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This paper presents an electron microscopic analysis of the behavior and morphology of the sex chromosomes and autosomes during prophase I in the common shrew, Sorex araneus L. The pairing patterns of the X/Y1Y2 and autosomal Robertsonian trivalents are described.
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.
As an alternative to the production and use of monoclonal antisynaptonemal complex (SC) antibodies to isolate SC genes, we have explored the use of polyclonal anti-SC antibodies to identify SC genes from a cDNA expression library. The method proved relatively simple, reliable, and fast and has yielded two SC genes. A homologue of one of these genes from a different species has previously been isolated in another laboratory.
The chiasma has been recognized as a major feature of meiosis both visually and functionally for > 85 years. But its functional basis remains poorly understood. In interaction with the spindle, it generally mediates the ultimate distribution of homologues to opposite poles at meiosis I to yield correct disjunction. Its establishment depends upon the presence of a completed reciprocal recombination (crossover) event, but its maintenance from the time of crossover completion until anaphase I (a period of substantial extent) requires additional functions. Evidence for the nature of these functions, their relationship to synapsis and conjectures on their place in the evolution of meiosis are discussed here.
The study of homologous recombination in the fission yeast Schizosaccharomyces pombe has recently been extended to the cytological analysis of meiotic prophase. Unlike in most eukaryotes no tripartite SC structure is detectable, but linear elements resembling axial cores of other eukaryotes are retained. They may be indispensable for meiotic recombination and proper chromosome segregation in meiosis I. In addition fission yeast shows interesting features of chromosome organization in vegetative and meiotic cells: Centromeres and telomeres cluster and associate with the spindle pole body. The special properties of fission yeast meiosis correlate with the absence of crossover interference in meiotic recombination. These findings are discussed. In addition homologous recombination in fission yeast is reviewed briefly.
The levels of meiotic chromosome pairing abnormalities observed in six Australian F1 Bos indicus x Bos taurus cattle crosses (mean = 23%) were significantly higher than those of the full-blood breeds (9%). The abnormal configurations in the F1 hybrids included partial pairing failure, multivalents, interlocks, and inversion pairing. Abnormal configurations were also present, but at lower frequency, in backcross hybrid bulls. The main types of abnormal configurations and the levels of XY-autosomal associations and autosomal asynapsis observed were unlikely to cause significant fertility problems in the hybrids.
Sex determination in the blue tilapia, Oreochromis aureus, is primarily a ZW female-ZZ male system. Here, by analysis of the pachytene meiotic chromosomes of O. aureus, we demonstrate the presence of two distinct regions of restricted pairing present only in heterogametic fish. The first, a subterminal region of the largest bivalent is located near to the region of unpairing found in the closely related species O. niloticus, while the second is in a small bivalent, most of which was unpaired. These results suggest that O. aureus has two separate pairs of sex chromosomes.
Whole-mount preparations of silver-stained spermatocytes and oocytes from Ts(512)31H mice were examined in the electron microscope. The 5(12) chromosome was associated with the XY bivalent in the large majority of spermatocytes, whereas in about one-half of the oocytes, the 5(12) was associated with either unpaired chromosomes or heterochromatic parts of chromosomes or showed self-synapsis. There was a tendency for 5(12) chromosomes to be more fully heterochromatic in oocytes than in spermatocytes. A large proportion of oocytes (50%) and a much smaller proportion of spermatocytes exhibited various errors of chromosome pairing, but these proportions were only marginally greater than in control gametocytes from mice with normal karyotypes. It is concluded that the observed errors of pairing bear no simple relation to the almost complete breakdown of spermatogenesis and the marked impairment of oogenesis that occur in tertiary trisomic Ts(5(12))31H mice.
A long-term (during 4 months) daily peroral injections of neoaquasept (NA) (a drinking water disinfections agent) at a dose corresponding to the normal level of consumption increases the number of spermatocytes in which the sexual bivalent associates with normal autosomal bivalents (up to 18.2%). In single cells a premature desynapsis of sex chromosomes at late pachytene was observed. There was the appearance of single cells with the X0 karyotype. A 3-fold excess of the normal consumption of NA causes an increase in the number of cells with the above disturbance in the SC structure and behaviour and causes the appearance of heteromorphic bivalents. On the 7th day after a single MTD injection of NA male mice displayed a sharp (up to 27.9%) increase in the number of cells in which the sexual bivalent associated with autosomal bivalents, formation of univalents of autosomal and sex chromosomes, SC degeneration.
Spermatocytes from the mole, Talpa occidentalis, a species that includes both XX males and intersexes, were surface-spread and silver-stained to substage meiotic prophase from early zygonema through pachynema. In zygonema, only the Z2 and Z3 substages were found. This stage differed in comparison with such species as the Chinese hamster, laboratory mouse, and deer mouse, which belong to orders other than Insectivora. Pachynema, in which five substages were established (P1-P5), seems to be a more homogeneous stage, and remarkable differences with respect to the above-mentioned species were not found. Synaptic adjustment was demonstrated in X-Y pairing. Nonhomologous pairing was evident at the Y-centromeric region and considered likely in the proximal arm of this chromosome. In addition to sequencing the events taking place during zygonema and pachynema in males from a wild population in which some members show sex reversal, our finding represents the first attempt to substage zygonema and pachynema in an Insectivore species, thus contributing to current knowledge of the nature and degree of variability in the mammalian synaptic process.
