Simultaneous detection of chromosomes X, Y, 13, 18, and 21 by fluorescence in situ hybridization in blastomeres obtained from preimplantation embryos

Insights into embryonic chromosomal instability: mechanisms of DNA elimination during mammalian preimplantation development

Mammalian preimplantation embryos often contend with aneuploidy that arose either by the inheritance of meiotic errors from the gametes, or from mitotic mis-segregation events that occurred following fertilization. Regardless of the origin, mis-segregated chromosomes become encapsulated in micronuclei (MN) that are spatially isolated from the main nucleus. Much of our knowledge of MN formation comes from dividing somatic cells during tumorigenesis, but the error-prone cleavage-stage of early embryogenesis is fundamentally different. One unique aspect is that cellular fragmentation (CF), whereby small subcellular bodies pinch off embryonic blastomeres, is frequently observed. CF has been detected in both in vitro and in vivo-derived embryos and likely represents a response to chromosome mis-segregation since it only appears after MN formation. There are multiple fates for MN, including sequestration into CFs, but the molecular mechanism(s) by which this occurs remains unclear. Due to nuclear envelope rupture, the chromosomal material contained within MN and CFs becomes susceptible to double stranded-DNA breaks. Despite this damage, embryos may still progress to the blastocyst stage and exclude chromosome-containing CFs, as well as non-dividing aneuploid blastomeres, from participating in further development. Whether these are attempts to rectify MN formation or eliminate embryos with poor implantation potential is unknown and this review will discuss the potential implications of DNA removal by CF/blastomere exclusion. We will also extrapolate what is known about the intracellular pathways mediating MN formation and rupture in somatic cells to preimplantation embryogenesis and how nuclear budding and DNA release into the cytoplasm may impact overall development.

The Effect of Teratozoospermia on Sex Chromosomes in Human Embryos

Purpose

The aim of this study is to evaluate the effect of abnormal semen morphology on the frequency of sex chromosomal abnormalities in embryos obtained by ICSI, which represents the first to be studied in Egyptian population.

Methods

Forty-two couples suffering from male infertility due to teratozoospermia were divided into two groups: patients with severe and moderate teratozoospermia (group A and B, respectively). All involved couples were subjected to careful history taking and had a normal clinical examination and karyotype. Females were subjected to hormonal assays, pelvic ultrasound, hysterosalpingography and yielded normal results, while male partners were subjected to computerized semen analysis. Preimplantation genetic diagnosis was performed for all suitably developed embryos including embryo biopsy, fixation of biopsied cells and fluorescent in situ hybridization (FISH) analysis.

Results

Couples included in the two groups were found to be homogenous in terms of age of both partners and duration of infertility. Interpretation of FISH results was performed by evaluation of embryos’ chromosomal constitution as regards abnormalities in chromosomes X, Y and 18. Twenty-seven embryos (48.2%) were found chromosomally abnormal in group A, while only 14 embryos (25.0%) were found chromosomally abnormal in group B. Aneuploidies involved only sex chromosomes were tripled in group A embryos when compared to their frequency in group B embryos (26.8% and 8.3%, respectively) with statistically significant difference between the two groups (p=0.002). Monosomies were the most common type of aneuploidy and were significantly higher in group A (14.3%) when compared to group B (3.6%) (p=0.047). Embryos with mosaic abnormalities were more common in group A (12.5%) when compared to group B (3.6%), however not statistically significantly different (p= 0.162). A significant difference between the two studied groups as regards the total number of potentially viable chromosomal abnormalities detected and the potentially viable sex chromosomal aneuploidies detected (p<0.001 and p=0.002), respectively.

Conclusion

The cases with severe teratozoospermia undergoing ICSI treatment can display a higher rate of sex chromosome aneuploidies in their embryos (threefold) than cases with moderate teratozoospermia.

Evaluation of the impact of sperm morphology on embryo aneuploidy rates in a donor oocyte program

This study investigates the correlation between sperm morphology and the incidence of embryo aneuploidy in an oocyte donation program. A total of 1,165 embryos from 103 patients have been analyzed by fluorescent in situ hybridization (FISH) for numerical abnormalities in chromosome numbers 13, 18, 21, X, and Y. Data has been evaluated in five groups according to sperm morphology, which has been assessed according to the Kruger's strict criteria. The results did not show any difference in paternal (p = 0.878), maternal (p = 0.873), and donor ages (p = 0.871), sperm counts (p = 0.782) and motility (p = 0.124), and fertilization rate (p = 0.080) among the groups. However, total aneuploidy rate (p < 0.001) and its derivatives (trisomy p = 0,042, monosomy p = 0,004) differed significantly and they were reversibly correlated with sperm morphology (rho correlation test; total aneuploidy p < 0.001, trisomy p < 0.001, monosomy p = 0.004). Therefore, these results suggested that diminished sperm quality is correlated to the aneuploidy rate in preimplantation embryos.

ABBREVIATIONS

FISH: fluorescence in situ hybridization; ICSI: intracytoplasmic sperm injection; HCG: human chorionic gonadotropin.

