Journal articles: 'Spindle bipolarity'

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Bird, Alexander W., and Anthony A. Hyman. "Building a spindle of the correct length in human cells requires the interaction between TPX2 and Aurora A." Journal of Cell Biology 182, no. 2 (July 28, 2008): 289–300. http://dx.doi.org/10.1083/jcb.200802005.

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To assemble mitotic spindles, cells nucleate microtubules from a variety of sources including chromosomes and centrosomes. We know little about how the regulation of microtubule nucleation contributes to spindle bipolarity and spindle size. The Aurora A kinase activator TPX2 is required for microtubule nucleation from chromosomes as well as for spindle bipolarity. We use bacterial artificial chromosome–based recombineering to introduce point mutants that block the interaction between TPX2 and Aurora A into human cells. TPX2 mutants have very short spindles but, surprisingly, are still bipolar and segregate chromosomes. Examination of microtubule nucleation during spindle assembly shows that microtubules fail to nucleate from chromosomes. Thus, chromosome nucleation is not essential for bipolarity during human cell mitosis when centrosomes are present. Rather, chromosome nucleation is involved in spindle pole separation and setting spindle length. A second Aurora A–independent function of TPX2 is required to bipolarize spindles.

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Ganem, Neil J., and Duane A. Compton. "The KinI kinesin Kif2a is required for bipolar spindle assembly through a functional relationship with MCAK." Journal of Cell Biology 166, no. 4 (August 9, 2004): 473–78. http://dx.doi.org/10.1083/jcb.200404012.

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Although the microtubule-depolymerizing KinI motor Kif2a is abundantly expressed in neuronal cells, we now show it localizes to centrosomes and spindle poles during mitosis in cultured cells. RNAi-induced knockdown of Kif2a expression inhibited cell cycle progression because cells assembled monopolar spindles. Bipolar spindle assembly was restored in cells lacking Kif2a by treatments that altered microtubule assembly (nocodazole), eliminated kinetochore–microtubule attachment (loss of Nuf2), or stabilized microtubule plus ends at kinetochores (loss of MCAK). Thus, two KinI motors, MCAK and Kif2a, play distinct roles in mitosis, and MCAK activity at kinetochores must be balanced by Kif2a activity at poles for spindle bipolarity. These treatments failed to restore bipolarity to cells lacking the activity of the kinesin Eg5. Thus, two independent pathways contribute to spindle bipolarity, with the Eg5-dependent pathway using motor force to drive spindle bipolarity and the Kif2a-dependent pathway relying on microtubule polymer dynamics to generate force for spindle bipolarity.

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Yukawa, Masashi, Tomoki Kawakami, Masaki Okazaki, Kazunori Kume, Ngang Heok Tang, and Takashi Toda. "A microtubule polymerase cooperates with the kinesin-6 motor and a microtubule cross-linker to promote bipolar spindle assembly in the absence of kinesin-5 and kinesin-14 in fission yeast." Molecular Biology of the Cell 28, no. 25 (December 2017): 3647–59. http://dx.doi.org/10.1091/mbc.e17-08-0497.

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Accurate chromosome segregation relies on the bipolar mitotic spindle. In many eukaryotes, spindle formation is driven by the plus-end–directed motor kinesin-5 that generates outward force to establish spindle bipolarity. Its inhibition leads to the emergence of monopolar spindles with mitotic arrest. Intriguingly, simultaneous inactivation of the minus-end–directed motor kinesin-14 restores spindle bipolarity in many systems. Here we show that in fission yeast, three independent pathways contribute to spindle bipolarity in the absence of kinesin-5/Cut7 and kinesin-14/Pkl1. One is kinesin-6/Klp9 that engages with spindle elongation once short bipolar spindles assemble. Klp9 also ensures the medial positioning of anaphase spindles to prevent unequal chromosome segregation. Another is the Alp7/TACC-Alp14/TOG microtubule polymerase complex. Temperature-sensitive alp7cut7pkl1 mutants are arrested with either monopolar or very short spindles. Forced targeting of Alp14 to the spindle pole body is sufficient to render alp7cut7pkl1 triply deleted cells viable and promote spindle assembly, indicating that Alp14-mediated microtubule polymerization from the nuclear face of the spindle pole body could generate outward force in place of Cut7 during early mitosis. The third pathway involves the Ase1/PRC1 microtubule cross-linker that stabilizes antiparallel microtubules. Our study, therefore, unveils multifaceted interplay among kinesin-dependent and -independent pathways leading to mitotic bipolar spindle assembly.

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Gayek, A. Sophia, and Ryoma Ohi. "Kinetochore-microtubule stability governs the metaphase requirement for Eg5." Molecular Biology of the Cell 25, no. 13 (July 2014): 2051–60. http://dx.doi.org/10.1091/mbc.e14-03-0785.

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The mitotic spindle is a bipolar, microtubule (MT)-based cellular machine that segregates the duplicated genome into two daughter cells. The kinesin-5 Eg5 establishes the bipolar geometry of the mitotic spindle, but previous work in mammalian cells suggested that this motor is unimportant for the maintenance of spindle bipolarity. Although it is known that Kif15, a second mitotic kinesin, enforces spindle bipolarity in the absence of Eg5, how Kif15 functions in this capacity and/or whether other biochemical or physical properties of the spindle promote its bipolarity have been poorly studied. Here we report that not all human cell lines can efficiently maintain bipolarity without Eg5, despite their expressing Kif15. We show that the stability of chromosome-attached kinetochore-MTs (K-MTs) is important for bipolar spindle maintenance without Eg5. Cells that efficiently maintain bipolar spindles without Eg5 have more stable K-MTs than those that collapse without Eg5. Consistent with this observation, artificial destabilization of K-MTs promotes spindle collapse without Eg5, whereas stabilizing K-MTs improves bipolar spindle maintenance without Eg5. Our findings suggest that either rapid K-MT turnover pulls poles inward or slow K-MT turnover allows for greater resistance to inward-directed forces.

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Wolff, Ian D., Michael V. Tran, Timothy J. Mullen, Anne M. Villeneuve, and Sarah M. Wignall. "Assembly of Caenorhabditis elegans acentrosomal spindles occurs without evident microtubule-organizing centers and requires microtubule sorting by KLP-18/kinesin-12 and MESP-1." Molecular Biology of the Cell 27, no. 20 (October 15, 2016): 3122–31. http://dx.doi.org/10.1091/mbc.e16-05-0291.

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Although centrosomes contribute to spindle formation in most cell types, oocytes of many species are acentrosomal and must organize spindles in their absence. Here we investigate this process in Caenorhabditis elegans, detailing how acentrosomal spindles form and revealing mechanisms required to establish bipolarity. Using high-resolution imaging, we find that in meiosis I, microtubules initially form a “cage-like” structure inside the disassembling nuclear envelope. This structure reorganizes so that minus ends are sorted to the periphery of the array, forming multiple nascent poles that then coalesce until bipolarity is achieved. In meiosis II, microtubules nucleate in the vicinity of chromosomes but then undergo similar sorting and pole formation events. We further show that KLP-18/kinesin-12 and MESP-1, previously shown to be required for spindle bipolarity, likely contribute to bipolarity by sorting microtubules. After their depletion, minus ends are not sorted outward at the early stages of spindle assembly and instead converge. These proteins colocalize on microtubules, are interdependent for localization, and can interact, suggesting that they work together. We propose that KLP-18/kinesin-12 and MESP-1 form a complex that functions to sort microtubules of mixed polarity into a configuration in which minus ends are away from the chromosomes, enabling formation of nascent poles.

