The Effects of Blastomere Biopsy and Oxygen Tension on Bovine Embryo Development, Rate of Apoptosis and Interferon-? Secretion

Vitrification yields higher cryo-survival rate than slow freezing in biopsied bovine in vitro produced blastocysts

Vitrification and slow freezing are the two commonly used embryo cryopreservation methods. In most studies, vitrification of intact embryos has proven superior in several respects, including cell and embryo survival and pregnancy rate. However, there is a lack of data for comparing these two methods in in vitro produced (IVP) bovine blastocysts, which have been subjected to the retrieval of trophectoderm (TE) biopsy. Day 7 IVP blastocysts were pooled and randomized into four groups: 1) non-biopsy (NB), 2) biopsy (B), 3) biopsy-vitrification (BV), 4) biopsy-slow freeze (BSF). The blastocysts in the B, BV, and BSF groups were subjected to TE biopsy. For the B group, this was followed by 5 hours (h) incubation and subsequent scoring of the biopsy-survival (re-expansion) rate before processing for further analyses. For the BV and BSF groups, the biopsy procedure was followed by 2 h incubation, allowing for a quick re-expansion, after which the blastocysts were subjected to vitrification and slow freezing, respectively. After warming and thawing, respectively, they were then incubated for 5 h followed by scoring the cryo-survival (re-expansion) rates before processing for further analyses. These included quantification of ICM and TE cells, cleaved caspase-3- and TUNEL-positive cells, quantitative PCR on cellular stress markers (SOD1 and PRDX1), and ultrastructural analysis. The biopsy-survival rate in the B group was 94% (307/326). The cryo-survival rate in BV (86%, 138/161) was higher than that in BSF (57%, 81/142; P < 0.001). No differences were noted between the average ICM, TE, and total cell numbers of the groups. The percentages of cleaved caspase-3-positive cells were higher in BV vs. NB (P < 0.05), in BSF vs. NB (P < 0.001), and in BSF vs. B (P < 0.001). The percentages of TUNEL-positive cells were higher in BV vs. NB (P < 0.05) and in BSF vs. NB (P < 0.001). The levels of mRNA abundance for SOD1 and PRDX1 in B, BV, and BSF were not different from that in NB. The ultrastructural analysis of blastocysts in the BV and BSF groups showed distension of extracellular spaces and appearance of intracellular vacuoles in the ICM, distension of mitochondria, and disorganization of mitochondrial cristae in both ICM and TE, and weakened tight junctions between adjacent TE cells. In summary, our findings demonstrate that vitrification yields a higher cryo-survival rate than slow freezing in biopsied bovine IVP blastocysts. However, biopsy-vitrification and biopsy-slow-freeze values are comparable in terms of ICM, TE, and total blastocyst cell numbers, as well as cleaved caspase-3- and TUNEL-positive cell rates. Moreover, biopsy and cryopreservation performed alone had no effect on ICM, TE, total blastocyst cell numbers, or TUNEL-positive cell rates. Biopsy and vitrification performed alone had no effect on the cleaved caspase-3 positive cell rates, whereas slow freezing resulted in an increased rate. Furthermore, double traumatization with a combination of biopsy and cryopreservation, either vitrification or slow freezing, resulted in increased rates of cleaved caspase-3- and TUNEL-positive cells.

Effects of oxygen concentrations on developmental competence and transcriptomic profile of yak oocytes

Oxygen concentration influences oocyte quality and subsequent embryo development, but it remains unclear whether oxygen concentrations affect the developmental competence and transcriptomic profile of yak oocytes. In this study, we investigated the effects of different oxygen concentrations (5% versus 20%) on the developmental competence, reactive oxygen species (ROS) levels, glutathione (GSH) content, and transcriptomic profile of yak oocytes. The results showed that a low oxygen concentration significantly increased the maturation rate of yak oocytes (81.2 ± 2.2% vs 75.9 ± 1.3%) and the blastocyst quality of yak in vitro fertilized embryos. Analysis of ROS and GSH showed that a low oxygen concentration reduced ROS levels and increased the content of GSH (75.05 ± 7.1 ng/oocyte vs 50.63 ± 5.6 ng/oocyte). Furthermore, transcriptomic analysis identified 120 differentially expressed genes (DEGs) between the two groups of oocytes. Gene enrichment analysis of the DEGs indicated multiple cellular processes, including oxidative phosphorylation, transcription regulation, mitochondrial regulation, oestrogen signalling pathway, HIF-1 signalling pathway, TNF signalling pathway, were involved in the response to oxygen concentration alterations. Taken together, these results indicated that a low oxygen concentration improved the developmental competence of yak oocytes.

