A Meiotic Chromosomal Core Consisting of Cohesin Complex Proteins Recruits DNA Recombination Proteins and Promotes Synapsis in the Absence of an Axial Element in Mammalian Meiotic Cells

The behavior of meiotic chromosomes differs in several respects from that of their mitotic counterparts, resulting in the generation of genetically distinct haploid cells. This has been attributed in part to a meiosis-specific chromatin-associated protein structure, the synaptonemal complex. This complex consist of two parallel axial elements, each one associated with a pair of sister chromatids, and a transverse filament located between the synapsed homologous chromosomes. Recently, a different protein structure, the cohesin complex, was shown to be associated with meiotic chromosomes and to be required for chromosome segregation. To explore the functions of the two different protein structures, the synaptonemal complex and the cohesin complex, in mammalian male meiotic cells, we have analyzed how absence of the axial element affects early meiotic chromosome behavior. We find that the synaptonemal complex protein 3 (SCP3) is a main determinant of axial-element assembly and is required for attachment of this structure to meiotic chromosomes, whereas SCP2 helps shape the in vivo structure of the axial element. We also show that formation of a cohesin-containing chromosomal core in meiotic nuclei does not require SCP3 or SCP2. Our results also suggest that the cohesin core recruits recombination proteins and promotes synapsis between homologous chromosomes in the absence of an axial element. A model for early meiotic chromosome pairing and synapsis is proposed.     

The Ecm11-Gmc2 Complex Promotes Synaptonemal Complex Formation through Assembly of Transverse Filaments in Budding Yeast

During meiosis, homologous chromosomes pair at close proximity to form the synaptonemal complex (SC). This association is mediated by transverse filament proteins that hold the axes of homologous chromosomes together along their entire length. Transverse filament proteins are highly aggregative and can form an aberrant aggregate called the polycomplex that is unassociated with chromosomes. Here, we show that the Ecm11-Gmc2 complex is a novel SC component, functioning to facilitate assembly of the yeast transverse filament protein, Zip1. Ecm11 and Gmc2 initially localize to the synapsis initiation sites, then throughout the synapsed regions of paired homologous chromosomes. The absence of either Ecm11 or Gmc2 substantially compromises the chromosomal assembly of Zip1 as well as polycomplex formation, indicating that the complex is required for extensive Zip1 polymerization. We also show that Ecm11 is SUMOylated in a Gmc2-dependent manner. Remarkably, in the unSUMOylatable ecm11 mutant, assembly of chromosomal Zip1 remained compromised while polycomplex formation became frequent. We propose that the Ecm11-Gmc2 complex facilitates the assembly of Zip1 and that SUMOylation of Ecm11 is critical for ensuring chromosomal assembly of Zip1, thus suppressing polycomplex formation.     

Sex chromosomes, synapsis, and cohesins: a complex affair

During first meiotic prophase, homologous chromosomes are held together by the synaptonemal complex, a tripartite proteinaceous structure that extends along the entire length of meiotic bivalents. While this feature is applicable for autosomes, sex chromosomes often escape from this rule. Many species present sex chromosomes that differ between them in their morphology, length, and gene content. Moreover, in some species, sex chromosomes appear in a single dose in one of the sexes. In all of these cases, the behavior of sex chromosomes during meiosis is conspicuously affected, and this includes the assembly and dynamics of the synaptonemal complex. We review in this study the structure of the synaptonemal complex in the sex chromosomes of three groups of organisms, namely: mammals, orthopterans, and hemipterans, which present different patterns of sex chromosome structure and behavior. Of special interest is the analysis of the organization of the axial/lateral elements of the synaptonemal complex in relation to other axial structures organized along meiotic chromosomes, mainly the cohesin axis. The differences found in the behavior of both axial structures reveal that while the organization of a cohesin axis along sex chromosomes is a conserved feature in most organisms and it shows very little morphological variations, the axial/lateral elements of the synaptonemal complex present a wide range of structural modifications on these chromosomes.Electronic Supplementary Material Supplementary material is available for this article at The synaptonemal complex—50 years     

