Synaptonemal Complex Studies Research Articles

Cytogenetic Analysis of Lagria villosa (Coleoptera, Tenebrionidae): Emphasis on the Mechanism of Association of the Xyp Sex Chromosomes

The Xy_p sex determination mechanism is the system most frequent and ancestral to Coleoptera. Moreover, the presence of argyrophilous material associated with the sex bivalent is described as being responsible for the maintenance and association of these chromosomes. There are no karyotype data available regarding the genus Lagria and no consensus in the literature regarding the argyrophilous material present in the lumen of sex bivalent. Therefore, the aim of this work was to investigate the mechanism of sex chromosome bivalent association in Lagria villosa by analyzing the argyrophilous nature of the material present in the Xy_p lumen. It was also intended to characterize L. villosa cytogenetically. The analysis of meiotic cells showed 2n = 18 = 16+Xy_p for males and 2n = 18 = 16+XX in females and the meiotic formula was 2n = 8^II+Xy_p. The C-banding showed blocks of pericentromeric heterochromatin in all chromosomes except in the y_p chromosome. In these regions, the use of fluorochromes revealed the presence of heterochromatin containing GC rich DNA sequences. The study of synaptonemal complex showed a gradual increase in the electron-density of the axial elements of the sex chromosomes and their association with strongly electron-dense material. The pepsin pretreatment revealed that the material impregnated by silver is protein.

SC-karyotyping on electronic microscopy (EM) analysis of synaptonemal complexes (SC) spermocytes of silver fox (Vulpes fulvus)

We present an electronic microscopy (EM) analysis of synaptonemal complexes (SC) spermatocytes of male silver fox Vulpes fulvus at the pachytene stage. The SC-karyotypes of pachetene cells were made and described. Knowledge of normal SC-karyotype is necessary to reveal synaptic abnormalities of autosome and sex bivalents during the pachytene. It was indicated that EM analysis of SC-spermatocytes—the study of synaptonemal complexes in agricultural animals—is a very good instrument for comparative analysis of normal SC-karyotype of foxes that carry chromosomal abnormalities and in fur-bearing animals as well.

Robertsonian Heterozygosity and Male Sterility/Robertsonian Hetrozygotie und Sterilität des Mannes

Meiotic and synaptonemal complex studies using electron microscopy were carried out on infertile man with a 13/14 translocation. Synaptonemal complex analysis showed a typical trivalent with incomplete pairing of the acrocentric elements. The sterilizing effect caused by the failure of synapsis is discussed. This pairing failure has a diagnostic value and a poor prognosis.

Synapsis in supernumerary chromosomes of Prochilodus lineatus (Teleostei: Prochilodontidae)

Summary Meiotic analysis performed on a sample of 10 specimens of Prochilodus lineatus revealed continuous filaments of different sizes stained by AgNO3, corresponding to the bivalent of the normal complement. Small supernumerary chromosomes were observed as isolated and well stained bodies, scattered among the other elements. Synaptonemal complex studies have shown that the beginning of chromosome pairing process in P. lineatus usually occurs from the telomeres to the pericentromeric region. At the end of the pachytene 27 bivalents are perfectly paired and the small supernumerary chromosomes of this species are seen as bivalents, trivalents, or tetravalents. The central region of these small chromosomes show a trick staining when they formed bivalents or tetravalents. This portion seems to correspond to the pericentromeric region of the regular chromosomes with the heterochromatic characteristic of B chromosomes.

Paracentric inversion involving a NOR-bearing chromosome of rainbow trout (Oncorhyncus mykiss): electron microscopy studies of the synaptonemal complex

SUMMARYCytogenetic studies conduced on a sample of 19 specimens of rainbow trout (Oncorhyncus mykiss) showed that 6 presented two chromosomes with a single subterminal AgNOR on the short arms and 13 presented one chromosome with a single subterminal Ag-NOR and a second chromosome with two small subterminal Ag-NORs. Synaptonemal complex studies showed the presence of a pairing failure involving the two lateral elements (LEs) of the NOR-bearing chromosomes only in those specimens with two different NOR-bearing chromosomes, suggesting that the chromosomes with two Ag-NORs originated from a paracentric inversion involving a terminal segment of the original NOR-bearing chromosome. A comparative analysis between three normal and three heterozygous fishes suggest that in the latter group the LEs of the NOR-bearing chromosomes initiate the synaptic process in a more delayed manner, the synapsis develops more quickly, and the nucleolus stays associated with chromosomes for a longer time.

