SEARCH · PubMed Health

Results for “Synaptonemal Complex”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources

PubMed2006

From early homologue recognition to synaptonemal complex formation.

This review focuses on various aspects of chromosome homology searching and their relationship to meiotic and vegetative pairing and to the silencing of unpaired copies of genes. Chromosome recognition and pairing is a prominent characteristic of meiosis; however, for some organisms, this association (complete or partial) is also a normal part of nuclear organization. The multiple mechanisms suggested to contribute to homologous pairing are analyzed. Recognition of DNA/DNA homology also plays an important role in detecting DNA segments that are present in inappropriate number of copies before and during meiosis. In this context, the mechanisms of methylation induced premeiotically, repeat-induced point mutation, meiotic silencing by unpaired DNA, and meiotic sex chromosome inactivation will be discussed. Homologue juxtaposition during meiotic prophase can be divided into three mechanistically distinct steps, namely, recognition, presynaptic alignment, and synapsis by the synaptonemal complex (SC). In most organisms, these three steps are distinguished by their dependence on DNA double-strand breaks (DSBs). The coupling of SC initiation to (and downstream effects of) DSB formation and the exceptions to this dependency are discussed. Finally, this review addresses the specific factors that appear to promote chromosome movement at various stages of meiotic prophase, most particularly at the bouquet stage, and on their significance for homologue pairing and/or achieving a final pachytene configuration.

Animals↗

PubMed2000

Cytogenetic analysis of Epicauta atomaria (Meloidae) and Palembus dermestoides (Tenebrionidae) with Xyp sex determination system using standard staining, C-bands, NOR and synaptonemal complex microspreading techniques.

The mitotic and meiotic chromosomes of the beetles Epicauta atomaria (Meloidae) and Palembus dermestoides (Tenebrionidae) were analysed using standard staining, C-banding and silver impregnation techniques. We determine the diploid and haploid chromosome numbers, the sex determination system and describe the chromosomal morphology, the C-banding pattern and the chromosome(s) bearing NORs (nucleolar organizer regions). Both species shown 2n = 20 chromosomes, the chromosomal meioformula 9 + Xyp, and regular chromosome segregation during anaphases I and II. The chromosomes of E. atomaria are basically metacentric or submetacentric and P. dermestoides chromosomes are submetacentric or subtelocentric. In both beetles the constitutive heterochromatin is located in the pericentromeric region in all autosomes and in the Xp chromosome; additional C-bands were observed in telomeric region of the short arm in some autosomes in P. dermestoides. The yp chromosome did not show typical C-bands in these species. As for the synaptonemal complex, the nucleolar material is associated to the 7th bivalent in E. atomaria and 3rd and 7th bivalents in P. dermestoides. Strong silver impregnated material was observed in association with Xyp in light and electron microscopy preparations in these species and this material was interpreted to be related to nucleolar material.

Animals↗

PubMed1995

Nuclear foci of mammalian Rad51 recombination protein in somatic cells after DNA damage and its localization in synaptonemal complexes.

Rad51 protein of Saccharomyces cerevisiae is a structural homolog of the Escherichia coli recombination enzyme RecA. In yeast, the Rad51 protein is required for mitotic and meiotic recombination and for repair of double-strand breaks in DNA. We have used antibodies raised against the homologous human protein, HsRad51, expressed in E. coli, to visualize the spatial distribution of the protein in mammalian somatic and meiotic cells. In cultured human cells, the HsRad51 protein is concentrated in multiple discrete foci in the nucleoplasm; it is largely absent from cytoplasm and nucleoli. After treatment of cells with methyl methanesulfonate, ultraviolet irradiation, or 137Cs irradiation, the percentage of cells with HsRad51 protein immunofluorescence increases; the same cells show unscheduled DNA synthesis. Induction of Rad51 foci is blocked by inhibitors of transcription. In mouse pachytene spermatocytes, the mouse homolog of Rad51 protein is highly enriched in synaptonemal complexes that are formed between the paired homologous chromosomes during meiotic prophase. We conclude that the mammalian proteins homologous to yeast Rad51 are involved in repair of DNA damage and recombinational repair during meiosis.

Animals↗

PubMed1987

Synaptonemal complex spreading in Allium ursinum: pericentric asynapsis and axial thickenings.

