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McIntosh JR. Anaphase A. Semin Cell Dev Biol 2021; 117:118-126. [PMID: 33781672 DOI: 10.1016/j.semcdb.2021.03.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 03/16/2021] [Accepted: 03/16/2021] [Indexed: 10/21/2022]
Abstract
Anaphase A is the motion of recently separated chromosomes to the spindle pole they face. It is accompanied by the shortening of kinetochore-attached microtubules. The requisite tubulin depolymerization may occur at kinetochores, at poles, or both, depending on the species and/or the time in mitosis. These depolymerization events are local and suggest that cells regulate microtubule dynamics in specific places, presumably by the localization of relevant enzymes and microtubule-associated proteins to specific loci, such as pericentriolar material and outer kinetochores. Motor enzymes can contribute to anaphase A, both by altering microtubule stability and by pushing or pulling microtubules through the cell. The generation of force on chromosomes requires couplings that can both withstand the considerable force that spindles can generate and simultaneously permit tubulin addition and loss. This chapter reviews literature on the molecules that regulate anaphase microtubule dynamics, couple dynamic microtubules to kinetochores and poles, and generate forces for microtubule and chromosome motion.
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Affiliation(s)
- J Richard McIntosh
- Dept. of Molecular, Cellular, and Developmental Biology University of Colorado, Boulder, CO 80309-0347, USA.
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2
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Tolic´ IM, Pavin N. Mitotic spindle: lessons from theoretical modeling. Mol Biol Cell 2021; 32:218-222. [PMID: 33507108 PMCID: PMC8098832 DOI: 10.1091/mbc.e20-05-0335] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Revised: 11/23/2020] [Accepted: 11/24/2020] [Indexed: 11/16/2022] Open
Abstract
Cell biology is immensely complex. To understand how cells work, we try to find patterns and suggest hypotheses to identify underlying mechanisms. However, it is not always easy to create a coherent picture from a huge amount of experimental data on biological systems, where the main players have multiple interactions or act in redundant pathways. In such situations, when a hypothesis does not lead to a conclusion in a direct way, theoretical modeling is a powerful tool because it allows us to formulate hypotheses in a quantitative manner and understand their consequences. A successful model should not only reproduce the basic features of the system but also provide exciting predictions, motivating new experiments. Much is learned when a model based on generally accepted knowledge cannot explain experiments of interest, as this indicates that the original hypothesis needs to be revised. In this Perspective, we discuss these points using our experiences in combining experiments with theory in the field of mitotic spindle mechanics.
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Affiliation(s)
- Iva M. Tolic´
- Division of Molecular Biology, Rud¯er Boškovic´ Institute, 10000 Zagreb, Croatia
| | - Nenad Pavin
- Department of Physics, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia
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O'Toole E, Morphew M, McIntosh JR. Electron tomography reveals aspects of spindle structure important for mechanical stability at metaphase. Mol Biol Cell 2019; 31:184-195. [PMID: 31825721 PMCID: PMC7001478 DOI: 10.1091/mbc.e19-07-0405] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Metaphase spindles exert pole-directed forces on still-connected sister kinetochores. The spindle must counter these forces with extensive forces to prevent spindle collapse. In small spindles, kinetochore microtubules (KMTs) connect directly with the poles, and countering forces are supplied either by interdigitating MTs that form interpolar bundles or by astral MTs connected to the cell cortex. In bigger spindles, particularly those without structured poles, the origin of extensive forces is less obvious. We have used electron tomography of well-preserved metaphase cells to obtain structural evidence about interactions among different classes of MTs in metaphase spindles from Chlamydomonas rheinhardti and two strains of cultured mammalian cells. In all these spindles, KMTs approach close to and cross-bridge with the minus ends of non-KMTs, which form a framework that interdigitates near the spindle equator. Although this structure is not pole-connected, its organization suggests that it can support kinetochore tension. Analogous arrangements of MTs have been seen in even bigger spindles, such as metaphase spindles in Haemanthus endosperm and frog egg extracts. We present and discuss a hypothesis that rationalizes changes in spindle design with spindle size based on the negative exponential distribution of MT lengths in dynamically unstable populations of tubulin polymers.
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Affiliation(s)
- Eileen O'Toole
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Boulder, CO 80309
| | - Mary Morphew
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Boulder, CO 80309
| | - J Richard McIntosh
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Boulder, CO 80309
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Tolić IM. Mitotic spindle: kinetochore fibers hold on tight to interpolar bundles. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2018; 47:191-203. [PMID: 28725997 PMCID: PMC5845649 DOI: 10.1007/s00249-017-1244-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Revised: 06/30/2017] [Accepted: 07/02/2017] [Indexed: 12/24/2022]
Abstract
When a cell starts to divide, it forms a spindle, a micro-machine made of microtubules, which separates the duplicated chromosomes. The attachment of microtubules to chromosomes is mediated by kinetochores, protein complexes on the chromosome. Spindle microtubules can be divided into three major classes: kinetochore microtubules, which form k-fibers ending at the kinetochore; interpolar microtubules, which extend from the opposite sides of the spindle and interact in the middle; and astral microtubules, which extend towards the cell cortex. Recent work in human cells has shown a close relationship between interpolar and kinetochore microtubules, where interpolar bundles are attached laterally to kinetochore fibers almost all along their length, acting as a bridge between sister k-fibers. Most of the interpolar bundles are attached to a pair of sister kinetochore fibers and vice versa. Thus, the spindle is made of modules consisting of a pair of sister kinetochore fibers and a bundle of interpolar microtubules that connects them. These interpolar bundles, termed bridging fibers, balance the forces acting at kinetochores and support the rounded shape of the spindle during metaphase. This review discusses the structure, function, and formation of kinetochore fibers and interpolar bundles, with an emphasis on how they interact. Their connections have an impact on the force balance in the spindle and on chromosome movement during mitosis because the forces in interpolar bundles are transmitted to kinetochore fibers and hence to kinetochores through these connections.
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Affiliation(s)
- Iva M Tolić
- Division of Molecular Biology, Ruđer Bošković Institute, Bijenička cesta 54, 10000, Zagreb, Croatia.
