C. elegans condensin promotes mitotic chromosome architecture, centromere organization, and sister chromatid segregation during mitosis and meiosis

Structural maintenance of chromosomes (SMC) complexes are key organizers of chromosome architecture in all kingdoms of life. Despite seemingly divergent functions, such as chromosome segregation, chromosome maintenance, sister chromatid cohesion, and mitotic chromosome compaction, it appears that these complexes function via highly conserved mechanisms and that they represent a novel class of DNA translocases.

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A quantitative map of human Condensins provides new insights into mitotic chromosome architecture

The Journal of Cell Biology ◽

10.1083/jcb.201801048 ◽

2018 ◽

Vol 217 (7) ◽

pp. 2309-2328 ◽

Cited By ~ 80

Author(s):

Nike Walther ◽

M. Julius Hossain ◽

Antonio Z. Politi ◽

Birgit Koch ◽

Moritz Kueblbeck ◽

...

Keyword(s):

Mitotic Chromosome ◽

Maximum Size ◽

Correlation Spectroscopy ◽

Loop Model ◽

Absolute Abundance ◽

Superresolution Microscopy ◽

Chromosome Architecture ◽

Fluorescence Correlation ◽

Chromatid Segregation ◽

Early Anaphase

The two Condensin complexes in human cells are essential for mitotic chromosome structure. We used homozygous genome editing to fluorescently tag Condensin I and II subunits and mapped their absolute abundance, spacing, and dynamic localization during mitosis by fluorescence correlation spectroscopy (FSC)–calibrated live-cell imaging and superresolution microscopy. Although ∼35,000 Condensin II complexes are stably bound to chromosomes throughout mitosis, ∼195,000 Condensin I complexes dynamically bind in two steps: prometaphase and early anaphase. The two Condensins rarely colocalize at the chromatid axis, where Condensin II is centrally confined, but Condensin I reaches ∼50% of the chromatid diameter from its center. Based on our comprehensive quantitative data, we propose a three-step hierarchical loop model of mitotic chromosome compaction: Condensin II initially fixes loops of a maximum size of ∼450 kb at the chromatid axis, whose size is then reduced by Condensin I binding to ∼90 kb in prometaphase and ∼70 kb in anaphase, achieving maximum chromosome compaction upon sister chromatid segregation.

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Shugoshin is essential for meiotic prophase checkpoints in C. elegans

10.1101/258830 ◽

2018 ◽

Author(s):

Tisha Bohr ◽

Christian R. Nelson ◽

Stefani Giacopazzi ◽

Piero Lamelza ◽

Needhi Bhalla

Keyword(s):

Sister Chromatid ◽

Meiotic Prophase ◽

Meiotic Chromosome ◽

Sister Chromatid Cohesion ◽

Chromosomal Protein ◽

Loss Of Function ◽

Chromosome Architecture ◽

C Elegans ◽

Meiotic Chromosomes ◽

Chromatid Cohesion

AbstractThe conserved factor Shugoshin is dispensable in C. elegans for the two-step loss of sister chromatid cohesion that directs the proper segregation of meiotic chromosomes. We show that the C. elegans ortholog of Shugoshin, SGO-1, is required for checkpoint activity in meiotic prophase. This role in checkpoint function is similar to that of the meiotic chromosomal protein, HTP-3. Null sgo-1 mutants exhibit additional phenotypes similar to that of a partial loss of function allele of HTP-3: premature synaptonemal complex disassembly, the activation of alternate DNA repair pathways and an inability to recruit a conserved effector of the DNA damage pathway, HUS-1. SGO-1 localizes to pre-meiotic nuclei, when HTP-3 is present but not yet loaded onto chromosome axes, suggesting an early role in regulating meiotic chromosome metabolism. We propose that SGO-1 acts during pre-meiotic replication to ensure fully functional meiotic chromosome architecture, rendering these chromosomes competent for checkpoint activity and normal progression of meiotic recombination. Given that most research on Shugoshin has been focused on its regulation of sister chromatid cohesion in meiosis, this novel role may be conserved but previously uncharacterized in other organisms. Further, our findings expand the repertoire of Shugoshin’s functions beyond coordinating regulatory activities at the centromere.