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Prigozhina, Natalie L., Richard A. Walker, C. Elizabeth Oakley, and Berl R. Oakley. "γ-Tubulin and the C-Terminal Motor Domain Kinesin-like Protein, KLPA, Function in the Establishment of Spindle Bipolarity inAspergillus nidulans." Molecular Biology of the Cell 12, no. 10 (October 2001): 3161–74. http://dx.doi.org/10.1091/mbc.12.10.3161.

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Previous research has found that a γ-tubulin mutation inSchizosaccharomyces pombe is synthetically lethal with a deletion of the C-terminal motor domain kinesin-like protein genepkl1, but the lethality of the double mutant prevents a phenotypic analysis of the synthetic interaction. We have investigated interactions between klpA1, a deletion of an Aspergillus nidulans homolog of pkl1, and mutations in the mipA, γ-tubulin gene. We find that klpA1 dramatically increases the cold sensitivity and slightly reduces the growth rate at all temperatures, of threemipA alleles. In synchronized cells we find thatklpA1 causes a substantial but transient inhibition of the establishment of spindle bipolarity. At a restrictive temperature,mipAD123 causes a slight, transient inhibition of spindle bipolarity and a more significant inhibition of anaphase A. In the mipAD123/klpA1 strain, formation of bipolar spindles is more strongly inhibited than in theklpA1 single mutant and many spindles apparently never become bipolar. These results indicate, surprisingly, that γ-tubulin and the klpA kinesin have overlapping roles in the establishment of spindle bipolarity. We propose a model to account for these data.

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Godinho, Susana A. "The principles of spindle bipolarity." Nature Reviews Molecular Cell Biology 20, no. 6 (April 24, 2019): 325. http://dx.doi.org/10.1038/s41580-019-0135-1.

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Cassimeris, Lynne, and Justin Morabito. "TOGp, the Human Homolog of XMAP215/Dis1, Is Required for Centrosome Integrity, Spindle Pole Organization, and Bipolar Spindle Assembly." Molecular Biology of the Cell 15, no. 4 (April 2004): 1580–90. http://dx.doi.org/10.1091/mbc.e03-07-0544.

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The XMAP215/Dis1 MAP family is thought to regulate microtubule plus-end assembly in part by antagonizing the catastrophe-promoting function of kin I kinesins, yet XMAP215/Dis1 proteins localize to centrosomes. We probed the mitotic function of TOGp (human homolog of XMAP215/Dis1) using siRNA. Cells lacking TOGp assembled multipolar spindles, confirming results of Gergely et al. (2003. Genes Dev. 17, 336–341). Eg5 motor activity was necessary to maintain the multipolar morphology. Depletion of TOGp decreased microtubule length and density in the spindle by ∼20%. Depletion of MCAK, a kin I kinesin, increased MT lengths and density by ∼20%, but did not disrupt spindle morphology. Mitotic cells lacking both TOGp and MCAK formed bipolar and monopolar spindles, indicating that TOGp and MCAK contribute to spindle bipolarity, without major effects on MT stability. TOGp localized to centrosomes in the absence of MTs and depletion of TOGp resulted in centrosome fragmentation. TOGp depletion also disrupted MT minus-end focus at the spindle poles, detected by localizations of NuMA and the p150 component of dynactin. The major functions of TOGp during mitosis are to focus MT minus ends at spindle poles, maintain centrosome integrity, and contribute to spindle bipolarity.

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Zhang, Xin, Stephanie C. Ems-McClung, and Claire E. Walczak. "Aurora A Phosphorylates MCAK to Control Ran-dependent Spindle Bipolarity." Molecular Biology of the Cell 19, no. 7 (July 2008): 2752–65. http://dx.doi.org/10.1091/mbc.e08-02-0198.

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During mitosis, mitotic centromere-associated kinesin (MCAK) localizes to chromatin/kinetochores, a cytoplasmic pool, and spindle poles. Its localization and activity in the chromatin region are regulated by Aurora B kinase; however, how the cytoplasmic- and pole-localized MCAK are regulated is currently not clear. In this study, we used Xenopus egg extracts to form spindles in the absence of chromatin and centrosomes and found that MCAK localization and activity are tightly regulated by Aurora A. This regulation is important to focus microtubules at aster centers and to facilitate the transition from asters to bipolar spindles. In particular, we found that MCAK colocalized with NuMA and XMAP215 at the center of Ran asters where its activity is regulated by Aurora A-dependent phosphorylation of S196, which contributes to proper pole focusing. In addition, we found that MCAK localization at spindle poles was regulated through another Aurora A phosphorylation site (S719), which positively enhances bipolar spindle formation. This is the first study that clearly defines a role for MCAK at the spindle poles as well as identifies another key Aurora A substrate that contributes to spindle bipolarity.

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Connolly, Amy A., Kenji Sugioka, Chien-Hui Chuang, Joshua B. Lowry, and Bruce Bowerman. "KLP-7 acts through the Ndc80 complex to limit pole number in C. elegans oocyte meiotic spindle assembly." Journal of Cell Biology 210, no. 6 (September 14, 2015): 917–32. http://dx.doi.org/10.1083/jcb.201412010.

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During oocyte meiotic cell division in many animals, bipolar spindles assemble in the absence of centrosomes, but the mechanisms that restrict pole assembly to a bipolar state are unknown. We show that KLP-7, the single mitotic centromere–associated kinesin (MCAK)/kinesin-13 in Caenorhabditis elegans, is required for bipolar oocyte meiotic spindle assembly. In klp-7(−) mutants, extra microtubules accumulated, extra functional spindle poles assembled, and chromosomes frequently segregated as three distinct masses during meiosis I anaphase. Moreover, reducing KLP-7 function in monopolar klp-18(−) mutants often restored spindle bipolarity and chromosome segregation. MCAKs act at kinetochores to correct improper kinetochore–microtubule (k–MT) attachments, and depletion of the Ndc-80 kinetochore complex, which binds microtubules to mediate kinetochore attachment, restored bipolarity in klp-7(−) mutant oocytes. We propose a model in which KLP-7/MCAK regulates k–MT attachment and spindle tension to promote the coalescence of early spindle pole foci that produces a bipolar structure during the acentrosomal process of oocyte meiotic spindle assembly.

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Zhao, Wei, Jie Liu, Xiaoming Zhang, and Lih-Wen Deng. "MLL5 maintains spindle bipolarity by preventing aberrant cytosolic aggregation of PLK1." Journal of Cell Biology 212, no. 7 (March 21, 2016): 829–43. http://dx.doi.org/10.1083/jcb.201501021.

