SnapShot: Regulators I Karen Lyle, Praveen Kumar, and Torsten Wittmann Department of Cell and Tissue Biology, University of California, San Francisco, CA 94143, USA

Representative Biochemical family function H. sapiens D. melanogaster C. elegans A. thaliana S. cerevisiae S. pombe γ- γ-TuSC provides TUBG1 γTub23C TBG-1 ATGCP2 Tub4 Gtb1 primary nucleation TUBG2 γTub37C TUBG1 site γ-tubulin contribute to GCP2 Dgrip84 Ce-Grip-1 AtSpc97p Spc97 Alp4 complex nucleation GCP3 Dgrip91 AtSpc98p Spc98 Alp6 proteins ( γ -tuRc) (GCPs) contribute to GCP4 Dgrip75 AtGCP4 Gfh1p nucleation, γ-TuRC GCP5 Dgrip128 AtGCP5 Mod21 integrity and assembly

-tubulin Ring complex γ -tubulin GCP6 Dgrip163 AtGCP6 Alp16 Augmin recruits γ-TuRC to hDgt6 Dgt2, Dgt3, Dgt4, spindle Dgt5, Dgt6 Centrosomin controls γ-TuRC Cnn (centrosomin) Mto1 distribution microtubule nucleators microtubule Cep192 recruits NEDD1 to Cep192 D-Spd2 SPD-2 NEDD1 recruits γ-TuRC to NEDD1 Dgp71WD At-Nedd1 centrosome -tuRc Regulators γ -tuRc Rsp1 regulates γ-TuRC Rsp1 dispersion Bicaudal -dependent BICD1 BicD (bicaudal D) BICD-1 ■/spindle assembly minus end anchor ■Tissue-specifi c microtubule organization Microtubule cell cortex interactions links microtubule *DSP ■ Plant-specifi c protein families minus ends to ■ desmosomes *Mutation or overexpression linked to disease Proteins Anchoring minus end minus end anchor Ninein Nudel minus end anchor NDEL1 NudE NUD-2 Ndl1 EBs promote both rescue EB1 EBP-1, EBP-3 AtEB1C Bim1 Mal3 and catastrophe, directly recognize EB2 growing microtubule ends EB3 EB1 AtEB1A, AtEB1B XMAP215, processively *chTOG (CKAP5) Msps (mini spindles) ZYG-9 MOR1 Stu2 Dis1, Alp14 chTOG accelerate polymerization CLIPs promote rescue in cells *CLIP-170 CLIP-190 Bik1 Tip1 and in vitro CLIP-115 CRMP-2 binds tubulin dimers, *CRMP-2 UNC-33 promotes assembly SPIRAL suppresses growth SPR1, SP1L microtubule Assembly Promoters microtubule pauses SPR2, SP2L /Op18 promotes catastrophe, *Stathmin/Op18 stathmin inhibits polymerization, highly expressed in SCG10, SCLIP, developing neurons RB3 MAP18 inhibits polymerization MAP18 -8 and depolymerize Kif2A KLP10A KLP-7 Kip3 Klp5, Klp6 13 (internal microtubules from Kif2B KLP59C motor domain) both ends

Promoters MCAK/Kif2C KLP59D Kif18A KLP67A direct Regulators of microtubule Polymerization dynamics Regulators of microtubule direct Kinesin-14 depolymerizes Kar3 microtubule disassembly microtubule (C-terminal microtubules from the motor domain) plus end Katanin severs microtubules Katanin p60/p80 D-Kat60 MEI-1 AtKTN1, AtKSS Spastin severs microtubules *SPG4 D-Spastin SPAS-1 Fidgetin severs microtubules FIGN D-Fidgetin FIGL-1 Proteins severing microtubule microtubule