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Random segregation of chromatids at mitosis in Saccharomyces cerevisiae.

Genetics ◽

10.1093/genetics/127.3.463 ◽

1991 ◽

Vol 127 (3) ◽

pp. 463-473 ◽

Cited By ~ 1

Author(s):

M W Neff ◽

D J Burke

Keyword(s):

Saccharomyces Cerevisiae ◽

Sister Chromatid ◽

Mitotic Chromosome ◽

Sister Chromatid Exchanges ◽

Daughter Cells ◽

Quantitative Measurements ◽

Chromatid Segregation ◽

Dna Strands ◽

Random Segregation ◽

Chromatid Exchanges

Abstract Previous experiments suggest that mitotic chromosome segregation in some fungi is a nonrandom process in which chromatids of the same replicative age are destined for cosegregation. We have investigated the pattern of chromatid segregation in Saccharomyces cerevisiae by labeling the DNA of a strain auxotrophic for thymidine with 5-bromodeoxyuridine. The fate of DNA strands was followed qualitatively by immunofluorescence microscopy and quantitatively by microphotometry using an anti-5-bromodeoxyuridine monoclonal antibody. Chromatids of the same replicative age were distributed randomly to daughter cells at mitosis. Quantitative measurements showed that the amount of fluorescence in the daughter nuclei derived from parents with hemilabeled chromosomes diminished in intensity by one half. The concentration of 5-bromodeoxyuridine used in the experiments had little effect on the frequency of either homologous or sister chromatid exchanges. We infer that the 5-bromodeoxyuridine was distributed randomly due to mitotic segregation of chromatids and not via sister chromatid exchanges.

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A quantitative map of human Condensins provides new insights into mitotic chromosome architecture

10.1101/237834 ◽

2018 ◽

Cited By ~ 1

Author(s):

Nike Walther ◽

M. Julius Hossain ◽

Antonio Z. Politi ◽

Birgit Koch ◽

Moritz Kueblbeck ◽

...

Keyword(s):

Mitotic Chromosome ◽

Super Resolution ◽

Maximum Size ◽

Correlation Spectroscopy ◽

Loop Model ◽

Chromosome Architecture ◽

Fluorescence Correlation ◽

Chromatid Segregation ◽

Early Anaphase ◽

Super Resolution Microscopy

AbstractThe two Condensin complexes in human cells are essential for mitotic chromosome structure. We used homozygous genome editing to fluorescently tag Condensin I and II subunits and mapped their absolute abundance, spacing and dynamic localization during mitosis by fluorescence correlation spectroscopy-calibrated live cell imaging and super-resolution microscopy. While ∼35,000 Condensin II complexes are stably bound to chromosomes throughout mitosis, ∼195,000 Condensin I complexes dynamically bind in two steps, in prometaphase and early anaphase. The two Condensins rarely co-localize at the chromatid axis, where Condensin II is centrally confined but Condensin I reaches ∼50% of the chromatid diameter from its center. Based on our comprehensive quantitative data, we propose a three-step hierarchical loop model of mitotic chromosome compaction: Condensin II initially fixes loops of a maximum size of ∼450 kb at the chromatid axis whose size is then reduced by Condensin I binding to ∼90 kb in prometaphase and ∼70 kb in anaphase, achieving maximum chromosome compaction upon sister chromatid segregation.

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Chromatid cohesion during mitosis: lessons from meiosis

Journal of Cell Science ◽

10.1242/jcs.112.16.2607 ◽

1999 ◽

Vol 112 (16) ◽

pp. 2607-2613 ◽

Cited By ~ 4

Author(s):

C.L. Rieder ◽

R. Cole

Keyword(s):

Sister Chromatid ◽

Mitotic Chromosome ◽

Sister Chromatid Cohesion ◽

Centromere Region ◽

Equal Distribution ◽

Chromatid Cohesion ◽

Mitosis And Meiosis

The equal distribution of chromosomes during mitosis and meiosis is dependent on the maintenance of sister chromatid cohesion. In this commentary we review the evidence that, during meiosis, the mechanism underlying the cohesion of chromatids along their arms is different from that responsible for cohesion in the centromere region. We then argue that the chromatids on a mitotic chromosome are also tethered along their arms and in the centromere by different mechanisms, and that the functional action of these two mechanisms can be temporally separated under various conditions. Finally, we demonstrate that in the absence of a centromeric tether, arm cohesion is sufficient to maintain chromatid cohesion during prometaphase of mitosis. This finding provides a straightforward explanation for why mutants in proteins responsible for centromeric cohesion in Drosophila (e.g. ord, mei-s332) disrupt meiosis but not mitosis.

