scholarly journals THE STRUCTURE OF THE CENTRAL REGION IN THE SYNAPTONEMAL COMPLEXES OF HAMSTER AND CRICKET SPERMATOCYTES

1973 ◽  
Vol 56 (1) ◽  
pp. 145-152 ◽  
Author(s):  
Alberto J. Solari ◽  
Montrose J. Moses
Keyword(s):  
Synaptonemal Complex ◽  
Central Region ◽  
Essential Role ◽  
Amorphous Material ◽  
Central Element ◽  
House Cricket ◽  
Widespread Occurrence ◽  
Whole Mount ◽  
Additional Protein ◽  
Surface Spreading

The fine structure of bivalents from golden hamster and house cricket spermatocytes has been studied with a whole mount surface-spreading method combined with negative staining. The elements of the synaptonemal complex show detail of structure which is absent in other preparative procedures. The transverse filaments found in the central region of the synaptonemal complex from both species are straight and have a similar width, 1 6–1 8 nm These filaments occur mainly in bundles The central element differs in architecture in the two species In hamster bivalents it is formed of longitudinal stretches of filaments 1.6–1 8 nm wide and a small amount of an amorphous material similar to that of the lateral elements In the cricket, the central element contains transverse fibrils which are continuous with the transverse filaments of the central region, and an amorphous material lying mainly along the sides of the central element All of the components of the central region of the synaptonemal complex are resistant to pancreatic DNase. The overlapping ends of the transverse filaments, together with additional protein material, make up the central element The widespread occurrence and close morphological and histochemical interspecies similarities of the transverse filaments indicate that they serve an essential role, probably one concerned with holding synapsed bivalents together via the lateral elements. Restrictions placed by the observations reported here on current models of the synaptonemal complex are discussed.

scholarly journals A close-to-native structure of the synaptonemal complex

2021 ◽  
Author(s):  
Rosario Ortiz ◽  
Olga M Echeverria ◽  
Sergej Masich ◽  
Christer Hoog ◽  
Abrahan Hernandez-Hernandez
Keyword(s):  
Electron Microscopy ◽  
Genetic Variability ◽  
Synaptonemal Complex ◽  
Central Region ◽  
Genetic Material ◽  
Central Element ◽  
Structural Models ◽  
Super Resolution ◽  
Native Structure ◽  
Homologous Chromosomes

Genetic variability in sexually reproducing organisms results from an exchange of genetic material between homologous chromosomes. The genetic exchange mechanism is dependent on the synaptonemal complex (SC), a protein structure localized between the homologous chromosomes. Current structural models of the SC are based on electron microscopy, super resolution, and expansion microscopy studies using chemical fixatives and sample dehydration of gonads, which are methodologies known to produce structural artifacts. We have developed a novel electron microscopy sample-preparation approach where pachytene cells are isolated from mouse testis by FACS, followed by cryo-fixation and cryo-substitution to achieve visualization of a close-to-native structure of the SC. We found that the central region of the SC was wider than previously recognized, and the transverse filaments more densely packed in the central region. Furthermore, we identified a structure nucleating the central element of the SC.

Synaptic defects of asynaptic homozygotes in maize at the electron microscope level

Genome ◽  
1996 ◽  
Vol 39 (6) ◽  
pp. 1194-1198 ◽  
Author(s):  
M. P. Maguire ◽  
R. W. Riess
Keyword(s):  
Electron Microscope ◽  
Key Words ◽  
Synaptonemal Complex ◽  
Central Region ◽  
Silver Staining ◽  
Central Element ◽  
Electron Microscope Level ◽  
Recombination Nodules ◽  
Element Type ◽  
Maize Plants

More detailed observations of the synaptonemal complex (SC) in asynaptic maize plants have been faciliated by superior silver-staining procedures. These suggest that central region components of the SC are strongly implicated as defective in asynaptic. Apparently homologous axial elements tend to follow roughly parallel courses within the nucleus at pachytene, in some short segments apparently synapsed and in others at wider separation than normal synapsis yet close enough to allow observation of thin central element segments and also occasional thin transverse element-type structures. This kind of transverse filament may be weakened and severely stretched yet associated with both axial elements. Small nodules, similar to recombination nodules, appear at corresponding positions in widely separated axial elements. Key words : synaptonemal complex, central element, transverse filament, recombination nodule.

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.