Couples,pairs, and clusters: mechanisms and implications of centromere associations in meiosis

Observations of a wide range of organisms show that the centromeres form associations of pairs or small groups at different stages of meiotic prophase. Little is known about the functions or mechanisms of these associations, but in many cases, synaptonemal complex elements seem to play a fundamental role. Two main associations are observed: homology-independent associations very early in the meiotic program—sometimes referred to as centromere coupling—and a later association of homologous centromeres, referred to as centromere pairing or tethering. The later centromere pairing initiates during synaptonemal complex assembly, then persists after the dissolution of the synaptonemal complex. While the function of the homology-independent centromere coupling remains a mystery, centromere pairing appears to have a direct impact on the chromosome segregation fidelity of achiasmatic chromosomes. Recent work in yeast, Drosophila, and mice suggest that centromere pairing is a previously unappreciated, general meiotic feature that may promote meiotic segregation fidelity of the exchange and non-exchange chromosomes.     

A Yeast Two-Hybrid Screen for SYP-3 Interactors Identifies SYP-4, a Component Required for Synaptonemal Complex Assembly and Chiasma Formation in Caenorhabditis elegans Meiosis

The proper assembly of the synaptonemal complex (SC) between homologs is critical to ensure accurate meiotic chromosome segregation. The SC is a meiotic tripartite structure present from yeast to humans, comprised of proteins assembled along the axes of the chromosomes and central region (CR) proteins that bridge the two chromosome axes. Here we identify SYP-4 as a novel structural component of the SC in Caenorhabditis elegans. SYP-4 interacts in a yeast two-hybrid assay with SYP-3, one of components of the CR of the SC, and is localized at the interface between homologs during meiosis. SYP-4 is essential for the localization of SYP-1, SYP-2, and SYP-3 CR proteins onto chromosomes, thereby playing a crucial role in the stabilization of pairing interactions between homologous chromosomes. In the absence of SYP-4, the levels of recombination intermediates, as indicated by RAD-51 foci, are elevated in mid-prophase nuclei, and crossover recombination events are significantly reduced. The lack of chiasmata observed in syp-4 mutants supports the elevated levels of chromosome nondisjunction manifested in high embryonic lethality. Altogether our findings place SYP-4 as a central player in SC formation and broaden our understanding of the structure of the SC and its assembly.     

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.     

PAIR3, an axis-associated protein, is essential for the recruitment of recombination elements onto meiotic chromosomes in rice

During meiosis, the paired homologous chromosomes are tightly held together by the synaptonemal complex (SC). This complex consists of two parallel axial/lateral elements (AEs/LEs) and one central element. Here, we observed that PAIR3 localized to the chromosome core during prophase I and associated with both unsynapsed AEs and synapsed LEs. Analyses of the severe pair3 mutant demonstrated that PAIR3 was essential for bouquet formation, homologous pairing and normal recombination, and SC assembly. In addition, we showed that although PAIR3 was not required for the initial recruitment of PAIR2, it was required for the proper association of PAIR2 with chromosomes. Dual immunostaining revealed that PAIR3 highly colocalized with REC8. Moreover, studies using a rec8 mutant indicated that PAIR3 localized to chromosomes in a REC8-dependent manner.     

The meiotic prophase in Bombyx mori females analyzed by three-dimensional reconstructions of synaptonemal complexes

