Initiation and progression of homologous chromosome synapsis in Crepis capillaris: Variations on a theme

Genome ◽  
1999 ◽  
Vol 42 (5) ◽  
pp. 867-873 ◽  
Author(s):  
R Banerjee ◽  
G H Jones
Keyword(s):  
Synaptonemal Complex ◽  
Plant Species ◽  
Homologous Chromosome ◽  
Chromosome Length ◽  
Large Sample ◽  
Crepis Capillaris ◽  
Chromosome Synapsis ◽  
Meiotic Synapsis ◽  
Mother Cells ◽  
Variations On A Theme

The model cytogenetic plant species Crepis capillaris (2x = 6), in which all 3 chromosomes are readily distinguished, was used to analyse the initiation and progression of meiotic synapsis in a large sample of spread and silver-stained pollen mother cells. Particular emphasis was placed on detecting general patterns or trends of synaptic order, both among different bivalents and within (along) individual bivalents, and investigating the consistency or otherwise of these synaptic patterns. The order of synaptic progression and completion was partly related to chromosome length; as in other species, shorter bivalents tended to complete synapsis ahead of longer ones. Individual bivalents also showed distinct patterns of synapsis, with a tendency for subterminal regions to initiate synapsis early, followed by multiple synaptic initiations in internal bivalent regions. However, the analysis showed that these synaptic patterns are only general trends and significant variations in synaptic order and pattern, among and within bivalents, occur in individual cells.Key words: meiosis, synapsis, synaptonemal complex, Crepis.

The effect on meiotic synapsis of a recombination modulator in Petunia hybrida

Genome ◽  
1992 ◽  
Vol 35 (3) ◽  
pp. 443-453 ◽  
Author(s):  
M. Abirached-Darmency ◽  
E. Tarenghi ◽  
J. H. de Jong
Keyword(s):  
Synaptonemal Complex ◽  
Petunia Hybrida ◽  
Major Gene ◽  
Three Dimensional ◽  
Morphological Difference ◽  
Regulatory System ◽  
Recombination Rates ◽  
Meiotic Synapsis ◽  
Mother Cells

In Petunia hybrida, a major gene called Rm1 is able to induce a considerable increase in the meiotic recombination rates. To monitor the effect of Rm1 on meiotic synapsis, synaptonemal complex (SC) formation was investigated in pollen mother cells of Rm1 Rm1 and rm1 rm1 plants. Three-dimensional serial-section reconstruction showed no morphological difference in their SC structure. In two-dimensional spreading nuclei, although extensive SC formation was observed in the absence of Rm1, our observations strongly suggest that SC formation is more regular and more efficient in the presence of Rm1. SC analysis showed that the reduced chiasma frequency observed in rm1 rm1 plants corresponds to a partial failure of synapsis involving chromosome ends, pericentric regions, and may also extend to the whole length of short chromosome arms. It is proposed that Rm1 probably corresponds to a regulatory system with multiple effects, including the course of synapsis and the extent and quality of SC formation.Key words: synaptonemal complex, synapsis, chiasma, recombination modulator gene, petunia.

Ultrastructure of meiotic pairing in B chromosomes of Crepis capillaris. I. One-B and two-B pollen mother cells

Genome ◽  
1989 ◽  
Vol 32 (4) ◽  
pp. 611-621 ◽  
Author(s):  
G. H. Jones ◽  
J. A. F. Whitehorn ◽  
S. M. Albini
Keyword(s):  
Synaptonemal Complex ◽  
Chromosome Pairing ◽  
Complex Surface ◽  
B Chromosome ◽  
B Chromosomes ◽  
Meiotic Pairing ◽  
Pollen Mother Cells ◽  
Crepis Capillaris ◽  
Axis Length ◽  
Mother Cells

Chromosome pairing of a small metacentric B chromosome in Crepis capillaris has been studied by synaptonemal complex surface spreading of pollen mother cells containing either one or two B chromosomes. The B-chromosome axis, on average, represents about 8.7% of the axis length of the standard A-chromosome set, which is less than the corresponding values for DNA content (10.6%) and mitotic chromosome volume (13.6%). Single B chromosomes commonly undergo fold-back pairing to give a symmetrical hairpin loop, which supports earlier suggestions that this B chromosome is an isochromosome. Two B chromosomes may show interarm pairing, exclusively, or interchromosome pairing, exclusively, or combinations of the two. Near the centromeres pairing occurs preferentially between arms of the same chromosome, but chromosome ends show random association. Some B chromosomes show anomalous pairing configurations, which may reflect further orders of reverse repeats within arms or, alternatively, nonhomologous pairing. The period of B-chromosome pairing is confined almost exclusively to zygotene, when the standard A chromosomes are pairing, but within this period their pairing is delayed relative to the A set. Individual B chromosomes at zygotene contain from one to three separate synaptonemal complex segments. These are widely distributed within the chromosomes, mainly in distal and interstitial regions; pairing is delayed around the centromere.Key words: B chromosomes, isochromosomes, synaptonemal complex.