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5
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Affiliation(s)
- Nenad Pavin
- Department of Physics, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia;
| | - Iva M. Tolić
- Division of Molecular Biology, Ruđer Bošković Institute, 10000 Zagreb, Croatia;
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Affiliation(s)
- Iva M Tolić
- a Division of Molecular Biology, Ruđer Bošković Institute , Zagreb , Croatia
| | - Nenad Pavin
- b Department of Physics , Faculty of Science, University of Zagreb , Zagreb , Croatia
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7
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Overlap microtubules link sister k-fibres and balance the forces on bi-oriented kinetochores. Nat Commun 2016; 7:10298. [PMID: 26728792 PMCID: PMC4728446 DOI: 10.1038/ncomms10298] [Citation(s) in RCA: 93] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 11/26/2015] [Indexed: 02/04/2023] Open
Abstract
During metaphase, forces on kinetochores are exerted by k-fibres, bundles of microtubules that end at the kinetochore. Interestingly, non-kinetochore microtubules have been observed between sister kinetochores, but their function is unknown. Here we show by laser-cutting of a k-fibre in HeLa and PtK1 cells that a bundle of non-kinetochore microtubules, which we term ‘bridging fibre', bridges sister k-fibres and balances the interkinetochore tension. We found PRC1 and EB3 in the bridging fibre, suggesting that it consists of antiparallel dynamic microtubules. By using a theoretical model that includes a bridging fibre, we show that the forces at the pole and at the kinetochore depend on the bridging fibre thickness. Moreover, our theory and experiments show larger relaxation of the interkinetochore distance for cuts closer to kinetochores. We conclude that the bridging fibre, by linking sister k-fibres, withstands the tension between sister kinetochores and enables the spindle to obtain a curved shape. During metaphase, k-fibre microtubules exert force on kinetochores, but there are also non-kinetochore microtubules close to kinetochores without a known function. Here the authors show that these microtubules, which they call bridging fibres, balance interkinetochore tension by bridging sister k-fibres.
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Wanner G, Schroeder-Reiter E, Ma W, Houben A, Schubert V. The ultrastructure of mono- and holocentric plant centromeres: an immunological investigation by structured illumination microscopy and scanning electron microscopy. Chromosoma 2015; 124:503-17. [DOI: 10.1007/s00412-015-0521-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2015] [Revised: 05/12/2015] [Accepted: 05/18/2015] [Indexed: 11/29/2022]
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Khatibzadeh N, Stilgoe AB, Bui AAM, Rocha Y, Cruz GM, Loke V, Shi LZ, Nieminen TA, Rubinsztein-Dunlop H, Berns MW. Determination of motility forces on isolated chromosomes with laser tweezers. Sci Rep 2014; 4:6866. [PMID: 25359514 PMCID: PMC4215326 DOI: 10.1038/srep06866] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Accepted: 10/13/2014] [Indexed: 12/14/2022] Open
Abstract
Quantitative determination of the motility forces of chromosomes during cell division is fundamental to understanding a process that is universal among eukaryotic organisms. Using an optical tweezers system, isolated mammalian chromosomes were held in a 1064 nm laser trap. The minimum force required to move a single chromosome was determined to be ≈ 0.8-5 pN. The maximum transverse trapping efficiency of the isolated chromosomes was calculated as ≈ 0.01-0.02. These results confirm theoretical force calculations of ≈ 0.1-12 pN to move a chromosome on the mitotic or meiotic spindle. The verification of these results was carried out by calibration of the optical tweezers when trapping microspheres with a diameter of 4.5-15 µm in media with 1-7 cP viscosity. The results of the chromosome and microsphere trapping experiments agree with optical models developed to simulate trapping of cylindrical and spherical specimens.
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Affiliation(s)
- Nima Khatibzadeh
- Beckman Laser Institute and Medical Clinic, University of California, Irvine, 1002 Health Sciences Road, Irvine, CA 92612, USA
| | - Alexander B Stilgoe
- School of Mathematics and Physics, The University of Queensland, St. Lucia, QLD, 4072, Australia
| | - Ann A M Bui
- School of Mathematics and Physics, The University of Queensland, St. Lucia, QLD, 4072, Australia
| | - Yesenia Rocha
- Beckman Laser Institute and Medical Clinic, University of California, Irvine, 1002 Health Sciences Road, Irvine, CA 92612, USA
| | - Gladys M Cruz
- Beckman Laser Institute and Medical Clinic, University of California, Irvine, 1002 Health Sciences Road, Irvine, CA 92612, USA
| | - Vince Loke
- School of Mathematics and Physics, The University of Queensland, St. Lucia, QLD, 4072, Australia
| | - Linda Z Shi
- Institute of Engineering in Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
| | - Timo A Nieminen
- School of Mathematics and Physics, The University of Queensland, St. Lucia, QLD, 4072, Australia
| | | | - Michael W Berns
- 1] Beckman Laser Institute and Medical Clinic, University of California, Irvine, 1002 Health Sciences Road, Irvine, CA 92612, USA [2] Institute of Engineering in Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
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Interplay Between Spindle Architecture and Function. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 306:83-125. [DOI: 10.1016/b978-0-12-407694-5.00003-1] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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11
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Total centromere size and genome size are strongly correlated in ten grass species. Chromosome Res 2012; 20:403-12. [PMID: 22552915 PMCID: PMC3391362 DOI: 10.1007/s10577-012-9284-1] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Revised: 04/11/2012] [Accepted: 04/12/2012] [Indexed: 01/05/2023]
Abstract
It has been known for decades that centromere size varies across species, but the factors involved in setting centromere boundaries are unknown. As a means to address this question, we estimated centromere sizes in ten species of the grass family including rice, maize, and wheat, which diverged 60~80 million years ago and vary by 40-fold in genome size. Measurements were made using a broadly reactive antibody to rice centromeric histone H3 (CENH3). In species-wide comparisons, we found a clear linear relationship between total centromere size and genome size. Species with large genomes and few chromosomes tend to have the largest centromeres (e.g., rye) while species with small genomes and many chromosomes have the smallest centromeres (e.g., rice). However, within a species, centromere size is surprisingly uniform. We present evidence from three oat–maize addition lines that support this claim, indicating that each of three maize centromeres propagated in oat are not measurably different from each other. In the context of previously published data, our results suggest that the apparent correlation between chromosome and centromere size is incidental to a larger trend that reflects genome size. Centromere size may be determined by a limiting component mechanism similar to that described for Caenorhabditis elegans centrosomes.
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Dhonukshe P, Vischer N, Gadella TWJ. Contribution of microtubule growth polarity and flux to spindle assembly and functioning in plant cells. J Cell Sci 2006; 119:3193-205. [PMID: 16868032 DOI: 10.1242/jcs.03048] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The spindle occupies a central position in cell division as it builds up the chromosome-separating machine. Here we analysed the dynamics of spindle formation in acentrosomal plant cells by visualizing microtubules labelled with GFP-EB1, GFP-MAP4 and GFP-alpha-tubulin and chromosomes marked by the vital dye SYTO82. During prophase, few microtubules penetrate the nuclear area, followed by nuclear envelope disintegration. During prometaphase, microtubules invading the nuclear space develop a spindle axis from few bipolar microtubule bundles, which is followed by spindle assembly. Using a novel quantitative kymograph analysis based on Fourier transformation, we measured the microtubule growth trajectories of the entire dynamic metaphase spindle. Microtubules initiating from spindle poles either pass through the metaphase plate to form interpolar microtubule bundles or grow until they reach chromosomes. We also noticed a minor fraction of microtubules growing away from the chromosomes. Microtubules grow at 10 microm/minute both at the spindle equator and at the spindle poles. Photobleached marks created on metaphase and anaphase spindles revealed a poleward tubulin flux. During anaphase, the velocity of tubulin flux (2 microm/minute) equals the speed of chromatid-separation. With these findings we identified spatially coordinated microtubule growth dynamics and microtubule flux-based chromosome-separation as important facets of plant spindle operation.
