TOPII and chromosome movement help remove interlocks between entangled chromosomes during meiosis

During the zygotene stage of meiosis, normal progression of chromosome synapsis and homologous recombination frequently lead to the formation of structural interlocks between entangled chromosomes. The persistence of interlocks through to the first meiotic division can jeopardize normal synapsis and occasionally chromosome segregation. However, they are generally removed by pachytene. It has been postulated that interlock removal requires one or more active processes, possibly involving topoisomerase II (TOPII) and/or chromosome movement. However, experimental evidence has been lacking. Analysis of a hypomorphic topII mutant and a meiosis-specific topII RNAi knockdown of Arabidopsis thaliana using immunocytochemistry and structured illumination microscopy (SIM) has now enabled us to demonstrate a role for TOPII in interlock resolution. Furthermore, analysis using a nucleoporin nup136 mutant, which affects chromosome movement, reveals that although TOPII activity is required for the removal of some interlock structures, for others, chromosome movement is also necessary. Thus, our study demonstrates that at least two mechanisms are required to ensure interlock removal.

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Structured Illumination Microscopy illuminates the nascale behaviors of cellulose synthase proteins in Arabidopsis thaliana

10.46678/pb.20.989647 ◽

2020 ◽

Author(s):

Sydney Duncombe

Keyword(s):

Arabidopsis Thaliana ◽

Cellulose Synthase ◽

Structured Illumination ◽

Structured Illumination Microscopy

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Making crossovers during meiosis

Biochemical Society Transactions ◽

10.1042/bst0331451 ◽

2005 ◽

Vol 33 (6) ◽

pp. 1451-1455 ◽

Cited By ~ 57

Author(s):

M.C. Whitby

Keyword(s):

Genetic Variation ◽

Homologous Recombination ◽

Chromosome Segregation ◽

Meiotic Recombination ◽

Meiotic Division ◽

Holliday Junctions ◽

Meiotic Spindle ◽

Homologous Chromosomes ◽

Dna Junctions

Homologous recombination (HR) is required to promote both correct chromosome segregation and genetic variation during meiosis. For this to be successful recombination intermediates must be resolved to generate reciprocal exchanges or ‘crossovers’ between the homologous chromosomes (homologues) during the first meiotic division. Crossover recombination promotes faithful chromosome segregation by establishing connections (chiasmata) between the homologues, which help guide their proper bipolar alignment on the meiotic spindle. Recent studies of meiotic recombination in both the budding and fission yeasts have established that there are at least two pathways for generating crossovers. One pathway involves the resolution of fully ligated four-way DNA junctions [HJs (Holliday junctions)] by an as yet unidentified endonuclease. The second pathway appears to involve the cleavage of the precursors of ligated HJs, namely displacement (D) loops and unligated/nicked HJs, by the Mus81-Eme1/Mms4 endonuclease.

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Superresolution expansion microscopy reveals the three-dimensional organization of the Drosophila synaptonemal complex

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1705623114 ◽

2017 ◽

Vol 114 (33) ◽

pp. E6857-E6866 ◽

Cited By ~ 67

Author(s):

Cori K. Cahoon ◽

Zulin Yu ◽

Yongfu Wang ◽

Fengli Guo ◽

Jay R. Unruh ◽

...

Keyword(s):

Synaptonemal Complex ◽

Chromosome Segregation ◽

Biological Sample ◽

3D Model ◽

Three Dimensional ◽

Optical Resolution ◽

Structured Illumination ◽

Structured Illumination Microscopy ◽

Homologous Chromosomes ◽

Superresolution Microscopy

The synaptonemal complex (SC), a structure highly conserved from yeast to mammals, assembles between homologous chromosomes and is essential for accurate chromosome segregation at the first meiotic division. In Drosophila melanogaster, many SC components and their general positions within the complex have been dissected through a combination of genetic analyses, superresolution microscopy, and electron microscopy. Although these studies provide a 2D understanding of SC structure in Drosophila, the inability to optically resolve the minute distances between proteins in the complex has precluded its 3D characterization. A recently described technology termed expansion microscopy (ExM) uniformly increases the size of a biological sample, thereby circumventing the limits of optical resolution. By adapting the ExM protocol to render it compatible with structured illumination microscopy, we can examine the 3D organization of several known Drosophila SC components. These data provide evidence that two layers of SC are assembled. We further speculate that each SC layer may connect two nonsister chromatids, and present a 3D model of the Drosophila SC based on these findings.

