Errors In Meiotic Division Research Articles

Mathematical modeling of human oocyte aneuploidy

Aneuploidy is the leading contributor to pregnancy loss, congenital anomalies, and in vitro fertilization (IVF) failure in humans. Although most aneuploid conceptions are thought to originate from meiotic division errors in the female germline, quantitative studies that link the observed phenotypes to underlying error mechanisms are lacking. In this study, we developed a mathematical modeling framework to quantify the contribution of different mechanisms of erroneous chromosome segregation to the production of aneuploid eggs. Our model considers the probabilities of all possible chromosome gain/loss outcomes that arise from meiotic errors, such as nondisjunction (NDJ) in meiosis I and meiosis II, and premature separation of sister chromatids (PSSC) and reverse segregation (RS) in meiosis I. To understand the contributions of different meiotic errors, we fit our model to aneuploidy data from 11,157 blastocyst-stage embryos. Our best-fitting model captures several known features of female meiosis, for instance, the maternal age effect on PSSC. More importantly, our model reveals previously undescribed patterns, including an increased frequency of meiosis II errors among eggs affected by errors in meiosis I. This observation suggests that the occurrence of NDJ in meiosis II is associated with the ploidy status of an egg. We further demonstrate that the model can be used to identify IVF patients who produce an extreme number of aneuploid embryos. The dynamic nature of our mathematical model makes it a powerful tool both for understanding the relative contributions of mechanisms of chromosome missegregation in human female meiosis and for predicting the outcomes of assisted reproduction.

Artificial oocyte activation with calcium ionophore does not cause a widespread increase in chromosome segregation errors in the second meiotic division of the oocyte

To study the effect of artificial oocyte activation (AOA) on chromosome segregation errors in the meiotic divisions. Prospective cohort study with historical control. Private/academic IVF centers. Fifty-six metaphase II oocytes were donated from 12 patients who had undergone IVF between June 2008 and May 2009. Oocytes were activated by 40 minutes' exposure to 100 μM calcium-ionophore. The activated oocyte was tubed and analyzed by array comparative genomic hybridization and/or single-nucleotide polymorphism genotyping and maternal haplotyping (meiomapping). A control sample of embryos derived from normally fertilized oocytes was included for comparison. Incidence of chromosome segregation errors in artificially activated and normally fertilized oocytes in relation to pronuclear evaluation. Of 49 oocytes that survived the warming procedure, thirty-nine (79.6%) activated. Most activated normally, resulting in extrusion of the second polar body and formation of a single or no pronucleus (2PB1PN: 30 of 39, 76.9%; or 2PB0PN: 5 of 39, 12.8%). Twenty-seven of these were analyzed, and 16 (59.3%) were euploid, showing no effect of AOA on meiotic segregation. Single-nucleotide polymorphism analysis of normally activated oocytes confirmed normal segregation of maternal chromosomes. No difference in the proportion of meiosis II type errors was observed between artificially activated oocytes (28.6%; 95% confidence interval 3.7%-71.0%) compared with embryos obtained from normally fertilized oocytes (44.4%; 95% confidence interval 13.7%-78.8%). The abnormally activated oocytes, with ≥2PN (4 of 39, 10.3%) were diploid, indicating a failure to coordinate telophase of meiosis II with polar body extrusion. From this preliminary dataset, there is no evidence that AOA causes a widespread increase in chromosome segregation errors in meiosis II. However, we recommend that it be applied selectively to patients with specific indications.

