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 775 records · Page 43Linked to original sources

PubMed1991

Persistence of two Y chromosomes through meiotic prophase and metaphase I in an XYY man.

Studies of spermatogenesis in an XYY male, presenting at a subfertility clinic, confirm the tendency for the germ cells to lose the second Y chromosome but for some XYY cells to reach metaphase I (MI). Light microscope studies of MI revealed the presence of YY bivalents and EM studies of microspread, silver-stained pachytene stages showed 30% of the cells to have two Y chromosomes; 13 out of 16 of these showing a YY synaptonemal complex. Strikingly, the Y axes show only partial synapsis; in no case was synapsis of the long arm heterochromatic regions apparent.

Humans↗

PubMed1990

Nuclear architecture of human pachytene spermatocytes: quantitative analysis of associations between nucleolar and XY bivalents.

Nucleolar association and heterochromatin coalescence have both been invoked as mechanisms involved in the origin of chromosomal associations between nucleolar bivalents themselves, as well as between these bivalents and the XY pair, during meiotic prophase in human spermatocytes. However, these mechanisms do not satisfactorily explain how associating bivalents meet each other within the nuclear space. To elucidate this problem, we have characterized different types of nucleolar-nucleolar and nucleolar-XY bivalent associations, and their frequencies, in light and electron microscope serial sections of spermatocyte nuclei. In the pachytene nucleus, nucleolar bivalent associations were found to involve only one nucleolar sphere of RNP granules connected through a fibrillar center to a chromatin mass composed of two, or more, nucleolar-bivalent short arms. Structural relationships between these elements were examined using 3D computer models of various nucleolar associations. XY and nucleolar bivalents were usually located towards the nuclear periphery associated with the inner face of the nuclear envelope. Some nucleolar bivalents, whether single or associated appeared beside or over XY chromatin. When nucleolar-bivalent short arms (BK) were found over nucleolar or over XY chromatin, their telomeres were unattached to the nuclear envelope and the corresponding synaptonemal complexes were not observed. Ninety nucleoli were found in sixty pachytene nuclei. Thirty six percent of these nucleoli were bound to associated BKs and the remaining 64% to single BKs. Over 40% of individual spermatocytes showed at least one cluster of associated BKs and about 20% presented single or multiple BKs associated with the XY pair. The frequencies of random BK associations, over the total or restricted areas of the nuclear envelope, were calculated according to a probabilistic nuclear model. A correspondence was found in comparing the observed frequencies of associated BKs with those calculated on the basis of bouquet formation. Such an analysis strongly suggests that the occurrence of associations between nucleolar bivalents may arise at random within the bouquet. Thus, the architecture of the meiocyte nucleus, particularly the organization of the bouquet, may be the primary mechanism by which nucleolar bivalents meet each other and, consequently, become associated either through common nucleolus formation or by heterochromatin coalescence.

Cell Nucleolus↗

PubMed1991

Three dimensional reconstruction of human pachytene spermatocyte nuclei of a 17;21 reciprocal translocation carrier: study of XY-autosome relationships.

A study of XY-autosome relationships at the pachytene stage in an infertile 17-21 reciprocal translocation carrier was undertaken by means of three dimensional reconstruction. Synaptonemal complexes and the sex vesicle were analysed on electron microscopic serial sections and the reconstruction was performed on transparent sheets and on a Samba 2000 (Alcatel TITN) image analysis system. All asynapsed segments were entirely included in the sex vesicle, the chromatin fibre of the autosomes and sex chromosomes being tightly intermingled. In one nucleus, the four arms of the quadrivalent were paired, except around the breakpoints where an interstitial asynapsis was observed. In the other nuclei, a terminal asynapsis involving one or two arms of the quadrivalent was found. In the sex vesicle, autosomal asynapsed segments showed the same morphological characteristics as those of X and Y chromosomes. This observation agrees with the hypothesis of the extension of gene inactivation from sex chromosomes to autosomes.

