Metaphase chromosome structure: Evidence for a radial loop model

Marsden, Margery P. F.; Laemmli, Ulrich Karl

doi:10.1016/0092-8674(79)90325-8

Cited by 515 publications

(317 citation statements)

References 15 publications

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“…EM visualization of DNA loops extending from a protein-rich chromosome body after histone depletion (Paulson & Laemmli 1977), plus visualization of structures consistent with a loop organization in serial-sectioned fixed cells (Marsden & Laemmli 1979, Adolph 1980, 1981, Adolph & Phelps 1982, Adolph et al 1986, Maeshima et al 2005, support a model for mitotic chromosome structure based on chromatin loops interconnected by a non-histone-protein-rich Fscaffold_ (Marsden & Laemmli 1979). In human cells, mitotic loops observed in EM experiments are 50Y100 kb in size.…”

Section: Large-scale Mitotic Chromosome Organizationmentioning

confidence: 77%

Micromechanical studies of mitotic chromosomes

2008

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Mitotic chromosomes respond elastically to forces in the nanonewton range, a property important to transduction of stresses used as mechanical regulatory signals during cell division. In addition to being important biologically, chromosome elasticity can be used as a tool for investigating the folding of chromatin. This paper reviews experiments studying stretching and bending stiffness of mitotic chromosomes, plus experiments where changes in chromosome elasticity resulting from chemical and enzyme treatments were used to analyse connectivity of chromatin inside chromosomes. Experiments with nucleases indicate that non-DNA elements constraining mitotic chromatin must be isolated from one another, leading to the conclusion that mitotic chromosomes have a chromatin Fnetwork_ or Fgel_ organization, with stretches of chromatin strung between Fcrosslinking_ points. The as-yet unresolved questions of the identities of the putative chromatin crosslinkers and their organization inside mitotic chromosomes are discussed.

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Section: Large-scale Mitotic Chromosome Organizationmentioning

confidence: 77%

Micromechanical studies of mitotic chromosomes

2008

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“…As described above, matrix or scaffold proteins in this model are a t the center of each 240 nm fiber, and thus would not require additional space at the center of the coil. The appearance of matrix (scaffold) proteins a t the center of disrupted metaphase chromosomes may be more apparent (preparation dependent) than real (49). Recent studies with antibodies to topoisomerase I1 have shown that this matrix bound enzyme does in fact follow the metaphase coil (5); it is possible that the observed opposite handedness of helical coils in each sister chromatid materializes after separation of the sister chromatids.…”

Section: Metaphasementioning

confidence: 99%

A unified model of eukaryotic chromosomes

1990

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A revised model of DNA packaging into chromosomes is presented. Its features are consistent with observed structural dimensions and the molecular periodicities related to transcription, replication and matrix attachment domains. Thetransitions between euchromatic, heterochromatic and metaphase states are explained simply. Molecular and physical properties of chromosomal bands, and their correlation with specific DNA sequence motifs are discussed.Key terms: Chromatin, chromosome structure, matrix, replication, Giemsa bands, repeated DNA The higher order molecular and physical structure of chromosomes is still poorly understood. The winding of the DNA double helix around histones to form 10 nm thick nucleosomes or "beads on a string," and the subsequent coiling of nucleosomes into solenoids of -30 nm x 10 nm is by now well-established. Each solenoid turn however encompasses only -1.2 kb of DNA, and is too small to embrace complex transcriptional and replication domains that may span several hundred kilobases of DNA. These larger "functional" units of DNA are likely to be arranged into hierarchical structures that can be recognized and conveniently utilized in a n orderly fashion. On a purely structural level, the delineation of metaphase chromosome bands by Giemsa staining suggests that such hierarchies exist; Giemsa bands encompass megabase (Mb) stretches of DNA and are not meaningless artifacts; for example, Giemsalight bands are preferentially digested by trypsin, indicating structural andior molecular components are specifically organized in these compartments, and overall binding patterns may be conserved in evolution (27). Furthermore, domains of similar large size, that may correspond to Giemsa bands, are involved in sister chromatid exchanges, translocations and replication. Sam Latt made many original contributions to the molecular organization of the genome, and one of his eminent contributions was the delineation of sister chromatid exchanges (32). In his honor, we present a physical model of chromosome structure that encompasses units of this size.We here build an updated model that incorporates the longer features of molecular gene organization that have become apparent in the last 10 years. Such features include units that range in size from very long linear lengths of DNA, as defined by chromosome banding techniques, pulse-field gel electrophoresis (PFGE), and high-resolution non-isotopic in-situ hybridization, through smaller DNA lengths of 30-120kb that periodically attach to matrix proteins and replication complexes. To date, no model of chromosome structure adequately addresses the folding or compaction of these longer DNA lengths in both interphase and metaphase chromosomes of known dimensions. Since these dimensional constraints are essential to any realistic model of chromosome folding, we first address the actual sizes of chromosome domains i n both interphase and metaphase chromosomes. The structure of interphase chromosomes is pivotal, since interphase cells carry out key functions such as...