High follicle-stimulating hormone increases aneuploidy in human oocytes matured in vitro

To study the effect of FSH on the aneuploidy risk of human oocytes matured in vitro. Prospective study. Hospital-based IVF center. Patients with male factor infertility undergoing intracytoplasmic sperm injection (ICSI) cycles. Immature oocytes were put into five groups according to the FSH concentration (0, 5.5, 22, 100, and 2,000 ng/mL) in in vitro maturation (IVM) medium. Spindles were observed under a polarized microscope before polar body biopsy. Fixed polar bodies and corresponding oocytes were examined on chromosomes 13, 16, 18, 21, and 22 by fluorescence in situ hybridization. Oocytes matured in 5.5 and 2,000 ng/mL FSH were immunostained for tubulin and chromatin. Aneuploidy rate, spindle visualization rate, and spindle morphology. The frequency rates of aneuploidy were 26.7%, 23.3%, 36.75%, 46.67%, and 63.3% in the five FSH groups, respectively. There was a significantly higher aneuploidy rate in oocytes matured in the 2,000 ng/mL FSH group. The spindle visualization rates assessed under PolScope were not significantly different between aneuploid and normal oocytes. There was no difference in spindle morphology between the 2,000 and 5.5 ng/mL FSH groups. High-concentration FSH in IVM medium significantly increased the first meiotic division error, resulting in more aneuploid oocytes during IVM.

Errors at mitotic segregation early in oogenesis and at first meiotic division in oocytes from donor females: Comparative genomic hybridization analyses in metaphase II oocytes and their first polar body

The aim of this work is to analyze, using the comparative genomic hybridization technique, the frequencies and the mechanisms involved in the production of aneuploidy events in donor oocytes. The results showed that 32.1% of them were aneuploid, with 51.7% of those originating from first meiotic division errors and 48.3% from the presence of aneuploid oogonium.

The contradictory information on the distribution of non-disjunction and pre-division in female gametes

Valuable information on the cytogenetic constitution of female gametes has been deduced from the direct, so-called conventional analysis of oocytes remaining unfertilized in programmes of assisted reproduction. Additional, indirect conclusions have become possible by PGD of the polar bodies. Both techniques provided evidence for the co-existence of two aneuploidy-causing mechanisms during first maternal meiosis; non-disjunction (ND) of bivalents results in the loss or gain of whole chromosomes in metaphase II complements, whereas a precocious division (pre-division, PD) of univalents leads to the loss or gain of single chromatids. As to the distribution of ND and PD, however, direct oocyte chromosome studies and PGD tell surprisingly different stories. Moreover, first and second polar body analyses contradict the data derived from DNA polymorphism studies concerning the distribution of first and second meiotic division errors. An increased awareness of these problems appears necessary because important decisions are made on the basis of PGD results.

Chromosomal abnormalities in a series of 6733 human oocytes in preimplantation diagnosis for age-related aneuploidies

Most chromosomal abnormalities originate from female meiosis and contribute significantly to pregnancy failures, particularly in women of advanced maternal age. A total of 8382 oocytes were obtained in 1297 IVF cycles from patients of advanced maternal age (mean 38.5 years). Following a standard IVF protocol, oocytes were tested following removal and fluorescence in-situ hybridization (FISH) analysis of the first (PB1) and second polar bodies (PB2), using probes specific for chromosomes 13, 16, 18, 21 and 22 (Vysis). FISH results were available in 6733 (80.3%) oocytes tested, 3509 (52.1%) of which were aneuploid, with the remaining 3224 (47.9%) normal oocytes available for transfer. In all, 41.7% of oocytes had meiosis I errors, compared to 35.1% with meiosis II errors. Abnormalities in meiosis I were represented by extra chromatids in 15.4%, missing chromatids in 48.1%, missing chromosomes in 5.9%, extra chromosomes in 0.5%, and complex abnormalities in 30.1%. The proportions of abnormal oocytes with missing or extra chromatids in meiosis II were 36.6 and 41.2% respectively, with the remaining oocytes having complex abnormalities, involving missing or extra chromatids of different chromosomes (22.1%) following meiosis II. Overall, 41.8% oocytes had meiosis I, 30.7% meiosis II, and 27.6% both meiotic division errors. A total of 45.1% of the abnormal oocytes had complex errors, involving the same chromosome in both meiotic divisions (21.5%), or different chromosomes (78.5%), of which 74.8% were with abnormalities of two, and 25.2% with abnormalities of three chromosomes studied. Of 3224 detected aneuploidy-free zygotes, 2587 were transferred in 1100 treatment cycles (2.35 embryos per transfer), resulting in 241 (21.9%) clinical pregnancies and 176 healthy children born, suggesting a positive clinical outcome following aneuploidy testing of oocytes in a group of IVF patients of average age 38.5 years.

