scholarly journals The Bending Rigidity of Mitotic Chromosomes

2002 ◽  
Vol 13 (6) ◽  
pp. 2170-2179 ◽  
Author(s):  
Michael G. Poirier ◽  
Sertac Eroglu ◽  
John F. Marko
Keyword(s):  
Cross Section ◽  
Mitotic Chromosome ◽  
Chromosome Structure ◽  
Bending Rigidity ◽  
Elastic Rod ◽  
Mitotic Chromosomes ◽  
Bending Elasticity ◽  
Thermal Bending ◽  
Rule Out

The bending rigidities of mitotic chromosomes isolated from cultured N. viridescens (newt) and Xenopusepithelial cells were measured by observing their spontaneous thermal bending fluctuations. When combined with simultaneous measurement of stretching elasticity, these measurements constrain models for higher order mitotic chromosome structure. We measured bending rigidities of B ∼10−22 N · m2 for newt and ∼10−23 N · m2 forXenopus chromosomes extracted from cells. A similar bending rigidity was measured for newt chromosomes in vivo by observing bending fluctuations in metaphase-arrested cells. Following each bending rigidity measurement, a stretching (Young's) modulus of the same chromosome was measured in the range of 102 to 103 Pa for newt and Xenopus chromosomes. For each chromosome, these values of B and Y are consistent with those expected for a simple elastic rod, B ≈ YR4, where R is the chromosome cross-section radius. Our measurements rule out the possibility that chromosome stretching and bending elasticity are principally due to a stiff central core region and are instead indicative of an internal structure, which is essentially homogeneous in its connectivity across the chromosome cross-section.

scholarly journals Topoisomerase IIα is essential for maintenance of mitotic chromosome structure

2020 ◽  
Vol 117 (22) ◽  
pp. 12131-12142 ◽  
Author(s):  
Christian F. Nielsen ◽  
Tao Zhang ◽  
Marin Barisic ◽  
Paul Kalitsis ◽  
Damien F. Hudson
Keyword(s):  
Cell Cycle ◽  
Chromosome Segregation ◽  
Mitotic Chromosome ◽  
Chromosome Structure ◽  
Chromatin Condensation ◽  
Chromosome Condensation ◽  
Mitotic Chromosomes ◽  
Topoisomerase Iiα ◽  
Mitotic Chromosome Condensation

Topoisomerase IIα (TOP2A) is a core component of mitotic chromosomes and important for establishing mitotic chromosome condensation. The primary roles of TOP2A in mitosis have been difficult to decipher due to its multiple functions across the cell cycle. To more precisely understand the role of TOP2A in mitosis, we used the auxin-inducible degron (AID) system to rapidly degrade the protein at different stages of the human cell cycle. Removal of TOP2A prior to mitosis does not affect prophase timing or the initiation of chromosome condensation. Instead, it prevents chromatin condensation in prometaphase, extends the length of prometaphase, and ultimately causes cells to exit mitosis without chromosome segregation occurring. Surprisingly, we find that removal of TOP2A from cells arrested in prometaphase or metaphase cause dramatic loss of compacted mitotic chromosome structure and conclude that TOP2A is crucial for maintenance of mitotic chromosomes. Treatments with drugs used to poison/inhibit TOP2A function, such as etoposide and ICRF-193, do not phenocopy the effects on chromosome structure of TOP2A degradation by AID. Our data point to a role for TOP2A as a structural chromosome maintenance enzyme locking in condensation states once sufficient compaction is achieved.

scholarly journals In vivo dissection of the chromosome condensation machinery

2002 ◽  
Vol 156 (5) ◽  
pp. 805-815 ◽  
Author(s):  
Brigitte D. Lavoie ◽  
Eileen Hogan ◽  
Douglas Koshland
Keyword(s):  
Topoisomerase Ii ◽  
Mitotic Chromosome ◽  
Chromosome Structure ◽  
Histone H3 ◽  
Chromosome Condensation ◽  
Chromatin Binding ◽  
Condensin Complex ◽  
Topo Ii ◽  
Structural Maintenance Of Chromosome

The machinery mediating chromosome condensation is poorly understood. To begin to dissect the in vivo function(s) of individual components, we monitored mitotic chromosome structure in mutants of condensin, cohesin, histone H3, and topoisomerase II (topo II). In budding yeast, both condensation establishment and maintenance require all of the condensin subunits, but not topo II activity or phospho-histone H3. Structural maintenance of chromosome (SMC) protein 2, as well as each of the three non-SMC proteins (Ycg1p, Ycs4p, and Brn1p), was required for chromatin binding of the condensin complex in vivo. Using reversible condensin alleles, we show that chromosome condensation does not involve an irreversible modification of condensin or chromosomes. Finally, we provide the first evidence of a mechanistic link between condensin and cohesin function. A model discussing the functional interplay between cohesin and condensin is presented.

