In vitro development and cell allocation of porcine blastocysts derived by aggregation of in vitro fertilized embryos

Blastomere aggregation using phytohemagglutinin-L improves the establishment efficiency of porcine parthenogenesis-derived embryonic stem-like cell lines

Aggregation of blastomeres is a promising method to improve the developmental competence of blastocysts and may be useful for the production of chimeric animals and the establishment of embryonic stem cell lines by increasing inner cell masses. Here, we determined the optimal conditions for blastomere aggregation using phytohemagglutinin-L (PHA-L) and examined PHA-L efficiency by comparing it with Well of the Well (WOW), a general blastomere aggregation method. As a result, we confirmed that treatment with 15 μg/ml PHA-L for 144 h was effective for blastomere aggregation and embryonic development of three zona-free 2-cell stage embryos (TZ2Es) after parthenogenetic activation (PA). The TZ2Es cultured with PHA-L showed a significantly (p < 0.05) higher blastomere aggregation rate than the WOW method (93.5 ± 1.9% vs. 78.0 ± 8.5%). In addition, our results demonstrated that TZ2Es aggregation through PHA-L improved the quality of PA-derived blastocysts and improved porcine embryonic stem-like cell (pESLCs) seeding efficiency and quality of colonies. It was also observed that PHA-L-derived pESLC could remain undifferentiated and exhibit typical embryonic stem cell pluripotency markers, embryoid body (EB)-forming ability, and differentiation into cell lineages of three germ layers. Pig blastomere aggregation technology is expected to improve embryo quality and the efficiency of embryonic stem cell establishment and embryoid-body formation. It can also be used in blastocyst complementation systems and in the production of chimeric animals.

Analysis of trophectoderm markers in domestic cat blastocysts cultured without zona pellucida

Domestic cat embryos generated by in vitro fertilization (IVF) and cultured without the zona pellucida have a reduced implantation capacity after embryo transfer at the blastocyst stage. The objective of this study was to evaluate the expression of trophectoderm markers in domestic cat blastocysts cultured without the zona pellucida. Two experimental groups were selected: (1) domestic cat embryos generated by IVF and cultured in vitro normally (zona intact group, ZI); and (2) domestic cat embryos generated by IVF and cultured in vitro without a zona pellucida (zona-free group, ZF). In the ZF group, the zona pellucida of the presumptive zygote was removed and these were cultured using the well of the well (WOW) system. In vitro culture was carried out for 7 days. The cleavage, morula and blastocyst rates were estimated. Finally, the relative expression levels of the trophectoderm markers TEAD4, YAP1, CDX2 and EOMES, the cell adhesion marker E-cadherin and the apoptosis marker CASP3 were evaluated by RT-qPCR in the blastocysts. The Wilcoxon test was used to evaluate differences (P < 0.05). No differences were observed in the cleavage, morula and blastocyst rates between the ZF and ZI groups. No differences were found in the expression of TEAD4, CDX2, E-cadherin and CASP3 between groups. The expression of YAP1 and EOMES was higher in ZF blastocysts than in ZI blastocysts. In conclusion, the in vitro culture without the zona pellucida generates an overexpression of YAP1 and EOMES in the domestic cat blastocysts. More studies are needed to confirm if this overexpression might affect in vivo development.

In vivo dynamic 3D imaging of oocytes and embryos in the mouse oviduct

Developmental biologists have always relied on imaging to shed light on dynamic cellular events. However, processes such as mammalian fertilization and embryogenesis are generally inaccessible for direct imaging. In consequence, how the oviduct (fallopian tube) facilitates the transport of gametes and preimplantation embryos continues to be unanswered. Here we present a combination of intravital window and optical coherence tomography for dynamic, volumetric, in vivo imaging of oocytes and embryos as they are transported through the mouse oviduct. We observed location-dependent circling, oscillating, and long-distance bi-directional movements of oocytes and embryos that suggest regulatory mechanisms driving transport and question established views in the field. This in vivo imaging approach can be combined with a variety of genetic and pharmacological manipulations for live functional analysis, bringing the potential to investigate reproductive physiology in its native state.

Wang and Larina present in vivo volumetric imaging of oocytes and embryos as they are transported through the mouse oviduct with optical coherence tomography and an intravital microscopy. The study reveals complex dynamics of oocytes and embryos that suggest a regulatory role of cilia and oviductal contractions in driving the transport.