Multi-locus (ML)-FISH is a reliable tool for nondisjunction studies in human oocytes

In the present study, we developed a fluorescence in situ hybridization (FISH) strategy, which allows a reliable determination of the chromatid number of specific chromosomes in mature human oocytes. 168 unfertilized oocytes were analyzed by dual-color FISH with two direct-labeled locus-specific DNA probes for chromosome 13 and 21. To exclude FISH failures, metaphases with abnormal signal patterns were reanalyzed by multi-locus-FISH (ML-FISH) for chromosome 13 and 21. Following dual-color FISH, abnormal signal patterns were detected in 21 out of 108 metaphases (19.4%). 17 of these metaphases were reanalyzed by ML-FISH. In contrast to the first FISH, seven metaphases showed normal signal patterns after rehybridization, whereas ten metaphases remained abnormal. Out of these real aneuploid metaphases, five showed gain or loss of a single signal (= chromatid), two showed missing double signals (= chromosome) and three showed both. In conclusion, locus-specific FISH probes facilitate differentiation between first meiotic nondisjunction of whole chromosomes and prematurely divided chromatids. Moreover, simultaneous hybridization with a second locus-specific probe on the same chromatid (ML-FISH) helps to differentiate between FISH failures and real meiotic division errors and therefore, allows a more reliable analysis of aneuploidies in human oocytes.

General ageing and ovarian ageing

The age related decrease in female fertility is associated with a decrease in follicle numbers and oocyte quality. Meiotic division errors, mitochondrial DNA mutations and ageing itself have been suggested to play a part in the age associated reduction in oocyte quality. During the past decades several hypothesis have been proposed, trying to explain the underlying mechanisms. However, none of them is yet conclusive. This review will consider the main hypotheses regarding the age related reduction in oocyte quality. This will be reviewed together with recent results of studies analysing a possible relationship between ageing and ovarian ageing. On the basis of our own results and those presented in the literature, it is concluded that ovarian ageing may only be related to specific aspects of general ageing.

The origin of 47,XXY and 47,XXX aneuploidy: heterogeneous mechanisms and role of aberrant recombination.

We investigated the parent and cell division of origin of the additional sex chromosome in 142 males with a 47,XXY constitution and 50 females with a 47,XXX constitution. In 66 of the 47,XXY males the additional chromosome was paternal in origin and in 76 it was maternal in origin, while among the 47,XXX females only 5 had an additional paternal X chromosome, the remaining 45 having an additional maternal chromosome. Among the 107 maternally derived aneuploids for whom it was possible to determine the cell division of origin, 73 were the result of a mat MI error, 24 the result of a mat MII error and 10 the result of a post zygotic mitotic (PZM) error involving the maternal X chromosome. Among those in which the non-disjunction was attributable to an error at the first meiotic division (MI) we observed three different mechanisms of origin. Approximately 30% were associated with complete absence of recombination (nullichiasmate); approximately 24% were associated with a normal number of recombinant events but an abnormal distribution of exchanges (perturbed recombination), while approximately 45% were associated with a normal number and distribution of recombinant events (normochiasmate). Nondisjunction due to an error at the second meiotic division (MII) was associated with a slight reduction in the total number of recombinant events and an abnormal distribution of exchanges. Thus of the four different meiotic mechanisms of origin, three were associated with an abnormal number and/or distribution of exchange events. There was no evidence of an increased paternal age in the aneuploids of paternal origin.(ABSTRACT TRUNCATED AT 250 WORDS)

