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PubMed1987

The nature of the 1;29 translocation in cattle as revealed by synaptonemal complex analysis using electron microscopy.

Synaptonemal complex analyses were carried out by electron microscopy on surface-spread spermatocytes of one normal bull and two bulls that were heterozygous for the so-called 1;29 translocation. The autosomal bivalents of the normal karyotype, which could be arranged by size in a series, demonstrated kinetochores at the terminally located attachment plaques. One autosomal bivalent was clearly larger than the rest and apparently consisted of the long arm of the 1;29 translocation. The 1;29 translocation was the longest autosome in the set and had a kinetochore in a subtelocentric position. Some of the autosome pairs had nucleolus organizer regions in telomeric regions. The X and Y chromosomes, which were not paired at zygotene, demonstrated association in a very short segment at early pachytene; in no cells could a synaptonemal complex be seen between the X and Y. Very often the sex chromosomes were dissociated. At zygotene, a few, usually large, bivalents were unpaired proximally. This always also involved the proximal parts of the arms of the 1;29 translocation and their normal homologs. At early pachytene, the 1;29 trivalent, although to a less extensive degree, was also unpaired in the pericentric region. Configurations in which one chromosome, either 1 or 29, was completely paired with its corresponding arm in the 1;29 translocation chromosome also occurred. When unpaired proximally, the size of chromosome 1 agreed fairly well with the size of its corresponding arm, but the size of chromosome 29 was considerably larger than the corresponding arm of the 1;29 translocation chromosome. During late zygotene and early pachytene, the percent difference between chromosome 29 and its corresponding arm decreased, and at mid and late pachytene there had been a complete synaptic adjustment. The size difference and pairing behavior indicated that a deletion of the kinetochore and the most proximal segment of chromosome 29 had preceded the fusion with chromosome 1 into the 1;29 translocation. The unique structural appearance of the 1;29 translocation chromosome compared to that of other centric fusion translocations in cattle lends support to the theory of a monophyletic origin of the 1;29 translocation. The importance of the pairing behavior observed in governing recombination and chromosome disjunction is briefly discussed.

Animals↗

PubMed1978

Meiotic chromosome pairing and synaptonemal complex transformation in Culex pipiens oocytes.

The synaptonemal complexes of the oocytes of the mosquito Culex pipiens quinquefasciatus have been reconstructed from serial sections. A diffuse structure, probably a chromocenter composed of centromeric heterochromatin, was present during pachytene. As no synaptonemal complexes were visible inside the chromocenter the continuity of the 2 arms of a bivalent was lost. The telomeric ends were clustered on a small area of the nuclear membrane in a bouquet arrangement; they were associated in pairs, and sometimes joined through a special structure. One pair was composed of the 2 telomeres of the shortest bivalent and a ring configuration was thus formed. The other 2 chromosomes may form one or two rings. During a short transitional stage, after the disappearence of the synaptonemal complexes, several thousand annuli, 1200-1500 A in diameter, were present in the nuclei. The annuli disappeared as material originating mainly from the transverse filaments of the synaptonemal complexes formed a "capsule" around the chromosomes during diplotene.

Animals↗

PubMed1991

Stage-specific damage to synaptonemal complexes and metaphase chromosomes induced by X rays in male mouse germ cells.

Synaptonemal complexes reveal mutagen-induced effects in germ cell meiotic chromosomes. This study was aimed at characterizing relationships between damage to synaptonemal complexes and metaphase I chromosomes following radiation exposure at various stages of spermatogenesis. Male mice were irradiated with doses of 0, 2, or 4 Gy, and spermatocytes were harvested at times consistent with earlier exposures as spermatogonial stem cells, preleptotene cells (premeiotic DNA synthesis), or meiotic prophase cells. After stem-cell exposure, twice as many rearrangements were observed in synaptonemal complexes as in metaphase I chromosomes. Irradiation during premeiotic DNA synthesis resulted in dose-related increases in synaptonemal complex breakage and rearrangements (including novel forms) and in metaphase chromosomal aberrations. Following prophase exposure, various types and levels of damage to synaptonemal complexes and metaphase chromosomes were observed. Irradiation of zygotene cells led to high frequencies of chromosome multivalents in metaphase I without a correspondingly high level of damage in preceding prophase synaptonemal complexes. Thus irradiation of premeiotic and meiotic cells results in variable relationships between damage to synaptonemal complexes and metaphase chromosomes. Interpretations of these relationships are based upon what is known about both radiation clastogenesis and the structural/temporal relationships between synaptonemal complexes at prophase and chromosomes at metaphase I of meiosis.

Animals↗

PubMed1995

The central region of the synaptonemal complex revealed in three dimensions.