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Faithful chromosome segregation with bipolar spindle formation is critical for the maintenance of genomic stability. Perturbation of this process often leads to severe mitotic failure, contributing to tumorigenesis. MLL5 has been demonstrated to play vital roles in cell cycle progression and the maintenance of genomic stability. Here, we identify a novel interaction between MLL5 and PLK1 in the cytosol that is crucial for sustaining spindle bipolarity during mitosis. Knockdown of MLL5 caused aberrant PLK1 aggregation that led to acentrosomal microtubule-organizing center (aMTOC) formation and subsequent spindle multipolarity. Further molecular studies revealed that the polo-box domain (PBD) of PLK1 interacted with a binding motif on MLL5 (Thr887-Ser888-Thr889), and this interaction was essential for spindle bipolarity. Overexpression of wild-type MLL5 was able to rescue PLK1 mislocalization and aMTOC formation in MLL5-KD cells, whereas MLL5 mutants incapable of interacting with the PBD failed to do so. We thus propose that MLL5 preserves spindle bipolarity through maintaining cytosolic PLK1 in a nonaggregated form.

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Mitchison, T. J., P. Maddox, A. Groen, L. Cameron, Z. Perlman, R. Ohi, A. Desai, E. D. Salmon, and T. M. Kapoor. "Bipolarization and Poleward Flux Correlate duringXenopusExtract Spindle Assembly." Molecular Biology of the Cell 15, no. 12 (December 2004): 5603–15. http://dx.doi.org/10.1091/mbc.e04-05-0440.

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We investigated the mechanism by which meiotic spindles become bipolar and the correlation between bipolarity and poleward flux, using Xenopus egg extracts. By speckle microscopy and computational alignment, we find that monopolar sperm asters do not show evidence for flux, partially contradicting previous work. We account for the discrepancy by describing spontaneous bipolarization of sperm asters that was missed previously. During spontaneous bipolarization, onset of flux correlated with onset of bipolarity, implying that antiparallel microtubule organization may be required for flux. Using a probe for TPX2 in addition to tubulin, we describe two pathways that lead to spontaneous bipolarization, new pole assembly near chromatin, and pole splitting. By inhibiting the Ran pathway with excess importin-alpha, we establish a role for chromatin-derived, antiparallel overlap bundles in generating the sliding force for flux, and we examine these bundles by electron microscopy. Our results highlight the importance of two processes, chromatin-initiated microtubule nucleation, and sliding forces generated between antiparallel microtubules, in self-organization of spindle bipolarity and poleward flux.

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Liu, Q., and J. V. Ruderman. "Aurora A, mitotic entry, and spindle bipolarity." Proceedings of the National Academy of Sciences 103, no. 15 (March 31, 2006): 5811–16. http://dx.doi.org/10.1073/pnas.0601425103.

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Connolly, Amy A., Valerie Osterberg, Sara Christensen, Meredith Price, Chenggang Lu, Kathy Chicas-Cruz, Shawn Lockery, Paul E. Mains, and Bruce Bowerman. "Caenorhabditis elegansoocyte meiotic spindle pole assembly requires microtubule severing and the calponin homology domain protein ASPM-1." Molecular Biology of the Cell 25, no. 8 (April 15, 2014): 1298–311. http://dx.doi.org/10.1091/mbc.e13-11-0687.

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In many animals, including vertebrates, oocyte meiotic spindles are bipolar but assemble in the absence of centrosomes. Although meiotic spindle positioning in oocytes has been investigated extensively, much less is known about their assembly. In Caenorhabditis elegans, three genes previously shown to contribute to oocyte meiotic spindle assembly are the calponin homology domain protein encoded by aspm-1, the katanin family member mei-1, and the kinesin-12 family member klp-18. We isolated temperature-sensitive alleles of all three and investigated their requirements using live-cell imaging to reveal previously undocumented requirements for aspm-1 and mei-1. Our results indicate that bipolar but abnormal oocyte meiotic spindles assemble in aspm-1(-) embryos, whereas klp-18(-) and mei-1(-) mutants assemble monopolar and apolar spindles, respectively. Furthermore, two MEI-1 functions—ASPM-1 recruitment to the spindle and microtubule severing—both contribute to monopolar spindle assembly in klp-18(-) mutants. We conclude that microtubule severing and ASPM-1 both promote meiotic spindle pole assembly in C. elegans oocytes, whereas the kinesin 12 family member KLP-18 promotes spindle bipolarity.

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Shrestha, Sanjay, Lori Jo Wilmeth, Jarrett Eyer, and Charles B. Shuster. "PRC1 controls spindle polarization and recruitment of cytokinetic factors during monopolar cytokinesis." Molecular Biology of the Cell 23, no. 7 (April 2012): 1196–207. http://dx.doi.org/10.1091/mbc.e11-12-1008.

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The central spindle is a postanaphase array of microtubules that plays an essential role in organizing the signaling machinery for cytokinesis. The model by which the central spindle organizes the cytokinetic apparatus is premised on an antiparallel arrangement of microtubules, yet cells lacking spindle bipolarity are capable of generating a distal domain of ectopic furrowing when forced into mitotic exit. Because protein regulator of cytokinesis (PRC1) and kinesin family member 4A (KIF4A) are believed to play a principal role in organizing the antiparallel midzone array, we sought to clarify their roles in monopolar cytokinesis. Although both factors localized to the distal ends of microtubules during monopolar cytokinesis, depletion of PRC1 and KIF4A displayed different phenotypes. Cells depleted of PRC1 failed to form a polarized microtubule array or ectopic furrows following mitotic exit, and recruitment of Aurora B kinase, male germ cell Rac GTPase-activating protein, and RhoA to the cortex was impaired. In contrast, KIF4A depletion impaired neither polarization nor ectopic furrowing, but it did result in elongated spindles with a diffuse distribution of cytokinetic factors. Thus, even in the absence of spindle bipolarity, PRC1 appears to be essential for polarizing parallel microtubules and concentrating the factors responsible for contractile ring assembly, whereas KIF4A is required for limiting the length of anaphase microtubules.

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Beaven, Robin, Ricardo Nunes Bastos, Christos Spanos, Pierre Romé, C. Fiona Cullen, Juri Rappsilber, Régis Giet, Gohta Goshima, and Hiroyuki Ohkura. "14-3-3 regulation of Ncd reveals a new mechanism for targeting proteins to the spindle in oocytes." Journal of Cell Biology 216, no. 10 (August 31, 2017): 3029–39. http://dx.doi.org/10.1083/jcb.201704120.

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The meiotic spindle is formed without centrosomes in a large volume of oocytes. Local activation of crucial spindle proteins around chromosomes is important for formation and maintenance of a bipolar spindle in oocytes. We found that phosphodocking 14-3-3 proteins stabilize spindle bipolarity in Drosophila melanogaster oocytes. A critical 14-3-3 target is the minus end–directed motor Ncd (human HSET; kinesin-14), which has well-documented roles in stabilizing a bipolar spindle in oocytes. Phospho docking by 14-3-3 inhibits the microtubule binding activity of the nonmotor Ncd tail. Further phosphorylation by Aurora B kinase can release Ncd from this inhibitory effect of 14-3-3. As Aurora B localizes to chromosomes and spindles, 14-3-3 facilitates specific association of Ncd with spindle microtubules by preventing Ncd from binding to nonspindle microtubules in oocytes. Therefore, 14-3-3 translates a spatial cue provided by Aurora B to target Ncd selectively to the spindle within the large volume of oocytes.

