The central region of the synaptonemal complex inBlaps cribrosa studied by electron microscope tomography

Chromosoma ◽  
1993 ◽  
Vol 102 (10) ◽  
pp. 669-681 ◽  
Author(s):  
Karin Schmekel ◽  
Jacob Wahrman ◽  
Ulf Skoglund ◽  
Bertil Daneholt
Genome ◽  
1996 ◽  
Vol 39 (6) ◽  
pp. 1194-1198 ◽  
Author(s):  
M. P. Maguire ◽  
R. W. Riess

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.


Author(s):  
T. Guha ◽  
A. Q. Siddiqui ◽  
P. F. Prentis

The Primary Spermatocytes represent a stage in spermatogenesis when the first meiotic cell division occurs. They are derived from Spermatogonium or Stem cell through mitotic division. At the zygotene phase of meiotic prophase the Synaptonemal complex appears in these cells in the space between the paired homologous chromosomes. Spermatogenesis and sperm structure in fish have been studied at the electron microscope level in a few species? However, no work has yet been reported on ultrastructure of tilapia, O. niloticus, spermatozoa and spermatogenetic process. In this short communication we are reporting the Ultrastructure of Primary Spermatocytes in tilapia, O. niloticus, and the fine structure of synaptonemal complexes seen in the spermatocyte nuclei.


Genetics ◽  
2003 ◽  
Vol 163 (2) ◽  
pp. 539-544 ◽  
Author(s):  
Hasanuzzaman Bhuiyan ◽  
Gunilla Dahlfors ◽  
Karin Schmekel

Abstract The synaptonemal complex (SC) keeps the synapsed homologous chromosomes together during pachytene in meiotic prophase I. Structures that resemble stacks of SCs, polycomplexes, are sometimes found before or after pachytene. We have investigated ndt80 mutants of yeast, which arrest in pachytene. SCs appear normal in spread chromosome preparations, but are only occasionally found in intact nuclei examined in the electron microscope. Instead, large polycomplexes occur in almost every ndt80 mutant nucleus. Immunoelectron microscopy using DNA antibodies show strong preferential labeling to the lateral element parts of the polycomplexes. In situ hybridization using chromosome-specific probes confirms that the chromosomes in ndt80 mutants are paired and attached to the SCs. Our results suggest that polycomplexes can be involved in binding of chromosomes and possibly also in synapsis.


1976 ◽  
Vol 22 (3) ◽  
pp. 521-530
Author(s):  
I. Minassian ◽  
L.G. Bell

Light- and electron-microscope autoradiography have been used to follow the incorporation of [3H]thymidine at different stages during the interphase of synchronously growing populations of Amoeba proteus. Two main patterns were found for tritiated thymidine incorporation, i.e. DNA synthesis. The major incorporation was in the central region of the nucleus, but a lesser degree of incorporation occurred in the nucleolar region. The bulk of this nucleolar DNA was found to be late replicating, i.e. it replicated during the G2 phase.


2005 ◽  
Vol 168 (5) ◽  
pp. 683-689 ◽  
Author(s):  
Kentaro Nabeshima ◽  
Anne M. Villeneuve ◽  
Monica P. Colaiácovo

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.


Genome ◽  
1991 ◽  
Vol 34 (6) ◽  
pp. 879-887 ◽  
Author(s):  
M. P. Maguire ◽  
A. M. Paredes ◽  
R. W. Riess

The phenotype of the desynaptic (dy) mutant of maize in microsporocytes at meiotic prophase was compared with normal microsporocytes of a closely related strain and with microsporocytes of a maize inbred line (KYS) assumed to be normal. Strikingly more univalents and open arms of bivalents were found in the mutant cells than in normal cells at diakinesis, and where there was heterozygosity for a distal knob (heterochromatic region), separation was usually equational, indicating the occurrence of normal crossing-over followed by failure of chiasma maintenance in the mutant. Differences found in the mutant by electron microscopy were a statistically significant wider dimension of the synaptonemal complex central region and also less twisting of synapsed configurations at pachytene. It is suggested that these are side-effect symptoms of a defect in the synaptonemal complex (or associated substance), which is expressed later as sporadic loss of chiasma maintenance.Key words: desynaptic, chiasma maintenance, synaptonemal complex.


2020 ◽  
Author(s):  
Min-Su Lee ◽  
Mika T. Higashide ◽  
Hyungseok Choi ◽  
Ke Li ◽  
Soogil Hong ◽  
...  

SummaryThe synaptonemal complex (SC) is a proteinaceous structure that mediates homolog engagement and genetic recombination during meiosis. Zip-Mer-Msh (ZMM) proteins promote crossover (CO) formation and initiate SC formation. In SC elongation, the SUMOylated SC component Ecm11 and its interacting protein Gmc2 facilitate the polymerization of Zip1, a SC-central region component in budding yeast. Through physical recombination, cytological, and genetic analyses, we here demonstrate that ecm11 and gmc2 mutants exhibit chromosome-specific defects in meiotic recombination. CO frequencies were reduced on a short chromosome (chromosome III), whereas CO and non-crossover (NCO) frequencies were increased on a long chromosome (chromosome VII). Further, persistent double-strand breaks (DSBs) occurred in unsynapsed chromosome regions during the late prophase, suggesting the presence of a negative regulation of DSB formation. The Ecm11-Gmc2 (EG) complex could participate in joint molecule (JM) processing and/or double-Holliday junction resolution for CO-designated recombination of the ZMM-dependent pathway. However, absence of the EG complex ameliorated the JM-processing defect in zmm mutants, suggesting a role of these proteins in suppression of ZMM-independent recombination. Therefore, the EG complex fosters ZMM-dependent processing and resolution of JMs while suppressing ZMM-independent JM processing and late DSB formation. Hence, EG-mediated SC central regions, which display properties similar to those of liquid crystals, may function as a compartment for sequestering recombination proteins in and out of the process to ensure meiosis specificity during recombination.


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