High developmental potential in vitro and in vivo of cattle embryos cloned without micromanipulators

Blastulation time measured with time-lapse system can predict in vitro viability of bovine blastocysts

The objective of this study was to evaluate the time of blastulation monitored by time-lapse technology to predict in vitro viability of bovine blastocysts. This technology can be a powerful tool for bovine embryos selection with higher implantation capacity and competence. Also, in humans an early blastulation is associated with higher quality and pregnancy rate. Cumulus oocyte complexes (COCs) were matured for 20 to 22 h and then fertilized by co-incubation of COCs and spermatozoa (10,000 sperm per oocyte) for 18 h. Presumptive zygotes were placed individually in microwells, in droplets of commercial culture medium. The Primo Vision TL system (EVO+; Vitrolife) captured digital images of developing embryos every 15 minutes. The time frame from IVF to the start of blastulation (tSB) and to blastocyst development (tB) was recorded. After day 7.5, the blastocysts were in vitro culture for 48 h until day 9.5 after IVF to evaluate post hatching development. In vitro viability was evaluated at day 9.5: those with a diameter greater than 200 μm and a total cell count greater than 180 were classified as viable (value 1), while the rest were classified as non in vitro viable (value 0). The area under the ROC curve (AUC) was estimated to determine the predictive power of in vitro viability through blastulation time. In addition, binary logistic regression analysis was used to generate a mathematical model with morphokinetic variables that allow the best prediction of in vitro viability. In 13 sessions, the blastocyst production rate was 46.2% (96/208). The cut-off time to discriminate early or late blastulation was 149.8 h. The post-hatching development of the embryos with early blastulation was 63.3% (31/49), being statistically superior (p = 0.001) than the late blastulation group 14.9% (7/47). Likewise, the time of blastulation showed an accuracy of 90.8% (p < 0.001) in predicting in vitro viability of bovine blastocysts. In conclusion, the selection of blastocysts based on blastulation time (< 155 h) and blastocyst diameter measured on day 7.5 after IVF (> 180 μm) maximizes the in vitro viability.

Sperm selection techniques in cattle: Microfilter device versus conventional methods

Microfluidics and microfilter devices have been developed to mimic the characteristics of the female reproductive tract, minimizing the risk of sperm damage. This study aimed to compare the use of a microfilter device versus conventional methods for sperm selection used in in vitro fertilization (IVF). For selecting spermatozoa, the pooled samples were processed in a microfilter device, swim-up and mini-Percoll gradient. Kinematic and morphometric parameters, vitality and DNA damage were analysed before and after sperm selection. After selection, 10,000 motile spermatozoa per oocyte were used in IVF drops. Embryos were assessed at three (cleavage rate) and seven (blastocyst rate) days post-IVF. Results of sperm kinematic parameters including average path velocity, velocity straight line, curvilinear velocity, linearity, lateral head displacement with the microfilter device were superior to density gradient (p < 0.05), but similar to swim-up method. Likewise, sperm DNA damage was significantly reduced using the microfilter device and swim-up method. Regarding the total sperm recovery rate post selection, results with the microfilter device (17.64%) and mini-Percoll gradient (18.27%) were higher than with swim-up method (6.52%). However, the cleavage and blastocyst rates were the lowest using the microfilter device. In conclusion, sperm selection using the microfilter device and swim-up method can improve kinematic parameters, although the mini Percoll gradient was the most efficient method for embryo production.

Domestic cat embryos generated without zona pellucida are capable of developing in vitro but exhibit abnormal gene expression and a decreased implantation rate