Serial sectioning followed by three dimensional reconstruction of lateral components of the synaptonemal complex have been used to follow chromosome pairing during the prophase of the achiasmatic meiotic division in the silkworm, Bombyx mori. During leptotene and early zygotene, the lateral components become attached to the nuclear envelope at a specific region, thus forming a chromosome bouquet. The attachment of lateral components to the nuclear envelope precedes the completion of the components between their attachment points. Synapsis and synaptonemal complex formation start during the period of lateral component organization in the individual nucleus. Telomeric movements on the nuclear envelope occur at two stages of the prophase: the chromosome pairing appears to be initiated by an association of unpaired ends of homologous chromosomes, the nature of this primary attraction and recognition being unknown. Secondly, the paired chromosomes become dispersed in the nucleus by shifting of attachment sites of completed synaptonemal complexes at the end of zygotene. This movement is possibly related to a membrane flow occurring during this stage. Membrane material is synthesized at the region of synaptonemal complex attachment. Later, the excess membrane material is shifted to the opposite pole where it protrudes into the lumen of the nuclei thus forming vacuoles. — Two previously undescribed features of chromosome pairing were revealed. In late zygotene, chromosome pairing and synaptonemal complex formation were frequently observed to be delayed or even prevented over a short distance by interlocking of two bivalents, both being attached to the nuclear envelope. Such interlocking of bivalents was not found in pachytene. Secondly, one nucleus was found in which two homologous chromosomes were totally unpaired while the remaining 27 bivalents were completed or in a progressed state of pairing. The lateral components of the two unpaired chromosomes had the same length and were located several microns apart, thus eliminating the possibility of a permanent association of homologous chromosomes before the onset of meiosis in Bombyx mori females. — During pachytene, one of the 8 cells belonging to the syncytial cell cluster characteristic of oogenesis continues the meiotic prophase whereas the remaining 7 cells, the nurse cells, enter a different developmental sequence, finally resulting in their degeneration. The synaptonemal complex of the oocyte develops into a sausage-like structure after pachytene by a deposition of dense material onto the lateral components, thus filling out most of the central region. The diameter of this modified synaptonemal complex reaches at least 300 nm, as compaired to a pachytene width of approximately 130 nm. Also, the length of synaptonemal complexes increases from 212 at zygotene/pachytene to at least 300 at the modified pachytene stage. In nurse cells, synaptonemal complexes are shed from the bivalents shortly after pachytene simultaneously with a condensation of the chromatin. These free synaptonemal complex fragments associate and form various aggregates, either more or less normal looking polycomplexes or various complex figures formed by reorganized synaptonemal complex subunits. Later stages have not been included in the present investigation.     

Involvement of synaptonemal complex proteins in sex chromosome segregation during marsupial male meiosis

Marsupial sex chromosomes break the rule that recombination during first meiotic prophase is necessary to ensure reductional segregation during first meiotic division. It is widely accepted that in marsupials X and Y chromosomes do not share homologous regions, and during male first meiotic prophase the synaptonemal complex is absent between them. Although these sex chromosomes do not recombine, they segregate reductionally in anaphase I. We have investigated the nature of sex chromosome association in spermatocytes of the marsupial Thylamys elegans, in order to discern the mechanisms involved in ensuring their proper segregation. We focused on the localization of the axial/lateral element protein SCP3 and the cohesin subunit STAG3. Our results show that X and Y chromosomes never appear as univalents in metaphase I, but they remain associated until they orientate and segregate to opposite poles. However, they must not be tied by a chiasma since their separation precedes the release of the sister chromatid cohesion. Instead, we show they are associated by the dense plate, a SCP3-rich structure that is organized during the first meiotic prophase and that is still present at metaphase I. Surprisingly, the dense plate incorporates SCP1, the main protein of the central element of the synaptonemal complex, from diplotene until telophase I. Once sex chromosomes are under spindle tension, they move to opposite poles losing contact with the dense plate and undergoing early segregation. Thus, the segregation of the achiasmatic T. elegans sex chromosomes seems to be ensured by the presence in metaphase I of a synaptonemal complex-derived structure. This feature, unique among vertebrates, indicates that synaptonemal complex elements may play a role in chromosome segregation.     