Association between amino acid turnover and chromosome aneuploidy during human preimplantation embryo development in vitro

This study investigated the relationship between human preimplantation embryo metabolism and aneuploidy rates during development in vitro. One hundred and eighty-eight fresh and cryopreserved embryos from 59 patients (33.9 +/- 0.6 years) were cultured for 2-5 days. The turnover of 18 amino acids was measured in spent media by high-performance liquid chromatography. Embryos were either fixed for interphase fluorescent in situ hybridization analysis of chromosomes 13, 18, 19, 21, X or Y, or were assayed for mitochondrial activity. Amino acid turnover was different (P < 0.05) between stage-matched fresh and cryopreserved embryos due to blastomere loss following warming. The proportion of embryos with aneuploid cells increased as cell division progressed from pronucleate- (23%) to late cleavage stages (50-70%). Asparagine, glycine and valine turnover was significantly different between uniformly genetically normal and uniformly abnormal embryos on Days 2-3 of culture. By Days 3-4, the profiles of serine, leucine and lysine differed between uniformly euploid versus aneuploid embryos. Gender significantly (P < 0.05) affected the metabolism of tryptophan, leucine and asparagine by cleavage-stage embryos. Pronucleate zygotes had a significantly higher proportion of active:inactive mitochondria compared with cleavage-stage embryos. Furthermore, mitochondrial activity was correlated (P < 0.05) with altered aspartate and glutamine turnover. These results demonstrate the association between the metabolism, cytogenetic composition and health of human embryos in vitro.

Different probe combinations for assessment of postzygotic chromosomal imbalances in human embryos

PURPOSE

We compared three different probe combinations for detection of postzygotic mosaic imbalances in human preimplantation embryos.

METHODS

Two hundred and two spare cleavage stage embryos were hybridized with fluorescently labelled DNA probe mixtures specific to chromosomes X, Y, 18 (N = 67), chromosomes 2, 7, 18 (N = 71), or chromosomes 13, 16, 18, 21, 22 (N = 64).

RESULTS

An overall higher incidence of abnormalities was detected using probe mixture for five (69%) or three (72%) autosomes compared to one autosome and chromosomes X and Y (54%). The rate of aneuploidy detected increased with the number of autosomes hybridized from 4% (X, Y, 18) to 11% (2, 7, 18) to 19% (13, 16, 18, 21, 22). Postzygotic mosaicism comprised the most frequent abnormality detected by all probe combinations, and the percentage detected by each was similar, 48% (X, Y, 18), 56% (2, 7,18), and 50% (13,16,18, 21, 22).

CONCLUSIONS

A probe combination of five autosomes, particularly those of clinical relevance, may be more beneficial for screening embryos from patients at risk of maternal-age-related aneuploidy. However, all three probe combinations are as efficient at identifying postzygotic mosaicism, and may be used for identifying embryos with less potential of developing to term.

The role of fluorescence in situ hybridization technologies in molecular diagnostics and disease management

Large genomic changes, such as aneuploidy, deletions, and other chromosomal rearrangements, have long been associated with pregnancy loss, congenital abnormalities, and malignancy. These genomic changes are quantitative, unambiguous, and fundamental in the transition of normal cells to abnormal ones. Detection of these large genetic changes has an increasingly important role in determining patient diagnosis and care, including therapeutic selection. We have developed two major product platforms that assess genomic changes at various levels of resolution. Fluorescence in situ hybridization (FISH) techniques and the related technology of array-based comparative genomic hybridization (CGH) allow detection of genesized or larger alterations in the genome. FISH is a robust DNA probe technology that can measure both balanced and unbalanced genomic changes on a cell-by-cell basis. In most instances, it is not dependent on metaphase chromosomes, and it is widely used in clinical diagnostics. Array-based CGH has much greater multiplexing capabilities than FISH. This technology has the potential to examine many regions of the genome simultaneously for changes in DNA copy number and identify complex patterns of gains and losses within the genome. In this article, we review several of the current medical applications of FISH and discuss such advanced techniques as CGH and array-based CGH.

Recent advances and future developments in PGD

PGD has now been practised for a decade. The basic techniques currently used involve embryo biopsy, polymerase chain reaction (PCR) and fluorescent in situ hybridization (FISH). Recent advances in molecular diagnostic techniques have included the use of fluorescent PCR, multiplex PCR and whole genome amplification. For cytogenetic analysis, many centres are now using five or more chromosome probes to examine for chromosome abnormalities, sexing and aneuploidy. Future improvements in molecular diagnosis include the use of quantitative PCR, DNA fingerprinting and microarray technology. Developments in methods to analyse chromosomes from a single cell have included interphase chromosome conversion, which has already been clinically applied, and the use of comparative genomic hybridization, which is still being developed. These methods will hopefully enable more accurate and a greater number of diseases to be diagnosed at the single cell level.

Determining the sex of bovine embryos using polymerase chain reaction results: a six-year retrospective study

Knowing the sex of embryos produced for use in an embryo transfer program can assist the dairy producer in managing his resources more effectively. A reliable procedure for accomplishing this goal is to apply PCR technology to the biopsy of an embryo. A description is provided of how the technique has been applied on a large scale in a commercial setting in western Canada between 1992 and 1997. A total of 4,183 embryos was biopsied over a 6-yr period. The sex was determined with more than 90% of the embryos. The results showed that there was a seasonal variation in the sex ratio, with more females being recorded in the period of least light (October to March), than in April to September. While both sire and embryo quality affected the sex ratio, the differences were too small to be of value in most breeding programs. Pregnancy rates with fresh sexed embryos (58 to 71%) were comparable to those with fresh unsexed embryos. The results following freezing and thawing of sexed embryos were low (37 to 66%) but sufficient to be viable commercially. When the sex assigned by PCR was verified by fetal sexing at 60 d of gestation, the error rate was 7%. This study demonstrates that sexing of embryos can be carried out on a large scale. Demand for quick, reliable determination of sex can be met in a cost effective manner. The pregnancy rates achieved with embryos after biopsy are suitable for use in a commercial setting.