Cell Nucleus↗

PubMed1994

Mammalian meiotic recombination: a reexamination.

Recombination nodules (RNs) are small electron-dense structures associated with the synaptonemal complex. Two types have been identified: early RNs present during zygonema-early pachynema, which are thought to be involved in gene conversion and synaptic initiation, and late RNs present during mid-to-late pachynema, which are thought to be involved in reciprocal recombination leading to chiasma formation. In organisms as diverse as Sodaria, Drosophila, and plants there is indeed a close correlation between the observed number of late RNs and crossovers, or their cytogenetic manifestation, chiasmata. However, as this reexamination of the human data shows, there is not a similar correlation in mammals. Instead, there is a severe deficiency in RNs in eutherian males and marsupial females near chromosome ends and other recombinational "hot spots" (defined genetically), or "localized chiasmata" (defined cytogenetically). Many of these sites of hyper-recombination correspond to sites of telomere or telomere-associated sequences. Together these observations suggest the possibility of a second, mechanistically different, recombination pathway that does not involve RNs, but may directly involve telomere or telomere-associated sequences. This pathway may be responsible for sex-specific hot-spots of recombination observed at highly localized sites throughout the genome.

Animals↗

PubMed1981

A light- and electron-microscopic investigation of gametogenesis in Typosyllis pulchra (Berkeley and Berkeley) (Polychaeta: Syllidae). I. Gonad structure and spermatogenesis.

Tryposyllis pulchra reproduces by the production of three to four gamete-bearing stolons (schizogamy) during consecutive 30--day periods. Although gonads are found in a large number of segments, only those in the posterior-most segments produce gametes and become incorporated into the developing stolon. The more anterior gonads remain undifferentiated and probably sexually undetermined until they are needed in future stolonizations. Gonial cells, which will eventually become either male or female, are ultrastructurally identical at the onset of each stolonization period. Spermatogenesis is marked by a short proliferative period followed by differentiation and spermiogenesis. The first ultrastructural signs of spermatogenesis were found in coelomic spermatogonia on day 10 of stolon formation. Spermatogonia are joined by intercellular bridges, which are maintained until the early spermatid stage. Synaptonemal complexes mark the onset of meiosis, which is apparently synchronized in the syncytial clusters of primary spermatocytes. Spermiogenesis occurs during the final 10 days of stonolization and a variety of stages is present within a single animal. All sperm mature by the time the stolon detaches. Acrosome formation and nuclear condensation are described in addition to the ultrastructure of mature sperm.

Acrosome↗

PubMed1984

Reproduction and sexual development in a freshwater gastrotrich. 3. Postparthenogenic development of primary oocytes and the X-body.

Six small cells are present in each of the bilateral gonads of parthenogenically reproductive Lepidodermella squammata. Early in the extended postparthenogenic phase of the life history, these cells undergo limited proliferation followed by differentiation. Primary oocytes of three types are present 0.3 days after deposition of the final parthenogenic egg: small oocytes with presynaptic nuclei; intermediate oocytes with nuclei containing synaptonemal complexes; and larger oocytes with a germinal vesicle. Oocytes persist without further development at least until day four of the postparthenogenic phase. Older isolated animals may contain and even deposit an enlarged egg, but successful progeny does not result. Oocytes are located at the anterior pole of each of the bilateral gonads, adjacent to developing male tissues producing sperm. More posterior cells in the gonad are initially undifferentiated in the postparthenogenic phase. Dorsal and central cells first show specialization for secretory activity, and by day four contain peripheral layers of RER and central accumulations of polymorphic secretion droplets. The posterior and ventral cells produce secretion droplets that aggregate into an enlarging bilobed structure called the X-body. Two or three cells in each gonad contribute secretions to the X-body, which is intracellular in a secondary syncytium formed by the contributing cells. Functions for the postparthenogenic gametes and for the X-body are not yet demonstrated.

Animals↗

PubMed1976

Oogenesis in the malaria Mosquito Anopheles gambiae.

