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Results for “Synaptonemal Complex”

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PubMed1998

Synaptonemal complex analysis of the X1X2Y trivalent in Mantis religiosa L. males: inferences on the origin and maintenance of the sex-determining mechanism.

Characterization of sex chromosomes in males of Mantis religiosa L. (2n = 24 + X1X2Y) was carried out by C-banding, silver staining and fluorescence in situ hybridization. They are meta- or submetacentric, their arms being designated as X1L, X1R, X2R, X2L, YL and YR. Meiotic behaviour of the sex trivalent was examined through the analysis of synaptonemal complexes (SCs), prometaphase I (metaphase I) and metaphase II nuclei. On the basis of the SC analysis, chromosomal length measurements at mitosis and prometaphase I and data from several orthopteran species, it is proposed that the breakpoints of the reciprocal translocation that originated this complex sex-determining mechanism were close to the centromeres of the X and the largest autosome, and that the asynapsed X1L and X2R regions observed in the sex trivalent at pachytene represent the original X chromosome. The X centromere being probably that of the X2 element because it lacks a partner in the SC pachytene trivalent. The relationship among synaptic pattern, chiasma localization and balanced segregation of the sex trivalent is also discussed.

Animals↗

PubMed1982

The synaptonemal complexes of Caenorhabditis elegans: pachytene karyotype analysis of male and hermaphrodite wild-type and him mutants.

Only five synaptonemal complexes (SC), representing the 5 autosomes, are present in wild-type, him-4 and him-8, Caenorhabditis elegans males, whereas there are six SCs, accounting for 5 autosomal bivalents and the XX bivalent, in the C. elegans hermaphrodite. The univalent X chromosome of the male is present as a heterochromatic 'X-body' in spermatocyte pachytene nuclei. The XX bivalent in wild-type, him-4 and him-8 hermaphrodites (SC1, 2.5 microns in length) represented 6% of the total karyotype length and a SC of this size is missing from the respective male karyotypes. This corresponds with the fact that the total male karyotype length is only approximately 94% that of the hermaphrodite. Associated with the central element of the SC are structures termed 'SC knobs' that were first described in the wild-type hermaphrodite. The six SC knobs present in the wild-type hermaphrodite oocyte pachytene nuclei and the two SC knobs in the male spermatocyte pachytene nuclei are apparently randomly placed with the exception that they are never found at the ends of the SC. This is also true in him-4 and him-8 in which case there are 3 and zero SC knobs in the hermaphrodites, respectively, and one SC knob each in the male pachytene nuclei. The decrease in number of SC knobs in hermaphrodite to male represents a true sex difference. The presence or absence of the SC knobs may influence the X chromosome nondisjunction process and this effect is not localized to the region of the SC on which the SC knob is located.

Animals↗

PubMed1984

The synaptonemal complex, recombination nodules and chiasmata in human spermatocytes.

Reconstruction from serial sections of 120 human spermatocyte nuclei, ranging in stage from leptotene to anaphase I, has led to the following conclusions. The reconstructed nuclei form a continuous sequence of developmental stages. With few exceptions, all of the bivalents are identifiable by length, centromere index and morphological markers. Crossing over is accompanied by a transformation of the recombination nodule (RN) into a fusiform bar lying across the synaptonemal complex (SC). The evolution of the crossover distribution at late pachytene is regulated at two levels both involving the SC. Each bivalent displays a pattern of SC regions - domains - with high affinity for RNs in the middle and low affinity at the ends. The occurrence of crossing over in a domain reduces the probability of attachment of new RNs and causes RNs not yet involved in crossing over to be released from that domain. Positive interference between crossovers is a consequence of these phenomena. At diplotene the degradation of the SC is initiated in regions with low affinity for RNs and small segments of the SC are retained at the crossover sites until late diakinesis. The site of crossing over is only identifiable by an RN for a certain period of time during pachytene. The distribution of total crossovers in a nucleus is similar but not identical to the distribution of chiasmata as seen in the light microscope. The number of crossovers has been estimated to be 70 and exceeds the number of chiasmata determined by light microscopy by a factor of 1.4.

Animals↗

PubMed1987

Cytogenetic studies on Cervus elaphus. II. Synaptonemal complexes and NOR activity during spermatogenesis.