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Maiato, Helder, Paula Sampaio, Catarina L. Lemos, John Findlay, Mar Carmena, William C. Earnshaw, and Claudio E. Sunkel. "MAST/Orbit has a role in microtubule–kinetochore attachment and is essential for chromosome alignment and maintenance of spindle bipolarity." Journal of Cell Biology 157, no. 5 (May 28, 2002): 749–60. http://dx.doi.org/10.1083/jcb.200201101.

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Multiple asters (MAST)/Orbit is a member of a new family of nonmotor microtubule-associated proteins that has been previously shown to be required for the organization of the mitotic spindle. Here we provide evidence that MAST/Orbit is required for functional kinetochore attachment, chromosome congression, and the maintenance of spindle bipolarity. In vivo analysis of Drosophila mast mutant embryos undergoing early mitotic divisions revealed that chromosomes are unable to reach a stable metaphase alignment and that bipolar spindles collapse as centrosomes move progressively closer toward the cell center and eventually organize into a monopolar configuration. Similarly, soon after depletion of MAST/Orbit in Drosophila S2 cells by double-stranded RNA interference, cells are unable to form a metaphase plate and instead assemble monopolar spindles with chromosomes localized close to the center of the aster. In these cells, kinetochores either fail to achieve end-on attachment or are associated with short microtubules. Remarkably, when microtubule dynamics is suppressed in MAST-depleted cells, chromosomes localize at the periphery of the monopolar aster associated with the plus ends of well-defined microtubule bundles. Furthermore, in these cells, dynein and ZW10 accumulate at kinetochores and fail to transfer to microtubules. However, loss of MAST/Orbit does not affect the kinetochore localization of D-CLIP-190. Together, these results strongly support the conclusion that MAST/Orbit is required for microtubules to form functional attachments to kinetochores and to maintain spindle bipolarity.

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Simeonov, Dimitre R., Katelyn Kenny, Lan Seo, Amanda Moyer, Jessica Allen, and Janet L. Paluh. "Distinct Kinesin-14 mitotic mechanisms in spindle bipolarity." Cell Cycle 8, no. 21 (November 2009): 3571–83. http://dx.doi.org/10.4161/cc.8.21.9970.

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Kenny, Katelyn, Lan Seo, Roland Zhou, and Janet L. Paluh. "Spindle and Pole Mechanisms in Bipolarity and Prophase Control of Spindle Elongation." Biophysical Journal 98, no. 3 (January 2010): 163a. http://dx.doi.org/10.1016/j.bpj.2009.12.882.

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Hatsumi, M., and S. A. Endow. "The Drosophila ncd microtubule motor protein is spindle-associated in meiotic and mitotic cells." Journal of Cell Science 103, no. 4 (December 1, 1992): 1013–20. http://dx.doi.org/10.1242/jcs.103.4.1013.

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The nonclaret disjunctional (ncd) protein is required for normal chromosome distribution in oocytes and early embryos. Mutants of ncd cause frequent nondisjunction and loss of chromosomes, suggesting a role for the protein in spindle function or chromosome movement in meiosis and early mitosis. The ncd protein contains a region of predicted sequence similarity to the microtubule motor protein, kinesin. In vitro motility assays have demonstrated that ncd is a motor that unexpectedly moves toward the minus ends of microtubules, opposite to the direction of kinesin movement. Using antibodies directed against nonconserved regions of the protein, we have localized the ncd motor protein to the meiotic and early mitotic spindle, and to spindles in a mitotically dividing cultured cell line. Its presence in the spindle of meiotic and mitotic cells implies a role for the protein as a spindle motor. The motor may play an essential role in establishing spindle bipolarity in meiosis.

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Jones, Laura A., Cécile Villemant, Toby Starborg, Anna Salter, Georgina Goddard, Peter Ruane, Philip G. Woodman, Nancy Papalopulu, Sarah Woolner, and Victoria J. Allan. "Dynein light intermediate chains maintain spindle bipolarity by functioning in centriole cohesion." Journal of Cell Biology 207, no. 4 (November 24, 2014): 499–516. http://dx.doi.org/10.1083/jcb.201408025.

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Cytoplasmic dynein 1 (dynein) is a minus end–directed microtubule motor protein with many cellular functions, including during cell division. The role of the light intermediate chains (LICs; DYNC1LI1 and 2) within the complex is poorly understood. In this paper, we have used small interfering RNAs or morpholino oligonucleotides to deplete the LICs in human cell lines and Xenopus laevis early embryos to dissect the LICs’ role in cell division. We show that although dynein lacking LICs drives microtubule gliding at normal rates, the LICs are required for the formation and maintenance of a bipolar spindle. Multipolar spindles with poles that contain single centrioles were formed in cells lacking LICs, indicating that they are needed for maintaining centrosome integrity. The formation of multipolar spindles via centrosome splitting after LIC depletion could be rescued by inhibiting Eg5. This suggests a novel role for the dynein complex, counteracted by Eg5, in the maintenance of centriole cohesion during mitosis.

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Sellitto, C., and R. Kuriyama. "Distribution of pericentriolar material in multipolar spindles induced by colcemid treatment in Chinese hamster ovary cells." Journal of Cell Science 89, no. 1 (January 1, 1988): 57–65. http://dx.doi.org/10.1242/jcs.89.1.57.

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Mitotic Chinese hamster ovary cells were obtained by treatment with microtubule drugs under various conditions, and the shape of spindles was analysed by phase-contrast microscopy of isolated spindles, and by indirect immunofluorescence staining of whole mitotic cells with anti-tubulin antibody. Bipolarity of spindles was maintained after treatment with 0.05 microM of colcemid for 3.5 h, but increased exposure to higher concentrations (0.32 microM) and for longer durations (5.5 h) led to a marked rise in multipolar spindles. Nocodazole treatment, on the other hand, failed to show a multiplicity of spindle poles even at 3.3 microM. Each pole of a multipolar spindle was associated with pericentriolar material, as shown by staining with an autoimmune serum specific for pericentriolar material. The number of locations with free pericentriolar material capable of polymerizing microtubules in vitro also increased with increasing numbers of spindle poles, suggesting that dispersion of the pericentriolar material resulted in the production of many microtubule-nucleating sites in multipolar spindles. The different efficiencies of recovery from different drugs, which have been known to be quite variable, may be partly due to the different extent of dispersion of the pericentriolar material.

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Cross, Marie K., and Maureen A. Powers. "Nup98 regulates bipolar spindle assembly through association with microtubules and opposition of MCAK." Molecular Biology of the Cell 22, no. 5 (March 2011): 661–72. http://dx.doi.org/10.1091/mbc.e10-06-0478.

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During mitosis, the nuclear pore complex is disassembled and, increasingly, nucleoporins are proving to have mitotic functions when released from the pore. We find a contribution of the nucleoporin Nup98 to mitotic spindle assembly through regulation of microtubule dynamics. When added to Xenopus extract spindle assembly assays, the C-terminal domain of Nup98 stimulates uncontrolled growth of microtubules. Conversely, inhibition or depletion of Nup98 leads to formation of stable monopolar spindles. Spindle bipolarity is restored by addition of purified, recombinant Nup98 C-terminus. The minimal required region of Nup98 corresponds to a portion of the C-terminal domain lacking a previously characterized function. We show association between this region of the C-terminus of Nup98 and both Taxol-stabilized microtubules and the microtubule-depolymerizing mitotic centromere–associated kinesin (MCAK). Importantly, we demonstrate that this domain of Nup98 inhibits MCAK depolymerization activity in vitro. These data support a model in which Nup98 interacts with microtubules and antagonizes MCAK activity, thus promoting bipolar spindle assembly.