scholarly journals Identification of a Chromosome-Targeting Domain in the Human Condensin Subunit CNAP1/hCAP-D2/Eg7

2002 ◽  
Vol 22 (16) ◽  
pp. 5769-5781 ◽  
Author(s):  
Alexander R. Ball, ◽  
John A. Schmiesing ◽  
Changcheng Zhou ◽  
Heather C. Gregson ◽  
Yoshiaki Okada ◽  
...  
Keyword(s):  
Mitotic Chromosome ◽  
Mitotic Chromosomes ◽  
Family Protein ◽  
Localization Signal ◽  
The Individual ◽  
Mitotic Chromosome Condensation ◽  
Structural Maintenance Of Chromosomes

ABSTRACT CNAP1 (hCAP-D2/Eg7) is an essential component of the human condensin complex required for mitotic chromosome condensation. This conserved complex contains a structural maintenance of chromosomes (SMC) family protein heterodimer and three non-SMC subunits. The mechanism underlying condensin targeting to mitotic chromosomes and the role played by the individual condensin components, particularly the non-SMC subunits, are not well understood. We report here characterization of the non-SMC condensin component CNAP1. CNAP1 contains two separate domains required for its stable incorporation into the complex. We found that the carboxyl terminus of CNAP1 possesses a mitotic chromosome-targeting domain that does not require the other condensin components. The same region also contains a functional bipartite nuclear localization signal. A mutant CNAP1 missing this domain, although still incorporated into condensin, was unable to associate with mitotic chromosomes. Successful chromosome targeting of deletion mutants correlated with their ability to directly bind to histones H1 and H3 in vitro. The H3 interaction appears to be mediated through the H3 histone tail, and a subfragment containing the targeting domain was found to interact with histone H3 in vivo. Thus, the CNAP1 C-terminal region defines a novel histone-binding domain that is responsible for targeting CNAP1, and possibly condensin, to mitotic chromosomes.

scholarly journals A Proposed Unified Mitotic Chromosome Architecture

2021 ◽  
Author(s):  
John Sedat ◽  
Angus McDonald ◽  
Herbert G Kasler ◽  
Eric Verdin ◽  
Hu Cang ◽  
...  
Keyword(s):  
Dna Sequences ◽  
Large Scale ◽  
Mitotic Chromosome ◽  
Chromosome Structure ◽  
Digital Pcr ◽  
Molecular Architecture ◽  
Cell Nuclei ◽  
Mitotic Chromosomes ◽  
Interphase Chromosome ◽  
Chromosome Architecture

A molecular architecture is proposed for an example mitotic chromosome, human Chromosome 10. This architecture is built on a previously described interphase chromosome structure based on Cryo-EM cellular tomography (1), thus unifying chromosome structure throughout the complete mitotic cycle. The basic organizational principle, for mitotic chromosomes, is specific coiling of the 11-nm nucleosome fiber into large scale approximately 200 nm structures (a Slinky (2, motif cited in 3) in interphase, and then further modification and subsequent additional coiling for the final structure. The final mitotic chromosome architecture accounts for the dimensional values as well as the well known cytological configurations. In addition, proof is experimentally provided, by digital PCR technology, that G1 T-cell nuclei are diploid, thus one DNA molecule per chromosome. Many nucleosome linker DNA sequences, the promotors and enhancers, are suggestive of optimal exposure on the surfaces of the large-scale coils.

scholarly journals Smc5-Smc6-Dependent Removal of Cohesin from Mitotic Chromosomes

2009 ◽  
Vol 29 (16) ◽  
pp. 4363-4375 ◽  
Author(s):  
Emily A. Outwin ◽  
Anja Irmisch ◽  
Johanne M. Murray ◽  
Matthew J. O'Connell
Keyword(s):  
Dna Damage ◽  
Chromosome Segregation ◽  
Topoisomerase Ii ◽  
Mitotic Chromosome ◽  
Chromosome Structure ◽  
Synthetic Lethality ◽  
Mitotic Chromosomes ◽  
Interphase Chromosome ◽  
Chromosome Arm ◽  
Null Mutants