Effects of PXD101 and Embryo Aggregation on the In Vitro Development of Mouse Parthenogenetic Embryos

To improve the isolation efficiency of parthenogenetic embryonic stem cells (pESCs) in mice, it is necessary to optimize the method to increase in vitro developmental competence of mice parthenogenetic blastocysts. Therefore, this study aims to investigate an optimal method for the production of mouse parthenogenetic blastocysts and isolation of pESC colonies by comparing the effects of two methods: (1) the treatment of histone deacetylase inhibitor PXD101 before, during, or after parthenogenetic activation; (2) parthenogenetic embryo aggregation; and (3) their combination treatment. The results suggest that application of PXD101 treatment and embryo aggregation could both improve the development of mouse parthenogenetic blastocysts (50 nM PXD101 treated 4 hours during activation and further 4 hours after activation: 40.0% vs. 20.0%; p < 0.05; two-cell embryo aggregation: 38.3% vs. 20.0%; p < 0.05) and also enhance the isolation rate of pESC colonies (PXD101: 33.3% vs. 11.8%; p < 0.05; two-cell embryo aggregation: 36.4% vs. 11.8%; p < 0.05). The combination of their treatments had the higher rate of parthenogenetic blastocyst development (41.7%) and significantly higher rate of pESC colony isolation from parthenogenetic blastocysts (45.0%); therefore, we concluded that the combination of these two methods (50 nM PXD101 treated for 8 hours and then aggregated at two-cell stage with 0.25% pronase for 10 minutes in our self-made concave) is considered the optimal way for the in vitro development of parthenogenetic blastocysts and subsequent pESC colony isolation in mice, opening new opportunities for application of this combination method to improve the parthenogenetic embryo development in other species.

Embryo aggregation regulates in vitro stress conditions to promote developmental competence in pigs

Embryo aggregation is a useful method to produce blastocysts with high developmental competence to generate more offspring in various mammals, but the underlying mechanism(s) regarding the beneficial effects are largely unknown. In this study, we investigated the effects of embryo aggregation using 4-cell stage embryos in in vitro developmental competence and the relationship of stress conditions in porcine early embryogenesis. We conducted aggregation using the well of the well system and confirmed that aggregation using two or three embryos was useful for obtaining blastocysts. Aggregated embryos significantly improved developmental competence, including blastocyst formation rate, blastomere number, ICM/TE ratio, and cellular survival rate, compared to non-aggregated embryos. Investigation into the relationship between embryo aggregation and stress conditions revealed that mitochondrial function increased, and oxidative and endoplasmic reticulum (ER)-stress decreased compared to 1X (non-aggregated embryos) blastocysts. In addition, 3X (three-embryo aggregated) blastocysts increased the expression of pluripotency, anti-apoptosis, and implantation related genes, and decreased expression of pro-apoptosis related genes. Therefore, these findings indicate that embryo aggregation regulates in vitro stress conditions to increase developmental competence and contributes to the in vitro production of high-quality embryos and the large-scale production of transgenic and chimeric pigs.

Comparison of pregnancy rates with transfer of in vivo produced embryos derived using multiple ovulation and embryo transfer (MOET) with in vitro produced embryos by somatic cell nuclear transfer (SCNT) in the dromedary camel (Camelus dromedaries)

In the present study, there was comparison of pregnancy rates with transfer of in vivo-produced embryos using multiple ovulation and embryo transfer (MOET) with in vitro-produced embryos by somatic cell nuclear transfer (SCNT) in dromedary camels. In vivo-produced embryos were collected from donors after super-stimulation of follicular development on day 7 after ovulation, while in vitro-derived embryos were produced using SCNT from in vivo-matured oocytes collected from camels after follicular development super-stimulation. As a result of estrous synchronization, all recipient camels for both groups were 1 day earlier in stage of estrous cycle than developmental status of embryos at the time of transfer. The animals into which embryos were transferred were monitored at 7-day intervals after embryo transfer for signs of pregnancy based on response to presence of a male and there was ultrasonic confirmation on days 35 and 60 subsequent to day of estrus in recipient animals. A greater proportion of recipients (P <  0.05) were considered pregnant based on response to male presence when there was transfer of MOET-(76.8 ± 3.2) compared with SCNT- (26.4 ± 2.4) derived embryos on day 14. There was no difference in pregnancy losses in subsequent weeks until day 60 between groups. There were also no differences in calving rates of females in which MOET- (91.7%) and SCNT- (93.3%) derived embryos were transferred. These results indicate pregnancies at day 60 with SCNT-derived embryos are sustained for the remainder of gestation periods similar to when there was transfer of MOET-derived embryos in dromedary camels.