The removal of the zona pellucida has been used to improve the in vitro development of domestic cat embryos generated by IVF and SCNT. However, the in vivo development of domestic cat embryos generated without the zona pellucida has not been evaluated. The objective of this study was to evaluate the effects of zona pellucida removal on the in vitro and in vivo development of domestic cat embryos generated by IVF. For this purpose, two experimental groups were created: 1) domestic cat embryos cultured in vitro (Zona-intact group, ZI) and 2) domestic cat embryos cultured in vitro without the zona pellucida (Zona-free group, ZF). Domestic cat embryos were generated by IVF and cultured in vitro for 8 days. In the ZF group, the zona pellucida was removed after IVF, and embryos were cultured using the well of the well system (WOW). Cleavage, morula and blastocyst rates were evaluated in both groups. The diameter and total cell number of blastocysts were assessed. Relative expression of pluripotency (OCT4, SOX2 and NANOG), differentiation (CDX2 and GATA6) and apoptotic markers (BAX and BCL2) was evaluated in blastocysts. Finally, to evaluate in vivo development, embryos at days 5, 6 and 7 of development were transferred into recipient domestic cats, and ultrasonography was performed to evaluate implantation. No differences were observed in the cleavage, morula or blastocyst rates between embryos from the ZI and ZF groups. The diameter (mean ± SD) of blastocysts from the ZF group was greater (253.4 ± 83.3 μm) than that from the ZI group (210.5 ± 78.5 μm). No differences were observed in the relative expression of OCT4, CDX2 or GATA6. However, the relative expression of SOX2 and NANOG was significantly reduced in ZF blastocysts compared to ZI blastocysts. Furthermore, the relative expression of BAX was higher in ZF blastocysts than in ZI blastocysts. Finally, four pregnancies were confirmed after the transfer of ZI embryos (n = 110). However, no pregnancies were observed after the transfer of ZF embryos at the morula or blastocyst stage (n = 56). In conclusion, domestic cat embryos cultured without the zona pellucida were able to develop in vitro until the blastocyst stage. However, the removal of the zona pellucida negatively affected the gene expression of pluripotency and apoptosis markers, and ZF embryos were unable to implant. This might indicate that the removal of the zona pellucida is detrimental for the implantation and in vivo development of domestic cat embryos.

Back to the future: optimised microwell culture of individual human preimplantation stage embryos

Although in vitro culture of human embryos is a crucial step in assisted reproduction, the lack of focused research hampers worldwide standardisation and consistent outcomes. Only 1.2% of research papers published in five leading journals in human reproduction in 2019 focused on in vitro culture conditions, creating the impression that the optimisation process has approached its limits. On the other hand, in vitro culture of mammalian embryos is based on old principles, while there is no consensus on basic issues as density, time, medium change, gas atmosphere and small technical details including the way of drop preparation. This opinion paper aims to highlight and analyse the slow advancement in this field and stimulate research for simple and affordable solutions to meet the current requirements. A possible way for advancement is discussed in detail. Selection of embryos with the highest developmental competence requires individual culture and modification of the widely used "drop under oil" approach. Current use of three-dimensional surfaces instead of large flat bottoms is restricted to time-lapse systems, but these wells are designed for optical clarity, not for the needs of embryos. The size and shape of the original microwells (Well of the Well; WOW) offer a practical and straightforward solution to combine the benefits of communal and individual incubation and improve the overall quality of cultured embryos.

Back to the future: optimised microwell culture of individual human preimplantation stage embryos

Although in vitro culture of human embryos is a crucial step in assisted reproduction, the lack of focused research hampers worldwide standardisation and consistent outcomes. Only 1.2% of research papers published in five leading journals in human reproduction in 2019 focused on in vitro culture conditions, creating the impression that the optimisation process has approached its limits. On the other hand, in vitro culture of mammalian embryos is based on old principles, while there is no consensus on basic issues as density, time, medium change, gas atmosphere and small technical details including the way of drop preparation. This opinion paper aims to highlight and analyse the slow advancement in this field and stimulate research for simple and affordable solutions to meet the current requirements. A possible way for advancement is discussed in detail. Selection of embryos with the highest developmental competence requires individual culture and modification of the widely used "drop under oil" approach. Current use of three-dimensional surfaces instead of large flat bottoms is restricted to time-lapse systems, but these wells are designed for optical clarity, not for the needs of embryos. The size and shape of the original microwells (Well of the Well; WOW) offer a practical and straightforward solution to combine the benefits of communal and individual incubation and improve the overall quality of cultured embryos.