The synaptonemal complex plays a key role in pairing of homologous chromosomes during meiosis. Its gross structure was already known by conventional electron microscopy, but only recently has it been possible to reveal the synaptonemal complex in three dimensions at higher resolution by electron microscope tomography. As the molecular analysis of meiosis is developing rapidly, a more thorough understanding of the principal organization of the synaptonemal complex is essential.

Journal Article↗

PubMed2005

Synaptonemal complex formation: where does it start?

The synaptonemal complex is a prominent, evolutionarily conserved feature of meiotic prophase. The assembly of this structure is closely linked to meiotic recombination. A recent study in budding yeast reveals an unexpected role in centromere pairing for a protein component of the synaptonemal complex, Zip1. These findings have implications for synaptonemal complex formation.

Centromere↗

PubMedDate not supplied

Synaptonemal complexes of Xenopus laevis.

Synaptonemal complexes (SCs) have been analyzed in spread Xenopus spermatocytes and oocytes. They showed all the usual features of animal SCs in addition to a high incidence of centromere mismatching. A centriole pair is visible throughout zygotene and pachytene. At zygotene the ends of SCs are markedly thickened and are clustered at the nuclear periphery.

Animals↗

PubMedDate not supplied

[Various properties of DNA from isolated fractions of the mouse synaptonemal complexes].

A fraction of synaptonemal complexes (SC) isolated from mouse spermatocytes has been electrophoretically purified in agarose gel. The DNA from the SC fraction constitutes approximately 0.5% of total nuclear DNA, and its molecules have length heterogeneity from 1 k.b. to 20 k.b. The content of beta-globin gene is the same in DNA from the SC fraction and in total nuclear DNA. The specificity of DNA from the SC fraction is manifested by higher contents of the repeated alternative sequences GT/CA and B1-sequence that is probably due to the processes of genetic meiotic recombination.

Animals↗

PubMed1996

Synaptonemal complexes: structure and function.

Synaptonemal complexes (SCs) are zipper-like structures which are assembled between homologous chromosomes during the prophase of the first meiotic division. Their assembly and disassembly correlate with the successive chromatin rearrangements of meiotic prophase, namely the condensation, pairing, recombination and disjunction of homologous chromosomes. It was originally thought that SCs created the preconditions for the homologous crossing over of chromosomes by bringing corresponding parts of homologous chromosomes in close apposition. However, this view has been gradually undermined during recent years, and ideas about the roles of SCs have radically changed. SCs are now considered to be structures that both control the number and distribution of reciprocal exchanges between homologous chromosomes (cross-overs) and convert cross-overs into functional chiasmata. How SCs fulfil these roles remains to be elucidated.

Animals↗

PubMed1998

The synaptonemal complex protein SCP3 can form multistranded, cross-striated fibers in vivo.

The synaptonemal complex protein SCP3 is part of the lateral element of the synaptonemal complex, a meiosis-specific protein structure essential for synapsis of homologous chromosomes. We have investigated the fiber-forming properties of SCP3 to elucidate its role in the synaptonemal complex. By synthesis of SCP3 in cultured somatic cells, it has been shown that SCP3 can self-assemble into thick fibers and that this process requires the COOH-terminal coiled coil domain of SCP3, as well as the NH2-terminal nonhelical domain. We have further analyzed the thick SCP3 fibers by transmission electron microscopy and immunoelectron microscopy. We found that the fibers display a transversal striation with a periodicity of approximately 20 nm and consist of a large number of closely associated, thin fibers, 5-10 nm in diameter. These features suggest that the SCP3 fibers are structurally related to intermediate filaments. It is known that in some species the lateral elements of the synaptonemal complex show a highly ordered striated structure resembling that of the SCP3 fibers. We propose that SCP3 fibers constitute the core of the lateral elements of the synaptonemal complex and function as a molecular framework to which other proteins attach, regulating DNA binding to the chromatid axis, sister chromatid cohesion, synapsis, and recombination.

3T3 Cells↗

PubMedDate not supplied

A method for producing synaptonemal complex complements in lily and mouse.

A whole-mount procedure for producing pachytene synaptonemal complex complements of Lilium longiflorum was developed. The method involves swelling of the meiotic nuclei followed by nonionic detergent lysis of the nuclear envelope. This technique adequately spreads out the long lily chromosomes while producing only minimal distortion of the chromosomal axes. The ultrastructure of the synaptonemal complex is normal, and the chromatin remains closely associated with the synaptonemal complex. The procedure also was used successfully to produce pachytene synaptonemal complex preparations of mouse chromosomes. In the mouse, the centromeric heterochromatin remains associated with the synaptonemal complex, but the euchromatin is more widely dispersed.

Animals↗

PubMed1987

Multiple synaptonemal complexes (polycomplexes): origin, structure and function.