The behavior and morphology of sex chromosomes pairing in spermatocytes of the brown rat have been studied by surface spreading, silver and phosphotungstic acid(PTA) staining techniques. The results are as follows. Sex chromosomes axial cores thicken before X and Y pairing. X Y pairing is delayed until early pachytene. The first pairing initiation site is located on telomere of the short arms of X and Y chromosomes. The second pairing initiation site is located on teltomere of the long arms of X and Y chromosomes or on the interstitial position of the long arms of X and Y. Pycnosis speed of sex axial cores is different with different stages during prophase I of meiosis. In middle Pachytene the almost whole Y is fully paired in SC association with about one-third the X. On the region of X-YSC, lateral elements of X-YSC divide into two skeins, bubble appears on one of the two skeins and the unpaired X and Y axial cores are in variable forms. X Y pairing initiation sites, relationship of X Y pairing and genetic homology and mechanism of thickening and variable X Y axial cores were discussed.
Zygotene and pachytene spermatocytes from Massey I (t1 5;26) and Massey II (t2 8; 11) translocation heterozygotes each contained one trivalent, often delayed in pairing, while cells from double Massey translocation heterozygotes had two such trivalents. As meiosis progressed, trivalents became fully paired, with acrocentric axes in a cis configuration. Abnormal pairing configurations often resulted from interactions between unpaired chromosome axes or segments. However, when two Massey trivalents were present in the same nucleus, there was no pairing interaction between them. In different Massey translocation heterozygotes, trivalent-involved pairing abnormalities occurred in 14-28% of cells, with XY-trivalent and XY-bivalent-trivalent associations being as high as 7.1-23.1%. In spermatocytes from single and double Massey translocation heterozygotes with normal-sized testes, the total SC abnormality frequency was 34.4% for the t1 heterozygotes, 27.1% for the t2 heterozygotes, and 21.4% for the double heterozygote. One Massey II heterozygote with one normal and one small testis had significantly higher SC abnormality frequency (54%) than normal rams. A trisomic cell was recorded in one ram and two hyperdiploid cells in another ram, but these were unrelated to the translocations. It is suggested that resolution of pairing abnormalities by synaptic adjustment is important in reducing the effects on fertility of the translocations.
BACKGROUND: The life cycle of most eukaryotic organisms includes a meiotic phase, in which diploid parental cells produce haploid gametes. During meiosis a single round of DNA replication is followed by two rounds of chromosome segregation. In the first, or reductional, division (meiosis I), which is unique to meiotic cells, homologous chromosomes segregate from one another, whereas in the second, or equational, division (Meiosis II) sister centromeres disjoin. Meiotic DNA replication precedes the initiation of recombination by programmed Spo11-dependent DNA double-strand breaks. Recent reports that meiosis-specific cohesion is established during meiotic S phase and that the length of S phase is modified by recombination factors (Spo11 and Rec8) raise the possibility that replication plays a fundamental role in the recombination process. RESULTS: To address how replication influences the initiation of recombination, we have used mutations in the B-type cyclin genes CLB5 and CLB6, which specifically prevent premeiotic replication in the yeast Saccharomyces cerevisiae. We find that clb5 and clb5 clb6 but not clb6 mutants are defective in DSB induction and prior associated changes in chromatin accessibility, heteroallelic recombination, and SC formation. The severity of these phenotypes in each mutant reflects the extent of replication impairment. CONCLUSIONS: This assemblage of phenotypes reveals roles for CLB5 and CLB6 not only in DNA replication but also in other key events of meiotic prophase. Links between the function of CLB5 and CLB6 in activating meiotic DNA replication and their effects on subsequent events are discussed.
In this paper we have compared the breeding performance of Tdy-negative XY, XXY and XYY females to assess the relative importance of the lack of a second X chromosome compared with the presence of a Y chromosome, in reducing fertility. The XY females were of poor fertility, although five of twelve produced at least one offspring. The XXY females had larger, more frequent litters, and a longer reproductive lifespan, implicating the lack of a second X as the major cause of the poor fertility of XY females. Nevertheless, XYY females appeared to be more seriously affected than the XY females, suggesting that the presence of the Y may be a contributory factor. Pachytene analysis demonstrated that the Y is a very inefficient pairing partner for the X during female meiosis. In XY females only 11% of pachytene cells had the X and Y paired; in XXY females the two X chromosomes paired and the Y was almost always a univalent, while in XYY females the X paired with a Y in only 15% of pachytene cells. The presence of unpaired sex chromosomes has previously been implicated as a cause of oocyte loss during pachytene, and the proportion of cells with unsynapsed sex chromosomes decreased as pachytene proceeded, suggesting that they were progressively eliminated. Significantly, protection against elimination was afforded not only by synapsis between sex chromosomes, but also by self-synapsis if a sex chromosome remained as a univalent. It is concluded that sex chromosome univalence leading to pachytene oocyte failure is responsible for the postnatal oocyte deficiency seen in XY females. A separate study has shown that XXY females have a similar level of oocyte deficiency. It is suggested that the presence of a second X chromosome improves the fertility of XXY females, compared with XY females, by improving oocyte quality and by eliminating the production of lethal XY and OY zygotes. The genotype frequencies for the offspring of XY and XYY females differed from those predicted from the pachytene data. The XY females showed a marked deficiency of XO offspring compared with XXY and XYY aneuploid offspring, whereas the XXY females had fewer than expected XXY and XYY aneuploid offspring.
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We describe in this paper the human male synaptic cycle using light and electron microscopy and the distribution of cells in the different stages of prophase I. The pattern of chromosome pairing and synapsis is an important tool to determine accurately whether a given synaptic behavior in infertile or sterile men is really abnormal or not. The relationship of prepachytene to pachytene cells is also important for the diagnosis of the different types of meiotic arrest at the primary spermatocyte level.
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