The activity of the nucleolus organizer regions (NORs) in various stages of spermatogenesis of the red deer was studied with the silver staining technique. The Ag-stainability of the NORs, an indicator of the transcriptional activity of the r-RNA genes, is present during the meiotic prophase until pachytene and is absent during the remainder of the meiotic prophase, to reappear during the first stages of spermiogenesis and then disappear again during the elongation phase of the spermatids. The development and behaviour of synaptonemal complexes (SCs) of primary spermatocytes were also studied with the silver staining technique under the light microscope. The organization of SC is similar to that of other mammalian species. The pairing behaviour of the axes of the sex chromosomes is described.

Animals↗

PubMed1988

Synaptonemal complex analysis of B-chromosome behavior in meiotic prophase I in the East-Asiatic mouse Apodemus peninsulae (Muridae, Rodentia).

The mitotic and meiotic chromosomes of four male East-Asiatic mice, Apodemus peninsulae, having three to seven chromosomes in addition to the standard karyotype (2n = 48), were investigated. B-chromosomes were represented by medium-sized metacentric and dotlike chromosomes. Mosaicism of bone marrow cells due to a numerical variation of accessory chromosomes was established for the males examined. Capacity of B-chromosomes to form axial elements and synaptonemal complexes in meiotic prophase I was revealed by electron microscopy. The occurrence of univalents of different morphology, bivalents, and multivalents, corresponding to B-chromosomes, was demonstrated. An increase in the number of B-chromosomes was found in spermatocytes at zygotene-pachytene relative to the number in bone marrow cells, which may be evidence of B-chromosome accumulation in the germ cell line of the East-Asiatic mouse.

Animals↗

PubMed1993

[Antibodies against Escherichia coli RecA protein reveal two nuclear proteins in bovine spermatocytes which interact with synaptonemal complex structures of meiotic chromosomes of various eukaryotic organisms].

Three RecA-like proteins were detected in bovine meiotic cells using antibodies against Escherichia coli RecA protein. After isolation and purification of these RecA-like proteins their molecular weights appeared to be equal to 37, 70 and 130 kD. The 37 kD protein accompanies all the stages of spermatogenesis up to the stage of mature spermatozoa. The 70 kD protein is detectable only in nuclei of cells at the stage of prophase I of meiotic division. These RecA-like proteins are involved in the formation of structural elements of the synaptonemal complex (SC) and are detected in the SC composition in meiotic cells not only of mammals but also of plants and insects, which suggests the evolutionary conservative character of these proteins.

Animals↗

PubMed2006

Testicular expression of synaptonemal complex protein 3 (SYCP3) messenger ribonucleic acid in 110 patients with nonobstructive azoospermia.

OBJECTIVE: To determine the expression of the synaptonemal complex protein-3 (SYCP3) gene in men with nonobstructive azoospermia. DESIGN: Cross-sectional case study. SETTING: Avesina Infertility Clinic, Tehran, Iran. PATIENT(S): One hundred and ten consecutive infertile men presenting nonobstructive azoospermia. INTERVENTION(S): Testicular biopsies for histopathological assessment and analyses of SYCP3 expression level by semiquantitative nested reverse transcription-polymerase chain reaction (RT-PCR). The SYCP3 levels were normalized to expression of the housekeeping phosphoglucomutase 1 gene. MAIN OUTCOME MEASURE(S): Expression of SYCP3 messenger ribonucleic acid (mRNA). Correlation of the histopathological findings with SYCP3 expression levels. RESULTS(S): Testicular SYCP3 mRNA expression was observed in 67/110 (60.9%) patients. The expression level correlated with the degree of spermatogenic failure. Although it was expressed in patients with spermatogenesis and maturation arrest, a lack of expression was seen in all of those men with spermatogonial arrest, Sertoli cell-only syndrome, and testicular atrophy. CONCLUSION(S): These data indicate that SYCP3 is expressed in human testis and is restricted to germ cells. Our findings, in association with those obtained in experimental animals, shows that lack of SYCP3 expression in human testis may have a negative effect on spermatogenesis and male fertility.

Adult↗

PubMed1997

The synaptonemal complexes of the nematode Caenorhabditis elegans: gametic response to retinol.

Retinol (RO) is essential for normal gene expression and progression of gametogenesis. Excessive amounts of RO in the diet results in the condition termed 'hypervitaminosis A' which severely affects gametogenesis. In the present work, the nematode Caenorhabditis elegans was grown in different concentrations of RO for up to seven generations. Decreased fecundity was positively correlated with increasing concentrations of RO with successive generations. Decreased nuclear volume was positively correlated with increasing RO concentration for each generation. Abnormal chromatin condensation was present along the bivalent and the lengths of the synaptonemal complexes (SC) were consistently longer than in the wild-type. Increasing RO concentration was also negatively correlated with the presence of SCs. The presence of disjunction regulator regions (DRR), which are decondensed regions of chromatin along the bivalent which occur in specific numbers, was negatively correlated with increasing RO concentration. By the third generation, DRRs were no longer observed in any of the organisms. This study shows that high levels of retinol in the diet affect gene expression, via changes in chromosome structure, and interferes with gamete production by inhibiting the pairing of homologous chromosomes during meiotic prophase.

