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.

scholarly journals Active gelation breaks time-reversal-symmetry of mitotic chromosome mechanics

2018 ◽  
Author(s):  
Matthäus Mittasch ◽  
Anatol W. Fritsch ◽  
Michael Nestler ◽  
Juan M. Iglesias-Artola ◽  
Kaushikaram Subramanian ◽  
...  
Keyword(s):  
Symmetry Breaking ◽  
Time Reversal ◽  
Mitotic Chromosome ◽  
Metaphase Plate ◽  
Time Reversal Symmetry ◽  
Newtonian Mechanics ◽  
Arrow Of Time ◽  
Cell Nuclei ◽  
Mitotic Chromosomes ◽  
Daughter Cells

AbstractIn cell division, mitosis is the phase in which duplicated sets of chromosomes are mechanically aligned to form the metaphase plate before being segregated in two daughter cells. Irreversibility is a hallmark of this process, despite the fundamental laws of Newtonian mechanics being time symmetric.Here we show experimentally that mitotic chromosomes receive the arrow of time by time-reversal-symmetry breaking of the underlying mechanics in prometaphase. By optically inducing hydrodynamic flows within prophase nuclei, we find that duplicated chromatid pairs initially form a fluid suspension in the nucleoplasm: although showing little motion on their own, condensed chromosomes are free to move through the nucleus in a time-reversible manner. Actively probing chromosome mobility further in time, we find that this viscous suspension of chromatin transitions into a gel after nuclear breakdown. This gel state, in which chromosomes cannot be moved by flows, persists even when chromosomes start moving to form the metaphase plate. Complemented by minimal reconstitution experiments, our active intra-nuclear micro-rheology reveals time-reversal-symmetry breaking of chromosome mechanics to be caused by the transition from a purely fluid suspension into an active gel.Graphical abstractOne sentence summaryFlows induced in living cell nuclei reveal the rheological changes that bring chromosomes under mechanical control during mitosis.

scholarly journals A Bromodomain Protein, MCAP, Associates with Mitotic Chromosomes and Affects G2-to-M Transition

2000 ◽  
Vol 20 (17) ◽  
pp. 6537-6549 ◽  
Author(s):  
Anup Dey ◽  
Jan Ellenberg ◽  
Andrea Farina ◽  
Allen E. Coleman ◽  
Tetsuo Maruyama ◽  
...  
Keyword(s):  
Mitotic Chromosome ◽  
Histone H3 ◽  
Growth Stimulation ◽  
Nuclear Factor ◽  
Cell Nuclei ◽  
Mitotic Chromosomes ◽  
H3 Phosphorylation ◽  
Chromosomal Condensation ◽  
Histone H3 Phosphorylation ◽  
Exquisite Specificity

ABSTRACT We describe a novel nuclear factor called mitotic chromosome-associated protein (MCAP), which belongs to the poorly understood BET subgroup of the bromodomain superfamily. Expression of the 200-kDa MCAP was linked to cell division, as it was induced by growth stimulation and repressed by growth inhibition. The most notable feature of MCAP was its association with chromosomes during mitosis, observed at a time when the majority of nuclear regulatory factors were released into the cytoplasm, coinciding with global cessation of transcription. Indicative of its predominant interaction with euchromatin, MCAP localized on mitotic chromosomes with exquisite specificity: (i) MCAP-chromosome association became evident subsequent to the initiation of histone H3 phosphorylation and early chromosomal condensation; and (ii) MCAP was absent from centromeres, the sites of heterochromatin. Supporting a role for MCAP in G2/M transition, microinjection of anti-MCAP antibody into HeLa cell nuclei completely inhibited the entry into mitosis, without abrogating the ongoing DNA replication. These results suggest that MCAP plays a role in a process governing chromosomal dynamics during mitosis.

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 A Proposed Unified Interphase Nucleus Chromosome Structure: Preliminary Preponderance of Evidence

2021 ◽  
Author(s):  
John Sedat ◽  
Angus McDonald ◽  
Hu Cang ◽  
Joseph S Lucas ◽  
Muthuvel Arigovindan ◽  
...  
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
Large Scale ◽  
Interphase Nucleus ◽  
Chromosome Structure ◽  
Electron Tomography ◽  
Hollow Structure ◽  
Interphase Chromosome ◽  
Transmission Electron ◽  
Cryo Electron Tomography ◽  
Scanning Transmission

Cellular cryo-electron tomography (CET) of the cell nucleus using Scanning Transmission Electron Microscopy (STEM) and the use of deconvolution (DC) processing technology has highlighted a large-scale, 100-300 nm interphase chromosome structure (LSS), that is present throughout the nucleus. This chromosome structure appears to coil the nucleosome 11-nm fiber into a defined hollow structure, analogous to a Slinky (S) (1, motif used in 2) helical spring. This S architecture can be used to build chromosome territories, extended to polytene chromosome structure, as well as to the structure of Lampbrush chromosomes.

