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 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.

Memoirs: The Structure of the Somatic Chromosomes of Alstroemeria and Bomarea

1934 ◽  
Vol s2-77 (305) ◽  
pp. 49-75
Author(s):  
FRANK W. JANE
Keyword(s):  
Early Prophase ◽  
Botanic Gardens ◽  
Botanic Garden ◽  
Metaphase Chromosomes ◽  
Birkbeck College ◽  
Late Prophase ◽  
Sister Chromatids ◽  
Spiral Form ◽  
Friendly Criticism ◽  
The University

1. Investigations have been made on the chromatin throughout mitosis in Alstroemeria and Bomarea, and an attempt has been made to interpret the observations. 2. Anaphase chromosomes contain single or double spirals and often chromomeres. The spiral chromonemata are held to arise from the chromomeres. 3. The resting reticulum is formed partly from the remains of the spirals, partly from the telophasic anastomoses between adjacent chromosomes. The chromomeres form the net-knots. 4. The spiral chromosomes seen in early prophase are not regarded as homologous with the anaphase chromonema. It is not certain that all the chromosomes of a nucleus assume the spiral form during prophase. 5. The paired chromatids arise during prophase by the connecting up of adjacent daughter chromomeres into two strips of chromatin. The chromosomes do not split longitudinally at any stage. 6. Connexions between the sister chromatids are regarded as remnants of the chromonema of the previous anaphase. In this respect the interpretation agrees with Martens theory of bilateral repartition. 7. Chromomeres appear in prophase as the chromatids emerge from the spiral stage. They cease to be visible in late prophase as the chromatids thicken and become densely chromatic. 8. Prolonged destaining of the early metaphase chromosomes shows that the chromomeres are still present. Each has divided to form two daughter chromomeres. Between the chromomeres on opposite sides of the chromatid appear connexions, the new chromonema. This investigation was begun at Birkbeck College, University of London, while I was the recipient of a maintenance grant from the Department of Scientific and Industrial Research. My thanks are due to the Trustees of the Dixon Fund for the loan of a suitable microscope; to the Directors of the Eoyal Botanic Gardens, Kew, the Chelsea Physic Garden, and the University Botanic Garden, Cambridge, for material; and especially to Professor Dame Helen Gwynne-Vaughan, under whose direction the work was carried out and who has encouraged me with friendly criticism and advice.

scholarly journals ELECTRON MICROSCOPIC OBSERVATIONS ON THE SUBMICROSCOPIC MORPHOLOGY OF THE MEIOTIC NUCLEUS AND CHROMOSOMES

1956 ◽  
Vol 2 (6) ◽  
pp. 785-796 ◽  
Author(s):  
E. De Robertis
Keyword(s):  
Meiotic Prophase ◽  
Early Prophase ◽  
Electron Microscopic ◽  
Metaphase Chromosomes ◽  
Late Prophase ◽  
Continuous Transition ◽  
Thin Sections ◽  
Nucleolar Material ◽  
Mean Diameter ◽  
The Mean

Thin sections of the testicular follicles of the grasshopper Laplatacris dispar were studied under the electron microscope. In the primary spermatocytes, during meiotic prophase, three main regions can be recognized within the nucleus: (1) the nucleolus and associated nucleolar material; (2) the interchromosomal regions with the dense particles; and (3) the chromosomes. The nucleolus is generally compact and is surrounded by nucleolar bodies that comprise aggregations of dense round particles 100 to 250 A in diameter. A continuous transition can be observed between these particles and those found isolated or in short chains in the interchromosomal spaces. Particles of similar size (mean diameter of 160 A) can be found associated with the nuclear membrane and in the cytoplasm. The chromosomes show different degrees of condensation in different stages of meiotic prophase. The bulk of the chromosome appears to be made of very fine and irregularly coiled filaments of macromolecular dimensions. Their length cannot be determined because of the thinness of the section but some of them can be followed without interruption for about 1000 to 2000 A. The thickness of the chromosome filaments seems to vary with different stages of prophase and in metaphase. In early prophase, filaments vary between 28 ± 7 A and 84 ± 7 A with a mean of 47 A, in late prophase the mean is about 70 A. In metaphase the filaments vary between 60 and 170 A with a mean of about 100 A. Neither the prophase nor the metaphase chromosomes have a membrane or other inhomogeneities. The finding of a macromolecular filamentous component of chromosomes is discussed in relation to the physicochemical literature on nucleoproteins and nucleic acids and as a result it is suggested that the thinnest chromosome filaments (28 ± 7 A) probably represent single deoxyribonucleoprotein molecules.

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 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 Ki-67 and condensins support the integrity of mitotic chromosomes through distinct mechanisms

2017 ◽  
Author(s):  
Masatoshi Takagi ◽  
Takao Ono ◽  
Toyoaki Natsume ◽  
Chiyomi Sakamoto ◽  
Mitsuyoshi Nakao ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Fluorescence Recovery After Photobleaching ◽  
Mitotic Chromosome ◽  
Structural Integrity ◽  
External Surface ◽  
Mitotic Chromosomes ◽  
Topoisomerase Iiα ◽  
Ki 67 ◽  
Nuclear Envelope Breakdown ◽  
Structural Maintenance Of Chromosomes