Animals↗

PubMed1997

Switching yeast from meiosis to mitosis: double-strand break repair, recombination and synaptonemal complex.

BACKGROUND: When Saccharomyces cerevisiae cells that have begun meiosis are transferred to mitotic growth conditions ('return-to-growth', RTG), they can complete recombination at high meiotic frequencies, but undergo mitotic cell division and remain diploid. It was not known how meiotic recombination intermediates are repaired following RTG. Using molecular and cytological methods, we investigated whether the usual meiotic apparatus could repair meiotically induced DSBs during RTG, or whether other mechanisms are invoked when the developmental context changes. RESULTS: Upon RTG, the rapid disappearance of meiotic features--double-strand breaks in DNA (DSBs), synaptonemal complex (SC), and SC related structures-was striking. In wild-type diploids, the repair of meiotic DSBs during RTG was quick and efficient, resulting in homologous recombination. Kinetic analysis of double-strand breakage and recombination indicated that meiotic DSB formation precedes the commitment to meiotic levels of recombination. DSBs were repaired in RTG in dmc1, but not rad51 mutants, hence repair did not occur by the usual meiotic mechanism which requires the Dmc1 gene product. In haploids, DSBs were also repaired quickly and efficiently upon RTG, showing that DSB repair did not require the presence of a homologous chromosome. In all strains examined, SC and related structures were not required for DSB repair or recombination following RTG. CONCLUSIONS: At least two pathways of DSB repair, which differ from the primary meiotic pathway(s), can occur during RTG: One involving interhomologue recombination, and another involving sister-chromatid exchange. DSB formation precedes commitment to recombination. SC elements appear to prevent sister chromatid exchange in meiosis.

Cell Cycle Proteins↗

PubMed2000

New occurrence of microchromosomes B in Moenkhausia sanctaefilomenae (Pisces, Characidae) from the Paraná River of Brazil: analysis of the synaptonemal complex.

The Moenkhausia sanctaefilomenae specimens showed a karyotype consisting of 2n = 50 chromosomes with 12 metacentrics, 36 submetacentrics and two subtelocentrics. In addition to the basic karyotype, all the males specimens have cells ranging from zero to two B microchromosomes in mitotic metaphases. These chromosomes were not observed in the female specimens. C-band analysis showed a distribution pattern of characteristic heterochromatin with interstitial and centromeric blocks. However, the B chromosomes were faintly stained with C-banding and were not fluorescent with CMA3 staining. The meiotic studies showed the formation of bivalents in metaphase I and in pachytene under an optical microscope. Through synaptonemal complex analysis with an electron microscope, the pachytene showed 25 bivalents completely paired and a small bivalent corresponding to the B chromosomes. In the same preparation, one of the B chromosomes was observed in a univalent form. On the basis of pairing behavior and morphology it is assumed that B chromosomes of M. sanctaefilomenae show homology between them and their evolutionary aspects are discussed.

Animals↗

PubMed1986

Nuclear aberrations and loss of synaptonemal complexes in response to diethylstilbestrol (DES) in Caenorhabditis elegans hermaphrodites.

In Caenorhabditis elegans, loss of viability and fertility is observed after treatment with DES. The decrease in life span is associated with senescent morphology of meiotic prophase nuclei, such that nuclei from young and old specimens cannot be differentiated. Aging in oocytes at the pachytene stage of meiotic prophase is manifested by nucleo-cytoplasmic aberrations, increased density of the nucleoplasm and cytoplasm and decrease in numbers of mitochondria. Increasing concentrations of DES are characterized by concomitant decrease in fertility and increased production of abnormal gametes. At DES concentrations higher than 1.25 micrograms/ml, synaptonemal complexes (SC) are absent from the nuclei, thus, effective pairing and segregation of homologous chromosomes is not possible. The absence of SCs may be the result of: a premeiotic colchicine-like effect that influences pairing of chromosomes; changes in the structure of the DNA due to DES binding that results in changes in expression of the DNA; and changes in temporal DNA synthesis in response to DES. Since the SC is essential for regulating pairing and subsequent separation of bivalents, the lack of an SC explains the loss of fertility, due to the production of unbalanced gametes, observed in DES-treated specimens.