Oogenesis has been followed with the electron microscope in 2 strains of the malaria mosquito Anopheles gambiae, from the emergence of the adult (oocytes at leptonema) till shortly before the oocytes are ready for oviposition. After pachynema the chromosomes form a karyosphere and a fibrous capsule develops around it. Work on other mosquitoes suggests that the capsule may be related to the synaptonemal complexes. Bot Anopheles strains contain at some time an extrachromosomal (not DNA-containing) body comparable to the karyosphere in size. Clusters of granules are present at the surface of the nucleolus and free in the nucleoplasm. Tentative results indicate that they may contain DNA. During oogenesis the nucleolus becomes very large, mainly because of proliferation of the nucleolonema. Towards the end of oocyte development of the nucleus assumes the large canoe-shape also seen in Aedes and Culex. Nucleolonema traverse the entire nucleus, and modified granular clusters are found throughout.

Animals↗

PubMed1975

The structure of symplasmic early oocytes and their enveloping sheath cells in the polychaete, Platynereis dumerilii.

1. Early oocytes of Platynereis dumerilii are found in clusters floating in the coelom. The oocytes of a cluster form a syncytium which is enveloped by several sheath cells. 2. At stage 2, only a single sheath cell per cluster remains, and it penetrates the group of rounded oocytes, enveloping each one of them. At stage 4, this cell contains a reticular basket made up of bundles of filaments and is inferred to be degenerating, from the presence of vacuoles, clumps of pigment-like material, and atypical mitochondria. 3. Synaptonemal complexes are typical of the nuclei of stage 2 oocytes. Oocytes of stage 4 (early vitellogenesis) contain stacks of endoplasmic reticulum in a distinctive arrangement, with interspersed electron-dense masses. Similar masses accumulate in the cytoplasm close to the nucleus and adjacent to the nuclear pores. 4. From the present observations, a physical supporting rather than a nutritive function is attributed to the sheath cell, which ensures cohesion among the oocytes connected with each other throughout the cluster phase by cytoplasmic bridges. This finding is discussed with respect to conclusions drawn from oocyte transplantation experiments.

Animals↗

PubMed1980

Immunochemical localization of contractile proteins in mammalian meiotic chromosomes.

Smooth muscle heavy myosin and actin have been detected in mouse and rat meiotic chromosomes, by indirect immunofluorescence performed on testis cryostat sections and isolated germ cells. Both contractile proteins are detectable in the nuclei of meiotic cells during the first prophase. The appearance and disappearance time of myosin and actin, however, is not synchronous. While actin is visible in small spots from resting to late diplotene spermatocytes, myosin appears as filaments in the primary spermatocytes from the zygotene to the early state of diplotene. The number of myosin filaments in the pachytene spermatocytes corresponds to the number of bivalent chromosomes, whereas actin spots constantly outnumber the pairing chromosomes by two units. These immunochemical observations suggest that the two contractile proteins are associated with the synaptonemal complex (SC). Myosin seems to be associated with the central region of the SC, while actin is present in its basal knob which is in connection with the nuclear membrane. The difference in number between myosin filaments and actin spots appears to be related to the peculiar behaviour of the pairing sex chromosomes. The presence of contractile proteins in the nuclei of primary spermatocytes seems to suggest that they might play a role in the process of pairing of homologous chromosomes.

Actins↗

PubMed1979

Ultrastructural observations on the oogenesis of Triops cancriformis (Crustacea, Notostraca). II. Early developmental states of the oocyte.

The first stages of the oogenesis of Triops cancriformis have been studied. At the outset the oocyte is smaller than the nurse cells. Meiosis begins with typical synaptonemal complexes. The significance of these complexes and of some other peculiar structures of germ cells, i.e., pore complexes and annuli within the nucleus, and annulate lamellae within the cytoplasm are discussed. The morphofunctional uniformity of some cytoplasmic structures (annulate lamellae, concentrically arranged ER, and yolk globules) in the oocyte as well as its nurse cells is also discussed.

