scholarly journals Mitotic chromosomes fold by condensin-dependent helical winding of chromatin loop arrays

2017 ◽  
Author(s):  
Johan H. Gibcus ◽  
Kumiko Samejima ◽  
Anton Goloborodko ◽  
Itaru Samejima ◽  
Natalia Naumova ◽  
...  
Keyword(s):  
Mitotic Chromosome ◽  
Conformation Analysis ◽  
Interphase Chromatin ◽  
Mitotic Chromosomes ◽  
Metaphase Chromosomes ◽  
Late Prophase ◽  
Nested Loops ◽  
Helical Winding ◽  
Progressive Growth ◽  
Helical Turn

AbstractDuring mitosis, chromosomes fold into compacted rod shaped structures. We combined imaging and Hi-C of synchronous DT40 cell cultures with polymer simulations to determine how interphase chromosomes are converted into compressed arrays of loops characteristic of mitotic chromosomes. We found that the interphase organization is disassembled within minutes of prophase entry and by late prophase chromosomes are already folded as arrays of consecutive loops. During prometaphase, this array reorganizes to form a helical arrangement of nested loops. Polymer simulations reveal that Hi-C data are inconsistent with solenoidal coiling of the entire chromatid, but instead suggest a centrally located helically twisted axis from which consecutive loops emanate as in a spiral staircase. Chromosomes subsequently shorten through progressive helical winding, with the numbers of loops per turn increasing so that the size of a helical turn grows from around 3 Mb (~40 loops) to ~12 Mb (~150 loops) in fully condensed metaphase chromosomes. Condensin is essential to disassemble the interphase chromatin conformation. Analysis of mutants revealed differing roles for condensin I and II during these processes. Either condensin can mediate formation of loop arrays. However, condensin II was required for helical winding during prometaphase, whereas condensin I modulated the size and arrangement of loops inside the helical turns. These observations identify a mitotic chromosome morphogenesis pathway in which folding of linear loop arrays produces long thin chromosomes during prophase that then shorten by progressive growth of loops and helical winding during prometaphase.One Sentence SummaryMitotic chromosome morphogenesis occurs through condensin-mediated disassembly of the interphase conformation and formation of extended prophase loop arrays that then shorten by loop growth and condensin-dependent helical winding.

scholarly journals A pathway for mitotic chromosome formation

Science ◽  
2018 ◽  
Vol 359 (6376) ◽  
pp. eaao6135 ◽  
Author(s):  
Johan H. Gibcus ◽  
Kumiko Samejima ◽  
Anton Goloborodko ◽  
Itaru Samejima ◽  
Natalia Naumova ◽  
...  
Keyword(s):  
Cell Cultures ◽  
Mitotic Chromosome ◽  
Dependent Manner ◽  
Mitotic Chromosomes ◽  
Chromatin Loops ◽  
Nested Loops ◽  
Helical Winding ◽  
Combined Imaging ◽  
Chromosome Formation ◽  
Differential Action

Mitotic chromosomes fold as compact arrays of chromatin loops. To identify the pathway of mitotic chromosome formation, we combined imaging and Hi-C analysis of synchronous DT40 cell cultures with polymer simulations. Here we show that in prophase, the interphase organization is rapidly lost in a condensin-dependent manner, and arrays of consecutive 60-kilobase (kb) loops are formed. During prometaphase, ~80-kb inner loops are nested within ~400-kb outer loops. The loop array acquires a helical arrangement with consecutive loops emanating from a central “spiral staircase” condensin scaffold. The size of helical turns progressively increases to ~12 megabases during prometaphase. Acute depletion of condensin I or II shows that nested loops form by differential action of the two condensins, whereas condensin II is required for helical winding.

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.”

scholarly journals An Improved Technique for High Resolution Mitotic Chromosome Studies in Solanum

HortScience ◽  
2005 ◽  
Vol 40 (1) ◽  
pp. 54-56 ◽  
Author(s):  
Qin Chen ◽  
Hai Y. Li
Keyword(s):  
Structural Changes ◽  
Mitotic Chromosome ◽  
Root Tips ◽  
Mitotic Chromosomes ◽  
Metaphase Chromosomes ◽  
Cytogenetic Studies ◽  
Breeding Schemes ◽  
Improved Technique ◽  
Mexican Species