In Allium ursinum meiotic pairing of homologues is always incomplete; a proximal region on each bivalent remains regularly unsynapsed even in late pachytene. The spatial correlation of the unsynapsed region with the kinetochore suggests that the kinetochore itself exerts an inhibitory effect on synapsis in its vicinity. This can be interpreted as the cytological basis of the 'centromere effect' on recombination in this species. Moreover, the high incidence of a pericentric inversion loop in a heterozygous chromosome pair shows that proximal pairing initiation is possible and that its failure cannot be responsible for pericentric asynapsis. The formation of the inversion loop is complicated by the need for two independent pairing initiation sites because synapsis cannot proceed across the pericentric region. It is proposed that the meiotic bouquet polarization helps in establishing the presynaptic alignment of the homologous sites within the inverted regions and hence to achieve a high rate of inversion loop formation. Thickenings of the axial/lateral elements are not distributed equally along the synaptonemal complex. They are underrepresented in unpaired axes but strikingly abundant at the borders with synapsed regions, suggesting their origin in the pairing forks during the process of synapsis. They are virtually always present at nucleolus-organizing regions and often they appear at corresponding sites on opposite lateral elements. Besides the thickenings several other kinds of axial deformities are present in unpaired axes.

Allium↗

PubMed1984

A method for preparing two-dimensional surface-spreads of synaptonemal complexes from plant meiocytes for light and electron microscopy.

A method has been developed for preparing two-dimensional surface spreads of synaptonemal complexes (SCs) from plant meiocytes for examination by light and/or electron microscopy. Clear, well-spread preparations of SCs and unpaired axial cores have been obtained from a range of meiotic prophase I stages (leptotene to pachytene) from Allium and Secale meiocytes.

Botany↗

PubMed1999

RAD51 and DMC1 form mixed complexes associated with mouse meiotic chromosome cores and synaptonemal complexes.

The eukaryotic RecA homologues RAD51 and DMC1 function in homology recognition and formation of joint-molecule recombination intermediates during yeast meiosis. The precise immunolocalization of these two proteins on the meiotic chromosomes of plants and animals has been complicated by their high degree of identity at the amino acid level. With antibodies that have been immunodepleted of cross-reactive epitopes, we demonstrate that RAD51 and DMC1 have identical distribution patterns in extracts of mouse spermatocytes in successive prophase I stages, suggesting coordinate functionality. Immunofluorescence and immunoelectron microscopy with these antibodies demonstrate colocalization of the two proteins on the meiotic chromosome cores at early prophase I. We also show that mouse RAD51 and DMC1 establish protein-protein interactions with each other and with the chromosome core component COR1(SCP3) in a two-hybrid system and in vitro binding analyses. These results suggest that the formation of a multiprotein recombination complex associated with the meiotic chromosome cores is essential for the development and fulfillment of the meiotic recombination process.

Adenosine Triphosphatases↗

PubMed1980

Synaptonemal complex karyotyping in spermatocytes of the Chinese hamster (Cricetulus griseus). IV. Light and electron microscopy of synapsis and nucleolar development by silver staining.

Synaptonemal complexes (SCs), X and Y axes, and various nucleolar structures stain preferentially with silver in surface microspread preparations and are analyzable by both light and electron microscopy. Central elements, kinetochore region material and nuclear annuli which stain with ethanolic phosphotungstic acid are seldom visible after silver staining. SCs can be characterized by length measurements equally well in light and electron micrographs, from which stages of pachytene can also be determined by differentiation of the axes of the XY pair. By electron microscopy, the lateral elements appear as single strands at zygotene and early pachytene, then become double in a plane perpendicular to that of the SC and appear denser and thicker until late pachytene when they become progressively more attenuated and again appear single. These transitions are difficult to explain in terms of separation of associated chromatids. Identification of various silver stained bodies as nucleoli is supported by their orange-red fluorescence with acridine orange. SCs, X and Y axes and associated sex body material are, with a few exceptions, virtually indistinguishable from the background yellow-green fluorescence of the chromatin. Comet-shaped nucleolar bodies are regularly associated with five (in one animal) or six (in two animals) SCs; their positions along particular SCs identifiable by relative lengths indicate these bodies to be expressions of nucleolus organizer regions. They first appear at leptotene in association with unpaired axes and undergo progressive changes through late pachytene, at which time they redistribute their contents coincident with disappearance of the SCs. A characteristic nucleolar double dense body appears at zygotene; unlike the comet-shaped nucleoli, it is unassociated with other nuclear structures, and is assumed to arise from coalescence of previously existing smaller dense bodies. - The silver staining method described is remarkable for the speed and simplicity with which large numbers of spermatocyte nuclei are obtainable for light and electron microscopy. The fidelity of the light microscopic counterpart of the electrom microscopic image has been directly assessed at different stages of pachytene. For cytogenetic analysis, critical information often lies beyond the limits of light optical resolution; the correlated electron microscopy required for verification is easily obtained with this method.

Animals↗

PubMed1985

The relationship between genome size and synaptonemal complex length in higher plants.