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“…From the level of the nucleosome, chromatin undergoes several changes in organization (Earnshaw, 1988;Filipski et al, 1990). A scaffold of proteins form an axis along which solenoidal chromatin loops are folded into rosettes, which then coalesce to form a sausage-shaped chromonema Marsden and Laemmli, 1979;Johnson, 1979, 1980;Earnshaw and Laemmli, 1983;Earnshaw, 1988). The metaphase chromosome consists of a folded or coiled chromonema (Manton, 1950).…”

Section: Introductionmentioning

confidence: 99%

In Vivo Analysis of Chromosome Condensation inSaccharomyces cerevisiae

Vas

Andrews

Matesky

et al. 2007

MBoC

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Although chromosome condensation in the yeast Saccharomyces cerevisiae has been widely studied, visualization of this process in vivo has not been achieved. Using Lac operator sequences integrated at two loci on the right arm of chromosome IV and a Lac repressor-GFP fusion protein, we were able to visualize linear condensation of this chromosome arm during G2/M phase. As previously determined in fixed cells, condensation in yeast required the condensin complex. Not seen after fixation of cells, we found that topoisomerase II is required for linear condensation. Further analysis of perturbed mitoses unexpectedly revealed that condensation is a transient state that occurs before anaphase in budding yeast. Blocking anaphase progression by activation of the spindle assembly checkpoint caused a loss of condensation that was dependent on Mad2, followed by a delayed loss of cohesion between sister chromatids. Release of cells from spindle checkpoint arrest resulted in recondensation before anaphase onset. The loss of condensation in preanaphase-arrested cells was abrogated by overproduction of the aurora B kinase, Ipl1, whereas in ipl1-321 mutant cells condensation was prematurely lost in anaphase/telophase. In vivo analysis of chromosome condensation has therefore revealed unsuspected relationships between higher order chromatin structure and cell cycle control. INTRODUCTIONAccurate chromosome segregation during mitosis is facilitated by the resolution of chromosomes into compact structures. From the level of the nucleosome, chromatin undergoes several changes in organization (Earnshaw, 1988;Filipski et al., 1990). A scaffold of proteins form an axis along which solenoidal chromatin loops are folded into rosettes, which then coalesce to form a sausage-shaped chromonema Marsden and Laemmli, 1979; Johnson, 1979, 1980;Earnshaw and Laemmli, 1983;Earnshaw, 1988). The metaphase chromosome consists of a folded or coiled chromonema (Manton, 1950). In a more recent model of chromosome organization, chromatin is folded into fibers around the central axis, which acts as a "glue" (Kireeva et al., 2004). In both of these models, the protein scaffold is proposed to condense linearly during mitosis.The mitotic scaffold was first observed in histone-depleted mammalian chromosomes and components of this protein scaffold have been of considerable interest (Adolphs et al., 1977;Paulson and Laemmli, 1977). In higher eukaryotes, the process of condensing chromosomes before anaphase requires a protein scaffold comprised of at least condensin and topoisomerase II (Earnshaw et al., 1985;Gasser et al., 1986;Adachi et al., 1991;Saitoh et al., 1994;Gimenez-Abian et al., 1995;Hirano et al., 1997;Maeshima and Laemmli, 2003). Condensin is a five-subunit complex that was first identified in Xenopus egg extracts (Hirano, 2005). Homologues of mitotic scaffold proteins are present in all eukaryotes (reviewed in Hirano, 2005). In the budding yeast Saccharomyces cerevisiae, homologues of the condensin complex, encoded by SMC2, SMC4, YCG1, YCS4, and BRN...

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Metaphase chromosome structure: Evidence for a radial loop model

Cited by 515 publications

References 15 publications

Micromechanical studies of mitotic chromosomes

Micromechanical studies of mitotic chromosomes

A unified model of eukaryotic chromosomes

In Vivo Analysis of Chromosome Condensation inSaccharomyces cerevisiae

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