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Ems-McClung, Stephanie C., Kathleen M. Hertzer, Xin Zhang, Mill W. Miller, and Claire E. Walczak. "The Interplay of the N- and C-Terminal Domains of MCAK Control Microtubule Depolymerization Activity and Spindle Assembly." Molecular Biology of the Cell 18, no. 1 (January 2007): 282–94. http://dx.doi.org/10.1091/mbc.e06-08-0724.

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Spindle assembly and accurate chromosome segregation require the proper regulation of microtubule dynamics. MCAK, a Kinesin-13, catalytically depolymerizes microtubules, regulates physiological microtubule dynamics, and is the major catastrophe factor in egg extracts. Purified GFP-tagged MCAK domain mutants were assayed to address how the different MCAK domains contribute to in vitro microtubule depolymerization activity and physiological spindle assembly activity in egg extracts. Our biochemical results demonstrate that both the neck and the C-terminal domain are necessary for robust in vitro microtubule depolymerization activity. In particular, the neck is essential for microtubule end binding, and the C-terminal domain is essential for tight microtubule binding in the presence of excess tubulin heterodimer. Our physiological results illustrate that the N-terminal domain is essential for regulating microtubule dynamics, stimulating spindle bipolarity, and kinetochore targeting; whereas the C-terminal domain is necessary for robust microtubule depolymerization activity, limiting spindle bipolarity, and enhancing kinetochore targeting. Unexpectedly, robust MCAK microtubule (MT) depolymerization activity is not needed for sperm-induced spindle assembly. However, high activity is necessary for proper physiological MT dynamics as assayed by Ran-induced aster assembly. We propose that MCAK activity is spatially controlled by an interplay between the N- and C-terminal domains during spindle assembly.

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Mountain, Vicki, Calvin Simerly, Louisa Howard, Asako Ando, Gerald Schatten, and Duane A. Compton. "The Kinesin-Related Protein, Hset, Opposes the Activity of Eg5 and Cross-Links Microtubules in the Mammalian Mitotic Spindle." Journal of Cell Biology 147, no. 2 (October 18, 1999): 351–66. http://dx.doi.org/10.1083/jcb.147.2.351.

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We have prepared antibodies specific for HSET, the human homologue of the KAR3 family of minus end-directed motors. Immuno-EM with these antibodies indicates that HSET frequently localizes between microtubules within the mammalian metaphase spindle consistent with a microtubule cross-linking function. Microinjection experiments show that HSET activity is essential for meiotic spindle organization in murine oocytes and taxol-induced aster assembly in cultured cells. However, inhibition of HSET did not affect mitotic spindle architecture or function in cultured cells, indicating that centrosomes mask the role of HSET during mitosis. We also show that (acentrosomal) microtubule asters fail to assemble in vitro without HSET activity, but simultaneous inhibition of HSET and Eg5, a plus end-directed motor, redresses the balance of forces acting on microtubules and restores aster organization. In vivo, centrosomes fail to separate and monopolar spindles assemble without Eg5 activity. Simultaneous inhibition of HSET and Eg5 restores centrosome separation and, in some cases, bipolar spindle formation. Thus, through microtubule cross-linking and oppositely oriented motor activity, HSET and Eg5 participate in spindle assembly and promote spindle bipolarity, although the activity of HSET is not essential for spindle assembly and function in cultured cells because of centrosomes.

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Sluder, G., E. A. Thompson, F. J. Miller, J. Hayes, and C. L. Rieder. "The checkpoint control for anaphase onset does not monitor excess numbers of spindle poles or bipolar spindle symmetry." Journal of Cell Science 110, no. 4 (February 15, 1997): 421–29. http://dx.doi.org/10.1242/jcs.110.4.421.

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Exit from mitosis in animal cells is substantially delayed when spindle assembly is inhibited, spindle bipolarity is disrupted, or when a monopolar spindle is formed. These observations have led to the proposal that animal cells have a ‘spindle assembly’ checkpoint for the metaphase-anaphase transition that monitors bipolar spindle organization. However, the existence of such a checkpoint is uncertain because perturbations in spindle organization can produce unattached kinetochores, which by themselves are known to delay anaphase onset. In this study we have tested if cells monitor bipolar spindle organization, independent of kinetochore attachment, by analyzing the duration of mitosis in sea urchin zygotes and vertebrate somatic cells containing multipolar spindles in which all kinetochores are attached to spindle poles. We found that sea urchin zygotes containing tripolar or tetrapolar spindles progressed from nuclear envelope breakdown to anaphase onset with normal timing. We also found that the presence of supernumerary, unpaired spindle poles did not greatly prolong mitosis. Observation of untreated PtK1 cells that formed tripolar or tetrapolar spindles revealed that they progressed through mitosis, on average, at the normal rate. More importantly, the interval between the bipolar attachment of the last monooriented chromosome and anaphase onset was normal. Thus, neither of these cell types can detect the presence of gross aberrations in spindle architecture that inevitably lead to aneuploidy. We conclude that animal cells do not have a checkpoint for the metaphase-anaphase transition that monitors defects in spindle architecture independent of the checkpoint that monitors kinetochore attachment to the spindle. For dividing cells in which spindle microtubule assembly is not experimentally compromised, we propose that the completion of kinetochore attachment is the event which limits the time of the metaphase-anaphase transition.

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Wilde, Andrew. "“HURP on” we're off to the kinetochore!" Journal of Cell Biology 173, no. 6 (June 19, 2006): 829–31. http://dx.doi.org/10.1083/jcb.200605150.

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RanGTP has a central role in spindle assembly, but the Ran-regulated factors required to initiate spindle bipolarity and stabilize MT growth toward the chromosomes remain unknown. However, three recent papers (Koffa et al., 2006; Sillje et al., 2006; Wong and Fang, 2006) have identified a single factor, HURP, that may encompass both of these properties.

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Hashimoto, Kaho, Takumi Chinen, and Daiju Kitagawa. "Mechanisms of spindle bipolarity establishment in acentrosomal human cells." Molecular & Cellular Oncology 7, no. 3 (April 3, 2020): 1743899. http://dx.doi.org/10.1080/23723556.2020.1743899.

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Zhang, Jingjing, Maoqing Wu, Shixuan Wang, Jagesh V. Shah, Patricia D. Wilson, and Jing Zhou. "Polycystic kidney disease protein fibrocystin localizes to the mitotic spindle and regulates spindle bipolarity." Human Molecular Genetics 19, no. 17 (June 16, 2010): 3306–19. http://dx.doi.org/10.1093/hmg/ddq233.