AbstractAlthough condensins play essential roles in mitotic chromosome assembly, Ki-67, a protein localizing to the periphery of mitotic chromosomes, had also been shown to make a contribution to the process. To examine their respective roles, we generated a set of HCT116-based cell lines expressing Ki-67 and/or condensin subunits that were fused with an auxin-inducible degron for their conditional degradation. Both the localization and the dynamic behavior of Ki-67 on mitotic chromosomes were not largely affected upon depletion of condensin subunits, and vice versa. When both Ki-67 and SMC2 (a core subunit of condensins) were depleted, ball-like chromosome clusters with no sign of discernible thread-like structures were observed. This severe defective phenotype was distinct from that observed in cells depleted of either Ki-67 or SMC2 alone. Our results show that Ki-67 and condensins, which localize to the external surface and the central axis of mitotic chromosomes, respectively, have independent yet cooperative functions in supporting the structural integrity of mitotic chromosomes.List of Abbreviations usedAIDauxin-inducible degronDOXdoxycyclineFRAPfluorescence recovery after photobleachingIAAindol-3-acetic acidmAClmAID-mClovermAChmAID-mCherryNEBDnuclear envelope breakdownSMCstructural maintenance of chromosomesSTLCS-Trityl-L-cysteinetopo IIαtopoisomerase IIα

scholarly journals Metaphase chromosome structure is dynamically maintained by condensin I-directed DNA (de)catenation

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Ewa Piskadlo ◽  
Alexandra Tavares ◽  
Raquel A Oliveira
Keyword(s):  
Topoisomerase Ii ◽  
Mitotic Chromosome ◽  
Chromosome Structure ◽  
De Novo ◽  
Metaphase Chromosomes ◽  
Chromosome Architecture ◽  
Complete Failure ◽  
Drosophila Embryos ◽  
Mitotic Chromatin

Mitotic chromosome assembly remains a big mystery in biology. Condensin complexes are pivotal for chromosome architecture yet how they shape mitotic chromatin remains unknown. Using acute inactivation approaches and live-cell imaging in Drosophila embryos, we dissect the role of condensin I in the maintenance of mitotic chromosome structure with unprecedented temporal resolution. Removal of condensin I from pre-established chromosomes results in rapid disassembly of centromeric regions while most chromatin mass undergoes hyper-compaction. This is accompanied by drastic changes in the degree of sister chromatid intertwines. While wild-type metaphase chromosomes display residual levels of catenations, upon timely removal of condensin I, chromosomes present high levels of de novo Topoisomerase II (TopoII)-dependent re-entanglements, and complete failure in chromosome segregation. TopoII is thus capable of re-intertwining previously separated DNA molecules and condensin I continuously required to counteract this erroneous activity. We propose that maintenance of chromosome resolution is a highly dynamic bidirectional process.

Unorthodox male meiosis in Trichosia pubescens (Sciaridae). Chromosome elimination involves polar organelle degeneration and monocentric spindles in first and second division

1994 ◽  
Vol 107 (1) ◽  
pp. 299-312 ◽  
Author(s):  
H. Fuge
Keyword(s):  
Meiotic Division ◽  
Metaphase Plate ◽  
Chromosome Elimination ◽  
Spindle Pole ◽  
Male Meiosis ◽  
Early Prophase ◽  
Late Prophase ◽  
Section Electron ◽  
The One ◽  
Polar Organelle

Male meiosis in Trichosia pubescens (Sciaridae) was investigated by means of serial section electron microscopy and immunofluorescence light microscopy. From earlier studies of another sciarid fly, Sciara coprophila (Phillips (1967) J. Cell. Biol. 33, 73–92), it is known that the spindle poles in sciarid spermatogonia are characterized by pairs of ‘giant centrioles’, ring-shaped organelles composed of large numbers of singlet microtubules. In the present study spermatocytes in early prophase of Trichosia were found to possess single giant centrioles at opposite sides of the nucleus. The obvious reduction in centriole number from the spermatogonial to the spermatocyte stage is suggested to be the result of a suppression of daughter centriole formation. In late prophase, a large aster is developed around the centriole at one pole. At the opposite pole no comparable aster is formed. Instead, a number of irregular centriolar components appear in this region, a process that is understood to be a degeneration of the polar organelle. The components of the degenerate pole migrate into a cytoplasmic protrusion (‘bud’), which later is also utilized for the elimination of paternal chromosomes. The existence of only one functional polar centre is the reason for the formation of a monopolar monocentric spindle in first meiotic division, which in turn is one of the prerequisites for the elimination of paternal chromosomes. While the set of maternal and L chromosomes orientates and probably moves towards the pole, paternal chromosomes seem to be unable to contact the pole, possibly due to an inactivation of their kinetochores. Retrograde (‘away from the pole’) chromosome motion not involving kinetochores is assumed. Eventually, paternal chromosomes move into the pole-distal bud and are eliminated by casting off, together with the components of the degenerate polar organelle. Chromosome elimination can be delayed until the second meiotic division. The spindle of the second meiotic division is bipolar and monocentric. One spindle pole is marked by the polar centre of first division. The opposite spindle apex is devoid of a polar centre. It is assumed that spindle bipolarity in the second division is induced by the amphi-orientated chromosomes themselves. The maternal and L chromosome set (except the non-disjunctional X chromosome, which is found near the polar centre) congress in a metaphase plate, divide and segregate. Of the two daughter nuclei resulting from the second meiotic division, the one containing the X chromatids is retained as the nucleus of the future spermatozoon. The other nucleus becomes again eliminated within a second cytoplasmic bud.

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