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 A simple biophysical model emulates budding yeast chromosome condensation

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Tammy MK Cheng ◽  
Sebastian Heeger ◽  
Raphaël AG Chaleil ◽  
Nik Matthews ◽  
Aengus Stewart ◽  
...  
Keyword(s):  
Binding Sites ◽  
Budding Yeast ◽  
Molecular Model ◽  
Biophysical Model ◽  
Molecular Architecture ◽  
Mitotic Chromosomes ◽  
Chromosome Architecture ◽  
Pairwise Interactions ◽  
Condensin Complex ◽  
Yeast Chromosome

Mitotic chromosomes were one of the first cell biological structures to be described, yet their molecular architecture remains poorly understood. We have devised a simple biophysical model of a 300 kb-long nucleosome chain, the size of a budding yeast chromosome, constrained by interactions between binding sites of the chromosomal condensin complex, a key component of interphase and mitotic chromosomes. Comparisons of computational and experimental (4C) interaction maps, and other biophysical features, allow us to predict a mode of condensin action. Stochastic condensin-mediated pairwise interactions along the nucleosome chain generate native-like chromosome features and recapitulate chromosome compaction and individualization during mitotic condensation. Higher order interactions between condensin binding sites explain the data less well. Our results suggest that basic assumptions about chromatin behavior go a long way to explain chromosome architecture and are able to generate a molecular model of what the inside of a chromosome is likely to look like.

scholarly journals Effects of altering histone post-translational modifications on mitotic chromosome structure and mechanics

2018 ◽  
Author(s):  
Ronald Biggs ◽  
Patrick Liu ◽  
Andrew D. Stephens ◽  
John F. Marko
Keyword(s):  
Large Scale ◽  
Mitotic Chromosome ◽  
Chromosome Doubling ◽  
Chromosome Length ◽  
Force Measurements ◽  
Mitotic Chromosomes ◽  
Post Translational Modifications ◽  
Daughter Cells ◽  
Histone Ptms ◽  
Canonical Histone

AbstractDuring cell division chromatin is compacted into mitotic chromosomes to aid faithful segregation of the genome between two daughter cells. Post-translational modifications (PTM) of histones alter compaction of interphase chromatin, but it remains poorly understood how these modifications affect mitotic chromosome stiffness and structure. Using micropipette-based force measurements and epigenetic drugs, we probed the influence of canonical histone PTMs that dictate interphase euchromatin (acetylation) and heterochromatin (methylation) on mitotic chromosome stiffness. By measuring chromosome doubling force (the force required to double chromosome length), we find that histone methylation, but not acetylation, contributes to mitotic structure and stiffness. We discuss our findings in the context of chromatin gel modeling of the large-scale organization of mitotic chromosomes.

scholarly journals Visualization of early chromosome condensation

2004 ◽  
Vol 166 (6) ◽  
pp. 775-785 ◽  
Author(s):  
Natashe Kireeva ◽  
Margot Lakonishok ◽  
Igor Kireev ◽  
Tatsuya Hirano ◽  
Andrew S. Belmont
Keyword(s):  
Large Scale ◽  
Mitotic Chromosome ◽  
Chromosome Structure ◽  
Early Prophase ◽  
Axial Distribution ◽  
Metaphase Chromosomes ◽  
Topoisomerase Iiα ◽  
Late Prophase ◽  
Chromatin Folding ◽  
Structural Maintenance Of Chromosomes

Current models of mitotic chromosome structure are based largely on the examination of maximally condensed metaphase chromosomes. Here, we test these models by correlating the distribution of two scaffold components with the appearance of prophase chromosome folding intermediates. We confirm an axial distribution of topoisomerase IIα and the condensin subunit, structural maintenance of chromosomes 2 (SMC2), in unextracted metaphase chromosomes, with SMC2 localizing to a 150–200-nm-diameter central core. In contrast to predictions of radial loop/scaffold models, this axial distribution does not appear until late prophase, after formation of uniformly condensed middle prophase chromosomes. Instead, SMC2 associates throughout early and middle prophase chromatids, frequently forming foci over the chromosome exterior. Early prophase condensation occurs through folding of large-scale chromatin fibers into condensed masses. These resolve into linear, 200–300-nm-diameter middle prophase chromatids that double in diameter by late prophase. We propose a unified model of chromosome structure in which hierarchical levels of chromatin folding are stabilized late in mitosis by an axial “glue.”

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