380 Cell 136, January 23, 2009 ©2009 Elsevier Inc. DOI 10.1016/j.cell.2009.01.010 See online version for legend and references. SnapShot: Microtubule Regulators I 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 is essential for many cellular processes, including , migration, and differentiation. Microtubules are dynamic polymers composed of α/β-tubulin dimers, and they switch 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 organization is controlled by the activity and distribution of nucleation sites and by the activity of microtubule-regulatory proteins. These proteins may influ- ence polymerization dynamics directly, may cut or bundle existing microtubules, or may stabilize microtubules indirectly. In cells, is mediated by the multisubunit γ-tubulin ring complex (γ-TuRC), which is recruited to or spindle poles by associated proteins such as Cep192. However, the regulation of microtubule nucleation is incompletely understood. In differentiated cells, microtubule minus ends are often redistributed away from the centrosome. For example, the protein ninein anchors minus ends to cell-cell junctions in polarized epithelial cells and to desmosomes in differentiated keratinocytes. Several different proteins influence microtubule polymerization dynamics by directly interacting with microtubule plus ends. EB-family proteins directly recognize biochemical or structural differ- ences at the growing microtubule plus ends, influence microtubule polymerization dynamics, and may act as adaptors that mediate the association of other proteins with growing microtubule plus ends. Proteins of the XMAP215 family are thought to enhance the microtubule polymerization rate by processively adding tubulin subunits to the growing microtubule plus ends. In contrast, the CRMP-2 protein in neurons enhances microtubule assembly by interacting with free tubulin dimers. Microtubule disassembly is promoted by two different mechanisms. Stathmin is a small protein that binds to tubulin dimers and lowers the pool of free tubulin avail- able for polymerization, thus decreasing the microtubule growth rate and increasing the frequency of spontaneous depolymerization (catastrophe). In contrast, internal motor domain bind directly to microtubule ends and use ATP hydrolysis to catalytically depolymerize microtubules. Microtubule-severing proteins cut existing microtubules, generating new minus and plus ends. The generation of short microtubule fragments by these proteins is important for the reorganization of the micro- tubule cytoskeleton without requiring complete microtubule disassembly. Because organization and dynamics of the microtubule cytoskeleton are crucial for many cellular functions, most direct regulators of microtubule nucleation, polymerization, and disassembly are involved in multiple cell processes. In addition, the existence of plant-specific families of microtubule regulatory proteins, such as SPIRAL, highlights important differences in microtubule function and organization between plants and animals.

Abbreviations chTOG, colonic hepatic tumor overexpressed ; CLIP, cytoplasmic linker protein; CRMP, collapsin response mediator protein; Dgt, dim γ-tubulin; EB, end-binding protein; KLP, kinesin-like protein; MAP, microtubule-associated protein; NEDD1, neural precursor cell expressed, developmentally downregulated gene 1; Spc, spindle pole body component; γ-TuRC, γ-tubulin ring complex; γ-TuSC, γ-tubulin small complex.

Acknowledgments

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

References

Baas, P.W., Karabay, A., and Qiang, L. (2005). Microtubules cut and run. Trends Cell Biol. 15, 518–524.

Bartolini, F., and Gundersen, G.G. (2006). Generation of noncentrosomal microtubule arrays. J. Cell Sci. 119, 4155–4163.

Cassimeris, L. (2002). The oncoprotein 18/stathmin family of microtubule destabilizers. Curr. Opin. Cell Biol. 14, 18–24.

Ehrhardt, D.W. (2008). Straighten up and fly right: microtubule dynamics and organization of non-centrosomal arrays in higher plants. Curr. Opin. Cell Biol. 20, 107–116.

Howard, J., and Hyman, A.A. (2007). Microtubule polymerases and depolymerases. Curr. Opin. Cell Biol. 19, 31–35.

Manning, J., and Kumar, S. (2007). NEDD1: function in microtubule nucleation, spindle assembly and beyond. Int. J. Biochem. Cell Biol. 39, 7–11.

Sharp, D.J., Mennella, V., and Buster, D.W. (2005). KLP10A and KLP59C: the dynamic duo of microtubule depolymerization. 4, 1482–1485.

Sonnenberg, A., and Liem, R.K. (2007). Plakins in development and disease. Exp. Cell Res. 313, 2189–2203.

Wiese, C., and Zheng, Y. (2006). Microtubule nucleation: gamma-tubulin and beyond. J. Cell Sci. 119, 4143–4153.

Wordeman, L. (2005). Microtubule-depolymerizing kinesins. Curr. Opin. Cell Biol. 17, 82–88.

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