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Studies performed on human trisomic 21 oocytes have revealed that during meiosis, the three homologues 21 synapse and, in some cases, achieve what looks like a trivalent. This implies that meiotic recombination takes place among the three homologous chromosomes 21, and to some extent, crossovers form between them. To see how meiotic recombination is in the presence of an extra chromosome 21, we analyzed the distribution of three recombination markers (γH2AX, RPA, and MLH1) on trisomic 21 oocytes at pachynema and, in particular, on chromosomes 21. Results clearly show how the presence of an extra chromosome 21 alters meiotic recombination progression, leading to the presence of a higher number of early recombination markers at pachynema. Moreover, the distribution on these chromosomes 21 of some of these markers is different in aneuploid oocytes. Finally, there is a substantial increase in the number of MLH1 foci, a marker of most crossovers in mammals, which is related to the number of synapsed chromosomes in pachynema. Thus, bivalents 21 had fewer MLH1 foci than partial or total trivalents, suggesting a close relationship between synapsis and crossover designation. All of the data presented suggest that the presence of an extra chromosome alters meiotic recombination globally in aneuploid human oocytes. [ABSTRACT FROM AUTHOR]

BACKGROUND Bisphenol A (BPA) is a ‘weak’ endocrine disruptor. The effect of BPA on human reproduction is controversial but has been related to meiotic anomalies, recurrent miscarriages and abnormal karyotypes. METHODS To evaluate the effects of BPA on survival, pairing-synapsis and meiotic recombination of human fetal oocytes, 21 510 oocytes from 12 cultured fetal ovaries were analyzed. Ovaries were cultured for 7, 14 or 21 days in control medium, dimethylsulfoxide-medium, BPA-medium and estradiol (E2)-medium. Meiotic pairing-synapsis and recombination were studied by immunofluorescence against lateral element protein, central element protein of the synaptonemal complex and chromosome axis cohesin REC8. Mismatch repair protein, MLH1, was used as a crossover (CO) marker. Meiotic progression was analyzed following the number of surviving oocytes at different meiotic stages found in each culture time and condition, and the total number of MLH1 foci found in oocytes from cultured ovaries. RESULTS Oocyte survival in vitro decreased with the addition of BPA to the medium (1 µM or greater). Oocyte degeneration was up to five times higher when BPA was added to culture medium. Moreover, oocytes exposed to BPA concentrations of 10 µM or higher presented approximately two times more MLH1 foci than unexposed cultured oocytes (P= 0.01). This was also observed in chromosome 21 from BPA-exposed oocytes, which had double the average number of MLH1 foci found in control oocytes (P= 0.001). E2 was used as a positive control of estrogen receptors activity, and E2 addition to the medium had similar effects on meiotic progression of oocytes from cultured ovaries. CONCLUSIONS Our findings show that BPA concentrations of 1 µM or higher decrease the survival of human fetal oocytes in vitro, and concentrations of 10 µM or higher increase MLH1 foci number. MLH1 is considered a CO marker, and thus an increase in MLH1 foci could indicate an increase in COs in BPA-exposed oocytes. These data suggest that BPA can act as a toxic substance, which has particular implications for human females and the critical events of meiotic prophase, such as pairing-synapsis and recombination processes, as well as oocyte survival. [ABSTRACT FROM PUBLISHER]

Background: Sister chromatid cohesion is essential for ordered chromosome segregation at mitosis and meiosis. This is carried out by cohesin complexes, comprising four proteins, which seem to form a ring-like complex. Data from animal models suggest that loss of sister chromatid cohesion may be involved in age-related non-disjunction in human oocytes. Here, we describe the distribution of cohesins throughout meiosis in human oocytes.Methods: We used immunofluorescence in human oocytes at different meiotic stages to detect cohesin subunits REC8, STAG3, SMC1 beta and SMC3, [also synaptonemal complex (SC) protein 3 and shugoshin 1]. Samples from euploid fetuses and adult women were collected, and 51 metaphase I (MI) and 113 metaphase II (MII) oocytes analyzed. SMC1 beta transcript levels were quantified in 85 maturing germinal vesicle (GV) oocytes from 34 women aged 19-43 years by real-time PCR.Results: At prophase I, cohesin subunits REC8, STAG3, SMC1 beta and SMC3 overlapped with the lateral element of the SC. Short cohesin fibers are observed in the oocyte nucleus during dictyate arrest. All four subunits are observed at centromeres and along chromosomal arms, except at chiasmata, at MI and are present at centromeric domains from anaphase I to MII. SMC1 beta transcripts were detected (with high inter-sample variability) in GV oocytes but no correlation between SMC1 beta mRNA levels and age was found.Conclusions: The dynamics of cohesins REC8, STAG3, SMC1 beta and SMC3 suggest their participation in sister chromatid cohesion throughout the whole meiotic process in human oocytes. Our data do not support the view that decreased levels of SMC1 beta gene expression in older women are involved in age-related non-disjunction. [ABSTRACT FROM AUTHOR]

BACKGROUND: Nowadays, oocyte donation is an extended practise in IVF programmes. However, to date, little information on aneuploidy frequency in oocytes from donors is available. Aneuploidy is one of the major causes of embryo and fetal wastage as well as of congenital mental and developmental disabilities. It is known that most aneuploidies are due to non-disjunction events occurring in the maternal germ line. Linkage studies have associated abnormal patterns of meiotic recombination to the origin of the non-disjunction event in many aneuploid conditions. [ABSTRACT FROM PUBLISHER]