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Affiliation(s)
- Pankaj Dhonukshe
- Section of Molecular Cytology and Centre for Advanced Microscopy, Swammerdam Institute for Life Sciences, University of Amsterdam, Kruislaan 316, 1098 SM Amsterdam, The Netherlands.
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Mitchison TJ. Mechanism and function of poleward flux in Xenopus extract meiotic spindles. Philos Trans R Soc Lond B Biol Sci 2005; 360:623-9. [PMID: 15897184 PMCID: PMC1569469 DOI: 10.1098/rstb.2004.1616] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In Xenopus extract meiotic spindles, microtubules slide continuously towards their minus ends, a process called poleward flux. This article discusses recent progress in determining the mechanism of poleward flux, and its functions in spindle organization and generating force on chromosomes. Bipolar organization is required for flux and inhibition of the mitotic kinesin Eg5 inhibits flux, suggesting the sliding force for flux is generated by Eg5 pushing anti-parallel microtubules apart. An important function of flux in spindle organization may be to transport minus ends nucleated at chromatin towards the pole. By pulling microtubules through attachment sites at kinetochores, flux may generate poleward force on metaphase chromosomes.
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Affiliation(s)
- T J Mitchison
- Department of Systems Biology, Harvard Medical School, Boston, MA, USA.
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Wolf KW, Mitchell A, Liu G. Centromere-Like Elements in Megaselia Spiracularis (Diptera: Phoridae): A Fine-Structure and Cytogenetic Study. Hereditas 2004. [DOI: 10.1111/j.1601-5223.1996.t01-1-00203.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Ohi R, Coughlin ML, Lane WS, Mitchison TJ. An inner centromere protein that stimulates the microtubule depolymerizing activity of a KinI kinesin. Dev Cell 2003; 5:309-21. [PMID: 12919681 DOI: 10.1016/s1534-5807(03)00229-6] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Mitosis requires precise control of microtubule dynamics. The KinI kinesin MCAK, a microtubule depolymerase, is critical for this regulation. In a screen to discover previously uncharacterized microtubule-associated proteins, we identified ICIS, a protein that stimulates MCAK activity in vitro. Consistent with this biochemical property, blocking ICIS function in Xenopus extracts with antibodies caused excessive microtubule growth and inhibited spindle formation. Prior to anaphase, ICIS localized in an MCAK-dependent manner to inner centromeres, the chromosomal region located in between sister kinetochores. From Xenopus extracts, ICIS coimmunoprecipitated MCAK and the inner centromere proteins INCENP and Aurora B, which are thought to promote chromosome biorientation. By immunoelectron microscopy, we found that ICIS is present on the surface of inner centromeres, placing it in an ideal location to depolymerize microtubules associated laterally with inner centromeres. At inner centromeres, MCAK-ICIS may destabilize these microtubules and provide a mechanism that prevents kinetochore-microtubule attachment errors.
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Affiliation(s)
- Ryoma Ohi
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
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Umesh TG, Ranganath RM. Ultrastructural Evidence for the Flawless Transmission of a Dicentric Chromosome in Aloe vera. L. CYTOLOGIA 2003. [DOI: 10.1508/cytologia.68.211] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Yu HG, Muszynski MG, Kelly Dawe R. The maize homologue of the cell cycle checkpoint protein MAD2 reveals kinetochore substructure and contrasting mitotic and meiotic localization patterns. J Biophys Biochem Cytol 1999; 145:425-35. [PMID: 10225945 PMCID: PMC2185073 DOI: 10.1083/jcb.145.3.425] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have identified a maize homologue of yeast MAD2, an essential component in the spindle checkpoint pathway that ensures metaphase is complete before anaphase begins. Combined immunolocalization of MAD2 and a recently cloned maize CENPC homologue indicates that MAD2 localizes to an outer domain of the prometaphase kinetochore. MAD2 staining was primarily observed on mitotic kinetochores that lacked attached microtubules; i.e., at prometaphase or when the microtubules were depolymerized with oryzalin. In contrast, the loss of MAD2 staining in meiosis was not correlated with initial microtubule attachment but was correlated with a measure of tension: the distance between homologous or sister kinetochores (in meiosis I and II, respectively). Further, the tension-sensitive 3F3/2 phosphoepitope colocalized, and was lost concomitantly, with MAD2 staining at the meiotic kinetochore. The mechanism of spindle assembly (discussed here with respect to maize mitosis and meiosis) is likely to affect the relative contributions of attachment and tension. We support the idea that MAD2 is attachment-sensitive and that tension stabilizes microtubule attachments.
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Affiliation(s)
- H G Yu
- Department of Botany, University of Georgia, Athens, Georgia 30602, USA
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McEwen BF, Ding Y, Heagle AB. Relevance of kinetochore size and microtubule-binding capacity for stable chromosome attachment during mitosis in PtK1 cells. Chromosome Res 1998; 6:123-32. [PMID: 9543015 DOI: 10.1023/a:1009239013215] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Chromosomes attach to the mitotic spindle via their kinetochores. The average number of spindle microtubules binding to each kinetochore varies with species, the stage of mitosis, and the length of time that the kinetochore has been attached to the spindle. In this report, we investigate how kinetochore microtubule number varies with kinetochore size and chromosome size in PtK1 cells. From an analysis of serial-section electron micrographs, we determined that the average surface area of metaphase, taxol-treated metaphase, and anaphase kinetochores is 0.16 +/- 0.05 microm2 (N = 181). Surprisingly, kinetochore microtubules are packed more densely on the smaller kinetochores, as seen by a reduction in the average spacing between kinetochore microtubules from 89 nm to 59 nm. Our interpretation of this result is that PtK1 cells require a minimum kinetochore microtubule-binding capacity for survival during repeated rounds of mitotic division. We estimate the lower limit to be 23 kinetochore microtubules and suggest that this capacity is required to ensure stable attachment during the dynamic and highly stochastic process of kinetochore fiber formation. There is a modest but statistically significant increase in kinetochore microtubule number with chromosome size, indicating that chromosome size is a minor determinant of kinetochore microtubule number.
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Affiliation(s)
- B F McEwen
- Division of Molecular Medicine, Wadsworth Center, New York State Department of Health, Albany 12201-0509, USA.