Laser assisted blastomere extrusion biopsy of in vitro produced cattle embryos-A potential high throughput, minimally invasive approach for sampling pre-morula and morula stage embryos

Whilst adoption of in vitro production (IVP) of cattle embryos and subsequent biopsy for genetic evaluation is increasing, biopsy techniques primarily used were developed to sample in vivo-produced blastocysts. This study was conducted to develop a laser-assisted blastomere extrusion approach for rapid and minimal-invasive biopsy of IVP cattle embryos at pre-morula to morula stages of development (Day 5 or 6 post-fertilisation). Embryo development into blastocysts was not compromised when ≤3 cells were collected by blastomere extrusion on Day 5 (44.4 ± 4.4 % and 34.3 ± 4.6 %) or Day 6 (58.0 ± 4.3 % and 57.5 ± 5.3 %) post-fertilisation compared with non-biopsied control embryos. Similarly, capacity to withstand cryopreservation was not different between embryos biopsied at Day 5 and 6 post-fertilisation and control-embryos (58.8 ± 6.0 %, 63.5 ± 5.6 %, and 56.0 ± 4.8 %, respectively). When more cells were collected from embryos at Day 6 post-fertilisation (≥8 compared to ≤3 cells), subsequent embryo development was not different (63.6 ± 6.1 % and 73.1 ± 6.2 %, respectively) nor was the capacity to withstand cryopreservation (67.9 ± 9.0 % and 62.5 ± 8.7 %, respectively). For biopsies on Day 6 post-fertilization, 95 % of samples produced a PCR product; however, when compared to the whole embryo PCR results, approximately 11 % of biopsy-samples classified as being from a male embryo were from female embryos (false positive), indicating DNA contamination between samples. In conclusion, results of this study indicate laser-assisted blastomere extrusion is a time efficient and minimally invasive approach to biopsy IVP morula and pre-morula cattle embryos to facilitate genetic analysis.

Effect of Group Embryo Culture under Low-Oxygen Tension in Benchtop Incubators on Human Embryo Culture: Prospective, Randomized, Controlled Trial

To evaluate the efficacy of group embryo culture under low-oxygen tension in benchtop incubators on human embryo development in vitro. The study was designed as a prospective, patient blind, randomized, controlled trial of a complex intervention. One hundred forty-eight women undergoing IVF were recruited in our fertility practice and randomized into two groups: intervention group (study culture strategy) or control group (control culture strategy). Intervention group embryos were cultured grouped under low-oxygen tension in benchtop incubators while control group embryos were cultured individually under atmospheric oxygen tension in large-box incubators. Using the study culture strategy, there were a significantly higher implantation rate (65.1% vs 49.2%; RR, 1.42; 95% CI, 1.17-1.73) and live birth delivery rate per embryo transfer (52.7% vs 39.5%; RR, 1.33; 95% CI, 1.02-1.75) with the first fresh embryo transfer. Cumulative implantation rate (56.7% vs 43.6%; RR, 1.30; 95% CI, 1.05-1.62) and cumulative live birth rate per embryo transfer (47.4% vs 36.2%; RR, 1.31; 95% CI, 1.01-1.69) were also statistically significantly increased in the study culture strategy. Human embryos exposed to our study culture condition strategy had statistically significant increased cumulative implantation rate and cumulative live birth rate per embryo transferred. Our findings suggest that this strategy specially favours poor quality embryos. Clinical Trial Registration Number: NCT01904006.

Individual culture and atmospheric oxygen during culture affect mouse preimplantation embryo metabolism and post-implantation development

RESEARCH QUESTION

Does single embryo culture under atmospheric or reduced oxygen alter preimplantation metabolism and post-implantation development compared with culture in groups?