There appears to be only a weak correlation between genome size and the corresponding total length of a complete set of synaptonemal complexes (SCs) based on published evidence for several fungal, plant, and animal species. This result is unexpected, considering the strong positive correlations between genome size (DNA amount) and total chromosome length and volume and between relative lengths of chromosomes and SCs. Because the observed weak correlation was based on limited data, we systematically investigated the relationship between genome size and SC length, using ten higher plant species. Two-dimensional spreads of SCs from primary microsporocytes at pachytene were prepared using a hypotonic bursting technique. The SC spreads were examined either by light or electron microscopy, and the lengths of at least ten complete sets of SCs were measured for each of the ten species. Additionally, the genome size of each species was determined from pollen tetrad protoplasts using flow cytometry. A strong correlation (r = 0.97) between total SC length and genome size was observed for higher plants, indicating a constant amount of DNA is associated with a given length of SC, at least when averaged over the whole genome.

Chromosomes↗

PubMed1978

Synaptonemal complex and crossing-over: structural support or interference?

Positive cross-over interference is attributed to the prevention of crossing-over by the growing synaptonemal complex. This conjecture is based on a report in the literature that the selection of prospective cross-over sites may actually precede a proper synapsis of homologous chromosomes during meiotic prophase. A genetic test of this notion is suggested using a properly marked trisomic configuration, applicable to a variety of organisms.

Animals↗

PubMed1984

The synaptonemal complex: does it have contractile proteins?

Actin and myosin are commonly involved in cell motility systems. This study attempts to identify these two proteins in the synaptonemal complex (SC), a nuclear organelle associated with chromosome pairing during meiotic prophase. The several experimental approaches reported here give no evidence of SC staining with either anti-myosin or anti-actin antibodies. These findings differ from those of other reportings.

Actins↗

PubMed1983

Synaptonemal complexes as indicators of induced structural change in chromosomes after irradiation of spermatogonia.

The incidence of multivalent formation has been compared in primary spermatocytes at pachytene, using synaptonemal complex preparations and at diakinesis/metaphase, using air-dried preparations, from testes of Syrian hamsters several weeks after exposure to an acute dose of X-rays. The pachytene preparations revealed nearly twice the number of multivalents found at diakinesis/metaphase I, and showed the ability to reveal types of structural alteration undetectable in conventional air-dried techniques.

Animals↗

PubMed1979

Synaptonemal complexes of mouse and human pachytene chromosomes visualized by silver staining in air-dried preparations.

A new method is described which allows light microscopy visualization of the synaptonemal complexes in primary spermatocytes. The conventional acetic acid-alcohol fixed and air-dried preparations can be used for the modified silver staining technique. Several hundred pachytene spermatocytes from a single mouse testis or human testicular biopsy can be examined. The prospective utilization of the present method is briefly discussed.

Animals↗

PubMed1981

Synaptonemal complex analysis of mouse chromosomal rearrangements. I. Cytogenetic observations on a tandem duplication.

Electron microscopy of surface-spread spermatocytes from mice heterozygous for a tandem duplication shows the heteromorphic synaptonemal complex (SC) to comprise two lateral elements of unequal length, the longer of which is buckled out in a characteristic loop, representing the unsynapsed portion of the duplication. The loop is a regular feature of late zygotene-early pachytene nuclei; it is longest at these early stages, but, through equalization of the two axes as a consequence of synaptic adjustment, it is replaced by a normal appearing SC at late pachytene. Because equalization, as indicated by a decrease in the percent difference between axes, may begin shortly after completion of synapsis, estimates of duplication segment length are restricted to a sample selected for least adjustment. --Although the mean position of the loop is constant at various pachytene substages, individual positions vary widely from cell to cell, consistent with the behavior expected of a duplication, but not of a deletion or an inversion. The length of the segment that is duplicated is estimated to be 22% of the normal chromosome, the midpoint of the segment is mapped at 0.61 of the chromosome distal to the kinetochore, and the ends of the segment are mapped at 0.50 to 0.72. Measurements of G-banded mitotic chromosomes give comparable values: duplication length, 24%; midpoint, 0.60, and segment ends, 0.48 and 0.71. This agreement constitutes further validation of the SC/spreading method for detecting and analyzing chromosomal rearrangements at pachytene and substantiates the fidelity with which the axes and SCs represent the behavior of chromosomes in synapsis.

Animals↗

PubMed1975

Synaptonemal complex complement of man in spreads of spermatocytes, with details of the sex chromosome pair.