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McEwen BF, Heagle AB, Cassels GO, Buttle KF, Rieder CL. Kinetochore fiber maturation in PtK1 cells and its implications for the mechanisms of chromosome congression and anaphase onset. J Cell Biol 1997; 137:1567-80. [PMID: 9199171 PMCID: PMC2137823 DOI: 10.1083/jcb.137.7.1567] [Citation(s) in RCA: 187] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Kinetochore microtubules (kMts) are a subset of spindle microtubules that bind directly to the kinetochore to form the kinetochore fiber (K-fiber). The K-fiber in turn interacts with the kinetochore to produce chromosome motion toward the attached spindle pole. We have examined K-fiber maturation in PtK1 cells using same-cell video light microscopy/serial section EM. During congression, the kinetochore moving away from its spindle pole (i.e., the trailing kinetochore) and its leading, poleward moving sister both have variable numbers of kMts, but the trailing kinetochore always has at least twice as many kMts as the leading kinetochore. A comparison of Mt numbers on sister kinetochores of congressing chromosomes with their direction of motion, as well as distance from their associated spindle poles, reveals that the direction of motion is not determined by kMt number or total kMt length. The same result was observed for oscillating metaphase chromosomes. These data demonstrate that the tendency of a kinetochore to move poleward is not positively correlated with the kMt number. At late prometaphase, the average number of Mts on fully congressed kinetochores is 19.7 +/- 6.7 (n = 94), at late metaphase 24.3 +/- 4.9 (n = 62), and at early anaphase 27.8 +/- 6.3 (n = 65). Differences between these distributions are statistically significant. The increased kMt number during early anaphase, relative to late metaphase, reflects the increased kMt stability at anaphase onset. Treatment of late metaphase cells with 1 microM taxol inhibits anaphase onset, but produces the same kMt distribution as in early anaphase: 28.7 +/- 7. 4 (n = 54). Thus, a full complement of kMts is not sufficient to induce anaphase onset. We also measured the time course for kMt acquisition and determined an initial rate of 1.9 kMts/min. This rate accelerates up to 10-fold during the course of K-fiber maturation, suggesting an increased concentration of Mt plus ends in the vicinity of the kinetochore at late metaphase and/or cooperativity for kMt acquisition.
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Affiliation(s)
- B F McEwen
- Wadsworth Center, Division of Molecular Medicine, New York State Department of Health, Albany, New York 12201-0509, USA.
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Abstract
In the course of anaphase, the chromosomal DNA is submitted to the traction of the spindle. Several physical problems are associated with this action. In particular, the sister chromatids are generally topologically intertwined at the onset of anaphase, and the removal of the intertwinings results from a coupling between the enzymatic action of type II DNA topoisomerases and the force exerted by the spindle. We propose a physical analysis of some of these problems: 1) We compare the maximum force the spindle can produce with the force required to break a DNA molecule, and define the conditions compatible with biological safety during anaphase. 2) We show that the behavior of the sister chromatids in the absence of type II DNA topoisomerases can be described by two distinct models: a chain pullout model accounts for the experimental observations made in the budding yeast, and a model of the mechanical rupture of rubbers accounts for the nondisjunction in standard cases. 3) Using the fluctuation-dissipation theorem, we introduce an effective protein friction associated with the strand-passing activity of type II DNA topoisomerases. We show that this friction can be used to describe the situation in which one chromosome passes entirely through another one. Possible experiments that could test these theoretical analyses are discussed.
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Affiliation(s)
- G Jannink
- Laboratoire Léon Brillouin (CEA-CNRS), Departement de Biologie Cellulaire et Moléculaire, CEA/Saclay, Gif-sur-Yvette, France
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Mitchison TJ, Salmon ED. Poleward kinetochore fiber movement occurs during both metaphase and anaphase-A in newt lung cell mitosis. J Biophys Biochem Cytol 1992; 119:569-82. [PMID: 1400593 PMCID: PMC2289668 DOI: 10.1083/jcb.119.3.569] [Citation(s) in RCA: 233] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Microtubules in the mitotic spindles of newt lung cells were marked using local photoactivation of fluorescence. The movement of marked segments on kinetochore fibers was tracked by digital fluorescence microscopy in metaphase and anaphase and compared to the rate of chromosome movement. In metaphase, kinetochore oscillations toward and away from the poles were coupled to kinetochore fiber shortening and growth. Marked zones on the kinetochore microtubules, meanwhile, moved slowly polewards at a rate of approximately 0.5 micron/min, which identifies a slow polewards movement, or "flux," of kinetochore microtubules accompanied by depolymerization at the pole, as previously found in PtK2 cells (Mitchison, 1989b). Marks were never seen moving away from the pole, indicating that growth of the kinetochore microtubules occurs only at their kinetochore ends. In anaphase, marked zones on kinetochore microtubules also moved polewards, though at a rate slower than overall kinetochore-to-pole movement. Early in anaphase-A, microtubule depolymerization at kinetochores accounted on average for 75% of the rate of chromosome-to-pole movement, and depolymerization at the pole accounted for 25%. When chromosome-to-pole movement slowed in late anaphase, the contribution of depolymerization at the kinetochores lessened, and flux became the dominant component in some cells. Over the whole course of anaphase-A, depolymerization at kinetochores accounted on average for 63% of kinetochore fiber shortening, and flux for 37%. In some anaphase cells up to 45% of shortening resulted from the action of flux. We conclude that kinetochore microtubules change length predominantly through polymerization and depolymerization at the kinetochores during both metaphase and anaphase as the kinetochores move away from and towards the poles. Depolymerization, though not polymerization, also occurs at the pole during metaphase and anaphase, so that flux contributes to polewards chromosome movements throughout mitosis. Poleward force production for chromosome movements is thus likely to be generated by at least two distinct molecular mechanisms.
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Affiliation(s)
- T J Mitchison
- Department of Pharmacology, University of California, San Francisco 94143-0450
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Abstract
We have analyzed the fine structure of 10 chromosomal fibers from mitotic spindles of PtK1 cells in metaphase and anaphase, using electron microscopy of serial thin sections and computer image processing to follow the trajectories of the component microtubules (MTs) in three dimensions. Most of the kinetochore MTs ran from their kinetochore to the vicinity of the pole, retaining a clustered arrangement over their entire length. This MT bundle was invaded by large numbers of other MTs that were not associated with kinetochores. The invading MTs frequently came close to the kinetochore MTs, but a two-dimensional analysis of neighbor density failed to identify any characteristic spacing between the two MT classes. Unlike the results from neighbor density analyses of interzone MTs, the distributions of spacings between kinetochore MTs and other spindle MTs revealed no evidence for strong MT-MT interactions. A three-dimensional analysis of distances of closest approach between kinetochore MTs and other spindle MTs has, however, shown that the most common distances of closest approach were 30-50 nm, suggesting a weak interaction between kinetochore MTs and their neighbors. The data support the ideas that kinetochore MTs form a mechanical connection between the kinetochore and the pericentriolar material that defines the pole, but that the mechanical interactions between kinetochore MTs and other spindle MTs are weak.