BACKGROUND: Little is known about the mechanisms that regulate meiosis in the human female fetus as a result of the technical difficulties in obtaining samples. Currently, there is no technique for human fetal oocyte culture that permits the maintenance of fetal ovarian tissue in vitro which allows the progression of meiosis in a reproducible and standardized way. [ABSTRACT FROM PUBLISHER]

Analyzes the pairing of process of homologs in ovaries from three trisomic fetuses in order to assess the effect of the presence of an extrachromosome 18 on the progress of chromosomal events in the female meiotic prophase. Chromosomal dynamics in trisomy 18 oocytes; Bouquet topology in trisomic oocytes; Pairings and synapsis of chromosome 18 during the meiotic prophase.

Chromosome segregation errors are a significant cause of aneuploidy among human neonates and often result from errors in female meiosis that occur during fetal life. For the latter reason, little is known about chromosome dynamics during female prophase I. Here, we analyzed chromosome reorganization, and centromere and telomere dynamics in meiosis in the human female by immunofluorescent staining of the SYCP3 and SYCP1 synaptonemal complex proteins and the course of recombinational DNA repair by IF of phospho-histone H2A.X (γ-H2AX), RPA and MLH1 recombination proteins. We found that SYCP3, but not SYCP1, aggregates appear in the preleptotene nucleus and some persist up to pachytene. Telomere clustering (bouquet stage) in oocytes lasted from late-leptotene to early pachytene—significantly longer than in the male. Leptotene and zygotene oocytes and spermatocytes showed strong γ-H2AX labeling, while γ-H2AX patches, which colocalized with RPA, were present on SYCP1-tagged pachytene SCs. This was rarely seen in the male and may suggest that synapsis installs faster with respect to progression of recombinational double-strand break repair or that the latter is slower in the female. It is speculated that the presence of γ-H2AX into pachytene highlights female-specific peculiarities of recombination, chromosome behavior and checkpoint control that may contribute to female susceptibility for aneuploidy. [ABSTRACT FROM AUTHOR]

Some studies have been carried out to analyze human female first meiotic prophase. Most of them use samples from foetuses collected after legal interruption of pregnancy. In some cases, a control population is needed and foetuses aborted for non-chromosomal reasons are used. The assumption of these samples as being euploids could perhaps represent an error. In this article, we describe an easy methodology to certify the euploidy of foetal ovarian tissue using an one-week somatic culture. Using this protocol, we have obtained a primary culture in 88.2% of the studied cases, material usable for being karyotyped in 93.3% of the cases, and a cytogenetic diagnosis was performed in 100% of these cases. Finding the same karyotype in cultured cells in cases in which we had a prenatal cytogenetic diagnosis has validated the technique, and in applying this protocol we have been able to check our prophase meiotic-study control population. [ABSTRACT FROM AUTHOR]

The effect of sera from mice bearing a T cell lymphoid leukaemia (LB) and the supernatants from short term cultures of the tumour cells were studied on cell proliferation using syngeneic and allogeneic normal and tumour cells. An inhibitory activity was demonstrated in 24-48 h supernatants of LB cells in culture and disappeared after 4 days of culture. Inhibitory activity was cytostatic but not cytotoxic and was non-specific since it inhibited the growth of both syngeneic and allogeneic normal and tumour cells. Such activity was found in the 105-1.3 x 105 Mr serum fraction after a Sephacryl S200 chromatography. Though sensitive to protease, trypsine or neuraminidase treatment, which indicated its glycoprotein nature, it remained stable after heating or freezing-thawing cycles as well as after alkaline, acid or hyaluronidase treatment. Addition of exogenous IL-2 abrogated inhibitory activity. ELISA showed the presence of soluble IL-2R both in LB conditioned medium and in above serum fraction. It is demonstrated that the inhibitory factor, soluble IL-2R, is produced by LB leukaemia cells, then secreted into blood and ascitic fluid or released into culture supernatants. Soluble IL-2R exerts inhibitory activity blocking cell proliferation and modulating immune response by binding to free IL-2. [ABSTRACT FROM AUTHOR]

Only little is known about the meiotic prophase events in human oocytes, although some of them are involved in the origin of aneuploidies. Here, a broad study of the pairing and synaptic processes in 3263 human euploid and 2613 aneuploid oocytes (47,XX, +21 and 47,XX, +13), using different techniques and methods, is presented in order to elucidate the characteristics of this essential meiotic process. Our results reaffirm the existence of a common high efficiency in the pairing process leading to the obtainment of a bivalent for all chromosomes studied in euploid and aneuploid cases. Nevertheless, this high efficiency was insufficient to consistently produce trivalents in aneuploid oocytes. Trivalent 21 was only observed in 48.8% of the 47,XX, +21 pachytene-stage oocytes studied, and trivalent 13 was found in 68.7% of the 47,XX, +13 pachytene-stage oocytes analyzed. Our data confirm the hypothesis which suggests that in human oocytes the presence of an extra chromosome could interfere in bouquet dynamics. In addition, the pairing process of the X chromosome is altered in trisomic 21 oocytes, providing evidence of the influence that an extra chromosome 21 may cause meiotic progression. [ABSTRACT FROM AUTHOR]