The prevalence of embryonic remnants following the recovery of post-hatching bovine embryos produced in vitro or by somatic cell nuclear transfer

Chromatin accessibility memory of donor cells disrupts bovine somatic cell nuclear transfer blastocysts development

The post-transfer developmental capacity of bovine somatic cell nuclear transfer (SCNT) blastocysts is reduced, implying that abnormalities in gene expression regulation are present at blastocyst stage. Chromatin accessibility, as an indicator for transcriptional regulatory elements mediating gene transcription activity, has heretofore been largely unexplored in SCNT embryos, especially at blastocyst stage. In the present study, single-cell sequencing assay for transposase-accessible chromatin (scATAC-seq) of in vivo and SCNT blastocysts were conducted to segregate lineages and demonstrate the aberrant chromatin accessibility of transcription factors (TFs) related to inner cell mass (ICM) development in SCNT blastocysts. Pseudotime analysis of lineage segregation further reflected dysregulated chromatin accessibility dynamics of TFs in the ICM of SCNT blastocysts compared to their in vivo counterparts. ATAC- and ChIP-seq results of SCNT donor cells revealed that the aberrant chromatin accessibility in the ICM of SCNT blastocysts was due to the persistence of chromatin accessibility memory at corresponding loci in the donor cells, with strong enrichment of trimethylation of histone H3 at lysine 4 (H3K4me3) at these loci. Correction of the aberrant chromatin accessibility through demethylation of H3K4me3 by KDM5B diminished the expression of related genes (e.g., BCL11B) and significantly improved the ICM proliferation in SCNT blastocysts. This effect was confirmed by knocking down BCL11B in SCNT embryos to down-regulate p21 and alleviate the inhibition of ICM proliferation. These findings expand our understanding of the chromatin accessibility abnormalities in SCNT blastocysts and BCL11B may be a potential target to improve SCNT efficiency.

Assessing the Differential Abundance of Maternal Circulating MicroRNAs or Interferon-Stimulated Genes with Early Pregnancy

Interferon-stimulated genes (ISG) and microRNA (miRNA) present in maternal circulation have been reported to be diagnostic of pregnancy in cattle prior to day (d)30 of gestation. The objective of this study was to assess specific ISG and miRNA abundance on d 18 of gestation. Cattle were subjected to estrous synchronization and artificially inseminated to a single Angus sire. At time of insemination (d 0) and d 18 post-insemination, blood was collected and total RNA isolated. Differential abundance (DA) in specific ISG and miRNA between d 0 and d 18 samples in pregnant (n = 10) and open (n = 10) cows were assessed via RT-qPCR. The relative Ct values were normalized using abundance of cyclophilin or the geometric mean of specific miRNA for the ISG and miRNA genes of interest, respectively. The DA of the ISG were increased due to pregnancy (p < 0.05); however, there was no expected day of gestation by pregnancy interaction. Relative abundance of Bta-miR-16 increased on d18 regardless of pregnancy status (p < 0.05). None of the miRNA evaluated in this study were associated with pregnancy status. These data indicate that certain ISG may serve as early indicators of pregnancy in cattle, but abundance of the miRNA does not.

Interleukin-6 increases inner cell mass numbers in bovine embryos

Background

Work in other species suggests that interleukin-6 (IL6) promotes early embryo development. It was unclear whether IL6 serves as an embryokine in cultured bovine embryos. This work was undertaken to elucidate the role of IL6 during in vitro bovine embryo production.

Results

Transcripts for IL6 and its two cognate receptor subunits (IL6R, IL6ST) were confirmed in bovine embryos from the 1-cell to blastocyst stages. Supplementing 100 ng/ml recombinant bovine IL6 to in vitro-produced bovine embryos at day 1, 3 or 5 increased (P < 0.05) inner cell mass (ICM) cell number and the ICM:trophectoderm (TE) ratio but not TE cell number. No increase in ICM or TE cell number was observed after supplementation of 1 or 10 ng/ml IL6 beginning at either day 1 or 5. Sequential supplementation with 100 ng/ml IL6 at both day 1 and 5 (for a total of 200 ng/ml IL6) increased (P < 0.05) ICM cell number to a greater extent than supplementing IL6 at a single time period in one study but not a second study. Additionally, providing 200 ng/ml IL6 beginning at day 1 or 5 yielded no further increase on ICM cell numbers when compared to supplementing with 100 ng/ml IL6. IL6 treatment had no effect on cleavage or blastocyst formation in group culture. However, IL6 supplementation increased cleavage and day 8 blastocyst formation when bovine embryos were cultured individually.