DESIGN

Mouse embryos were cultured under 5% or 20% oxygen, individually or in groups of 10. Spent media were analysed after 48, 72 and 96 h of culture. Blastocysts were assessed by outgrowth assay or transferred to pseudo-pregnant recipients, and fetal and placental weight, length and morphology were assessed.

RESULTS

Compared with group culture, individually cultured blastocysts had lower net consumption of glucose and aspartate and higher glutamate production. Atmospheric oxygen reduced uptake of glucose and aspartate and increased production of glutamate and ornithine compared with 5% oxygen. Combining 20% oxygen and single culture resulted in further metabolic changes: decreased leucine, methionine and threonine consumption. Under 5% oxygen, individual culture decreased placental labyrinth area but had no other effects on fetal and placental development or outgrowth size compared with group culture. Under 20% oxygen, however, individual culture reduced outgrowth size and fetal and placental weight compared with group-cultured embryos.

CONCLUSIONS

Preimplantation metabolism of glucose and amino acids is altered by both oxygen and individual culture, and fetal weight is reduced by individual culture under atmospheric oxygen but not 5% oxygen. This study raises concerns regarding the increasing prevalence of single embryo culture in human IVF and adds to the existing evidence regarding the detrimental effects of atmospheric oxygen during embryo culture. Furthermore, these data demonstrate the cumulative nature of stress during embryo culture and highlight the importance of optimizing each element of the culture system.

In vitro culture of individual mouse preimplantation embryos: the role of embryo density, microwells, oxygen, timing and conditioned media

Single embryo culture is suboptimal compared with group culture, but necessary for embryo monitoring, and culture systems should be improved for single embryos. Pronucleate mouse embryos were used to assess the effect of culture conditions on single embryo development. Single culture either before or after compaction reduced cell numbers (112.2 ± 3.1; 110.2 ± 3.5) compared with group culture throughout (127.0 ± 3.4; P < 0.05). Reduction of media volume from 20 µl to 2 µl increased blastocyst cell numbers in single embryos cultured in 5% oxygen (84.4 ± 3.2 versus 97.8 ± 2.8; P < 0.05), but not in 20% oxygen (55.2 ± 2.9 versus 57.1 ± 2.8). Culture in microwell plates for the EmbryoScope and Primo Vision time-lapse systems changed cleavage timings and increased inner cell mass cell number (24.1 ± 1.0; 23.4 ± 1.2) compared with a 2 µl microdrop (18.4 ± 1.0; P < 0.05). Addition of embryo-conditioned media to single embryos increased hatching rate and blastocyst cell number (91.5 ± 4.7 versus 113.1 ± 4.4; P < 0.01). Single culture before or after compaction is therefore detrimental; oxygen, media volume and microwells influence single embryo development; and embryo-conditioned media may substitute for group culture.

Combined effects of individual culture and atmospheric oxygen on preimplantation mouse embryos in vitro

Embryos are routinely cultured individually, although this can reduce blastocyst development. Culture in atmospheric (20%) oxygen is also common, despite multiple detrimental effects on embryos. Although frequently occurring together, the consequences of this combination are unknown. Mouse embryos were cultured individually or grouped, under physiological (5%) or atmospheric (20%) oxygen. Embryos were assessed by time-lapse and blastocyst cell allocation. Compared with the control group (5% oxygen group culture), 5-cell cleavage (t5) was delayed in 5% oxygen individual culture and 20% oxygen group culture (59.91 ± 0.23, 60.70 ± 0.29, 63.06 ± 0.32 h post-HCG respectively, P < 0.05). Embryos in 20% oxygen individual culture were delayed earlier (3-cell cleavage), and at t5 cleaved later than embryos in other treatments (66.01 ± 0.40 h, P < 0.001), this delay persisting to blastocyst hatching. Compared with controls, hatching rate and cells per blastocyst were reduced in 5% oxygen single culture and 20% oxygen group culture (134.1 ± 3.4, 104.5 ± 3.2, 73.4 ± 2.2 cells, P < 0.001), and were further reduced in 20% oxygen individual culture (57.0 ± 2.8 cells, P < 0.001), as was percentage inner cell mass. These data indicate combining individual culture and 20% oxygen is detrimental to embryo development.