ABSTRACT The function of the essential cohesin-related Smc5-Smc6 complex has remained elusive, though hypomorphic mutants have defects late in recombination, in checkpoint maintenance, and in chromosome segregation. Recombination and checkpoints are not essential for viability, and Smc5-Smc6-null mutants die in lethal mitoses. This suggests that the chromosome segregation defects may be the source of lethality in irradiated Smc5-Smc6 hypomorphs. We show that in smc6 mutants, following DNA damage in interphase, chromosome arm segregation fails due to an aberrant persistence of cohesin, which is normally removed by the Separase-independent pathway. This postanaphase persistence of cohesin is not dependent on DNA damage, since the synthetic lethality of smc6 hypomorphs with a topoisomerase II mutant, defective in mitotic chromosome structure, is also due to the retention of cohesin on undamaged chromosome arms. In both cases, Separase overexpression bypasses the defect and restores cell viability, showing that defective cohesin removal is a major determinant of the mitotic lethality of Smc5-Smc6 mutants.

Structural Analysis of Large-Scale Chromatin Organization

1997 ◽  
Vol 3 (S2) ◽  
pp. 215-216
Author(s):  
A. S. Belmont ◽  
G. Li ◽  
G. Sudlow ◽  
T. Tumbar ◽  
Y. Strukov ◽  
...  
Keyword(s):  
Large Scale ◽  
Chromosome Structure ◽  
Protein Extraction ◽  
Light And Electron Microscopy ◽  
Chromatin Organization ◽  
Mitotic Chromosomes ◽  
Interphase Chromosome ◽  
Reconstruction Methods

Our laboratory is interested in understanding how 10 and 30 nm chromatin fibers fold to form interphase and mitotic chromosomes. Experimentally this has been a very difficult problem to investigate due to a number of technical difficulties. A common approach to this level of chromatin organization has been to use protein extraction conditions which experimentally “unravel” the native chromosome architecture. The difficulty with this approach is separating in vitro produced artifacts from remnants of in vivo structure.As an alternative strategy we are focusing on changes in interphase chromosome structure during cell cycle progression and initiation of transcription or DNA replication, with the goal of identifying intermediates in the pathway of chromosome condensation or decondensation. A key element of this strategy is preserving chromosome structure as close as possible to its in vivo structure while using 3-dimensional light and electron microscopy reconstruction methods to “computationally” unravel native chromosome structure.

Correction to: Contribution of advanced fluorescence nano microscopy towards revealing mitotic chromosome structure

2021 ◽  
Author(s):  
S. W. Botchway ◽  
S. Farooq ◽  
A. Sajid ◽  
I. K. Robinson ◽  
M. Yusuf
Keyword(s):  
Mitotic Chromosome ◽  
Chromosome Structure

The influence of fixation on the morphology of mitotic chromosomes

1986 ◽  
Vol 28 (4) ◽  
pp. 536-539 ◽  
Author(s):  
Axel J. J. Dietrich
Keyword(s):  
Acetic Acid ◽  
Chemical Composition ◽  
Strong Influence ◽  
Chromosome Structure ◽  
Human Lymphocytes ◽  
Chromosome Morphology ◽  
Mitotic Chromosomes ◽  
Specific Chemical ◽  
C Banding ◽  
Sister Chromatids

It is well known that there is a strong influence of fixation, i.e., acetic methanol versus formaldehyde, on the chromosome morphology at stages of the first meiotic division. In this study the influence of both these types of fixation on the morphology of mitotic chromosomes was examined in human lymphocytes. After methanol – acetic acid (3:1) fixation, the chromosomes show the "classical" condensed shape in which it is not always possible to recognize the two sister chromatids. These chromosomes are accessible to the conventional G-, R-, and C-banding techniques. After formaldehyde fixation at a relatively high pH, the chromosomes are thinner and longer (two to six times) when compared with chromosomes following methanol – acetic acid fixation. They show a scaffold-like morphology, sometimes with a halo of thin material around it. In all cases the two sister chromatids could be recognized. This chromosome structure could be easily stained with silver, Giemsa, 4,6-diamino-2-phenyl-indole (DAPI), and fluorescein isocyanate isomere 1 (FITC). The results obtained following these stainings gave no indication to any specific chemical composition of a probable central scaffold. The scaffold-like structures were not accessible to G-, R-, or C-banding techniques. The only effect observed following these banding techniques was the disappearance of the halo of thin material around the central scaffold-like structure.Key words: chromosome structure, fixation influence, human lymphocytes.

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