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Affiliation(s)
- K L McDonald
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder 80309-0347
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Wolf KW, Mertl HG, Traut W. Structure, mitotic and meiotic behaviour, and stability of centromere-like elements devoid of chromosome arms in the fly Megaselia scalaris (Phoridae). Chromosoma 1991; 101:99-108. [PMID: 1769280 DOI: 10.1007/bf00357059] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Minute elements detected in Megaselia scalaris (Phoridae, Diptera) lack chromosome arms but carry centromeres and possess kinetochore microtubules in mitosis as well as in meiosis. These centromere-like elements (CLEs) were present in two geographically independent strains of the fly. This indicates that their origin is not a recent event in the karyotype evolution of M. scalaris and that they are rather stable constituents of the karyotype. Most often, two CLEs were found in gonial and somatic mitosis. Spermatocytes contained one CLE. Two individuals examined deviated from this rule in that a metaphase spermatogonium showed three and an anaphase spermatogonium eight CLEs. These animals are believed to have been aneuploid relative to the CLEs. An analysis of spermatogonial division revealed that the CLEs behave like the centromeres of the regular chromosomes but seem to separate precociously, since they were closer to the spindle poles in late anaphase cells. Whereas the size of the CLEs was not significantly different between mitotic cells and secondary spermatocytes, the CLEs in primary spermatocytes were larger in volume by a factor of about 4.5 than those in mitosis and meiosis II. The additional material is interpreted as a glue that holds two CLEs together. This, in turn, is a prerequisite for orderly segregation. The function of the CLEs is not known. They are considered as B chromosomes reduced to the minimum required for segregation, the centromere.
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Affiliation(s)
- K W Wolf
- Institut für Biologie der Medizinischen Universität zu Lübeck, Federal Republic of Germany
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Wolf KW. Behavior of C-shaped microtubule endings in the cell. CELL MOTILITY AND THE CYTOSKELETON 1990; 17:59-67. [PMID: 2225089 DOI: 10.1002/cm.970170108] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The association of incomplete microtubule assemblies with either another incomplete structure or complete microtubules was studied in two organisms, the phytoflagellate Polytoma papillatum and the phorid fly Megaselia scalaris, using transmission electron microscopy. In the alga, hook-shaped appendages on cytoplasmic and spindle microtubules were detected. These resulted from the lateral association of a curved ribbon of protofilaments with the surface of a complete microtubular wall. In the fly, an S-shaped protofilament sheet was found embedded in the kinetochore plate of a prometaphase I spermatocyte. Tracing of the S-shaped element towards the spindle pole revealed that it was formed by the lateral junction of two curved protofilament sheets. In all cases, the C-shaped protofilament sheets represented the endings of complete microtubules. Incomplete microtubules are generally considered as representing intermediates of microtubule assembly and disassembly. Since high molecular weight proteins are believed to be responsible for maintaining microtubule-microtubule spacing, it is hypothesized that the endings of growing and shrinking microtubules are sparsely studded with these proteins; their depletion allows lateral microtubule contacts. In addition, the microtubule-microtubule contacts may be rendered possible by the flexibility of the slender elongated microtubule-associated molecules. Relatively long C-shaped protofilament appendages (0.6-1.4 microns) were detected in this study. Therefore, it is plausible to assume that the protofilament sheets are stabilized by contact with one another or with an intact tubule wall.
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Affiliation(s)
- K W Wolf
- Institut für Biologie der Medizinischen Universität, Lübeck, Federal Republic of Germany
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Wadsworth P, Shelden E, Rupp G, Rieder CL. Biotin-tubulin incorporates into kinetochore fiber microtubules during early but not late anaphase. J Cell Biol 1989; 109:2257-65. [PMID: 2681228 PMCID: PMC2115857 DOI: 10.1083/jcb.109.5.2257] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The dynamic behavior of kinetochore fiber microtubules has been examined in PtK1 cells during anaphase of mitosis. Cells in anaphase were injected with biotin-tubulin and, at various intervals after injection, fixed for light or electron microscopic immunolocalization of biotin-tubulin-containing microtubules. When cells in early to mid anaphase were injected with biotin-tubulin and fixed 1-2 min later, fluorescence was observed throughout the spindle, including the region of the kinetochore fibers. Electron microscopy of early to mid anaphase cells, after processing with immunogold methods, revealed both labeled and unlabeled microtubules in the kinetochore fibers; some labeled microtubules contacted the kinetochores. When late anaphase cells were injected with biotin-tubulin, and fixed a few minutes later, little fluorescence was observed in the kinetochore fibers. Electron microscopy confirmed that kinetochore fibers in late anaphase cells were refractory to tubulin incorporation. The results of these experiments demonstrate that the kinetochore fiber incorporates new microtubules during early anaphase but that this incorporation ceases in mid to late anaphase. Thus, microtubule turnover within the kinetochore fiber does not abruptly cease at the onset of anaphase and anaphase kinetochore fiber microtubules are more dynamic than previously suspected.
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Affiliation(s)
- P Wadsworth
- Department of Zoology, University of Massachusetts, Amherst 01003
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Bajer AS, Vantard M. Microtubule dynamics determine chromosome lagging and transport of acentric fragments. Mutat Res 1988; 201:271-81. [PMID: 3173377 DOI: 10.1016/0027-5107(88)90016-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The general direction of transport of spindle inclusions including acentric chromosome fragments during mitosis in endosperm of the higher plants Haemanthus is predictable and stage-dependent. Their segregation is random and they are usually eliminated from the spindle. This transport is superimposed on normal chromosome segregation. Thus, there are 2 superimposed mitotic transports: one which distributes kinetochores and the other which distributes spindle inclusions. The functional relation of these 2 transports to each other is not well understood. However, due to this 'non-kinetochore transport,' fragments may persist a few consecutive divisions before being permanently eliminated from the nucleus. Malfunction of kinetochores of any chromosome, resulting in the loss of their anchorage within the spindle, subjects them to 'non-kinetochore' transport and nearly certain, permanent elimination from the spindle. Additionally, experimental evidence presented here demonstrates that rapid polymerization (elongation) of microtubules may desynchronize anaphase and cause lagging of whole chromosomes. This may be one more, previously unconsidered, factor which may cause the malfunction of the kinetochore fiber and consequent elimination of one or a few chromosomes from the spindle.