Soluble ligands and their receptors in human embryo development and implantation

Extensive evidence suggests that soluble ligands and their receptors mediate human preimplantation embryo development and implantation. Progress in this complex area has been ongoing since the 1980s, with an ever-increasing list of candidates. This article specifically reviews evidence of soluble ligands and their receptors in the human preimplantation stage embryo and female reproductive tract. The focus will be on candidates produced by the human preimplantation embryo and those eliciting developmental responses in vitro, as well as endometrial factors related to implantation and receptivity. Pathways to clinical translation, including innovative diagnostics and other technologies, are also highlighted, drawing from this collective evidence toward facilitating joint improvements in embryo quality and endometrial receptivity. This strategy could not only benefit clinical outcomes in reproductive medicine but also provide broader insights into the peri-implantation period of human development to improve fetal and neonatal health.

Periconceptional influences on offspring sex ratio and placental responses

Maternal diet and secondary factors can strikingly influence fetal outcomes, including biasing offspring sex ratio and altering the molecular biological responses of the conceptus, namely within the placenta. Alterations in the in utero environment might also lead to profound developmental origin of health and disease (DOHaD) outcomes into adulthood, including increased risk for cardiovascular disease, obesity and cancer, with males in general being at greater risk for these diseases. Female mice maintained on a very high fat (VHF) diet birth more sons than those on a chow-based and low fat (LF), high carbohydrate diet, with the latter group producing more daughters. However, neither the underlying mechanisms that contribute to this shift in offspring sex ratio nor when they occur during pregnancy have been resolved. In this review, we consider the evidence that maternal diet and other factors influence secondary sex ratio in a variety of species, including humans, and discuss when this skewing might occur. Additionally, we examine how fetal sex and maternal diet influences gene expression patterns in the mouse placenta, which serves as the primary nutrient acquisition and communication organ between the mother and her developing pups. These adaptations to diet observed as changes in gene expression are likely to provide insight into how the placenta buffers the fetus proper from environmental shifts in nutrient availability during pregnancy and whether male and female conceptuses respond differently to such challenges.

Treatment of ovine oocytes with caffeine increases the accessibility of DNase I to the donor chromatin and reduces apoptosis in somatic cell nuclear transfer embryos

Caffeine treatment of ovine oocytes increases the activity of maturation-promoting factor (MPF) and mitogen-activated protein kinases (MAPKs) and, in somatic cell nuclear transfer (SCNT) embryos, increases the frequency of nuclear envelope breakdown (NEBD) and premature chromosome condensation (PCC). At the blastocyst stage, caffeine-treated SCNT embryos have increased cell numbers. One explanation for this is that NEBD and PCC release chromatin-bound somatic factors, allowing greater access of oocyte factors involved in DNA synthesis and nuclear reprogramming to donor chromatin. This could advance DNA replication and cleavage in the first cell cycle, resulting in increased cell numbers. Alternatively, increased MAPK activity may affect localisation of heat shock proteins (HSPs) and reduce apoptosis. To investigate these possibilities, we investigated chromatin accessibility, the timing of DNA synthesis and first cleavage, the localisation of HSP27 during early development and the frequency of apoptotic nuclei at the blastocyst stage. Compared with control SCNT (non-caffeine treatment), caffeine treatment (10 mM caffeine for 6 h prior to activation) increased the accessibility of DNase I to donor chromatin (P < 0.05 at 1.5 h post activation (h.p.a.)), advanced DNA synthesis (43.5% v. 67.6%, respectively; P < 0.01 at 6 h.p.a.) and first cleavage (27.3% v. 40.5% at 20 h.p.a., respectively) and increased nuclear localisation of HSP27. Although development to the blastocyst stage was not affected, caffeine increased total cell numbers (98.5 v. 76.6; P < 0.05) and reduced the frequency of apoptotic nuclei (11.27% v. 20.3%; P < 0.05) compared with control SCNT group.