Assessment of DNA fragmentation and aneuploidy on poor quality human embryos

Effect of cytoplasmic fragmentation on embryo development, quality, and pregnancy outcome: a systematic review of the literature

The role of cytoplasmic fragmentation in human embryo development and reproductive potential is widely recognized, albeit without standard definition nor agreed upon implication. While fragmentation is best understood to be a natural process across species, the origin of fragmentation remains incompletely understood and likely multifactorial. Several factors including embryo culture condition, gamete quality, aneuploidy, and abnormal cytokinesis seem to have important role in the etiology of cytoplasmic fragmentation. Fragmentation reduces the volume of cytoplasm and depletes embryo of essential organelles and regulatory proteins, compromising the developmental potential of the embryo. While it has been shown that degree of fragmentation and embryo implantation potential are inversely proportional, the degree, pattern, and distribution of fragmentation as it relates to pregnancy outcome is debated in the literature. This review highlights some of the challenges in analysis of fragmentation, while revealing trends in our evolving knowledge of how fragmentation may relate to functional development of the human embryos, implantation, and pregnancy outcome.

Effect of DNA damage of cumulus oophorus cells and lymphocytes analyzed by alkaline comet assay on oocyte quality and intracytoplasmic sperm injection success among patients with polycystic ovary syndrome

AIM

Cumulus oophorus cells (COC) exhibit a close relationship with the oocytes. We aimed to determine the role of the DNA integrity of COC and lymphocytes on the oocyte and embryo quality and intracytoplasmic sperm injection (ICSI) success.

METHODS

The COC obtained with the mechanical denudation of each oocyte and the lymphocytes obtained on oocyte retrieval day from 69 infertile polycystic ovary syndrome (PCOS) patients were used. The tail length, tail moment and tail DNA percentage were evaluated using an alkaline comet assay. The oocytes and embryos were graded. Clinical pregnancy was defined as the presence of a gestational sac with a beating heart.

RESULTS

All of the DNA integrity parameters of the COC and lymphocytes were similar between the good and poor quality oocytes and between the good and poor quality embryos. There was no relationship between the DNA damage parameters and the fertilization and clinical pregnancy. The day 2 hormone levels, body mass index and age were negatively correlated with the DNA integrity parameters. No links were found between the embryo and oocyte scores and the DNA damage parameters.

CONCLUSION

The DNA integrity of the COC and lymphocytes did not seem to be related to the oocyte and embryo quality and ICSI success.

Apoptosis and developmental capacity of vitrified parthenogenetic pig blastocysts

This study was conducted to evaluate whether the poor developmental capacity of pig embryos after vitrification was related to the occurrence of apoptosis. Parthenogenetic blastocysts were used as the research material. The blastocoel recovery rate, mitochondrial membrane potential (ΔΨm), amount of early apoptosis, activities of several caspases, and relative abundance of mRNA of apoptosis-related genes involved in mitochondria and death receptor apoptotic pathways were detected before or after vitrification. The results indicate that the blastocoel recovery rate (31.0%) and total cells (31.8) of vitrified blastocysts were less than those of fresh blastocysts (100% and 38.2, P <  0.05). The ΔΨm of vitrified blastocysts was 0.46, which was less than that of fresh blastocysts (1.02, P <  0.05). The rate of apoptotic cells in vitrified blastocysts (8.1%) after TUNEL (TdT-mediated dUTP Nick-End Labeling) assay was markedly greater than that in fresh blastocysts (3.9%, P <  0.05). The pan-caspase, caspase-3, caspase-8 and caspase-9 activities of vitrified blastocysts (20.7, 20.6, 17.6 and 19.9) were markedly greater than those of fresh blastocysts (7.4, 6.5, 5.5 and 6.3, P <  0.05). The real-time PCR results indicated that relative abundance of caspase-8 and TNF-α mRNA from death receptor apoptotic pathway and caspase-9 for the mitochondrial apoptotic pathway genes in the vitrified group were greater than those in the fresh group P <  0.05). The relative abundance of Bcl-2 and SOD-1 mRNA for the mitochondrial pathway genes in the vitrified group was less than those in the fresh group (P <  0.05). In conclusion, the poor developmental capacity of vitrified parthenogenetic pig blastocysts was closely related with apoptosis. Both mitochondria and death receptor-mediated apoptotic pathways participated the occurrence of this apoptosis.