Effect of BMP15 and/or AMH during in vitro maturation of oocytes from involuntarily culled dairy cows

The high metabolic activity to which the dairy cattle are exposed to maintain milk production altered steroid metabolism that affects reproductive physiology and reduce oocyte competence. Our aims were (a) to characterize the competence of immature oocytes collected from dairy cattle based on the expression of genes in cumulus cells (CCs) and (b) to improve oocyte competence to support preimplantation embryo development by the supplementation of maturation medium with bone morphogenetic protein 15 (BMP15) and/or anti-mullerian hormone (AMH). Oocyte donors were identified at the moment of ovary collection and grouped by involuntarily culled dairy cows (Holstein breed) or beef cattle. The embryo development speed to blastocyst of the cull dairy cattle versus beef cattle (control group) was lower. Besides, <10% of oocytes (with CC biopsies) derived from dairy cattle were able to develop to the blastocyst stage. In addition, a higher level of expression and a positive correlation were observed in the expression of most of the genes evaluated (LUM, KRT18, KRT8, CLIC3, BMPR1B, and SLC38A3) in the cumulus-oocyte complexes that produced blastocysts versus those which did not develop correctly (arrested development). Further, use of BMP15 in the maturation of oocytes from dairy cattle seems to increase competence, modulating the expression of OCT4, SOX2, CDX2, GATA6, and TP1 in resulting blastocysts.

Factors and molecules that could impact cell differentiation in the embryo generated by nuclear transfer

Somatic cell nuclear transfer is a technique to create an embryo using an enucleated oocyte and a donor nucleus. Nucleus of somatic cells must be reprogrammed in order to participate in normal development within an enucleated egg. Reprogramming refers to the erasing and remodeling of cellular epigenetic marks to a lower differentiation state. Somatic nuclei must be reprogrammed by factors in the oocyte cytoplasm to a rather totipotent state since the reconstructed embryo must initiate embryo development from the one cell stage to term. In embryos reconstructed by nuclear transfer, the donor genetic material must respond to the cytoplasmic environment of the cytoplast and recapitulate this normal developmental process. Enucleation is critically important for cloning efficiency because may affect the ultrastructure of the remaining cytoplast, thus resulting in a decline or destruction of its cellular compartments. Nonetheless, the effects of in vitro culturing are yet to be fully understood. In vitro oocyte maturation can affect the abundance of specific transcripts and are likely to deplete the developmental competence. The epigenetic modifications established during cellular differentiation are a major factor determining this low efficiency as they act as epigenetic barriers restricting reprogramming of somatic nuclei. In this review we discuss some factors that could impact cell differentiation in embryo generated by nuclear transfer.

Identification and characteristics of extracellular vesicles from bovine blastocysts produced in vitro

Extracellular vesicles (EVs) have been identified within different body fluids and cell culture media. However, there is very little information on the secretion of these vesicles during early embryonic development. The aims of this work were first to demonstrate the secretion of extracellular vesicles by pre-implantation bovine embryos and second to identify and characterize the population of EVs secreted by bovine blastocysts during the period from day seven to nine of embryo culture and its correlation with further embryo development up to day 11. Bovine embryos were produced by in vitro fertilization (IVF) or parthenogenetic activation (PA) and cultured until blastocyst stage. Blastocyst selection was performed at day 7 post IVF/PA considering two variables: stage of development and quality of embryos. Selected blastocysts were cultured in vitro for 48 hours in groups (exp. 1) or individually (exp. 2) in SOF media depleted of exosomes. At day 9 post IVF/PA the media was collected and EVs isolated by ultracentrifugation. Transmission electron microscopy revealed the presence of heterogeneous vesicles of different sizes and population: microvesicles (MVs) and exosomes (EXs) of rounded shape, enclosed by a lipid bi-layer and ranging from 30 to 385 nm of diameter. Flow cytometry analysis allowed identifying CD63 and CD9 proteins as exosome markers. Nanoparticle tracking analysis generated a large number of variables, which required the use of multivariate statistics. The results indicated that the concentration of vesicles is higher in those blastocysts with arrested development from day 9 up to day 11 of in vitro development (6.7 x 10⁸ particles/ml) derived from IVF (p <0.05), compared to PA blastocysts (4.7 x 10⁸ particles/ml). Likewise, the profile (concentration and diameter) of particles secreted by embryos derived from IVF were different from those secreted by PA embryos. In conclusion, we demonstrated that bovine blastocysts secrete MVs/EXs to the culture media. Data suggest that characteristics of the population of EVs vary depending on embryo competence.

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.