Conclusions

These results implicate IL6 as an embryokine that specifically increases ICM cell numbers in bovine embryos and facilitates bovine blastocyst development in embryos cultured individually.

Embryo splitting affects the transcriptome during elongation stage of in vitro-produced bovine blastocysts

Embryo splitting has been used for the production of identical twins and to increase the pregnancy rate per available embryo. Split blastocysts can develop to term; however, little is known about the impact on gene expression of split embryos, especially at the whole transcriptome level. This work was aimed to evaluate the effect of blastocyst splitting on global gene expression profile at the elongation stage. For that, split and time-matched nonsplit (control group) bovine blastocysts were transferred to a bovine recipient and recovered at Day 17 of development. The number of collected embryos, their size, and global gene expression was compared between both groups. From 16 transferred split embryos, six (37.5%) were collected, whereas nine elongated were recovered from 17 nonsplit (52.9%). Neither the recovery rate nor the average length of the elongated embryos was significantly different between both groups. However more than 50% of embryos from the control group had a length surpassing 100 mm, whereas only 33% of the split embryos reached that size. Global gene expression was performed in individual elongated embryos from both groups using Two-Color Microarray-Based Gene Expression Analysis. From detected genes, 383 (1.31%) were differentially expressed between both groups, among them, 185 (0.63%) were downregulated and 198 (0.67%) genes were upregulated in split embryos. Bioinformatic analysis of differentially expressed genes revealed that embryo splitting affects transcriptomes of resulting elongated embryos, mainly downregulating genes involved in matrix remodelation, control of growth, detoxification, and transport of metabolites. These in turns might have a detrimental impact on the developmental potential of produced embryos.

Splitting of IVP bovine blastocyst affects morphology and gene expression of resulting demi-embryos during in vitro culture and in vivo elongation

Embryo splitting might be used to increase offspring yield and for molecular analysis of embryo competence. How splitting affects developmental potential of embryos is unknown. This research aimed to study the effect of bovine blastocyst splitting on morphological and gene expression homogeneity of demi-embryos and on embryo competence during elongation. Grade I bovine blastocyst produced in vitro were split into halves and distributed in nine groups (3 × 3 setting according to age and stage before splitting; age: days 7-9; stage: early, expanded and hatched blastocysts). Homogeneity and survival rate in vitro after splitting (12 h, days 10 and 13) and the effect of splitting on embryo development at elongation after embryo transfer (day 17) were assessed morphologically and by RT-qPCR. The genes analysed were OCT4, SOX2, NANOG, CDX2, TP1, TKDP1, EOMES, and BAX. Approximately 90% of split embryos had a well conserved defined inner cell mass (ICM), 70% of the halves had similar size with no differences in gene expression 12 h after splitting. Split embryos cultured further conserved normal and comparable morphology at day 10 of development; this situation changes at day 13 when embryo morphology and gene expression differed markedly among demi-embryos. Split and non-split blastocysts were transferred to recipient cows and were recovered at day 17. Fifty per cent of non-split embryos were larger than 100 mm (33% for split embryos). OCT4, SOX2, TP1 and EOMES levels were down-regulated in elongated embryos derived from split blastocysts. In conclusion, splitting day-8 blastocysts yields homogenous demi-embryos in terms of developmental capability and gene expression, but the initiation of the filamentous stage seems to be affected by the splitting.

The aggregation of four reconstructed zygotes is the limit to improve the developmental competence of cloned equine embryos

Embryo aggregation has been demonstrated to improve cloning efficiency in mammals. However, since no more than three embryos have been used for aggregation, the effect of using a larger number of cloned zygotes is unknown. Therefore, the goal of the present study was to determine whether increased numbers of cloned aggregated zygotes results in improved in vitro and in vivo embryo development in the equine. Zona-free reconstructed embryos (ZFRE's) were cultured in the well of the well system in four different experimental groups: I. 1x, only one ZFRE per microwell; II. 3x, three per microwell; III. 4x, four per microwell; and IV. 5x, five ZFRE's per microwell. Embryo size was measured on day 7, after which blastocysts from each experimental group were either a) maintained in culture from day 8 until day 16 to follow their growth rates, b) fixed to measure DNA fragmentation using the TUNEL assay, or c) transferred to synchronized mares. A higher blastocyst rate was observed on day 7 in the 4x group than in the 5x group. Non-aggregated embryos were smaller on day 8 compared to those aggregated, but from then on the in vitro growth was not different among experimental groups. Apoptotic cells averaged 10% of total cells of day 8 blastocysts, independently of embryo aggregation. Only pregnancies resulting from the aggregation of up to four embryos per microwell went beyond the fifth month of gestation, and two of these pregnancies, derived from experimental groups 3x and 4x, resulted in live cloned foals. In summary, we showed that the in vitro and in vivo development of cloned zona-free embryos improved until the aggregation of four zygotes and declined when five reconstructed zygotes were aggregated.