The Multiple Roles of Cohesin in Meiotic Chromosome Morphogenesis and Pairing

Sister chromatid cohesion, mediated by cohesin complexes, is laid down during DNA replication and is essential for the accurate segregation of chromosomes. Previous studies indicated that, in addition to their cohesion function, cohesins are essential for completion of recombination, pairing, meiotic chromosome axis formation, and assembly of the synaptonemal complex (SC). Using mutants in the cohesin subunit Rec8, in which phosphorylated residues were mutated to alanines, we show that cohesin phosphorylation is not only important for cohesin removal, but that cohesin's meiotic prophase functions are distinct from each other. We find pairing and SC formation to be dependent on Rec8, but independent of the presence of a sister chromatid and hence sister chromatid cohesion. We identified mutations in REC8 that differentially affect Rec8's cohesion, pairing, recombination, chromosome axis and SC assembly function. These findings define Rec8 as a key determinant of meiotic chromosome morphogenesis and a central player in multiple meiotic events.     

Mutations in the Chromosomal Passenger Complex and the Condensin Complex Differentially Affect Synaptonemal Complex Disassembly and Metaphase I Configuration in Drosophila Female Meiosis

Production of haploid gametes relies on the specially regulated meiotic cell cycle. Analyses of the role of essential mitotic regulators in meiosis have been hampered by a shortage of appropriate alleles in metazoans. We characterized female-sterile alleles of the condensin complex component dcap-g and used them to define roles for condensin in Drosophila female meiosis. In mitosis, the condensin complex is required for sister-chromatid resolution and contributes to chromosome condensation. In meiosis, we demonstrate a role for dcap-g in disassembly of the synaptonemal complex and for proper retention of the chromosomes in a metaphase I-arrested state. The chromosomal passenger complex also is known to have mitotic roles in chromosome condensation and is required in some systems for localization of the condensin complex. We used the QA26 allele of passenger component incenp to investigate the role of the passenger complex in oocyte meiosis. Strikingly, in incenp^QA26 mutants maintenance of the synaptonemal complex is disrupted. In contrast to the dcap-g mutants, the incenp mutation leads to a failure of paired homologous chromosomes to biorient, such that bivalents frequently orient toward only one pole in prometaphase and metaphase I. We show that incenp interacts genetically with ord, suggesting an important functional relationship between them in meiotic chromosome dynamics. The dcap-g and incenp mutations cause maternal effect lethality, with embryos from mutant mothers arrested in the initial mitotic divisions.     

HAL-2 Promotes Homologous Pairing during Caenorhabditis elegans Meiosis by Antagonizing Inhibitory Effects of Synaptonemal Complex Precursors

During meiosis, chromosomes align with their homologous pairing partners and stabilize this alignment through assembly of the synaptonemal complex (SC). Since the SC assembles cooperatively yet is indifferent to homology, pairing and SC assembly must be tightly coordinated. We identify HAL-2 as a key mediator in this coordination, showing that HAL-2 promotes pairing largely by preventing detrimental effects of SC precursors (SYP proteins). hal-2 mutants fail to establish pairing and lack multiple markers of chromosome movement mediated by pairing centers (PCs), chromosome sites that link chromosomes to cytoplasmic microtubules through nuclear envelope-spanning complexes. Moreover, SYP proteins load inappropriately along individual unpaired chromosomes in hal-2 mutants, and markers of PC-dependent movement and function are restored in hal-2; syp double mutants. These and other data indicate that SYP proteins can impede pairing and that HAL-2 promotes pairing predominantly but not exclusively by counteracting this inhibition, thereby enabling activation and regulation of PC function. HAL-2 concentrates in the germ cell nucleoplasm and colocalizes with SYP proteins in nuclear aggregates when SC assembly is prevented. We propose that HAL-2 functions to shepherd SYP proteins prior to licensing of SC assembly, preventing untimely interactions between SC precursors and chromosomes and allowing sufficient accumulation of precursors for rapid cooperative assembly upon homology verification.     

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.     