Viability and DNA fragmentation of rainbow trout embryos (Oncorhynchus mykiss) obtained from eggs stored at 4 °C

In vitro storage of salmonid eggs leads to aging of the cells causing a decline in quality and reducing their capacity to develop and produce embryos. The quality of salmonid embryos is assessed by morphologic analyses; however, data on the application of biomarkers to determine the cell viability and DNA integrity of embryos in these species are limited. The aim of this study was to evaluate the effect on embryo development, viability and DNA fragmentation in the embryonic cells of in vitro storage time at 4 °C of rainbow trout (Oncorhynchus mykiss) eggs. The embryos were obtained by IVF from eggs stored for 0 (control), 48, and 96 hours at 4 °C. At 72 hours after fertilization, dechorionated embryos were examined to determine percentages of developed embryos (embryos with normal cell division morphology), viability (LIVE/DEAD sperm viability kit), and DNA integrity (terminal deoxynucleotidyl transferase [TdT] dUTP nick-end labeling assay). The percentage of developing embryos decreased (P < 0.05) with storage time of the eggs (95.10 ± 2.55; 88.14 ± 4.50; 79.99 ± 6.60 for 0, 48, and 96 hours, respectively). Similarly, cell viability decreased (P < 0.05; 96.07 ± 7.15; 80.42 ± 8.55; 77.47 ± 7.88 for 0, 48, and 96 hours, respectively), and an increase (P < 0.05) in DNA fragmentation in the embryos was observed at 96-hour storage. A positive correlation was found between cell DNA fragmentation and storage time (r = 0.8173; P < 0.0001). The results revealed that terminal deoxynucleotidyl transferase [TdT] dUTP nick-end labeling assay technique is reliable mean to assess the state of the DNA in salmonid embryos and that in vitro eggs storage for 96h reduces embryo development and cell DNA integrity. DNA integrity evaluation constitutes a biomarker of the quality of the ova and resulting embryos so as to predict their capacity to produce good-quality embryos in salmonids, particularly under culture conditions.

Diploid, but not haploid, human embryonic stem cells can be derived from microsurgically repaired tripronuclear human zygotes

Human embryonic stem cells have shown tremendous potential in regenerative medicine, and the recent progress in haploid embryonic stem cells provides new insights for future applications of embryonic stem cells. Disruption of normal fertilized embryos remains controversial; thus, the development of a new source for human embryonic stem cells is important for their usefulness. Here, we investigated the feasibility of haploid and diploid embryo reconstruction and embryonic stem cell derivation using microsurgically repaired tripronuclear human zygotes. Diploid and haploid zygotes were successfully reconstructed, but a large proportion of them still had a tripolar spindle assembly. The reconstructed embryos developed to the blastocyst stage, although the loss of chromosomes was observed in these zygotes. Finally, triploid and diploid human embryonic stem cells were derived from tripronuclear and reconstructed zygotes (from which only one pronucleus was removed), but haploid human embryonic stem cells were not successfully derived from the reconstructed zygotes when two pronuclei were removed. Both triploid and diploid human embryonic stem cells showed the general characteristics of human embryonic stem cells. These results indicate that the lower embryo quality resulting from abnormal spindle assembly contributed to the failure of the haploid embryonic stem cell derivation. However, the successful derivation of diploid embryonic stem cells demonstrated that microsurgical tripronuclear zygotes are an alternative source of human embryonic stem cells. In the future, improving spindle assembly will facilitate the application of triploid zygotes to the field of haploid embryonic stem cells.

Role of chromosome stability and telomere length in the production of viable cell lines for somatic cell nuclear transfer

Background

Somatic cell nuclear transfer (SCNT) provides an appealing alternative for the preservation of genetic material in non-domestic and endangered species. An important prerequisite for successful SCNT is the availability of good quality donor cells, as normal embryo development is dependent upon proper reprogramming of the donor genome so that embryonic genes can be appropriately expressed. The characteristics of donor cell lines and their ability to produce embryos by SCNT were evaluated by testing the effects of tissue sample collection (DART biopsy, PUNCH biopsy, post-mortem EAR sample) and culture initiation (explant, collagenase digestion) techniques.

Results

Differences in initial sample size based on sample collection technique had an effect on the amount of time necessary for achieving primary confluence and the number of population doublings (PDL) produced. Thus, DART and PUNCH biopsies resulted in cultures with decreased lifespans (<30 PDL) accompanied by senescence-like morphology and decreased normal chromosome content (<40% normal cells at 20 PDL) compared to the long-lived (>50 PDL) and chromosomally stable (>70% normal cells at 20 PDL) cultures produced by post-mortem EAR samples. Chromosome stability was influenced by sample collection technique and was dependent upon the culture's initial telomere length and its rate of shortening over cell passages. Following SCNT, short-lived cultures resulted in significantly lower blastocyst development (≤ 0.9%) compared to highly proliferative cultures (11.8%). Chromosome stability and sample collection technique were significant factors in determining blastocyst development outcome.

Conclusion

These data demonstrate the influence of culture establishment techniques on cell culture characteristics, including the viability, longevity and normality of cells. The identification of a quantifiable marker associated with SCNT embryo developmental potential, chromosome stability, provides a means by which cell culture conditions can be monitored and improved.

Comet assay of cumulus cells and spermatozoa DNA status, and the relationship to oocyte fertilization and embryo quality following ICSI

It has been postulated that apoptosis may affect cumulus cell and sperm DNA integrity, and therefore influence the outcome of assisted reproductive techniques. This study investigates apoptotic levels in both cumulus cells and spermatozoa, and their relationship with fertilization and embryo quality after intracytoplasmic sperm injection (ICSI). The neutral comet assay was performed on cumulus cells and semen samples from 55 couples with male factor infertility undergoing ICSI treatment. Cells were fixed in agarose on comet assay slides, lysed in a neutral buffer and submitted to electrophoresis. The cells were stained with SYBR green fluorescent dye, which binds to double-stranded DNA and upon excitation emits light. Analysis showed that there was no correlation between apoptosis levels and the outcome of ICSI (fertilization and embryo quality).

