 or -stabilizing proteins are poorly understood. Microtubule-based motor proteins that have no documented effects on microtubule dynamics are not included in this table. Abbreviations APC, adenomatous polyposis coli protein; CLAMP, Calponin-homology and microtubule-associated protein; CLASP, CLIP-associated protein; HURP, hepatoma-upreg- ulated 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, von Hippel-Lindau syndrome protein; WVD, wave-dampened. ACKNOWLEDGMENTS T.W. is supported by NIH R01GM079139. K.L. is supported by NIH/NIDCR training grant 5T32DE007306. REFERENCES Akhmanova, A., and Steinmetz, M.O. (2008). Tracking the ends: a dynamic protein network controls the fate of microtubule tips. Nat. Rev. Mol. Cell Biol. 9, 309–322. Amos, L.A. (2008). The tektin family of microtubule-stabilizing proteins. Genome Biol. 9, 229. Bosc, C., Andrieux, A., and Job, D. (2003). STOP proteins. Biochemistry 42, 12125–12132. Clarke, P.R., and Zhang, C. (2008). Spatial and temporal coordination of mitosis by Ran GTPase. Nat. Rev. Mol. Cell Biol. 9, 464–477. Davis, T.N., and Wordeman, L. (2007). Rings, bracelets, sleeves, and chevrons: new structures of kinetochore proteins. Trends Cell Biol. 17, 377–382. Dehmelt, L., and Halpain, S. (2005). The MAP2/Tau family of microtubule-associated proteins. Genome Biol. 6, 204. DeWard, A.D., and Alberts, A.S. (2008). Microtubule stabilization: formins assert their independence. Curr. Biol. 18, R605–R608. Halpain, S., and Dehmelt, L. (2006). The MAP1 family of microtubule-associated proteins. Genome Biol. 7, 224. Manning, A.L., and Compton, D.A. (2008). Structural and regulatory roles of nonmotor spindle proteins. Curr. Opin. Cell Biol. 20, 101–106. Peset, I., and Vernos, I. (2008). The TACC proteins: TACC-ling microtubule dynamics and centrosome function. Trends Cell Biol. 18, 379–388. 566.e1 Cell 136, February 6, 2009 ©2009 Elsevier Inc. DOI 10.1016/j.cell.2009.01.011.