Meiotic Cohesin Promotes Pairing of Nonhomologous Centromeres in Early Meiotic Prophase

A period of pairing between nonhomologous centromeres occurs early in meiosis in a diverse collection of organisms. This early, homology-independent, centromere pairing, referred to as centromere coupling in budding yeast, gives way to an alignment of homologous centromeres as homologues synapse later in meiotic prophase. The regulation of centromere coupling and its underlying mechanism have not been elucidated. In budding yeast, the protein Zip1p is a major component of the central element of the synaptonemal complex in pachytene of meiosis, and earlier, is essential for centromere coupling. The experiments reported here demonstrate that centromere coupling is mechanistically distinct from synaptonemal complex assembly. Zip2p, Zip3p, and Red1p are all required for the assembly of Zip1 into the synaptonemal complex but are dispensable for centromere coupling. However, the meiotic cohesin Rec8p is required for centromere coupling. Loading of meiotic cohesins to centromeres and cohesin-associated regions is required for the association of Zip1 with these sites, and the association of Zip1 with the centromeres then promotes coupling. These findings reveal a mechanism that promotes associations between centromeres before the assembly of the synaptonemal complex, and they demonstrate that chromosomes are preloaded with Zip1p in a manner that may promote synapsis.     

Whole mount electron microscopy of meiotic chromosomes and the synaptonemal complex

The mechanism by which homologous chromosomes pair and crossover has been a major unsolved problem in genetics. Thin section electron microscopy of the synaptonemal complex has not provided enough details to allow any significant insight into this problem. Whole mount preparations of the testis of mice, quail, crayfish, and frogs provided a striking improvement in visualization of the morphological features of meiotic chromosomes. These studies, when combined with the use of deoxyribonuclease and trypsin allowed the following conclusions. 1. The synaptonemal complex (lateral and central elements with connecting L-C fibers) is composed of protein. 2. Contrary to common speculation the central element is not the pairing surface of homologous chromosomes. 3. The L-C fibers, averaging 75–100 Å in width, extend from the lateral elements and meet to form the central element which is usually composed of four fibers. 4. During leptotene, homologous axial elements, although unpaired for most of their length, attach next to each other at the nuclear membrane. 5. Short segments of the chromatin fibers attach to the lateral elements. These points of attachment are clustered, producing the chromomeres seen by light microscopy. 6. The chromatin fibers extend out from the lateral element as loops. Lampbrush chromosomes are thus not restricted to oogenesis but are common to all meiotic chromosomes.Since the morphological features of the central element of the synaptonemal complex persist despite extensive deoxyribonuclease digestion, pairing is perhaps best visualized as a two-step process consisting of a) chromosomal pairing during which the proteinaceous synaptonemal complex pulls homologous chromosomes into approximate association with each other, and b) molecular pairing, which probably takes place in the area around the synaptonemal complex.Supported by NIH Grants GM-15886 and C-2568, and The Charles and Henrietta Detoy Research Fellowship.     

The CSN/COP9 Signalosome Regulates Synaptonemal Complex Assembly during Meiotic Prophase I of Caenorhabditis elegans

The synaptonemal complex (SC) is a conserved protein structure that holds homologous chromosome pairs together throughout much of meiotic prophase I. It is essential for the formation of crossovers, which are required for the proper segregation of chromosomes into gametes. The assembly of the SC is likely to be regulated by post-translational modifications. The CSN/COP9 signalosome has been shown to act in many pathways, mainly via the ubiquitin degradation/proteasome pathway. Here we examine the role of the CSN/COP9 signalosome in SC assembly in the model organism C. elegans. Our work shows that mutants in three subunits of the CSN/COP9 signalosome fail to properly assemble the SC. In these mutants, SC proteins aggregate, leading to a decrease in proper pairing between homologous chromosomes. The reduction in homolog pairing also results in an accumulation of recombination intermediates and defects in repair of meiotic DSBs to form the designated crossovers. The effect of the CSN/COP9 signalosome mutants on synapsis and crossover formation is due to increased neddylation, as reducing neddylation in these mutants can partially suppress their phenotypes. We also find a marked increase in apoptosis in csn mutants that specifically eliminates nuclei with aggregated SC proteins. csn mutants exhibit defects in germline proliferation, and an almost complete pachytene arrest due to an inability to activate the MAPK pathway. The work described here supports a previously unknown role for the CSN/COP9 signalosome in chromosome behavior during meiotic prophase I.     