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30

Wang, Ya-Peng, Shu-Tao Qi, Yanchang Wei, Zhao-Jia Ge, Lei Chen, Yi Hou, Ying-Chun Ouyang, Heide Schatten, Jian-Guo Zhao, and Qing-Yuan Sun. "Knockdown of UCHL5IP causes abnormalities in γ-tubulin localisation, spindle organisation and chromosome alignment in mouse oocyte meiotic maturation." Reproduction, Fertility and Development 25, no. 3 (2013): 495. http://dx.doi.org/10.1071/rd12300.

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UCHL5IP is one of the subunits of the haus complex, which is important for microtubule generation, spindle bipolarity and accurate chromosome segregation in Drosophila and human mitotic cells. In this study, the expression and localisation of UCHL5IP were explored, as well as its functions in mouse oocyte meiotic maturation. The results showed that the UCHL5IP protein level was consistent during oocyte maturation and it was localised to the meiotic spindle in MI and MII stages. Knockdown of UCHL5IP led to spindle defects, chromosome misalignment and disruption of γ-tubulin localisation in the spindle poles. These results suggest that UCHL5IP plays critical roles in spindle formation during mouse oocyte meiotic maturation.

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Wilson, P. G., M. T. Fuller, and G. G. Borisy. "Monastral bipolar spindles: implications for dynamic centrosome organization." Journal of Cell Science 110, no. 4 (February 15, 1997): 451–64. http://dx.doi.org/10.1242/jcs.110.4.451.

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Implicit to all models for mitotic spindle assembly is the view that centrosomes are essentially permanent structures. Yet, immunofluorescence revealed that spindles in larval brains of urchin mutants in Drosophila were frequently monastral but bipolar; the astral pole contained a centrosome while the opposing anastral pole showed neither gamma tubulin nor a radial array of astral microtubules. Thus, mutations in the urchin gene seem to uncouple centrosome organization and spindle bipolarity in mitotic cells. Hypomorphic mutants showed a high frequency of monastral bipolar spindles but low frequencies of polyploidy, suggesting that monastral bipolar spindles might be functional. To test this hypothesis, we performed pedigree analysis of centrosome distribution and spindle structure in the four mitotic divisions of gonial cells. Prophase gonial cells showed two centrosomes, suggesting cells entered mitosis with the normal number of centrosomes and that centrosomes separated during prophase. Despite a high frequency of monastral bipolar spindles, the end products of the four mitotic divisions were equivalent in size and chromatin content. These results indicate that monastral bipolar spindles are functional and that the daughter cell derived from the anastral pole can assemble a functional bipolar spindle in the subsequent cell cycle. Cell proliferation despite high frequencies of monastral bipolar spindles can be explained if centrosome structure in mitotic cells is dynamic, allowing transient and benign disorganization of pericentriolar components. Since urchin proved to be allelic to KLP61F which encodes a kinesin related motor protein (Heck et al. (1993) J. Cell Biol. 123, 665–671), our results suggest that motors influence the dynamic organization of centrosomes.

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Jin, Zhe‐Long, Namgoong Suk, and Nam‐Hyung Kim. "TP53BP1 regulates chromosome alignment and spindle bipolarity in mouse oocytes." Molecular Reproduction and Development 86, no. 9 (July 2, 2019): 1126–37. http://dx.doi.org/10.1002/mrd.23228.

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Shao, Hua, Chunqi Ma, Xuan Zhang, Ruizhen Li, Ann L. Miller, William M. Bement, and X. Johné Liu. "Aurora B regulates spindle bipolarity in meiosis in vertebrate oocytes." Cell Cycle 11, no. 14 (January 15, 2012): 2672–80. http://dx.doi.org/10.4161/cc.21016.

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Chan, A., and W. Z. Cande. "Maize meiotic spindles assemble around chromatin and do not require paired chromosomes." Journal of Cell Science 111, no. 23 (December 1, 1998): 3507–15. http://dx.doi.org/10.1242/jcs.111.23.3507.

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To understand how the meiotic spindle is formed and maintained in higher plants, we studied the organization of microtubule arrays in wild-type maize meiocytes and three maize meiotic mutants, desynaptic1 (dsy1), desynaptic2 (dsy2), and absence of first division (afd). All three meiotic mutations have abnormal chromosome pairing and produce univalents by diakinesis. Using these three mutants, we investigated how the absence of paired homologous chromosomes affects the assembly and maintenance of the meiotic spindle. Before nuclear envelope breakdown, in wild-type meiocytes, there were no bipolar microtubule arrays. Instead, these structures formed after nuclear envelope breakdown and were associated with the chromosomes. The presence of univalent chromosomes in dsy1, dsy2, and afd meiocytes and of unpaired sister chromatids in the afd meiocytes did not affect the formation of bipolar spindles. However, alignment of chromosomes on the metaphase plate and subsequent anaphase chromosome segregation were perturbed. We propose a model for spindle formation in maize meiocytes in which microtubules initially appear around the chromosomes during prometaphase and then the microtubules self-organize. However, this process does not require paired kinetochores to establish spindle bipolarity.

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Breuer, Manuel, Agnieszka Kolano, Mijung Kwon, Chao-Chin Li, Ting-Fen Tsai, David Pellman, Stéphane Brunet, and Marie-Hélène Verlhac. "HURP permits MTOC sorting for robust meiotic spindle bipolarity, similar to extra centrosome clustering in cancer cells." Journal of Cell Biology 191, no. 7 (December 20, 2010): 1251–60. http://dx.doi.org/10.1083/jcb.201005065.

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In contrast to somatic cells, formation of acentriolar meiotic spindles relies on the organization of microtubules (MTs) and MT-organizing centers (MTOCs) into a stable bipolar structure. The underlying mechanisms are still unknown. We show that this process is impaired in hepatoma up-regulated protein (Hurp) knockout mice, which are viable but female sterile, showing defective oocyte divisions. HURP accumulates on interpolar MTs in the vicinity of chromosomes via Kinesin-5 activity. By promoting MT stability in the spindle central domain, HURP allows efficient MTOC sorting into distinct poles, providing bipolarity establishment and maintenance. Our results support a new model for meiotic spindle assembly in which HURP ensures assembly of a central MT array, which serves as a scaffold for the genesis of a robust bipolar structure supporting efficient chromosome congression. Furthermore, HURP is also required for the clustering of extra centrosomes before division, arguing for a shared molecular requirement of MTOC sorting in mammalian meiosis and cancer cell division.

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36

Rasamizafy, Sylvia Fenosoa, Claude Delsert, Gabriel Rabeharivelo, Julien Cau, Nathalie Morin, and Juliette van Dijk. "Mitotic Acetylation of Microtubules Promotes Centrosomal PLK1 Recruitment and Is Required to Maintain Bipolar Spindle Homeostasis." Cells 10, no. 8 (July 22, 2021): 1859. http://dx.doi.org/10.3390/cells10081859.