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Induced Chromosomal Exchange Directs the Segregation of Recombinant Chromatids in Mitosis of Drosophila

Genetics ◽

10.1093/genetics/150.1.173 ◽

1998 ◽

Vol 150 (1) ◽

pp. 173-188 ◽

Cited By ~ 2

Author(s):

Kelly J Beumer ◽

Sergio Pimpinelli ◽

Kent G Golic

Keyword(s):

Chromosome Segregation ◽

Sister Chromatid ◽

Evolutionary Relationship ◽

Genetic Exchange ◽

Cytological Evidence ◽

Reciprocal Translocations ◽

Chromatid Segregation ◽

Proximal Site ◽

Chromatid Cohesion ◽

Mitosis And Meiosis

Abstract In meiosis, the segregation of chromosomes at the reductional division is accomplished by first linking homologs together. Genetic exchange generates the bivalents that direct regular chromosome segregation. We show that genetic exchange in mitosis also generates bivalents and that these bivalents direct mitotic chromosome segregation. After FLP-mediated homologous recombination in G2 of the cell cycle, recombinant chromatids consistently segregate away from each other (x segregation). This pattern of segregation also applies to exchange between heterologs. Most, or all, cases of non-x segregation are the result of exchange in G1. Cytological evidence is presented that confirms the existence of the bivalents that direct this pattern of segregation. Our results implicate sister chromatid cohesion in maintenance of the bivalent. The pattern of chromatid segregation can be altered by providing an additional FRT at a more proximal site on one chromosome. We propose that sister chromatid exchange occurs at the more proximal site, allowing the recombinant chromatids to segregate together. This also allowed the recovery of reciprocal translocations following FLP-mediated heterologous recombination. The observation that exchange can generate a bivalent in mitotic divisions provides support for a simple evolutionary relationship between mitosis and meiosis.

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glp-3 Is Required for Mitosis and Meiosis in the Caenorhabditis elegans Germ Line

Genetics ◽

10.1093/genetics/145.1.111 ◽

1997 ◽

Vol 145 (1) ◽

pp. 111-121 ◽

Cited By ~ 1

Author(s):

Lisa C Kadyk ◽

Eric J Lambie ◽

Judith Kimble

Keyword(s):

Caenorhabditis Elegans ◽

Germ Cells ◽

Germ Line ◽

Stem Cell Population ◽

Phenotypic Characterization ◽

Loss Of Function ◽

Dapi Staining ◽

Cell Cycles ◽

C Elegans ◽

Mitosis And Meiosis

The germ line is the only tissue in Caenorhabditis elegans in which a stem cell population continues to divide mitotically throughout life; hence the cell cycles of the germ line and the soma are regulated differently. Here we report the genetic and phenotypic characterization of the glp-3 gene. In animals homozygous for each of five recessive loss-of-function alleles, germ cells in both hermaphrodites and males fail to progress through mitosis and meiosis, but somatic cells appear to divide normally. Germ cells in animals grown at 15° appear by DAPI staining to be uniformly arrested at the G2/M transition with <20 germ cells per gonad on average, suggesting a checkpoint-mediated arrest. In contrast, germ cells in mutant animals grown at 25° frequently proliferate slowly during adulthood, eventually forming small germ lines with several hundred germ cells. Nevertheless, cells in these small germ lines never undergo meiosis. Double mutant analysis with mutations in other genes affecting germ cell proliferation supports the idea that glp-3 may encode a gene product that is required for the mitotic and meiotic cell cycles in the C. elegans germ line.

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