Synaptonemal complex studies in male mice treated with cyproterone acetate or with testosterone

Male mice were injected either with cyproterone acetate (CyAc) or with testosterone enanthate (TE) separately or in combination with estradiol benzoate (E2B) from the neonatal period on or during adulthood. Neonatally treated animals were killed on d28 or d60, whereas all treated adults were killed on d60. Synaptonemal complexes (SCs) were analyzed under the electron microscope. Various SC anomalies were recorded. The frequency of SC alterations was higher in neonatally treated mice injected with E2B alone or in combination with CyAc (range 9.6–23.7%) than in those injected separately with TE or CyAc (range 2–3.9%). In treated neonates, combination of CyAc and E2B treatment increased the prevalence of synaptic impairments (range 11–23.5%). However, whenever TE was added to E2B treatment a significant reduction of these impairments was observed (range 11–2.4 and 23.7–9.7% respectively). In treated adult mice the prevalence of SC anomalies was low (range 2.4–3.1%) whatever hormone was injected. Furthermore, the combination of estradiol with CyAc had no increasing effect on the induction of synaptic alterations. In E2B-treated animals, those injected during the neonatal period were more susceptible than those treated in adulthood. In mice injected separately with TE or CyAc such a difference of sensitivity between neonates and adults was not noticeable. This work demonstrates that testosterone deficiency is partly responsible for E2B-induced SC alterations. However, inhibition of testosterone action at the level of testicular target cells, such as that resulting from administration of cyproterone acetate, is less harmful to the synaptic process of meiosis.

The effect of 13;14 Robertsonian translocations on germ-cell differentiation in infertile males

Two infertile men heterozygous for a 13;14 Robertsonian (Rb) translocation were investigated by means of synaptonemal complex studies, testicular histology, and semen analysis. In both individuals interaction between the Rb trivalent and the XY pair was observed. Twenty percent of pachytene cells analyzed in one patient showed XY-trivalent association which correlated with malformed spermatids; the higher rate of XY-trivalent association (approximately 47%) in the second proband corresponded with complete spermatogenic arrest. The data presented indicate a positive correlation between increased frequency of XY trivalent association and the degree of germ-cell impairment.

Chromosome pairing and recombination in mice heterozygous for different translocations in chromosomes 16 and 17

In order to clarify the relationship between meiotic pairing and recombination, an electron microscopic (EM) study of synaptonemal complexes (SC) and an analysis of chiasma frequency and distribution were made in male mice singly and doubly heterozygous for Robertsonian [Rb(16.17)7Bnr] and reciprocal [T(16:17)43H] translocations and also in tertiary trisomics for the proximal region of chromosome 17. In all these genotypes an extensive zone of asynapsis/desynapsis around the breakpoints was revealed. At the same time a high frequency of non-homologous pairing was observed in precentromeric regions of acrocentric chromosomes. The presence in the proximal region of chromosome 17 of the t haplotype did not affect the synaptic behaviour of this region. Chiasma frequency in the proximal region of chromosome 17 in the T(16:17)43H heterozygotes and trisomics was increased when compared with that in Robertsonian heterozygotes.

Synaptonemal complex studies of the common shrew (Sorex araneus). Comparison of Robertsonian heterozygotes and homozygotes by light microscopy

Chromosome pairing at prophase I of meiosis was orderly in the common shrew. The frequency of univalance was low and nonhomologous pairing between bivalents or involving the sex trivalent (XY1Y2) was absent. The true X and Y chromosomes were attached in an end-to-end configuration. In “simple” Robertsonian heterozygotes autosomal trivalents were formed. Most of these (64 per cent) exhibited straight pairing. Otherwise, side arms were formed from the centromeric regions of the acrocentrics which were almost invariably in a cis orientation and usually paired with each other.

Analysis of synaptonemal complexes in two fertile heterozygous boars, both carriers of a reciprocal translocation involving an acrocentric chromosome.