Animals↗

PubMed1981

Elevated recombination and pairing structures during meiotic arrest in yeast of the nuclear division mutant cdc5.

A diploid strain of yeast, homozygous for the mutation cdc5-1, undergoes a normal meiosis at 25 degrees C. At the nonpermissive temperature of 34 degrees C, meiosis is arrested at the first meiotic division, after premeiotic DNA replication and recombination commitment have taken place. Haploidisation commitment does not occur at 34 degrees C. Electron microscopy reveals that synaptons (synaptonemal complexes) are formed and the stage of arrest is characterised by a prevalence of "modified synaptons", which consist of paired lateral elements lacking the central elements. Prolonged incubation at this stage of arrest results in unusually high recombination levels, perhaps related to the synaptonal structures observed. Temperature shift-up experiments (transfers of cell from 25 degrees C to 34 degrees C at various times during meiosis) reveal that the CDC5 function is required for both the first and the second divisions of meiosis.

Hot Temperature↗

PubMed1991

CDC7 protein kinase activity is required for mitosis and meiosis in Saccharomyces cerevisiae.

The product of the CDC7 gene of Saccharomyces cerevisiae has multiple cellular functions, being needed for the initiation of DNA synthesis during mitosis as well as for synaptonemal complex formation and commitment to recombination during meiosis. The CDC7 protein has protein kinase activity and contains the conserved residues characteristic of the protein kinase catalytic domain. To determine which of the cellular functions of CDC7 require this protein kinase activity, we have mutated some of the conserved residues within the CDC7 catalytic domain and have examined the ability of the mutant proteins to support mitosis and meiosis. The results indicate that the protein kinase activity of the CDC7 gene product is essential for its function in both mitosis and meiosis and that this activity is potentially regulated by phosphorylation of the CDC7 protein.

Alleles↗

PubMed1987

Development of the first meiotic prophase stages in human fetal oocytes observed by light and electron microscopy.

The development of the first meiotic prophase stages was studied in two series of human female embryos and fetuses aborted for social reasons. The first series (64 embryos or fetuses aborted at 6-24 weeks of gestation) was used mainly to perfect the methods applied to obtain chromosome preparations and synaptonemal complex spreads. The second series (37 embryos or fetuses aborted at 9-24 weeks of gestation) was used to establish the timing and to characterize the different stages of prophase I. Leptotene-zygotene figures were observed in some embryos at 10 weeks of gestation. Typical zygotene figures were seen at 11-22 weeks. Pachytenes were first observed at 12-13 weeks, and the proportion of these figures was usually lower than 40%. Diplotenes were seen in fetuses with a gestational age of 14 weeks or more. The duration of the process in the human female is thus about 3-4 weeks, a similar period to that described for the male.

Embryo, Mammalian↗

PubMed1983

A light- and electron microscopic analysis of meiotic prophase in female mice.

In the paper we describe meiotic prophase of female mice on successive days of embryonic and early postnatal development. For this purpose we used three different techniques on ovarian material, i.e., Giemsa staining for the light microscopic study of chromatin, silver staining for the light microscopic study of the synaptonemal complex (SC), and agar filtration followed by uranyl acetate staining for the electron microscopic study of the SC. In all types of preparation it was impossible to distinguish leptotene stages, and we conclude that if leptotene really exists, it is of very short duration.--Two types of zygotene stages were found: the "normal" one, resembling zygotene stages in male mice, and a second type that has never been described in males and is characterized by, probably stable, unpaired regions together with totally unpaired axial elements of the SC.--The duration of pachytene was found to be 3-4 days, which is considerably shorter than in males. During early diplotene despiralization of the chromatin and disintegration of the axes of the SC were usually found together with desynapsis.--A considerable variation in distribution of meiotic stages was found between different litters in the same day of gestation. Fetuses in the same litter showed no significant variation. However, the oocytes in an ovary did not pass through meiosis synchronously, with differences up several days. The appearance of chromosomes in a highly contracted state could not be interpreted as a preleptotene condensation stage but probably is a mitotic phenomenon.