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Affiliation(s)
- A S Bajer
- Department of Biology, University of Oregon, Eugene 97403
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Chromosomes and Kinetochores do More in Mitosis than Previously Thought. CHROMOSOME STRUCTURE AND FUNCTION 1988. [DOI: 10.1007/978-1-4613-1037-2_2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
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Rothwell SW, Grasser WA, Baker HN, Murphy DB. The relative contributions of polymer annealing and subunit exchange to microtubule dynamics in vitro. J Cell Biol 1987; 105:863-74. [PMID: 3624310 PMCID: PMC2114778 DOI: 10.1083/jcb.105.2.863] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Microtubules that are free of microtubule-associated protein undergo dynamic changes at steady state, becoming longer but fewer in number with time through a process which was previously assumed to be based entirely on mechanisms of subunit exchange at polymer ends. However, we recently demonstrated that brain and erythrocyte microtubules are capable of joining end-to-end and suggested that polymer annealing may also affect the dynamic behavior of microtubules in vitro (Rothwell, S. W., W. A. Grasser, and D. B. Murphy, 1986, J. Cell Biol. 102:619-627). In the present study, we first show that annealing is a general property of cytoplasmic microtubules and is not a specialized characteristic of erythrocyte microtubules by documenting annealing between tryosinolated and detyrosinolated brain microtubules. We then examine the contributions of polymer annealing and subunit exchange to microtubule dynamics by analyzing the composition and length of individual polymers in a mixture of brain and erythrocyte microtubules by immunoelectron microscopy. In concentrated preparations of short-length microtubules at polymer-mass steady state, annealing was observed to be the principal factor responsible for the increase in polymer length, whereas annealing and subunit exchange contributed about equally to the reduction in microtubule number.
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Steffen W. Relationship between the arrangement of microtubules and chromosome behaviour of syntelic autosomal univalents during prometaphase in crane fly spermatocytes. Chromosoma 1986; 94:412-8. [PMID: 3829829 DOI: 10.1007/bf00328642] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
During meiotic prometaphase of crane fly spermatocytes, syntelic autosomal univalents are able to move between the spindle poles several times. The relationship between the behaviour of chromosomes and the arrangement of microtubules during this stage was studied using a fixation technique (Nicklas et al. 1979) which makes it possible to examine a certain cell in an electron microscope after live observation. After reorientation, when a syntelic univalent had started moving towards the opposite spindle pole, a short chromosome fibre was found. When a univalent had reached the equator, a chromosome fibre could be traced up to the spindle apex. During the movement towards the opposite spindle pole the degree of disorder in the chromosome fibre was high, whereas it was low in the fibre of a motionless univalent. The degree of disorder was determined by the relative proportion of skew fibre microtubules. At the beginning of reorientation a chromosome fibre was still present, but later, it was no longer possible to recognize such a fibre. Instead of a chromosome fibre, a bundle of microtubules laterally associated with the kinetochore was observed. Some microtubules of this bundle had a direct contact with the kinetochore. These observations strongly hint that the laterally associated microtubules have an important function in the reorientation of syntelic autosomal univalents.
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Bastmeyer M, Fuge H. The distribution of intermicrotubular bridges in meiotic spindles of the crane fly. Chromosoma 1986; 94:419-24. [PMID: 3829830 DOI: 10.1007/bf00328643] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The distribution of intermicrotubular bridges in spindles of tipulid spermatocytes (Pales ferruginea, first meiotic division) was analyzed using serial sections of pre-selected cells. Bridges were found in all spindle regions, including kinetochore microtubules and free microtubules in the chromosome fiber. The dimensions of bridges were variable, ranging between 60 and 300 A in length and 40 and 190 A in thickness. Bridges seem to be randomly distributed. No accumulation in or absence from particular spindle regions was detected. Quantitative analysis revealed a linear, positive correlation between the number of microtubules and the number of microtubule pairs capable of forming bridges and, on the other hand, between microtubule pairs and intermicrotubular bridges. The possible composition and significance of bridges are discussed.
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Cohn SA, Tippit DH, Spurck TP. Microtubule dynamics in the spindle. II. A thermodynamic and kinetic description. J Theor Biol 1986; 122:277-301. [PMID: 3626574 DOI: 10.1016/s0022-5193(86)80121-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
We have previously presented a model for the assembly and disassembly of mitotic spindle microtubules (MTs) (Pickett-Heaps et al., 1986). In this paper, we describe the thermodynamics of such spindle MT assembly and present equations to describe the polymerization kinetics of different classes of spindle MTs. These equations are used to predict, in terms of kinetics parameters, the magnitude of forces extant on spindle MTs and to define the critical force needed to halt MT assembly. We calculate several of these forces for a hypothetical model cell; our predicted value for the force generated along kinetochore fibers is in close agreement with measured values taken from living cells. The model and its implications are discussed with reference to other recent models of spindle and MT dynamics.
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Abstract
We have developed microdensitometer-computer correlation techniques to analyze the arrangement of microtubule arms and bridges (i.e., microtubule-associated proteins [MAPs]). A microdensitometer was used to scan immediately adjacent to the wall of longitudinally sectioned microtubules in positive transparency electron micrographs. Signal enhancement procedures were applied to the digitized densitometer output to produce a binary sequence representing the apparent axial spacing of MAP projections. These enhanced records were analyzed in two ways. (a) Autocorrelograms were formed for each record and correlogram peaks from a group of scans were pooled to construct a peak frequency histogram. (b) Cross-correlation was used to optimize the match between each enhanced record and templates predicted by different models of MAP organization. Seven symmetrical superlattices were considered as well as single axial repeats. The analyses were repeated with randomly generated records to establish confidence levels. Using the above methods, we analyzed the intrarow bridges of the Saccinobaculus axostyle and the MAP2 projections associated with brain microtubules synthesized in vitro. We confirmed a strict 16-nm axial repeat for axostyle bridges. For 26 MAP2 records, the only significant match was to a 12-dimer superlattice model (P less than 0.002). However, we also found some axial distances between MAP2 projections which were compatible with the additional spacings predicted by a 6-dimer superlattice. Therefore, we propose that MAP2 projections are arranged in a "saturated 12-dimer, unsaturated 6-dimer" superlattice, which may be characteristic of a wide variety of MAPs.
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Steffen W. Three-dimensional architecture of chromosome fibres in the crane fly: co-oriented autosomal bivalents and amphitelic sex univalents during prometaphase. Chromosoma 1986. [DOI: 10.1007/bf00286988] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Pickett-Heaps JD, Tippit DH, Cohn SA, Spurck TP. Microtubule dynamics in the spindle. Theoretical aspects of assembly/disassembly reactions in vivo. J Theor Biol 1986; 118:153-69. [PMID: 3713209 DOI: 10.1016/s0022-5193(86)80131-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The mitotic spindle contains several classes of microtubules (MTs) whose lengths change independently during mitosis. Precise control over MT polymerization and depolymerization during spindle formation, anaphase chromosome movements, and spindle breakdown is necessary for successful cell division. This model proposes the site of addition and removal of MT subunits in each of four classes of spindle MTs at different stages of mitosis, and suggests how this addition and removal is controlled. We propose that spindle poles and kinetochores significantly alter the assembly-disassembly kinetics of associated MT ends. Control of MT length is further modulated by localized forces affecting assembly and disassembly kinetics of individual sets of MTs.