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Integrity of the human centromere DNA repeats is protected by CENP-A, CENP-C, and CENP-T

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1615133114 ◽

2017 ◽

Vol 114 (8) ◽

pp. 1928-1933 ◽

Cited By ~ 47

Author(s):

Simona Giunta ◽

Hironori Funabiki

Keyword(s):

Chromosome Segregation ◽

Satellite Dna ◽

Replicative Senescence ◽

Alternative Methods ◽

Dna Repeats ◽

Structured Illumination ◽

Structured Illumination Microscopy ◽

Satellite Repeat ◽

Culture Cells ◽

Centromeric Repeat

Centromeres are highly specialized chromatin domains that enable chromosome segregation and orchestrate faithful cell division. Human centromeres are composed of tandem arrays of α-satellite DNA, which spans up to several megabases. Little is known about the mechanisms that maintain integrity of the long arrays of α-satellite DNA repeats. Here, we monitored centromeric repeat stability in human cells using chromosome-orientation fluorescent in situ hybridization (CO-FISH). This assay detected aberrant centromeric CO-FISH patterns consistent with sister chromatid exchange at the frequency of 5% in primary tissue culture cells, whereas higher levels were seen in several cancer cell lines and during replicative senescence. To understand the mechanism(s) that maintains centromere integrity, we examined the contribution of the centromere-specific histone variant CENP-A and members of the constitutive centromere-associated network (CCAN), CENP-C, CENP-T, and CENP-W. Depletion of CENP-A and CCAN proteins led to an increase in centromere aberrations, whereas enhancing chromosome missegregation by alternative methods did not, suggesting that CENP-A and CCAN proteins help maintain centromere integrity independently of their role in chromosome segregation. Furthermore, superresolution imaging of centromeric CO-FISH using structured illumination microscopy implied that CENP-A protects α-satellite repeats from extensive rearrangements. Our study points toward the presence of a centromere-specific mechanism that actively maintains α-satellite repeat integrity during human cell proliferation.

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The crossover function of MutSγ is activated via Cdc7-dependent stabilization of Msh4

10.1101/386458 ◽

2018 ◽

Cited By ~ 1

Author(s):

Wei He ◽

H.B.D. Prasada Rao ◽

Shangming Tang ◽

Nikhil Bhagwat ◽

Dhananjaya S. Kulkarni ◽

...

Keyword(s):

Homologous Recombination ◽

Chromosome Segregation ◽

Holliday Junctions ◽

Strand Exchange ◽

Crossing Over ◽

Chromosome Synapsis ◽

Meiotic Crossover ◽

Dna Strand Exchange ◽

Dna Strand ◽

Fundamental Mechanism

SUMMARYThe MutSγ complex, Msh4-Msh5, binds DNA joint-molecule (JM) intermediates during homologous recombination to promote crossing over and accurate chromosome segregation at the first division of meiosis. MutSγ facilitates the formation and biased resolution of crossover-specific JM intermediates called double Holliday junctions. Here we show that these activities are governed by regulated proteasomal degradation. MutSγ is initially inactive for crossing over due to an N-terminal degron on Msh4 that renders it unstable. Activation of MutSγ requires the Dbf4-dependent kinase, Cdc7 (DDK), which directly phosphorylates and thereby neutralizes the Msh4 degron. Phosphorylated Msh4 is chromatin bound and requires DNA strand exchange and chromosome synapsis, implying that DDK specifically targets MutSγ that has already bound nascent JMs. Our study establishes regulated protein degradation as a fundamental mechanism underlying meiotic crossover control.

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