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Tubulin post-translational modifications regulate microtubule properties and functions. Mitotic spindle microtubules are highly modified. While tubulin detyrosination promotes proper mitotic progression by recruiting specific microtubule-associated proteins motors, tubulin acetylation that occurs on specific microtubule subsets during mitosis is less well understood. Here, we show that siRNA-mediated depletion of the tubulin acetyltransferase ATAT1 in epithelial cells leads to a prolonged prometaphase arrest and the formation of monopolar spindles. This results from collapse of bipolar spindles, as previously described in cells deficient for the mitotic kinase PLK1. ATAT1-depleted mitotic cells have defective recruitment of PLK1 to centrosomes, defects in centrosome maturation and thus microtubule nucleation, as well as labile microtubule-kinetochore attachments. Spindle bipolarity could be restored, in the absence of ATAT1, by stabilizing microtubule plus-ends or by increasing PLK1 activity at centrosomes, demonstrating that the phenotype is not just a consequence of lack of K-fiber stability. We propose that microtubule acetylation of K-fibers is required for a recently evidenced cross talk between centrosomes and kinetochores.

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Marcus, A. I., W. Li, H. Ma, and R. J. Cyr. "A Kinesin Mutant with an Atypical Bipolar Spindle Undergoes Normal Mitosis." Molecular Biology of the Cell 14, no. 4 (April 2003): 1717–26. http://dx.doi.org/10.1091/mbc.e02-09-0586.

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Motor proteins have been implicated in various aspects of mitosis, including spindle assembly and chromosome segregation. Here, we show that acentrosomal Arabidopsis cells that are mutant for the kinesin, ATK1, lack microtubule accumulation at the predicted spindle poles during prophase and have reduced spindle bipolarity during prometaphase. Nonetheless, all abnormalities are rectified by anaphase and chromosome segregation appears normal. We conclude that ATK1 is required for normal microtubule accumulation at the spindle poles during prophase and possibly functions in spindle assembly during prometaphase. Because aberrant spindle morphology in these mutants is resolved by anaphase, we postulate that mitotic plant cells contain an error-correcting mechanism. Moreover, ATK1 function seems to be dosage-dependent, because cells containing one wild-type allele take significantly longer to proceed to anaphase as compared with cells containing two wild-type alleles.

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Matthies, H. J., H. B. McDonald, L. S. Goldstein, and W. E. Theurkauf. "Anastral meiotic spindle morphogenesis: role of the non-claret disjunctional kinesin-like protein." Journal of Cell Biology 134, no. 2 (July 15, 1996): 455–64. http://dx.doi.org/10.1083/jcb.134.2.455.

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We have used time-lapse laser scanning confocal microscopy to directly examine microtubule reorganization during meiotic spindle assembly in living Drosophila oocytes. These studies indicate that the bipolarity of the meiosis I spindle is not the result of a duplication and separation of centrosomal microtubule organizing centers (MTOCs). Instead, microtubules first associate with a tight chromatin mass, and then bundle to form a bipolar spindle that lacks asters. Analysis of mutant oocytes indicates that the Non-Claret Disjunctional (NCD) kinesin-like protein is required for normal spindle assembly kinetics and stabilization of the spindle during metaphase arrest. Immunolocalization analyses demonstrate that NCD is associated with spindle microtubules, and that the centrosomal components gamma-tubulin, CP-190, and CP-60 are not concentrated at the meiotic spindle poles. Based on these observations, we propose that microtubule bundling by the NCD kinesin-like protein promotes assembly of a stable bipolar spindle in the absence of typical MTOCs.

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39

Petry, S., C. Pugieux, F. J. Nedelec, and R. D. Vale. "Augmin promotes meiotic spindle formation and bipolarity in Xenopus egg extracts." Proceedings of the National Academy of Sciences 108, no. 35 (August 15, 2011): 14473–78. http://dx.doi.org/10.1073/pnas.1110412108.

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40

Oshimori, Naoki, Miho Ohsugi, and Tadashi Yamamoto. "The Plk1 target Kizuna stabilizes mitotic centrosomes to ensure spindle bipolarity." Nature Cell Biology 8, no. 10 (September 17, 2006): 1095–101. http://dx.doi.org/10.1038/ncb1474.

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41

Goshima, Gohta, Mirjam Mayer, Nan Zhang, Nico Stuurman, and Ronald D. Vale. "Augmin: a protein complex required for centrosome-independent microtubule generation within the spindle." Journal of Cell Biology 181, no. 3 (April 28, 2008): 421–29. http://dx.doi.org/10.1083/jcb.200711053.

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Since the discovery of γ-tubulin, attention has focused on its involvement as a microtubule nucleator at the centrosome. However, mislocalization of γ-tubulin away from the centrosome does not inhibit mitotic spindle formation in Drosophila melanogaster, suggesting that a critical function for γ-tubulin might reside elsewhere. A previous RNA interference (RNAi) screen identified five genes (Dgt2–6) required for localizing γ-tubulin to spindle microtubules. We show that the Dgt proteins interact, forming a stable complex. We find that spindle microtubule generation is substantially reduced after knockdown of each Dgt protein by RNAi. Thus, the Dgt complex that we name “augmin” functions to increase microtubule number. Reduced spindle microtubule generation after augmin RNAi, particularly in the absence of functional centrosomes, has dramatic consequences on mitotic spindle formation and function, leading to reduced kinetochore fiber formation, chromosome misalignment, and spindle bipolarity defects. We also identify a functional human homologue of Dgt6. Our results suggest that an important mitotic function for γ-tubulin may lie within the spindle, where augmin and γ-tubulin function cooperatively to amplify the number of microtubules.

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Schuyler, Scott C., Jenny Y. Liu, and David Pellman. "The molecular function of Ase1p." Journal of Cell Biology 160, no. 4 (February 17, 2003): 517–28. http://dx.doi.org/10.1083/jcb.200210021.

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The midzone is the domain of the mitotic spindle that maintains spindle bipolarity during anaphase and generates forces required for spindle elongation (anaphase B). Although there is a clear role for microtubule (MT) motor proteins at the spindle midzone, less is known about how microtubule-associated proteins (MAPs) contribute to midzone organization and function. Here, we report that budding yeast Ase1p is a member of a conserved family of midzone-specific MAPs. By size exclusion chromatography and velocity sedimentation, both Ase1p in extracts and purified Ase1p behaved as a homodimer. Ase1p bound and bundled MTs in vitro. By live cell microscopy, loss of Ase1p resulted in a specific defect: premature spindle disassembly in mid-anaphase. Furthermore, when overexpressed, Ase1p was sufficient to trigger spindle elongation in S phase–arrested cells. FRAP revealed that Ase1p has both a very slow rate of turnover within the midzone and limited lateral diffusion along spindle MTs. We propose that Ase1p functions as an MT cross-bridge that imparts matrix-like characteristics to the midzone. MT-dependent networks of spindle midzone MAPs may be one molecular basis for the postulated spindle matrix.

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43

Hong, Kyung Uk, Young Soo Park, Yeon-Sun Seong, Dongmin Kang, Chang-Dae Bae, and Joobae Park. "Functional Importance of the Anaphase-Promoting Complex-Cdh1-Mediated Degradation of TMAP/CKAP2 in Regulation of Spindle Function and Cytokinesis." Molecular and Cellular Biology 27, no. 10 (March 5, 2007): 3667–81. http://dx.doi.org/10.1128/mcb.01386-06.