An improved method is described for the isolation of potato metaphase chromosomes for karyotypic and cytogenetic studies. Root tips from diploid Mexican species, Solanum pinnatisectum (2n = 2x = 24) and tetraploid cultivated S. tuberosum (2n = 4x = 48) were given four different pretreatments. The synthetic pyrethroid, Ambush, was the most stable and effective pretreatment reagent, providing the highest percentage of mitotic chromosomes at metaphase and the best spread of countable chromosomes for cytogenetic studies. Compared with an Ambush pretreatment at concentrations of 100-400 ppm, 1 to 10 ppm Ambush produced more easily distinguished chromosomes, which can be useful for comprehensive observation and karyotype analysis in both 2x and 4x potato species. This improved technique for examining mitotic chromosomes will be helpful in describing karyotypes, characterization of new hybrids, and identifying chromosome structural changes that are important in breeding schemes.

scholarly journals Centromeric Localization of Dispersed Pol III Genes in Fission Yeast

2010 ◽  
Vol 21 (2) ◽  
pp. 254-265 ◽  
Author(s):  
Osamu Iwasaki ◽  
Atsunari Tanaka ◽  
Hideki Tanizawa ◽  
Shiv I.S. Grewal ◽  
Ken-ichi Noma
Keyword(s):  
Genome Organization ◽  
Gene Locus ◽  
Mitotic Chromosome ◽  
Three Dimensional ◽  
Rrna Genes ◽  
Mitotic Chromosomes ◽  
Gene Encoding ◽  
5S Rrna Genes ◽  
Pol Iii ◽  
Mitotic Chromosome Condensation

The eukaryotic genome is a complex three-dimensional entity residing in the nucleus. We present evidence that Pol III–transcribed genes such as tRNA and 5S rRNA genes can localize to centromeres and contribute to a global genome organization. Furthermore, we find that ectopic insertion of Pol III genes into a non-Pol III gene locus results in the centromeric localization of the locus. We show that the centromeric localization of Pol III genes is mediated by condensin, which interacts with the Pol III transcription machinery, and that transcription levels of the Pol III genes are negatively correlated with the centromeric localization of Pol III genes. This centromeric localization of Pol III genes initially observed in interphase becomes prominent during mitosis, when chromosomes are condensed. Remarkably, defective mitotic chromosome condensation by a condensin mutation, cut3-477, which reduces the centromeric localization of Pol III genes, is suppressed by a mutation in the sfc3 gene encoding the Pol III transcription factor TFIIIC subunit, sfc3-1. The sfc3-1 mutation promotes the centromeric localization of Pol III genes. Our study suggests there are functional links between the process of the centromeric localization of dispersed Pol III genes, their transcription, and the assembly of condensed mitotic chromosomes.

Polytene and mitotic chromosome analysis in Ceratitis capitata (Diptera; Tephritidae)

1986 ◽  
Vol 28 (2) ◽  
pp. 180-188 ◽  
Author(s):  
D. G. Bedo
Keyword(s):  
X Chromosome ◽  
Silver Staining ◽  
Mitotic Chromosome ◽  
Ceratitis Capitata ◽  
Fat Body ◽  
Polytene Chromosomes ◽  
Chromosome Analysis ◽  
Mitotic Chromosomes ◽  
Chromosome Separation ◽  
Ectopic Pairing

Polytene chromosomes were found in several larval and pupal tissues of the Medfly, Ceratitis capitata, during a search for chromosomes suitable for detailed cytological analysis. Well-banded highly polytene chromosomes, which could be adequately separated and spread, were found in trichogen cells of the spatulate superior orbital bristles of male pupae. These chromosomes proved suitable for full polytene analysis. Thoracic trichogen cells of both male and female pupae also contain useful polytene chromosomes, although they are considerably thinner and thus more difficult to analyze. Contrasting with those in pupal trichogen cells, the chromosomes in the salivary glands, Malphighian tubules, midgut, hindgut, and fat body of larvae and pupae were difficult to prepare because of high levels of ectopic pairing and chromosome fragmentation. In hindgut preparations partial separation of up to three chromosomes was achieved, but in all other tissues no useful chromosome separation was possible. In trichogen polytene cells, five banded chromosomes and a prominent heterochromatic network associated with a nucleolus are found. The mitotic chromosomes respond to C- and Q-banding and silver staining with considerable variation. This is especially so in the X chromosome, which displays an extensive array of bands following both Q-banding and silver staining. Comparison of Q-banded metaphase and polytene chromosomes demonstrates that the five autosomes are represented by conventional polytene chromosomes, while the sex chromosomes are contained in the heterochromatic net, most of which fluoresces strongly. This suggests that the Q-bands of the mitotic X chromosome are replicated to a greater extent than the nonfluorescent material in polytene cells. This investigation shows C. capitata to have excellent cytological material for both polytene and mitotic analysis.Key words: Ceratitis capitata, Medfly, chromosomes (polytene), banding (chromosome).