An electron microscopic study of synaptonemal complexes in two heterozygous fertile boars, one a carrier of a 4;14 reciprocal translocation and the second a carrier of this translocation associated with a 3;7 reciprocal translocation, is reported. The results showed heterologous pairing in almost all quadrivalents, as well as a lack of XY-quadrivalent association. This seemed to be a common feature of translocations in pigs, even if at least one acrocentric chromosome is involved, and may represent a significant meiotic mechanism that prevents spermatocyte loss, while the production of genetically unbalanced gametes leads to loss of progeny through abortion.

Synaptonemal complex studies in the male.

Observations in synaptemal complexes in men carrying structural or numerical chromosomal anomalies are reviewed. Chromosome pairing in patients with extra chromosomes, Robertsonian translocations, reciprocal translocations and pericentric inversions is described. Synaptic anomalies in patients with abnormal seminograms, homosynapsis, asynapsis and heterosynapsis and other pairing abnormalities are also discussed.

Study of synaptonemal complexes in human semen: results in the first 26 consecutive cases.

Synaptonemal complex studies can be carried out in the spermatogenic cells present in the ejaculate. The technique could advantageously avoid the need for a testicular biopsy for synaptic analysis and it is an excellent complement to classical meiotic studies in semen.

SYNAPTIC ADAPTATION IN DEER MICE: A CELLULAR MECHANISM FOR KARYOTYPIC ORTHOSELECTION.

Corresponding Editor: J. B. Spofford

Sequential study of synaptonemal complexes in mouse spermatocytes by light and electron microscopy

Synaptonemal complex (SC) studies in male mice from the beginning of meiosis to its completion (7–40 days of age) indicate: (1) the existence of a leptotene stage with fragmented and completely unpaired axial elements; (2) that synapsis begins at several different initiation points of the axial elements, resulting in X-shaped and Y-shaped configurations; (3) that interlocking of axial elements at zygotene is a normal phenomenon; and (4) that zygotene (presynaptic) and diplotene (postsynaptic) configurations are different from each other.

Meiotic and synaptonemal complex studies in a 14/21 translocation carrier.

Meiotic studies in a sterile carrier of a 14/21 translocation showed a meiotic arrest, with degeneration of primary spermatocytes. Silver staining of pachytene cells revealed the presence of a trivalent. Its synaptonemal complex was quite similar to that described in previous light and electron microscopy studied in mammalian species. The observation of a trivalent with pairing in trans-configuration and the presence of desynaptic synaptonemal complexes in early pachytene could explain the relatively high incidence of non-disjunction in human D/G translocations and the spermatogenic disintegration sometimes seen in these cases.

Meiotic and synaptonemal complex studies in 45 subfertile males.

We describe the results of meiotic and synaptonemal complex (SC) studies in a selected series of 45 subfertile males with different meiotic and seminal alterations. SC anomalies (pairing anomalies, fragmented SCs, or presynaptic arrest) were observed in 32 cases (71.1%). In 31% of the abnormal cases, meiotic anomalies could only be detected through the study of SCs. The origin of synaptic anomalies may be related to the assembly of myosin molecules along the chromosomes. SC analysis should become routine in the study of subfertile males.

A method for the sequential study of synaptonemal complexes by light and electron microscopy

A method is described for the sequential study of synaptonemal complexes by light and electron microscopy. The method is easy, permits one to determine the geometry of chromosome pairing, and should become a routine procedure in the diagnosis of human male subfertility. It should also be useful to establish the risk of recurrence of chromosome aberrations in the progeny of carriers of chromosome rearrangements.

Notizen: Electron Microscopy of Synaptonemal Complexes in Semithin Sections

The technique of osmium tetroxide fixation followed by a treatment with p-phenylenediamine was applied to mouse testes in order to analyze pachytene nuclei. Observation of Epon semithin sections (0.25--0.5 micrometer) in conventional electron microscopy revealed the presence of positively stained synaptonemal complexes surrounded by unstained chromatin. The present results show that by using this method a suitable contrast and resolution can be achieved for semithin sections, which facilitates the topographical study of synaptonemal complexes.