Human pachytene chromosome pairs have been characterized electron microscopically in spread preparations on the basis of synaptonemal complex length, kinetochore position and attached nucleoli when present. The X and Y chromosomes can be followed by their filamentous axial cores from partial synapsis, through precocious disjuction and end-to-end attachment, to differentiation of a network in the sex chromosome pair.

Cell Nucleolus↗

PubMed1977

Synaptonemal complex karyotyping in Melanoplus differentialis.

The chromosomal axes of the spermatocytes of the grasshopper Melanoplus differentialis have been studied with a modification of the microspreading procedure used previously. The whole complement of synaptonemal complexes (SCs) and the axis of the X chromosome have been described and measured. The relative length of each SC is characteristic and constant and permits the construction of an idiogram. Relative lengths of SCs are almost equal to the relative lengths of mitotic chromosomes of spermatogonia (with the exception of the X chromosome), thus extending to an invertebrate the relationship between SCs and mitotic chromosomes that has been demonstrated in mammals. All the SCs except the 3 smallest (which are apparently telocentric) show a small short arm beyond the kinetochore. The progression of changes in the chromosomal axes during meiotic prophase has been staged by centriolar behaviour. During leptotene, axes are first formed near the nuclear envelope at a special (polar) region. SCs also begin to appear in the polar region and extend towards the nuclear interior. The beginning and completion of synapsis is not synchronous among bivalents. The X-axis is formed in midzygotene and shows a characteristic sequence of changes in shape during pachytene. Cells in post-synaptic stages show whole chromosome complements with characteristic chiasmatic configurations. Kinetochores are prominent and bipartite during diplotene-diakinesis.

Animals↗

PubMed1981

XY pair associates with the synaptonemal complex of autosomal male-sterile translocations in pachytene spermatocytes of the mouse (Mus musculus).

Analysis of the chromosome behaviour at pachytene has been performed by means of the silver staining technique visualizing the synaptonemal complexes (SCs) in male mice heterozygous for the male-sterile translocations T(5;12)31Hm T(16;17)43H and T(7;19)145H, respectively. the T(9;17)138Ca male heterozygotes and T43H/T43H homozygous males were used as fertile controls. The sterile mice displayed a high frequency (about 60%) of pachytene spermatocytes with autosomal translocation configuration located in close vicinity of the XY pair. The dense round body (XAB), normally located near the X-chromosome axis in fertile males, exhibited abnormal affinity to translocation configuration in the sterile translocation heterozygotes. The incomplete synapsis of autosomes involved in translocation configuration was observed in more than 70% of the pachytene spermatocytes with the male-sterile translocations but less than 20% of the cells from T138Ca fertile male.s. A hypothesis relating the spermatogenic arrest of carriers of male-sterile rearrangements to the presumed interference with X chromosome inactivation in male meiosis is discussed.

Animals↗

PubMed1985

Induced structural changes in chromosomes of the Syrian hamster after X-irradiation of spermatogonia: comparison of dose-response curves derived from synaptonemal complexes and from air-dried preparations of metaphase I.

The dose-response relationships of the induction of structural change in chromosomes after X-irradiation of spermatogonia have been determined from analyses of synaptonemal complexes in pachytene spermatocytes and from air-dried preparations of metaphase I. The dose-response curves were superficially the same shape, with a peak yield of cells containing a multivalent at 4 Gy, although only in the pachytene data was there any statistically significant hump. The pachytene preparations were much more sensitive, revealing nearly twice the proportion of cells containing multivalents than found at metaphase.

Animals↗

PubMed1978

Lateral element cross connections of the synaptonemal complex and their relationship to chiasmata in rat spermatocytes.

Observations are presented in support of the hypothesis that at meiotic prophase a reciprocal crossover is accompanied by a crossover of the lateral elements of the synaptonemal complex, SC (Moens, 1974). Rat spermatocyte nuclei in developmental stage VII (Clermont, 1972) of the seminiferous epithelium cycle, but not pachytene nuclei in stages I to VI, were found to have SC modifications in the form of a cross connection between the lateral elements. In structure these crossover elements, CO elements, resemble the lateral element. It is found in a variety of positions, usually more or less perpendicular to the SC but also slanted or parallel along the central element or detached from the SC. Reconstructions of entire nuclei indicate an average of one such CO element per SC and a nonrandom distribution of CO elements among the SCs. Because the crossing-over of lateral elements produces a 180 degree twist or removes a 180 degree twist, the pattern of SC coiling was examined. Coiling starts in early pachytene prior to CO element formation. At stage VII one nucleus had a total of 78 coils, all counter clockwise, and another nucleus had 97 such 180 degree coils. It is noted that if SC coils are associated with the process of crossing-over, then the regulation of crossover distribution such as chiasma position interference has an explanation in the structure and behavior of the SC.

Animals↗