Multiple synaptonemal complexes (polycomplexes) (PC) are similar in structure to synaptonemal complexes (SC) and are also highly conserved through evolution. They have been described in over 70 organisms throughout all life forms. The appearance of PCs are restricted to meiotic and germ-line derived tissues and are most commonly present after SC formation. However, in a number of animals and plants, both extra- and intranuclear PCs are present during premeiotic and pre-pachytene stages. The structure and biochemical composition of PCs is similar to SCs that the basic unit is tripartite, consisting of two lateral elements and a central region (in which transverse elements are located), and the dimensions of such structures are equivalent. Stacking of SC subunits, while still maintaining equivalent SC dimensions, creates a problem since the lateral elements (LE) would then be twice as thick in the PC as compared to the SC. Recently, it has been shown that the LE of the SC is actually multistranded, thus the LE of each subunit of the PC is half as thick as its counterpart in the SC.

Animals↗

PubMed2005

Two novel proteins recruited by synaptonemal complex protein 1 (SYCP1) are at the centre of meiosis.

Completion of meiosis in mammals depends on the formation of the synaptonemal complex, a tripartite structure that physically links homologous chromosomes during prophase I. Several components of the synaptonemal complex are known, including constituents of the cohesin core, the axial/lateral element and the transverse filaments. No protein has previously been identified as an exclusive component of the central element. Mutations in some synaptonemal-complex proteins results in impaired meiosis. In humans, cases of male infertility have been associated with failure to build the synaptonemal complex. To search for new components of the meiotic machinery, we have used data from microarray expression profiling and found two proteins localising solely to the central element of the mammalian synaptonemal complex. These new proteins, SYCE1 and CESC1, interact with the transverse filament protein SYCP1, and their localisation to the central element appears to depend on recruitment by SYCP1. This suggests a role for SYCE1 and CESC1 in synaptonemal-complex assembly, and perhaps also stability and recombination.

Animals↗

PubMed1996

[Ultrastructural and immunocytochemical analysis of the synaptonemal complex at the initiation of synapsis].

The synaptonemal complexes (SCs) are nuclear structures specific for meiosis. They have a central role in homolog chromosomes coupling; they are essential in crossing over events and chromosomic segregation during the first meiotic division. When its joining ends in pakiteno stage, each synaptonemal extends along the bivalent joining the ends to nuclear wrapping. The SCs are characterized by the presence of two lateral elements and a central region. The lateral elements are parallel and equidistant. The chromatine of homolog chromosomes fixes in a series of loops to these elements. The central region is between the lateral elements. It is formed by the latero-medial fibers and the medial element. The first ones are perpendicularly oriented to the longitudinal axis of CS and connect lateral elements with the medial element. The recombination modules have an active role in recombination processes and quiasma formation, they are associated, at intervals, with the central region among the homolog chromosomes. The localization and function of nucleic acids in formation and coupling of synaptonemal complex is little known, so methodologic alternatives are looked for to resolve this type of problems. In this work, ADN distribution in chicken ovocytes in cigotene, using techniques for electronic microscopy of immuno-oro, were studied. Besides, cytochemical techniques, were used as preferential contrast for ADN or preferential for ribonucleoproteins (RNPs). The combination of preferential tincture for RNPs and immunolocalization of ADN show that chromatin accumulates jointly with ribonucleoproteins in nor coupled lateral elements and the presence of numerous RNPs fibers distributed around lateral elements. Recombination nodules were found among lateral elements during the coupling, these nodules are PTA positives, which means ADN presence, and so, ADN presence among lateral elements. THe presence of a bridge of marked fibers with coloidal gold (ADN) uniting not coupled lateral elements, suggests ADN as a sort of macromollecule forming synapsis sites.

Animals↗

PubMed1988

Dependence on genic balance for synaptonemal complex formation in Drosophila melanogaster.

Electron microscopic examination of gonads of Drosophila melanogaster with different genotypes, including a metafemale 3X;2A and an intersex XXY;3A have revealed that the formation of synaptonemal complexes is controlled by the genic balance, i.e., the ratio of X chromosomes to autosomes. The Y chromosome is not involved in the genetic control of the formation of precursors of the central element of synaptonemal complexes in males, nor does it disturb their formation in XXY females. Hyperploidy for sections 1-3A and 18A-20 of the X chromosome does not lead to the appearance of synaptonemal complexes in males and does not interfere with their formation in females. Females hyperploid for extensive regions of the X chromosome (sections 1-11A, 11A-20, and 8C-20) are fertile and show apparently normal formation of synaptonemal complexes. Hyperploidy for sections 8C-11A of the X results in a sharp decrease in the viability of females, in abnormal differentiation of ovary cells, and in the lack of synaptonemal complexes. These data suggest a possible important role for the sections 8C-11A in the genic balance controlling the formation of synaptonemal complexes in D. melanogaster. The lack of synaptonemal complexes in hypoploid females may be the result of abnormal cell differentiation in gonads.