STAG3, a novel gene encoding a protein involved in meiotic chromosome pairing and location of STAG3-related genes flanking the Williams-Beuren syndrome deletion.

Chromatin rearrangements in the meiotic prophase are characterized by the assembly and disassembly of synaptonemal complexes (SC), a protein structure that stabilizes the pairing of homologous chromosomes in prophase. We report the identification of human and mouse cDNA coding for stromalin 3 (STAG3), a new mammalian stromalin member of the synaptonemal complex. The stromalins are a group of highly conserved proteins, represented in several organisms from yeast to humans. Stromalins are characterized by the stromalin conservative domain (SCD), a specific motif found in all proteins of the family described to date. STAG3 is expressed specifically in testis, and immunolocalization experiments show that STAG3 is associated to the synaptonemal complex. As the protein encoded by the homologous gene (Scc3p) in Saccharomyces cerevisiae was found to be a subunit of a cohesin complex that binds chromosomes until the onset of anaphase, our data suggest that STAG3 is involved in chromosome pairing and maintenance of synaptonemal complex structure during the pachytene phase of meiosis in a cohesin-like manner. We have mapped the human STAG3 gene to the 7q22 region of chromosome 7; six human STAG3-related genes have also been mapped: two at 7q22 near the functional gene, one at 7q11.22, and three at 7q11.23, two of them flanking the breakpoints commonly associated with the Williams-Beuren syndrome (WBS) deletion. Since the WBS deletion occurs as a consequence of unequal meiotic crossing over, we suggest that STAG3 duplications predispose to germline chromosomal rearrangement within this region.     

The perinuclear microtubule-organizing center and the synaptonemal complex of higher plants share a common antigen: its putative transfer and role in meiotic chromosomal ordering

Recognition of homologous chromosomes during meiotic prophase is associated in most cases with the formation of the synaptonemal complex along the length of the chromosome. Telomeres, located at the nuclear periphery, are preferential initiation sites for the assembly of the synaptonemal complex. In most eukaryotic cells, telomeres cluster in a restricted area, leading to the bouquet configuration in leptotene-zygotene, while this typical organization progressively disappears in late zygotene-pachytene. We wondered whether such striking changes in the intranuclear ordering and pairing of meiotic chromosomes during the progression of prophase I could be correlated with activity of the centrosome and/or microtubule-organizing center (MTOC). Plant cells may be used as a model of special interest for this study as the whole nuclear surface acts as an MTOC, unlike other cell types where MTOCs are restricted to centrosomes or spindle pole bodies. Using a monoclonal antibody (mAb 6C6) raised against isolated calf centrosomes we found that the 6C6 antigen is present over the entire surface of the plant meiotic nucleus, in early prophase I, before chromosomal pairing. At zygotene, short fragments of chromosomes become stained near the nuclear envelope and within the nucleus. At pachytene, after complete synapsis, the labeling specifically concentrates within the synaptonemal complexes, although the nuclear surface is no longer reactive. Ultrastructural localization using immunogold labeling indicates that the 6C6 antigen is colocalized with the synaptonemal complex structures. Later in metaphase I, the antigen is found at the kinetochores. Our data favor the idea that the 6C6 antigen may function as a particular chromosomal passenger-like protein. These observations shed new light on the molecular organization of the plant synaptonemal complex and on the redistribution of cytoskeleton-related antigens during initiation of meiosis. They suggest that antigens of MTOCs are relocated to chromosomes during the synapsis process starting at telomeres and contribute to the spatial arrangement of meiotic chromosomes. Such cytoskeleton-related antigens may acquire different functions depending on their localization, which is cell-cycle regulated.     

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.