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ABSTRACT Cytoskeleton-associated protein 2 (CKAP2), also known as tumor-associated microtubule-associated protein (TMAP), is a novel microtubule-associated protein that is frequently upregulated in various malignances. However, its cellular functions remain unknown. A previous study has shown that its protein level begins to increase during G1/S and peaks at G2/M, after which it decreases abruptly. Ectopic overexpression of TMAP/CKAP2 induced microtubule bundling related to increased microtubule stability. TMAP/CKAP2 overexpression also resulted in cell cycle arrest during mitosis due to a defect in centrosome separation and subsequent formation of a monopolar spindle. We also show that degradation of TMAP/CKAP2 during mitotic exit is mediated by the anaphase-promoting complex bound to Cdh1 and that the KEN box motif near the N terminus is necessary for its destruction. Compared to the wild type, expression of a nondegradable mutant of TMAP/CKAP2 significantly increased the occurrence of spindle defects and cytokinesis failure. These results suggest that TMAP/CKAP2 plays a role in the assembly and maintenance of mitotic spindles, presumably by regulating microtubule dynamics, and its destruction during mitotic exit serves an important role in the completion of cytokinesis and in the maintenance of spindle bipolarity in the next mitosis.

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Yukawa, Masashi, Chiho Ikebe, and Takashi Toda. "The Msd1–Wdr8–Pkl1 complex anchors microtubule minus ends to fission yeast spindle pole bodies." Journal of Cell Biology 209, no. 4 (May 18, 2015): 549–62. http://dx.doi.org/10.1083/jcb.201412111.

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The minus ends of spindle microtubules are anchored to a microtubule-organizing center. The conserved Msd1/SSX2IP proteins are localized to the spindle pole body (SPB) and the centrosome in fission yeast and humans, respectively, and play a critical role in microtubule anchoring. In this paper, we show that fission yeast Msd1 forms a ternary complex with another conserved protein, Wdr8, and the minus end–directed Pkl1/kinesin-14. Individual deletion mutants displayed the identical spindle-protrusion phenotypes. Msd1 and Wdr8 were delivered by Pkl1 to mitotic SPBs, where Pkl1 was tethered through Msd1–Wdr8. The spindle-anchoring defect imposed by msd1/wdr8/pkl1 deletions was suppressed by a mutation of the plus end–directed Cut7/kinesin-5, which was shown to be mutual. Intriguingly, Pkl1 motor activity was not required for its anchoring role once targeted to the SPB. Therefore, spindle anchoring through Msd1–Wdr8–Pkl1 is crucial for balancing the Cut7/kinesin-5–mediated outward force at the SPB. Our analysis provides mechanistic insight into the spatiotemporal regulation of two opposing kinesins to ensure mitotic spindle bipolarity.

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Vanneste, David, Masatoshi Takagi, Naoko Imamoto, and Isabelle Vernos. "The Role of Hklp2 in the Stabilization and Maintenance of Spindle Bipolarity." Current Biology 19, no. 20 (November 2009): 1712–17. http://dx.doi.org/10.1016/j.cub.2009.09.019.

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Colombié, Nathalie, Christel Vérollet, Paula Sampaio, André Moisand, Claudio Sunkel, Henri-Marc Bourbon, Michel Wright, and Brigitte Raynaud-Messina. "The Drosophila γ-Tubulin Small Complex Subunit Dgrip84 Is Required for Structural and Functional Integrity of the Spindle Apparatus." Molecular Biology of the Cell 17, no. 1 (January 2006): 272–82. http://dx.doi.org/10.1091/mbc.e05-08-0722.

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γ-Tubulin, a protein critical for microtubule assembly, functions within multiprotein complexes. However, little is known about the respective role of γ-tubulin partners in metazoans. For the first time in a multicellular organism, we have investigated the function of Dgrip84, the Drosophila orthologue of the Saccharomyces cerevisiae γ-tubulin-associated protein Spc97p. Mutant analysis shows that Dgrip84 is essential for viability. Its depletion promotes a moderate increase in the mitotic index, correlated with the appearance of monopolar or unpolarized spindles, impairment of centrosome maturation, and increase of polyploid nuclei. This in vivo study is strengthened by an RNA interference approach in cultured S2 cells. Electron microscopy analysis suggests that monopolar spindles might result from a failure of centrosome separation and an unusual microtubule assembly pathway via centriolar triplets. Moreover, we point to an involvement of Dgrip84 in the spindle checkpoint regulation and in the maintenance of interphase microtubule dynamics. Dgrip84 also seems essential for male meiosis, ensuring spindle bipolarity and correct completion of cytokinesis. These data sustain that Dgrip84 is required in some aspects of microtubule dynamics and organization both in interphase and mitosis. The nature of a minimal γ-tubulin complex necessary for proper microtubule organization in the metazoans is discussed.

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McClelland, Sarah E., Satyarebala Borusu, Ana C. Amaro, Jennifer R. Winter, Mukta Belwal, Andrew D. McAinsh, and Patrick Meraldi. "The CENP-A NAC/CAD kinetochore complex controls chromosome congression and spindle bipolarity." EMBO Journal 26, no. 24 (November 15, 2007): 5033–47. http://dx.doi.org/10.1038/sj.emboj.7601927.

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Mayer, T. U. "Small Molecule Inhibitor of Mitotic Spindle Bipolarity Identified in a Phenotype-Based Screen." Science 286, no. 5441 (October 29, 1999): 971–74. http://dx.doi.org/10.1126/science.286.5441.971.

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Mann, Barbara J., Sai K. Balchand, and Patricia Wadsworth. "Regulation of Kif15 localization and motility by the C-terminus of TPX2 and microtubule dynamics." Molecular Biology of the Cell 28, no. 1 (January 2017): 65–75. http://dx.doi.org/10.1091/mbc.e16-06-0476.

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Mitotic motor proteins generate force to establish and maintain spindle bipolarity, but how they are temporally and spatially regulated in vivo is unclear. Prior work demonstrated that a microtubule-associated protein, TPX2, targets kinesin-5 and kinesin-12 motors to spindle microtubules. The C-terminal domain of TPX2 contributes to the localization and motility of the kinesin-5, Eg5, but it is not known whether this domain regulates kinesin-12, Kif15. We found that the C-terminal domain of TPX2 contributes to the localization of Kif15 to spindle microtubules in cells and suppresses motor walking in vitro. Kif15 and Eg5 are partially redundant motors, and overexpressed Kif15 can drive spindle formation in the absence of Eg5 activity. Kif15-dependent bipolar spindle formation in vivo requires the C-terminal domain of TPX2. In the spindle, fluorescent puncta of GFP-Kif15 move toward the equatorial region at a rate equivalent to microtubule growth. Reduction of microtubule growth with paclitaxel suppresses GFP-Kif15 motility, demonstrating that dynamic microtubules contribute to Kif15 behavior. Our results show that the C-terminal region of TPX2 regulates Kif15 in vitro, contributes to motor localization in cells, and is required for Kif15 force generation in vivo and further reveal that dynamic microtubules contribute to Kif15 behavior in vivo.

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Al-Obaidi, Naowras, Timothy J. Mitchison, Craig M. Crews, and Thomas U. Mayer. "Identification of MAC1: A Small Molecule That Rescues Spindle Bipolarity in Monastrol-Treated Cells." ACS Chemical Biology 11, no. 6 (April 28, 2016): 1544–51. http://dx.doi.org/10.1021/acschembio.6b00203.

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Journal articles on the topic 'Spindle bipolarity'

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