scholarly journals Functional Analysis of Kinetochore Assembly in Caenorhabditis elegans

2001 ◽  
Vol 153 (6) ◽  
pp. 1209-1226 ◽  
Author(s):  
Karen Oegema ◽  
Arshad Desai ◽  
Sonja Rybina ◽  
Matthew Kirkham ◽  
Anthony A. Hyman
Keyword(s):  
Caenorhabditis Elegans ◽  
Chromosome Segregation ◽  
Mitotic Chromosome ◽  
Mitotic Chromosomes ◽  
Cell Stage ◽  
Kinetochore Assembly ◽  
Chromosomal Passenger ◽  
Complete Failure ◽  
Spindle Microtubules ◽  
The One

In all eukaryotes, segregation of mitotic chromosomes requires their interaction with spindle microtubules. To dissect this interaction, we use live and fixed assays in the one-cell stage Caenorhabditis elegans embryo. We compare the consequences of depleting homologues of the centromeric histone CENP-A, the kinetochore structural component CENP-C, and the chromosomal passenger protein INCENP. Depletion of either CeCENP-A or CeCENP-C results in an identical “kinetochore null” phenotype, characterized by complete failure of mitotic chromosome segregation as well as failure to recruit other kinetochore components and to assemble a mechanically stable spindle. The similarity of their depletion phenotypes, combined with a requirement for CeCENP-A to localize CeCENP-C but not vice versa, suggest that a key step in kinetochore assembly is the recruitment of CENP-C by CENP-A–containing chromatin. Parallel analysis of CeINCENP-depleted embryos revealed mitotic chromosome segregation defects different from those observed in the absence of CeCENP-A/C. Defects are observed before and during anaphase, but the chromatin separates into two equivalently sized masses. Mechanically stable spindles assemble that show defects later in anaphase and telophase. Furthermore, kinetochore assembly and the recruitment of CeINCENP to chromosomes are independent. These results suggest distinct roles for the kinetochore and the chromosomal passengers in mitotic chromosome segregation.

scholarly journals Chromosome disentanglement driven via optimal compaction of loop-extruded brush structures

2019 ◽  
Vol 116 (50) ◽  
pp. 24956-24965 ◽  
Author(s):  
Sumitabha Brahmachari ◽  
John F. Marko
Keyword(s):  
Expression Patterns ◽  
Polymer Brush ◽  
Mitotic Chromosomes ◽  
Mechanical Stiffness ◽  
Structural Reorganization ◽  
Metaphase Chromosomes ◽  
Dna Topoisomerase ◽  
Topo Ii ◽  
Strand Passage

Eukaryote cell division features a chromosome compaction–decompaction cycle that is synchronized with their physical and topological segregation. It has been proposed that lengthwise compaction of chromatin into mitotic chromosomes via loop extrusion underlies the compaction-segregation/resolution process. We analyze this disentanglement scheme via considering the chromosome to be a succession of DNA/chromatin loops—a polymer “brush”—where active extrusion of loops controls the brush structure. Given type-II DNA topoisomerase (Topo II)-catalyzed topology fluctuations, we find that interchromosome entanglements are minimized for a certain “optimal” loop that scales with the chromosome size. The optimal loop organization is in accord with experimental data across species, suggesting an important structural role of genomic loops in maintaining a less entangled genome. Application of the model to the interphase genome indicates that active loop extrusion can maintain a level of chromosome compaction with suppressed entanglements; the transition to the metaphase state requires higher lengthwise compaction and drives complete topological segregation. Optimized genomic loops may provide a means for evolutionary propagation of gene-expression patterns while simultaneously maintaining a disentangled genome. We also find that compact metaphase chromosomes have a densely packed core along their cylindrical axes that explains their observed mechanical stiffness. Our model connects chromosome structural reorganization to topological resolution through the cell cycle and highlights a mechanism of directing Topo II-mediated strand passage via loop extrusion-driven lengthwise compaction.

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