Animals↗

PubMed2005

Synaptonemal complex karyotype of Eimeria tenella.

In most organisms, biological variability rests on the behaviour of the chromosomes in the meiotic context. Despite the importance of meiosis, very little is known about the meiotic behaviour of the Eimeria chromosomes. The aim of the present study is to describe the standard synaptonemal complex karyotype from Eimeria tenella oocyst spreads by electron microscopy. For that purpose, complete sets of pachytene synaptonemal complexes were obtained and the morphological pachytene karyotype was determined. The authors used a previously reported method that overcomes the difficulty of the extreme resistance of protozoan oocysts to disruption and permits the release of intact meiotic chromosomes. The chromosomes were selected under a light microscope and those selected were stained with phosphotungtic acid and studied by transmission electron microscopy. The authors confirmed 14 chromosomes, which were observed as synaptonemal complexes, and the karyotype was constructed by arranging synaptonemal complexes according to their relative lengths and kinetochore position. Components of the synaptonemal complex, lateral elements, central element, recombination nodules and kinetochore were observed. Measures of the kynetochore, width of the synaptonemal complex, diameter of the recombination nodule and length of the telomeres are given. Minimal and no significant differences were found between measures of chromosomes isolated from different Eimeria tenella strains. To the best of our knowledge, the present investigation for the first time identifies and describes the morphological characteristics of the synaptonemal complex of Eimeria tenella during the meiosis that occurs within the oocysts. In addition, the authors provide evidence of the presence of recombination nodules, suggesting that the recombination process may play an important role in the molecular evolution of this parasite.

Animals↗

PubMed1984

Composition and role of the synaptonemal complex.

The role of the synaptonemal complex (SC) in synapsis during meiotic prophase is examined in spermatocytes and oocytes of mice heterozygous for rearrangements, using light and electron microscopy of whole mount spreads. The duration of cytologically-characterized substages provides a morphological time axis for synaptic events. At zygotene, synapsis is restricted to homologous regions. A second phase of synapsis, indifferent to homology, follows in early pachytene. By a progressive process of synaptic adjustment, SC configurations, such as duplication buckles and inversion loops, are regularly eliminated and form straight, non-homologously synapsed SCs by late pachytene. In the mouse, crossing over probably occurs during the period of homologous synapsis in the first half of pachytene, suggesting an association between recombination events and synaptic adjustment. During this period, a low level of DNA synthesis, distinct from S-phase replication, is found by 3H-thymidine autoradiography to be localized to the SC, as would be expected if repair synthesis involved with crossing over occurred in SC-associated DNA. This DNA synthesis reaches a peak in pachytene concurrently with synaptic adjustment, suggesting that the two events may be related, possibly through the mediation of DNA-binding SC proteins. Using immunocytological techniques to identify SC proteins, a monoclonal antibody has been isolated that binds to formed SCs but not unpaired axes. Apparently specific for a central region component, the antibody also binds to intermediate filaments in the cytoplasm of cultured somatic cells, indicating possible functional attributes common to the meiotic and mitotic proteins.

Animals↗

PubMed1975

The synaptonemal complex and the spindle plaque during meiosis in yeast.

Meiosis in Saccharomyces cerevisiae proceeds principally in the same manner as in other Ascomycetes. Leptotene is characterized by unpaired lateral components and pachytene by the presence of extensive synaptonemal complexes. The synaptonemal complex has the same dimensions and is similar in structure to those described for other organisms. Chromosome counts can now be made by reconstructing the synaptonemal complexes. Diplotene nuclei consistently contain a single polycomplex. The behaviour, doubling and the fine structure of the spindle plaque provide additional markers for the different stages of meiosis.

Cell Nucleolus↗

PubMed1996

Expression of the meiosis-specific synaptonemal complex protein 1 in a heterologous system results in the formation of large protein structures.

The synaptonemal complex is a meiosis-specific structure essential for synapsis of homologous chromosomes. The synaptonemal complex protein 1 (SCP1) is a major constituent of the transversal filament, a fibrous structure that connects the central element of the synaptonemal complex with the two lateral elements. The SCP1 protein forms filamentous dimers with the two molecules that have the same polarity, with the C-termini being anchored in the lateral elements and the N-termini reaching into the central element. We investigated whether the SCP1 protein can take part in the formation of higher order protein structures by expressing it in a heterologous system. We find that expression of SCP1 in Swiss-3T3 fibroblast cells results in the formation of large protein structures. These protein structures resemble a higher order protein structure produced by overexpression of a yeast transversal filament protein in meiotic cells. Our results show that SCP1 is a structural protein and that it most likely is directly involved in the assembly of the synaptonemal complex.

3T3 Cells↗