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Scarcello LA, Janicke MA, LaFountain JR. Kinetochore microtubules in crane-fly spermatocytes: untreated, 2 degrees C-treated, and 6 degrees C-grown spindles. CELL MOTILITY AND THE CYTOSKELETON 1986; 6:428-38. [PMID: 3757074 DOI: 10.1002/cm.970060408] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
We investigated the involvement of kinetochore microtubules (kMTs) in mediating chromosome-to-pole connections in crane-fly (Nephrotoma suturalis and Nephrotoma ferruginea) spermatocytes. Two experimental treatments were used to yield spindles with reduced numbers of nonkinetochore microtubules (nkMTs). Short-term (10-15 min) exposure of spermatocytes to 2 degrees C caused depolymerization of the majority of nkMTs, resulting in a kMT:(kMT + nkMT) ratio of 0.76. Long-term (24h) exposure to 2 degrees C followed by recovery at 6 degrees C resulted in a kMT:(kMT + nkMT) ratio of 0.55, the spindle having more nkMTs than a 2 degrees C-treated spindle but fewer than an untreated spindle, in which the kMT:(kMT + nkMT) ratio was 0.27. The numbers and lengths of kMTs in 6 degrees C-grown spindles were similar to those in untreated cells, suggesting that the overall inhibition of MT assembly at 6 degrees C apparently did not affect the mechanism by which kMTs are formed. We observed most kMTs of early anaphase spindles to be long (greater than 3 microns), and many extended to the polar regions of the spindle. Thus, the crane-fly spindle appears not to be as atypical as it was previously suggested to be.
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Bajer AS, Molè-Bajer J. Reorganization of microtubules in endosperm cells and cell fragments of the higher plant Haemanthus in vivo. J Biophys Biochem Cytol 1986; 102:263-81. [PMID: 3941154 PMCID: PMC2114031 DOI: 10.1083/jcb.102.1.263] [Citation(s) in RCA: 101] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The reorganization of the microtubular meshwork was studied in intact Haemanthus endosperm cells and cell fragments (cytoplasts). This higher plant tissue is devoid of a known microtubule organizating organelle. Observations on living cells were correlated with microtubule arrangements visualized with the immunogold method. In small fragments, reorganization did not proceed. In medium and large sized fragments, microtubular converging centers formed first. Then these converging centers reorganized into either closed bushy microtubular spiral or chromosome-free cytoplasmic spindles/phragmoplasts. Therefore, the final shape of organized microtubular structures, including spindle shaped, was determined by the initial size of the cell fragments and could be achieved without chromosomes or centrioles. Converging centers elongate due to the formation of additional structures resembling microtubular fir trees. These structures were observed at the pole of the microtubular converging center in anucleate fragments, accessory phragmoplasts in nucleated cells, and in the polar region of the mitotic spindle during anaphase. Therefore, during anaphase pronounced assembly of new microtubules occurs at the polar region of acentriolar spindles. Moreover, statistical analysis demonstrated that during the first two-thirds of anaphase, when chromosomes move with an approximately constant speed, kinetochore fibers shorten, while the length of the kinetochore fiber complex remains constant due to the simultaneous elongation of their integral parts (microtubular fir trees). The half-spindle shortens only during the last one-third of anaphase. These data contradict the presently prevailing view that chromosome-to-pole movements in acentriolar spindles of higher plants are concurrent with the shortening of the half-spindle, the self-reorganizing property of higher plant microtubules (tubulin) in vivo. It may be specific for cells without centrosomes and may be superimposed also on other microtubule-related processes.
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Fuge H, Bastmeyer M, Steffen W. A model for chromosome movement based on lateral interaction of spindle microtubules. J Theor Biol 1985; 115:391-9. [PMID: 4033166 DOI: 10.1016/s0022-5193(85)80199-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Quantitative morphological studies of meiotic spindles in the crane fly Pales ferruginea (Fuge, 1980, 1984, 1985) were the basis for the development of a model explaining anaphase chromosome transport in higher eukaryotes. Two main features of chromosome fibres were important for the model: (1) the existence of microtubules oriented obliquely with respect to kinetochore microtubules, and (2) a higher degree of disorder in fibres exerting a pulling force. It is postulated that microtubules of the same polarity being inclined to each other at a certain angle are able to slide past each other by means of mechano-chemically active side-arms working in alternate succession. Sliding is suggested to lead to a displacement of microtubules and chromosomes in direction towards the poles. Furthermore, it is suggested that the chromosome fibre in anaphase becomes progressively disintegrated by fragmentation and disassembly of microtubules. Fragmentation may be induced by bending stress within the dynamic system.
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Nishikawa S, Kitamura H. Three-dimensional network of microtubules in secretory ameloblasts of rat incisors. Arch Oral Biol 1985; 30:1-11. [PMID: 3857882 DOI: 10.1016/0003-9969(85)90018-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Secretory ameloblasts appear to contain isolated microtubules and microtubules arranged in bundles associated with filaments or sheets of filaments. The relation between isolated and bundled microtubules in secretory ameloblasts was investigated by serial sections. Some isolated microtubules entered microtubule bundles in adjacent sections. Microtubules which diverged from a bundle sometimes converged into another bundle in other sections. Microtubules were associated with filaments or sheets of filaments for varying distances. It is concluded that isolated microtubules frequently form bundles by joining with other microtubules, and thus, microtubules make a three-dimensional network throughout the whole cytoplasm which is probably concerned with the transport of secretion granules.
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Fuge H. The three-dimensional architecture of chromosome fibres in the crane fly. II. Amphitelic sex univalents in meiotic anaphase I. Chromosoma 1985; 91:322-8. [PMID: 3979179 DOI: 10.1007/bf00328228] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Microtubules of amphitelically oriented sex univalent chromosome fibres were traced in longitudinal serial sections. The investigated chromosomes were from four different cells representing consecutive stages of anaphase segregation. A correlation was found between chromosome movement and a characteristic distribution of free microtubules (fMTs) oriented obliquely with respect to the kinetochore microtubules. During chromosome segregation the proportion of these skew fMTs (the proportion of skew fMTs is a measure of the degree of disorder in the fibre) is higher in the fibre pointing in the direction of movement than in the trailing fibre. The results are discussed in relation to spindle forces. Although the anaphase of amphitelic sex chromosomes is different in several respects (orientation of chromosome fibres, mutual connexion of chromosomes via kinetochore microtubules, spindle elongation occurring simultaneously), the observations on the distribution of fMTs in the chromosomes fibres is, in principle, compatible with those previously made on syntelic autosomes.