Animals↗

PubMed1989

Banding studies and synaptonemal complex analysis of an X-autosome translocation in the domestic pig.

In a litter of nine domestic pigs, a translocation between the X-chromosome and chromosome 13 was found in six individuals: four males and two females. The translocation was presumed to have originated in the dam. Banding studies indicated that the breaks preceding the translocation had occurred in a distal GTG-negative band of the long arm of the X, 15-30% of the length of Xq from the telomere, and proximally in chromosome 13, 15-25% from the centromere. The normal X of the females invariably replicated its DNA late. Synaptonemal complex analysis of spermatocytes demonstrated a quadrivalent in 75 of 85 analyzable cells (88.2%), and in 10 cells (11.8%) one trivalent and one univalent were found. Extensive nonhomologous pairings were visualized in the pachytene stage by applying an 'overlap' test measuring the sex chromosomes and collating their pairings. An arrest in male meiosis was verified histologically; no meiotic stages later than pachytene developed. This resulted in sterility, with considerable testicular hypoplasia. The records of female fertility were available only for the dam and did not show any deviations from the average of the herd.

Animals↗

PubMed1996

Mammalian ubiquitin-conjugating enzyme Ubc9 interacts with Rad51 recombination protein and localizes in synaptonemal complexes.

Hsubc9, a human gene encoding a ubiquitin-conjugating enzyme, has been cloned. The 18-kDa HsUbc9 protein is homologous to the ubiquitin-conjugating enzymes Hus5 of Schizosaccharomyces pombe and Ubc9 of Saccharomyces cerevisiae. The Hsubc9 gene complements a ubc9 mutation of S. cerevisiae. It has been mapped to chromosome 16p13.3 and is expressed in many human tissues, with the highest levels in testis and thymus. According to the Ga14 two-hybrid system analysis, HsUbc9 protein interacts with human recombination protein Rad51. A mouse homolog, Mmubc9, encodes an amino acid sequence that is identical to the human protein. In mouse spermatocytes, MmUbc9 protein, like Rad51 protein, localizes in synaptonemal complexes, which suggests that Ubc9 protein plays a regulatory role in meiosis.

Amino Acid Sequence↗

PubMed1998

Revised karyotype of Alouatta caraya (Primates: Platyrrhini) based on synaptonemal complex and banding analyses.

Most primates studied have the usual XX/XY sex-chromosome system. However, exceptions to this rule among howler monkeys have been suggested by several authors. Recently a quadrivalent was discovered in male meiosis of Alouatta caraya and it was established that this species has an X1X2Y1Y2 sex chromosome system. On that basis, a cytogenetic analysis of 25 males of this species is described, showing the corrected karyotype of this species. Each chromosome involved in the particular sex-chromosome system of this species is identified on the basis of mitotic chromosome measurements, G and C-banding patterns as well as on the relative measurements of synaptonemal complexes. It is now established that A. caraya has a karyotype with 2n = 52 in both sexes, and that the male one shows a single autosome #7 (X2) besides the X (X1) and the two products of the reciprocal translocation between the second autosome #7 and the Y chromosome (Y1 and Y2), while females show a homomorphic pair #7 (X2) and a pair of X1. The evolutionary implications of the exceptional primate species having composite sex-chromosome systems are discussed.

Alouatta↗

PubMed1999

Meiotic activation of rat pachytene spermatocytes with okadaic acid: the behaviour of synaptonemal complex components SYN1/SCP1 and COR1/SCP3.