Improved in vitro development of OPU-derived bovine (Bos taurus) embryos by group culture with agarose-embedded helper embryos

The average number of oocytes collected by ovum pick up (OPU) from Bos taurus cattle is <8 per live donor. The objective was to determine whether development of small numbers of cattle embryos (produced by OPU and IVF), was enhanced by including "helper" embryos, produced from abbatoir-derived oocytes and embedded in agarose. Oocytes were from abbatoir-derived ovaries (Experiments 1 and 2) or OPU of elite donors (Experiment 3). In Experiment 1, cleaved embryos (2-8 cells), were randomly allocated. Controls were groups of 1, 3, 5, 10, and 20 cleaved embryos cultured in 50 μL serum-free SOF, whereas treatments were groups of 1, 3, and 5 embryos freely cultured along with helpers in groups of either 9, 7 or 5 embedded in agarose per droplet. Therefore, there were 10 cleaved embryos per droplet in combinations of 1 + 9, 3 + 7 or 5 + 5 (free + helper), respectively. There was an increase in the progression to blastocyst for 1-5 embryos per droplet, compared to 10 and 20 (6.6-24.2% vs. 39.2-43.3%, P < 0.05). For the tested free embryos, those cultured with helpers had increased blastocyst development over their control counterparts (39.3-49.5% vs. 6.6-24.2%, P < 0.05). When the number of embryos per droplet was 10 or 20, blastocyst percentage was similar (39.2-49.5%, P > 0.05). In Experiment 2, addition of an agarose chip to the culture medium did not significantly affect development to the blastocyst stage. In Experiment 3, after fertilizing OPU oocytes with sorted X-sperm, a group of three cleaved embryos were cultured in a droplet with either seven helpers (3 + 7) or alone (3 + 0). Blastocyst development of OPU oocytes in the 3 + 7 group was 37.1%, higher than that in the 3 + 0 group (11.8%, P < 0.05). In conclusion, limited numbers of OPU/IVF oocytes had competent development when cultured with helpers (embedded in agarose to provide physical separation).

Changes in the expression of pluripotency-associated genes during preimplantation and peri-implantation stages in bovine cloned and in vitro produced embryos

In cattle, embryos elongate before implantation and after hatching. Changes in gene expression during this transition are not well studied. Especially important are variations in the expression of pluripotency-associated genes as a result of assisted reproductive biotechnologies, such as cloning and in vitro fertilization (IVF). We hypothesize that there will be a decline in the expression of key pluripotency-associated genes and an increase in the expression of IFN-tau in elongated embryos when compared with day-7 blastocysts. To test this we generated cloned and IVF bovine day-7 blastocyst and day-17 elongated embryos (day 0 = day of nucleus transfer or IVF). Gene expression in all embryos was assessed via RT-qPCR. OCT4 was overexpressed (p < 0.05) in the cloned blastocysts when compared with IVF. No differences in gene expression at this stage between cloned and IVF embryos were found for EOMES, NANOG and FGF4. At elongation EOMES, NANOG and FGF4 were upregulated in IVF embryos (p < 0.05). IFN-tau and OCT4 were expressed at similar levels. There were changes in the expression levels for all transcripts between blastogenesis and elongation. NANOG, IFN-tau and EOMES were overexpressed in all the elongated embryos (p < 0.05), FGF4 was underexpressed in both treatments. OCT4 dropped drastically in the cloned elongated embryos, but not in the IVF. Interestingly only adult donor cells (but not fetal) from which the cloned embryos originated also expressed high levels of OCT4. Our findings might help to understand the shift of gene expression during elongation and to identify key markers of embryonic development useful for embryo screening purposes.