Post-hatching development of in vitro bovine embryos from day 7 to 14 in vivo versus in vitro

This study evaluates the post-hatching development of in vitro-produced (IVP) embryos until Day 14. On Day 7, IVP embryos were either transferred to recipient uteruses or placed in a post-hatching development (PHD) system. As a control group, in vivo-produced (IVV), Day-7 embryos were also transferred to recipient uteruses. All groups were collected on Day 14 and were morphologically evaluated. Day-7 and Day-14 IVV and IVP embryos were used for quantification of eight genes (PLAC8, CD9, SLC2A1, SLC2A3, KRT8, SOD2, HSP1A1, and IFNT2) by reverse transcriptase qPCR. Day-14 embryos from the PHD system were smaller (2.92 ± 0.45 mm) and had a lower embryonic disk diameter (0.14 ± 0.00 mm) than those produced by IVV (24.18 ± 3.71; 0.29 ± 0.03 mm, respectively) or IVP (19.06 ± 2.43; 0.28 ± 0.01 mm) culture and transferred to the uterus (P > 0.05). Day-7 IVP embryos had a higher expression of the HSP1A1, SCL2A1, and SCL2A3 genes than IVV embryos. When these embryos were cultured in the uterus, no differences in gene expression were observed on Day 14. Conversely, Day-14 IVP embryos cultured in the PHD system showed a higher expression of PLAC8, SOD2, and SLC2A3 genes. It is concluded that Day-7 IVP embryos are different from IVV embryos in regards to gene expression, although exposure to the uterine environment during the elongation period allowed the IVP embryos to overcome this difference. In contrast, IVP embryos cultured in the PHD system were morphologically and molecularly different, being of poorer quality than those cultured in the uterus.

The combined treatment of calcium ionophore with strontium improves the quality of ovine SCNT embryo development

Poor embryo quality is a major problem that contributes to the failure of pregnancy in somatic cell nuclear transfer (SCNT). The aims of this study were to improve the quality of ovine SCNT embryos by modifying the conventional activation protocol with the addition of SrCl2. In order to achieve this objective we conducted a series of experiments with in vitro-matured oocytes to optimize conditions for oocyte activation with strontium, and subsequently applied the protocol to SCNT embryos. The results showed that in vitro-matured oocytes could be activated effectively by 10 mM SrCl2 + 5 mg/ml cytochalasin B (CB) for 5 h in the absence of Ca2+ and that the blastocyst rate on day 7 (33.2%) was similar to that in the control group (31.0%) (5 M calcium ionophore [IP] A23187 for 5 min and cultured in CB/cycloheximide [CHX] for 5 h; P > 0.05). In SCNT experiments, the total cell number/blastocyst (104.12 ± 6.86) in the IP + SrCl2/CB-treatment group was, however, significantly higher than that in the control group (81.07 ± 3.39; P < 0.05). Apoptotic index (12.29 ± 1.22%) was significantly lower than the control (17.60 ± 1.39%; P < 0.05) when a combination of IP and SrCl2/CB was applied to SCNT embryos. In addition, karyotyping of the SCNT embryos showed that the percentage of diploid blastocysts in the IP + SrCl2/CB-treatment group was slightly higher than that in the control (P > 0.05). We conclude that the modified activation protocol with IP + SrCl2/CB can improve significantly the quality of ovine SCNT embryos in terms of total cell number, apoptosis and ploidy.

Terminologies for the pre-attachment bovine embryo

There are numerous publications regarding bovine embryos, ranging from descriptions of their appearance and development to emerging techniques in the field of assisted reproductive technology (ART). Concurrently, several specialized terms have been developed to describe the bovine embryo. Many of these terms are simple, some are difficult to understand and use, and others are antiquated and may not be scientifically accurate. For example, use of terms such as syngamy, conception rate, implantation and embryo resorption should be revisited. This review presents a brief overview of current knowledge regarding the pre-attachment period of the bovine embryo and attempts to define the terms. In this process, conventional terminology is presented, and contemporary and novel terms are proposed from a biological perspective.