The synaptonemal complexes of Achlya recurva (Oomycetes): karyotype analysis and three-dimensional reconstruction of pachytene nuclei in antheridia and oogonia

1991 ◽  
Vol 69 (6) ◽  
pp. 1384-1395 ◽  
Author(s):  
Hobart R. Williamson ◽  
Pesach Ben Yitzchak
Keyword(s):  
Synaptonemal Complex ◽  
Organizer Region ◽  
Nucleolar Organizer Region ◽  
Nucleolus Organizer Region ◽  
Three Dimensional ◽  
Central Element ◽  
Three Dimensional Reconstruction ◽  
Synaptonemal Complexes ◽  
Sequence Of Events ◽  
Dimensional Reconstruction

Fifteen synaptonemal complexes, as determined by three-dimensional reconstruction of serial, ultrathin sections, were present within both antheridial and oogonial zygotene and pachytene nuclei of the oomyceteous fungus Achlya recurva, thus n = 15. The present study represents the first complete reconstruction of synaptonemal complexes in the genus Achlya. The occurrence of both zygonema and pachynema was simultaneous in antheridia and oogonia. Pachytene nuclei of antheridia and oogonia are small, 13 μm3 in volume, and the average length of the synaptonemal complexes ranged from 1.9 to 4.4 μm. Lateral elements at zygotene ranged from 1.2 to 4.7 μm. Both ends of each synaptonemal complex were attached randomly to the nuclear envelope, so a bouquet formation was not observed at pachytene. In A. recurva, the dimensions of the synaptonemal complex were as follows: overall width = 270 nm; the lateral elements = 75 nm each in width and the central region = 120 nm. There was no central element and associated transverse filaments, which may be associated with development of alternative reproductive strategies other than amphimixis, as in nematodes. Of the 15 synaptonemal complexes present, only the one carrying the nucleolus organizer region could be clearly identified from one nucleus to the next. The nucleolar organizer region was on the average 0.75 μm from the telomere in both zygotene and pachytene nuclei. There were an average of three recombination nodules in each nucleus. Synaptonemal complexes have been reported in over 80 different species of fungi and related protista. Karyotypic evolution in the oomycetes and fungi may be the result of poly-ploidization, followed by cytogenetic diversification involving aneuploidy and differing degrees of polyploidy. Such a sequence of events could explain the apparent polyphyletic formation of this group. Key words: karyotype, Oomycetes, pachytene, synaptonemal complexes, three-dimensional reconstruction.

scholarly journals Progression of meiotic recombination requires structural maturation of the central element of the synaptonemal complex

2008 ◽  
Vol 121 (15) ◽  
pp. 2445-2451 ◽  
Author(s):  
G. Hamer ◽  
H. Wang ◽  
E. Bolcun-Filas ◽  
H. J. Cooke ◽  
R. Benavente ◽  
...  
Keyword(s):  
Synaptonemal Complex ◽  
Meiotic Recombination ◽  
Central Element

Whole mount electron microscopy of meiotic chromosomes and the synaptonemal complex

Chromosoma ◽  
1970 ◽  
Vol 30 (3) ◽  
pp. 269-286 ◽  
Author(s):  
David E. Comings ◽  
Tadashi A. Okada
Keyword(s):  
Electron Microscopy ◽  
Synaptonemal Complex ◽  
Meiotic Chromosomes ◽  
Whole Mount

Development of helicoidal texture in the prerelease mucilage of quince (Cydonia oblonga) seed epidermis

1988 ◽  
Vol 66 (3) ◽  
pp. 460-467 ◽  
Author(s):  
R. M. Abeysekera ◽  
J. H. M. Willison
Keyword(s):  
Central Region ◽  
Liquid Crystalline ◽  
Amorphous Material ◽  
Epidermal Cells ◽  
Cydonia Oblonga ◽  
Thin Walled ◽  
Seed Epidermis ◽  
Developmental Phases ◽  
Transitional Phase ◽  
Helicoidal Texture

Quince (Cydonia oblonga Mill.) seed epidermis was examined cytologically during its development. Three developmental phases were delimited: immaturity, transition to maturity, and maturity. These cytological phases corresponded with phases of competence to release hydrated mucilage on wetting, immature tissue being completely incompetent and mature tissue fully competent. Growing cells of immature tissue were vacuolate and thin walled. By contrast, protoplasts of nongrowing mature epidermal cells had contracted to a remnant and been replaced by periplasmic deposits. Within these deposits, surrounded by amorphous material, were massive arrays of widely spaced microfibrils arranged helicoidally. In the oldest sample examined, periplasmic material appeared to be spewing through the broken outer walls of some cells. The periplasmic material is interpreted to be prerelease mucilage, which progressively fills the periplasm during a brief transitional phase. It seems that amorphous periplasmic material is deposited initially and microfibrils later intermingle with it. At some stage during filling of the periplasm, the microfibrils begin to organize, ultimately becoming helicoidal. Orderliness seems to begin in the central region of the periplasmic pool, not at its edges. It is proposed that nucleation of liquid crystalline helicoidal arrays occurs in the periplasm and that these arrays remain fluid until their disintegration during release as a result of hydration.

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.

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