Animals↗

PubMed1981

EM autoradiographic evidence that DNA synthesis occurs at recombination nodules during meiosis in Drosophila melanogaster females.

Serial section electron microscopic autoradiography was used to examine the relationship between recombination nodules and 3H-thymidine incorporation during pachytene in Drosophila melanogaster females. For both ellipsoidal and spherical recombination nodules, the number of nodules that are associated with an autoradiographic grain is higher than that expected by chance; this observation is consistent with the hypotheses that recombination involves DNA synthesis and that recombination nodules are the sites of meiotic recombination. Moreover, general DNA replication (S-phase) and synapsis (synaptonemal complex formation) were found to be temporally distinct events, contrary to previous reports; Drosophila females therefore are not exceptional in this regard.

Animals↗

PubMed1981

Pachytene karyotype analysis of tetraploid Meloidogyne hapla females by electron microscopy.

Pairing of homologous chromosomes results in the formation of 34 synaptonemal complexes (SC) at pachytene, corresponding to the 34 bivalents at metaphase I. No multivalent associations were observed and pairing occurs two-by-two. The modified SC, which lacks a central element, does not affect the pairing process. Only one end of the SC is attached to the nuclear envelope, although either end can attach. Total SC length and the number of recombination nodules in the tetraploid were about 1.5 times greater than in the diploid.

Aneuploidy↗

PubMed1984

Heterochromatin and nucleolus-organizer-region behaviour at male pachytene of Sus scrofa domestica.

In the domestic pig (2n = 38) two types of constitutive heterochromatin can be differentiated by fluorescence counterstaining techniques. All 24 biarmed autosomes and the X chromosome have chromomycin A3-positive centromeric C-bands, whereas all 12 acrocentric chromosomes exhibit DA-DAPI-positive centromeric heterochromatin. Fluorescence analysis of male pachytene nuclei revealed that the DA-DAPI-positive C-bands form one or two large chromocentres per cell, while the chromomycin A3-bright C-material is well scattered. Hence, the bivalents formed by the acrocentric chromosome pairs are centromerically associated, whilst the submetacentric bivalents are not. Counce-Meyer spreading techniques were used to study the structure of synaptonemal complexes (SCs) both by light and electron microscopy. In general, the SCs of the domestic pig resemble those described for other mammals. The SC formed by the X and the Y may include up to 94.5% of the Y chromosome. In silver-stained microspreads each of the bivalents (nos. 8 and 10) bearing the nucleolus-organizer-regions (NORs) is connected to a pair of nucleoli, indicating that all four NORs are active during early meiotic stages. By contrast, in the majority of mitotic metaphases of phytohaemagglutinin-stimulated lymphocytes only one pair (no. 10) exhibited Ag-NOR staining. The significance of the chromosome disposition in the pachytene nucleus is discussed with regard to heterochromatin composition and karyotype evolution.

Animals↗

PubMed1986

Oocyte development in XO foetuses of man and mouse: the possible role of heterologous X-chromosome pairing in germ cell survival.

The pairing characteristics of the X axis in XO human and mouse oocytes were studied by the spreading technique throughout meiotic prophase. In three human XO foetuses, germ cell development was seen to be largely blocked at the preleptotene stage. In XO mice on the other hand, oocytes surviving through pachytene increasingly show the X axis making a non-homologous association with itself or with an autosome. Such associations take the form hairpins or rings when self pairing occurs or triradial structures when involvement is with an autosome. Pairing initiation in the autosomes involved is disturbed by the X axis suggesting that the heterologous pairing seen is taking place at the earliest stage of synaptonemal complex formation, namely zygotene. It is suggested, that in the XO mouse, and perhaps also in rare fertile XO humans, survival, of a population of oocytes into the adult is ensured by the ability of the X axis to pair non-homologously at meiotic prophase, thus satisfying pairing requirements.

Animals↗