Meiotic synapsis of the Allium porrum B chromosome: evidence for a derived isochromosome origin

Genome ◽  
1996 ◽  
Vol 39 (6) ◽  
pp. 1199-1204 ◽  
Author(s):  
K. A. Khazanehdari ◽  
G. H. Jones
Keyword(s):  
B Chromosome ◽  
B Chromosomes ◽  
Allium Porrum ◽  
Chromosome Synapsis ◽  
Hairpin Loops ◽  
Different Types ◽  
Centric Shift ◽  
Meiotic Synapsis ◽  
Surface Spread ◽  
Mother Cells

Ultrastructural analysis of B chromosome synapsis in surface-spread (2B) pollen mother cells of the leek, Allium porrum, has clarified their structural organization and shed new light on their origin. In pachytene cells containing two B chromosomes, these chromosomes either formed a pair of univalents showing foldback hairpin loops or synapsed together to form bivalents of several different types. The synaptic configurations of univalents and bivalents indicate that these B chromosomes have a basically isochromosome organization, but this is modified by a slight centric shift giving an arm ratio of 1.1:1. This analysis adds to the growing number of B chromosomes that have been shown to be isochromosomes or isochromosome derivatives. Key words : Allium porrum, B chromosomes, synapsis, synaptonemal complex, isochromosome.

scholarly journals Structural analysis of the human SYCE2–TEX12 complex provides molecular insights into synaptonemal complex assembly

Open Biology ◽  
2012 ◽  
Vol 2 (7) ◽  
pp. 120099 ◽  
Author(s):  
Owen R. Davies ◽  
Joseph D. Maman ◽  
Luca Pellegrini
Keyword(s):  
Structural Analysis ◽  
Synaptonemal Complex ◽  
Recurrent Miscarriage ◽  
Central Element ◽  
Biological Data ◽  
Structural Basis ◽  
Structural Framework ◽  
Chromosome Synapsis ◽  
Heterotypic Interactions ◽  
Physical Features

The successful completion of meiosis is essential for all sexually reproducing organisms. The synaptonemal complex (SC) is a large proteinaceous structure that holds together homologous chromosomes during meiosis, providing the structural framework for meiotic recombination and crossover formation. Errors in SC formation are associated with infertility, recurrent miscarriage and aneuploidy. The current lack of molecular information about the dynamic process of SC assembly severely restricts our understanding of its function in meiosis. Here, we provide the first biochemical and structural analysis of an SC protein component and propose a structural basis for its function in SC assembly. We show that human SC proteins SYCE2 and TEX12 form a highly stable, constitutive complex, and define the regions responsible for their homotypic and heterotypic interactions. Biophysical analysis reveals that the SYCE2–TEX12 complex is an equimolar hetero-octamer, formed from the association of an SYCE2 tetramer and two TEX12 dimers. Electron microscopy shows that biochemically reconstituted SYCE2–TEX12 complexes assemble spontaneously into filamentous structures that resemble the known physical features of the SC central element (CE). Our findings can be combined with existing biological data in a model of chromosome synapsis driven by growth of SYCE2–TEX12 higher-order structures within the CE of the SC.

scholarly journals Crossing over is coupled to late meiotic prophase bivalent differentiation through asymmetric disassembly of the SC

2005 ◽  
Vol 168 (5) ◽  
pp. 683-689 ◽  
Author(s):  
Kentaro Nabeshima ◽  
Anne M. Villeneuve ◽  
Monica P. Colaiácovo
Keyword(s):  
Caenorhabditis Elegans ◽  
Symmetry Breaking ◽  
Synaptonemal Complex ◽  
Central Region ◽  
Meiotic Prophase ◽  
Homologous Chromosome ◽  
Meiotic Chromosome ◽  
Crossing Over ◽  
Γ Irradiation ◽  
Irradiation Treatment

Homologous chromosome pairs (bivalents) undergo restructuring during meiotic prophase to convert a configuration that promotes crossover recombination into one that promotes bipolar spindle attachment and localized cohesion loss. We have imaged remodeling of meiotic chromosome structures after pachytene exit in Caenorhabditis elegans. Chromosome shortening during diplonema is accompanied by coiling of chromosome axes and highly asymmetric departure of synaptonemal complex (SC) central region proteins SYP-1 and SYP-2, which diminish over most of the length of each desynapsing bivalent while becoming concentrated on axis segments distal to the single emerging chiasma. This and other manifestations of asymmetry along chromosomes are lost in synapsis-proficient crossover-defective mutants, which often retain SYP-1,2 along the full lengths of coiled diplotene axes. Moreover, a γ-irradiation treatment that restores crossovers in the spo-11 mutant also restores asymmetry of SYP-1 localization. We propose that crossovers or crossover precursors serve as symmetry-breaking events that promote differentiation of subregions of the bivalent by triggering asymmetric disassembly of the SC.

scholarly journals The Murine SCP3 Gene Is Required for Synaptonemal Complex Assembly, Chromosome Synapsis, and Male Fertility

2000 ◽  
Vol 5 (1) ◽  
pp. 73-83 ◽  
Author(s):  
Li Yuan ◽  
Jian-Guo Liu ◽  
Jian Zhao ◽  
Eva Brundell ◽  
Bertil Daneholt ◽  
...  
Keyword(s):  
Synaptonemal Complex ◽  
Male Fertility ◽  
Complex Assembly ◽  
Chromosome Synapsis
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