Differential gene expression in bovine elongated (Day 17) embryos produced by somatic cell nucleus transfer and in vitro fertilization

Somatic cloning in cattle is associated with impaired embryo development, caused by inappropriate epigenetic reprogramming during embryogenesis; however, there is a paucity of data regarding gene expression at the critical elongation and peri-implantation stages. The objective of the present study was to identify genes differentially expressed in bovine cloned embryos at Day 17 of development (Day 0=day of nucleus transfer or IVF). Day 7 blastocysts (Hand Made Cloned or IVP) were transferred to recipient cattle and collected at Day 17. The efficiency of recovery of elongated embryos was similar, however cloned embryos elongated less than IVP embryos (91.8+/-45.8 vs. 174+/-50mm) and fewer had embryonic discs (63 vs. 83%). Qualitative and quantitative PCR detected expression of OCT4, NANOG, IFNtau, EOMES, FGF4, SOX2, and CDX2 in all IVP embryos. In most cloned embryos, NANOG and FGF4 were absent (verified by qPCR); NANOG, EOMES, and FGF4 were underexpressed, whereas IFNtau was overexpressed in cloned embryos. Based on qPCRs, other genes, i.e., SPARC, SNRB1, and CBPP22, were down-regulated in cloned embryos, whereas HSP70 and TDKP1 were overexpressed. In bovine microarrays, 47 genes (3.6%) were deregulated in cloned embryos, including several involved in trophoblast growth and differentiation. In conclusion, we inferred that these data were indicative of incomplete epigenetic reprogramming after cloning; this could lead to aberrant gene expression and subsequently early pregnancy loss. There was an apparent association between incomplete morphological elongation and aberrant reprogramming of a subset of genes critical for early embryonic development.

MicroRNA expression profiling of elongated cloned and in vitro-fertilized bovine embryos

The objective of this study was to identify microRNAs (miRNAs) expressed in bovine (Bos Taurus) cloned embryos at Day 17 of development (Day 0=day of nucleus transfer or in vitro fertilization) during elongation. Day 7 bovine expanded blastocysts produced by hand made cloning (HMC) or in vitro fertilization were bulk-transferred to synchronized recipient cattle (48 HMC embryos to 10 recipients and 28 in vitro-produced embryos to four recipients). Elongated embryos were retrieved at Day 17; miRNAs were isolated and subjected to microarray screening using custom composite slides spotted with human, mouse, and rat and in silico-predicted miRNAs. An initial profile of expressed miRNAs was determined in cloned embryos and somatic donor cells; this profile changed after somatic cell nucleus transfer, identifying differentially expressed miRNAs between cloned and in vitro-produced bovine embryos. Furthermore, microarray data were validated using a miRNA-specific quantitative reverse transcription-polymerase chain reaction (qRT-PCR) approach (miR-Q). There was an 83% correlation (P=0.01) between microarray and qPCR data. Based on qRT-PCR, correct reprogramming of some miRNAs from the donor cells was confirmed in cloned bovine embryos, whereas other somatic miRNAs were not appropriately reprogrammed. Some of the miRNAs that were equally reprogrammed clustered on the same chromosomal location in the bovine genome. In conclusion, reprogramming of miRNAs seemed to occur in cloned bovine embryos. This could have profound implications for elucidating nuclear reprogramming in somatic cloning, as well as for the role of miRNAs in preimplantation mammalian development.

Elongation and gene expression in bovine cloned embryos transferred to temporary recipients

Elongated embryos provide a unique source of information about trophoblastic differentiation, gene expression and maternal-embryonic interactions; however they are difficult and costly to obtain, especially elongated cloned embryos. One alternative is their production in heterologous temporary recipients such as sheep and goats. We aimed to produce elongated bovine cloned embryos using heterologous transfer to temporary recipients. Day-7 cloned cattle blastocysts were transferred to the uteri of ewes and goats and recovered as elongated structures at day 17. We evaluated elongation, length, presence of embryonic disc and expression of several important genes for embryonic development. We also produced homologous (cloned cattle embryos transferred into cattle uteri). Cloned bovine blastocysts were able to proceed with preimplantation development through elongation with high efficiency despite the species to which they were transferred. In qualitative and quantitative RT-PCR experiments we found differences in the pattern of gene expression among embryos recovered from different species. Sox2, Nanog and FGF-4 were markedly deregulated. No previous reports about the expression pattern of the studied genes had been published for elongated bovine cloned embryos produced in intermediate recipients, furthermore, the pattern of expression of Nanog, Oct4, Eomes, Cdx2, IFN-tau, Dicer, FGF-4 and Sox2 shown here are novel for elongated cloned bovine embryos created by hand-made cloning. Our data confirmed that sheep and goats can be used as temporary recipients. This model could serve as a basis for further research on gene expression and cellular changes during bovine peri-implantation development.