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Nicklas RB. Mitosis in eukaryotic cells: an overview of chromosome distribution. BASIC LIFE SCIENCES 1985; 36:183-95. [PMID: 4096691 DOI: 10.1007/978-1-4613-2127-9_13] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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Janicke MA, LaFountain JR. Malorientation in half-bivalents at anaphase: analysis of autosomal laggards in untreated, cold-treated, and cold-recovering crane fly spermatocytes. J Biophys Biochem Cytol 1984; 98:859-69. [PMID: 6699088 PMCID: PMC2113135 DOI: 10.1083/jcb.98.3.859] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Exposing crane fly larvae to 6 degrees C or returning them to 22 degrees C after exposure to 6, 2, or 0.2 degrees C can induce any number of autosomes in their primary spermatocytes to lag near the spindle equator at anaphase. Autosomal laggards in cold-recovering cells are contained in bivalents until anaphase (Janicke, M. A., and J. R. LaFountain, 1982, Chromosoma, 85:619-631). We report here documentation that lagging autosomes in cold-treated and cold-recovering cells are maloriented. During meiosis I, half-bivalents usually associate with only one pole via kinetochore fibers, with sister chromatids being oriented to the same pole. In contrast, laggards had kinetochore microtubules (kMTs) extending from them toward both poles: one sister was oriented to one pole and the other had some or all of its kMTs extending toward the opposite pole. Bipolar malorientation of autosomal laggards also was observed in one untreated cell. The number of kMTs per half-bivalent was similar in lagging and non-lagging autosomes, and those kMTs were contained in long birefringent kinetochore fibers. The overall spindle structure in cold-recovering cells was similar to that observed in untreated anaphase cells. Giemsa-stained centromeric dots of sister chromatids were contiguous in non-laggards and separated in laggards at anaphase. We conclude that bipolar malorientations can exist at anaphase in chromosomes that remain paired until anaphase, that cold recovery increases the frequency of that anomaly, and that such malorientations may be one cause of anaphase lag.
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Hepler PK, Wolniak SM. Membranes in the mitotic apparatus: their structure and function. INTERNATIONAL REVIEW OF CYTOLOGY 1984; 90:169-238. [PMID: 6389413 DOI: 10.1016/s0074-7696(08)61490-4] [Citation(s) in RCA: 94] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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Stevens JK, Trogadis J. Computer-Assisted Reconstruction from Serial Electron Micrographs: A Tool for the Systematic Study of Neuronal form and Function. ACTA ACUST UNITED AC 1984. [DOI: 10.1016/b978-0-12-008305-3.50015-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
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Steffen W, Fuge H. Dynamic changes in autosomal spindle fibers during prometaphase in crane fly spermatocytes. Chromosoma 1982. [DOI: 10.1007/bf00327637] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Nicklas RB, Kubai DF, Hays TS. Spindle microtubules and their mechanical associations after micromanipulation in anaphase. J Biophys Biochem Cytol 1982; 95:91-104. [PMID: 6890559 PMCID: PMC2112378 DOI: 10.1083/jcb.95.1.91] [Citation(s) in RCA: 98] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Micromanipulation of living grasshopper spermatocytes in anaphase has been combined with electron microscopy to reveal otherwise obscure features of spindle organization. A chromosome is pushed laterally outside the spindle and stretched, and the cell is fixed with a novel, agar-treated glutaraldehyde solution. Two- and three-dimensional reconstructions from serial sections of seven cells show that kinetochore microtubules of the manipulated chromosome are shifted outside the confusing thicket of spindle microtubules and mechanical associations among microtubules are revealed by bent or shifted microtubules. These are the chief results: (a) The disposition of microtubules invariably is consistent with a skeletal role for spindle microtubules. (b) The kinetochore microtubule bundle is composed of short and long microtubules, with weak but recognizable mechanical associations among them. Some kinetochore microtubules are more tightly linked to one other microtubule within the bundle. (c) Microtubules of the kinetochore microtubule bundle are firmly connected to other spindle microtubules only near the pole, although some nonkinetochore microtubules of uncertain significance enter the bundle nearer to the kinetochore. (d) The kinetochore microtubules of adjacent chromosomes are mechanically linked, which provides an explanation for interdependent chromosome movement in "hinge anaphases." In the region of the spindle open to analysis after chromosome micromanipulation, microtubules may be linked mechanically by embedment in a gel, rather than by dynein or other specific, cross-bridging molecules.
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King SM, Hyams JS, Luba A. Absence of microtubule sliding and an analysis of spindle formation and elongation in isolated mitotic spindles from the yeast Saccharomyces cerevisiae. J Cell Biol 1982; 94:341-9. [PMID: 7050129 PMCID: PMC2112885 DOI: 10.1083/jcb.94.2.341] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Mitotic spindles were isolated from a cell division cycle mutant of the budding yeast Saccharomyces cerevisiae by the lysis of sphateroplasts on an air:buffer interface and were negatively stained with 1% gold thioglucose. Isolated spindles were incubated under conditions which promoted the sliding disintegration of parallel preparations of Tetrahymena axonemes, namely the addition of ATP to 20 microM. In no experiment was a corresponding change in microtubule organization of the spindle observed even when spindles were first pretreated with either 1-10 microgram/ml trypsin or 0.2-2% Triton X-100. During these experiments a number of spindles were isolated from cells that had passed through the imposed temperature block, and from the images obtained a detailed model of spindle formation and elongation has been constructed. Two sets of microtubules, one from each spindle pole body (SPB), completely interdigitate to form a continuous bundle, and a series of discontinuous microtubules are then nucleated by each SPB. As the spindle elongates, the number of microtubules continuous between the two SPBs decreases until, at a length of 4 micrometer, only one remains. The spindle, composed of only one microtubule, continues to elongate until it reaches the maximal nuclear dimension of 8 micrometer. The data obtained from negatively stained preparations have been verified in thin sections of wild-type cells. We suggest that, as in the later stages of mitosis only one microtubule is involved in the separation of the spindle poles, the microtubular spindle in S. cerevisiae is not a force-generating system but rather acts as a regulatory mechanism controlling the rate of separation.
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Rieder CL. The formation, structure, and composition of the mammalian kinetochore and kinetochore fiber. INTERNATIONAL REVIEW OF CYTOLOGY 1982; 79:1-58. [PMID: 6185450 DOI: 10.1016/s0074-7696(08)61672-1] [Citation(s) in RCA: 349] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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