The phosphatase inhibitor okadaic acid accelerates meiotic events in rodent germ cells in culture. Isolated pachytene spermatocytes treated with okadaic acid proceed to a metaphase I arrest in a few hours as opposed to the similar process in vivo, which requires several days. Leptotene/zygotene spermatocytes cannot be activated in this way, suggesting that okadaic acid enables cells to bypass a sensor of the meiotic progression, which is pachytene specific. We monitored the chromosome behaviour accompanying the transition to metaphase I in rat spermatocytes with antibodies against COR1/SCP3, a component of the meiotic chromosome cores, and against the synaptic protein, SYN1/SCP1. Okadaic acid induced a rapid synaptonemal complex dissolution and bivalent separation, followed by chromosome condensation and chiasmata formation, similar to the succession of events in untreated cells. The similarity between meiosis I induced with okadaic acid and the meiosis I events in vivo extends to the dissolution of the nuclear membrane and the disappearance of the microtubule network at the onset of metaphase I. This cell culture system provides a model for the in vivo transition from pachytene to metaphase I and therefore can be used in the study of this transition at the molecular level. The effect of okadaic acid is most likely mediated by the activation of tyrosine kinases, as addition of genistein, a general tyrosine kinase inhibitor, completely abolishes the observed effect of okadaic acid on chromosome metabolism. The okadaic acid-induced progression to the metaphase I arrest is not affected by the inhibition of protein synthesis. However, pachytene spermatocytes incubated in the presence of protein synthesis inhibitors for 6 hours show loss of synapsis which is abnormal in that it is not accompanied by chiasmata formation. The two meiosis-specific proteins, SYN1/SCP1 and COR1/SCP3, are efficiently phosphorylated in vitro by extracts from isolated pachytene cells. Extracts from cells that have reached metaphase I upon okadaic acid treatment, with concomitant displacement of SYN1/SCP1 and COR1/SCP3 from their chromosomes, do not have this capability. These data support the hypothesis that phosphorylation of SYN1/SCP1 and COR1/SCP3 targets their removal from the chromosomes and that activity of the kinases involved correlates with the presence of these two proteins on the chromosomes.

Animals↗

PubMed1990

Synaptonemal complex analysis in Talpa occidentalis spermatocytes (Insectivora, Mammalia). II. Evolution of the X-chromosome self-pairing process.

Zygotene and pachytene configurations of the X chromosome were studied in whole-mount, silver-stained preparations of spermatocytes from XY males from a population of Talpa occidentalis in which sex reversal has been described. The most striking finding in this study was a self-pairing conformation of the axial (differential) element of the X chromosome. This self-pairing was markedly constant in the site of initiation, which invariably involved the distal free end of the X and the region beyond the X-Y pairing segment, so that X-Y synapsis was never disturbed. In addition, self-pairing occurred later than autosomal synapsis and was accompanied by thickening of the axes, although this seemed to occur after the formation of an ordinary synaptonemal complex. The etiology of this phenomenon may be based on residual homology, possibly due to conservation of a primitive isochromosome throughout the karyotypic evolution of this species. However, the possible relationship between self-pairing and sex reversal remains obscure.

Animals↗

PubMed1982

The synaptonemal complexes of caenorhabditis elegans: comparison of wild-type and mutant strains and pachytene karyotype analysis of wild-type.

Normal synaptonemal complexes (SCs), consisting of two lateral elements and a central element, are present in wild-type, him-4 and him-8 mutant strains in both hermaphrodites and males of caenorhabditis elegans. Thus, the increase in rate of nondisjunction in the him mutants is not related to aberrant SC morphology. The wild-type hermaphrodite has six SCs, as determined from 3-D reconstruction analysis of serial section from electron microscopy. Thus, n=6 and this confirms early reports based on cytological studies with the light microscope. Only one end of the SC is attached to the nuclear envelope while the other end is free in the nucleoplasm and there is no apparent bouquet formation. Either end of the SC can attach to the nuclear envelope. The pairing behavior of the XX bivalent is normal and occurs synchronously with the autosomes. Electron dense bodies, or knobs, are associated with the SC via the central element and displace the chromatin for a distance of 200 nm. Each pachytene nucleus of the wild-type hermaphrodite has six such structures that are randomly dispersed along the bivalents such that some SCs have one or two knobs while others have none. Their function is unknown.

Animals↗

PubMed1981

A search for synaptonemal complexes in Ustilago maydis.

Germinating spores, germ-tubes (promycelia), gall tissue and spores developing in the gall were examined. No synaptonemal complexes (SCs) were found in any of these cell types. There are 3 possible explanations for this: (1) Ustilago maydis does not have SCs. This is the case in Schizosaccharomyces pombe (Olson, Eden, Egel-Mitani & Egel, 1978) and in many strains of Saccharomyces cerevisiae (e.g. see Byers & Goetch, 1975). (2) The SC might occur in spores either in the gall or before germination when the spore wall was too solid to allow examination of the contents by the methods used. (3) The SC was present, but for a very short time, and most of the cells examined were in any case not undergoing meiosis, so the SCs were not seen. (Large numbers of spores were examined, but few spores germinate and undergo normal meiotic division; also a minority of the cells in the gall are forming spores at any one time.) The gall was found to contain uninucleate single cells (i.e. it is a yeast, as it is in artificial culture medium) and virtually all these cells were haploid, 1 in 3000 recovered cells was diploid. It appears that the haploids fuse to form a heterokaryotic or diploid cell immediately before spore formation. A heterokaryotic phase is presumed to exist to establish and maintain the infection.

Basidiomycota↗