Embryo aneuploidy screening for repeated implantation failure and unexplained recurrent miscarriage

Among other factors, chromosomal abnormalities that originate from gametogenesis and preimplantation embryonic development are thought to be one of the major contributing factors for early embryonic death and failure of pregnancy. However, so far, no non-invasive technique exists that allows the detection of the chromosomal complement of an oocyte or a developing embryo as a whole. Rather, by removing polar bodies/blastomeres, recent developments on preimplantation genetic diagnosis for aneuploidy screening (PGD-AS) have paved the way to detect and possibly eliminate the majority of chromosomally abnormal embryos, thereby increasing the chance of a healthy pregnancy. This article summarizes the origin and impact of chromosomal abnormalities on human reproduction in cases with repeated implantation failure (RIF) and unexplained recurrent miscarriage. It also discusses recent advances regarding the possible benefits of PGD-AS in such cases.

Differential staining combined with TUNEL labelling to detect apoptosis in preimplantation bovine embryos

Development of accurate laboratory methods to assess embryo quality will improve the efficiency of embryo production from in-vitro culture systems. Currently, the techniques of TdT (terminal deoxynucleotidyl transferase)-mediated dUDP nick-end (TUNEL) labelling for the detection of apoptosis, and differential staining for determining the ratio of inner cell mass (ICM) to trophectoderm (TE) cells, are used separately to assess embryo quality in a range of different species. This paper reports a unique, simple and fast method for the assessment of embryo quality using differential staining of TE and ICM, but combined with TUNEL labelling (DST staining). This technique was used to investigate the effect of serum supplementation on total cell number, ICM:TE ratio and apoptosis index after in-vitro production of bovine embryos. Serum supplementation increased total cell number (P < 0.01), but reduced the ratio of ICM:TE cells. No differences were observed in the number of apoptotic nuclei between treatments, or in the localization of the apoptotic nuclei. However, more apoptotic nuclei were observed in ICM than TE cells in both culture groups. In conclusion, using DST, it has been possible to carry out both a qualitative and quantitative analysis of embryos produced using the two different methods. DST provides a means of assessing the effect of culture conditions on cell number of both embryo compartments (ICM and TE), as well as providing information on the localization of apoptotic nuclei within the blastocyst.

Effect of sperm DNA damage and sperm protamine deficiency on fertilization and embryo development post-ICSI

The aim of this study was to evaluate the effect of sperm DNA damage and protamine deficiency on fertilization and embryo development post-intracytoplasmic sperm injection (ICSI), and also to assess the effect of protamine deficiency on DNA damage. Semen samples were collected from 28 patients participating in the ICSI programme. Following sperm preparation and ICSI, the remaining processed semen samples were used to assess protamine deficiency and DNA damage employing chromomycin A3 (CMA3) staining and comet assay, respectively. Comet parameters, CMA3 percentage positivity, fertilization rate, embryo cleavage score and embryo quality score were assessed. Except for CMA3, none of the comet parameters showed significant correlation with fertilization rate. However, among comet parameters, head area and head intensity showed positive correlation with the embryo cleavage score, while comet mean intensity and head mean intensity showed a significant negative correlation with CMA3 positivity. Results of this study demonstrate that DNA fragmentation is more frequent in protamine-deficient spermatozoa. Unlike protamine deficiency, sperm DNA fragmentation does not preclude fertilization. Nonetheless, embryos derived from spermatozoa with high DNA damage have a lower potential to reach blastocyst stage.

Pronuclear morphology predicts embryo development and chromosome constitution

The relationship between pronuclear morphology on the one hand, and embryo development and chromosomal status on the other, was evaluated in 68 couples scheduled to undergo preimplantation genetic diagnosis because of advanced maternal age or recurrent implantation failure. Zygotes were grouped according to their pronuclear (PN) morphology. During the period from fertilization to embryo transfer, cleavage rate, embryo quality, blastocyst formation and results of the chromosomal analysis of 240 embryos were recorded. Both embryo cleavage characteristics and chromosome constitution were related to PN morphology. Embryos developing from zygotes with the normal PN pattern (pattern 0) cleaved faster and formed embryos with better morphology as compared with zygotes with abnormal PN patterns. Aneuploidy rate of embryos derived from zygotes with the normal PN pattern, with a single PN anomaly and with a double PN anomaly was 25.6, 73 and 83% respectively. Chromosomally normal embryos with the normal PN pattern progressed to the blastocyst stage at a higher rate (90%) than chromosomally normal embryos with a single (61%) or a double (40%) PN anomaly. The same relationship applied to chromosomally abnormal embryos. It is concluded that PN morphology predicts both the risk of embryo developmental arrest and that of chromosomal abnormalities.