Variable clinical expression of mosaic trisomy 16 in the newborn infant

Trisomy 16 is common in embryos and fetuses aborted early during development. Mosaicism for trisomy 16 is sometimes encountered during prenatal diagnosis, particularly with chorionic villi biopsy specimens, and, until recently, was thought to be confined to the placenta. However, recently, several liveborn infants with trisomy 16 mosaicism have been described. We report on an additional liveborn infant with trisomy 16 mosaicism and compare the clinical findings with those of the previously reported cases in an attempt to delineate a mosaic trisomy 16 syndrome. Cytogenetic analysis from our patient showed that there was a different proportion of abnormal cells in different tissues and that the anomaly was undetectable in blood lymphocyte cultures. This observation was consistent with some of the previous reports. DNA analysis of parents and child was carried out using a polymorphic dinucleotide marker that maps to the long arm of chromosome 16. This analysis showed that the extra chromosome 16 in the infant was maternal in origin and suggested that the nondisjunction was probably a first meiotic division error. Our results suggest that an investigation of multiple tissues is required before concluding that mosaicism is confined to the placenta. We conclude that a finding of trisomy 16 mosaicism at prenatal diagnosis should be regarded with extreme caution. This diagnosis may be associated with a highly variable phenotype that may occasionally be compatible with extrauterine life.

Trisomy in man.

Trisomy, occurring in at least 4% of pregnancies, is the most common chromosome abnormality in humans. The majority of trisomies are associated with single additional chromosome. The presence of an additional sex chromosome is often associated with physical, behavioral, and intellectual impairment. The presence of an additional autosome is even more serious, being associated with severe mental and physical retardation and frequently with death in infancy. This review discusses the incidence, parental origin, and etiology of human trisomy. The incidence of trisomy varies widely among different chromosomes. This variation appears to reflect a real difference in the frequency of the primary event leading to trisomy as well as in differential selection. Studies of parental origin have shown a 1st maternal meiotic division error to be the most frequent source of the additional chromosome, regardless of the chromosome involved or the maternal age. Although the magnitude of risk varies among chromosomes, increased maternal age is an important risk factor in trisomy. The incidence of trisomy 21 increases from .05% of livebirths at maternal age 20 years to over 3% of all livebirths at age 45 years. The effect of maternal age is most pronounced in double trisomies. It has been hypothesized that the relationship between increasing maternal age and trisomy is due to a gradient in the fetal ovary that affects chiasma freequency. While the basis for the maternal age effect remains unknown, it is almost certainly due to factors acting at or before conception. Epidemiologic studies suggest that maternal irradiation exposure may also lead to trisomy; however, the effective dosage level and the relationship to maternal age remain unknown. No effect of oral contraceptives, spermicides, or fertility drugs on the incidence of trisomy has been documented to date. Understanding of the mechanisms by which trisomies are produced represents a major challenge for human cytogenetics.

Sequence of centromere separation another mechanism for the origin of nondisjunction.

The most commonly accepted view about the origin of aneuploidy is that it is due to errors in meiotic division. However, its rare occurrence makes it difficult to explain recurrent births of trisomic children to some parents. This problem causes more serious concern when one accepts that an abnormal (n + 1 or n - 1) sperm would enter fertilization by overriding thousands, or even millions, of normal haploid sperms. Also, the failure of aneuploidy to be induced in the offspring of mammals treated with mutagens raises questions about the effectiveness of the accepted mode of origin of errors. Current concepts also do not explain why one observes more errors of meiotic I, than of meiotic II, origin. It is known that most chromosomes separating at meta-anaphase junction in mitosis follow a nonrandom, genetically controlled sequence of separation. The present proposal makes use of out-of-phase separation of a rare chromosome, like premature separation in mitosis of the X in elderly humans or of an 18 in parents of trisomy 18 children. The suggestion is made that such out-of-phase separation results in aneuploid cell lines by total failure of the centromere to separate or by it separating too early, before the spindle is formed. The prematurely separating centromeres, it appears, do not attach to spindle fibers and hence cause nondisjunction. Such nondisjunction in embryonic stages will produce apparently normal individuals with mosaicism in somatic and/or gametic tissue. An individual carrying mosaicism in gonadal tissue will produce a large number of abnormal gametes, one of which may have a reasonable chance of entering fertilization. This mode of origin of aneuploidy takes care of all questions raised above and finds support in the data available in the literature. Several of the suggestions made in the hypothesis are easily testable.