Strategies for improvement of cloning by somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) is a powerful tool that is being applied in a variety of fields as diverse as the cloning and production of transgenic animals, rescue of endangered species and regenerative medicine. However, cloning efficiency is still very low and SCNT embryos generally show poor developmental competency and many abnormalities. The low efficiency is probably due to incomplete reprogramming of the donor nucleus and most of the developmental problems are thought to be caused by epigenetic defects. Applications of SCNT will, therefore, depend on improvements in the efficiency of production of healthy clones. This review has summarised the progress and strategies that have been used to make improvements in various animal species, especially over the period 2010–2017, including strategies based on histone modification, embryo aggregation and mitochondrial function. There has been considerable investiagation into the mechanisms that underpin each strategy, helping us better understand the nature of genomic reprogramming and nucleus–cytoplasm interactions.

Novel histone deacetylase inhibitors and embryo aggregation enhance cloned embryo development and ES cell derivation in pigs

The histone deacetylase inhibitor (HDACi) has been investigated for treating cancers and many other diseases as well as enhancing the reprogramming efficiency in cloned embryos for decades. In the present study, we investigated the effects of two novel HDAC inhibitors, i.e., HDACi-14 and -79, at the concentrations of 0, 1, 2, or 4 μM on the development of embryos cloned by the oocyte bisection cloning technique (OBCT). Blastocyst rates for the reconstructed embryos reached 60% in the 2 μM HDACi-14-treated groups, which was higher (P < 0.05) compared to the untreated group (36.9%). Similarly, HDACi-79 treatment at 2 and 4 μM also conferred higher (P < 0.05) blastocyst rates than that of the untreated group (79.4, 74.2, and 50.0%, respectively). Both HDACi-14 and -79 treatments had no beneficial effect on total cell numbers and apoptotic indices of cloned embryos (P > 0.05). Histone acetylation profile by both HDACi-14 (2 μM) and -79 (2 μM) treatments demonstrated a drastic increase (P < 0.05) mainly in two-cell stage embryos when compared to the control group. After seeding on the feeder cells, the aggregated cloned blastocysts produced by the HDACi-79 treatment showed a significant increase of primary outgrowths compared to the control group (60.0% vs. 42.9%; P < 0.05). Finally, the cloned embryo-derived ES cell lines from aggregated cloned embryos produced from the HDACi-79-treated, HDACi-14-treated and control groups were established (5, 3, and 2 lines, respectively). In conclusion, the novel histone deacetylation inhibitors improve blastocyst formation and potentially increase the derivation efficiency of ES cell lines from the cloned porcine embryos produced in vitro. Depending on the purposes, some fine-tuning may be required to maximize its beneficial effects of these newly synthesized chemicals.

Effects of Embryo Aggregation and PXD101 on the In Vitro Development of Mouse Somatic Cell Nuclear Transfer Embryos

To improve the cloning efficiency of somatic cell nuclear transfer (SCNT) and to establish nuclear transfer embryonic stem cells (NT-ESCs) reliably, it is necessary to produce high-quality blastocysts derived from mice SCNT embryos. Therefore, the present study aims to investigate an optimal method for mouse SCNT embryo production and NT-ESCs derivation by comparing the effects of two methods: the treatment of histone deacetylase inhibitor PXD101 after SCNT, embryo aggregation and their combination treatment. The results suggest that embryo aggregation at four-cell stage and 50 nM PXD101 treated for 10 hours during and after activation could improve both mouse SCNT embryos' development (PXD101: 40.0% vs. 18.5%; p < 0.05; aggregation: 40.2% vs. 18.5%; p < 0.05) and also enhance the isolation rate of NT-ESCs (PXD101: 38.2% vs. 12.5%; p < 0.05; aggregation: 39.0% vs. 12.5%; p < 0.05). The combination of their treatments had a higher development rate (43.6%) and significantly higher NT-ESCs isolation rate (54.7%), therefore, we concluded that the combination of these two methods (50 nM PXD101 treated for 10 hours after SCNT and then aggregated at four-cell stage) is considered as the optimal way for the in vitro development of SCNT embryo and subsequent NT-ESCs isolation in mice, providing a new approach for the practical improvement of mouse cloning techniques and opening new opportunities to improve cloning efficiencies in other species.

Aggregation of cloned embryos in empty zona pellucida improves derivation efficiency of pig ES-like cells

The development of embryonic stem cells (ESCs) from large animal species has become an important model for therapeutic cloning using ESCs derived by somatic cell nuclear transfer (SCNT). However, poor embryo quality and blastocyst formation have been major limitations for derivation of cloned ESCs (ntESCs). In this study, we have tried to overcome these problems by treating these cells with histone deacetylase inhibitors (HDACi) and aggregating porcine embryos. First, cloned embryos were treated with Scriptaid to confirm the effect of HDACi on cloned embryo quality. The Scriptaid-treated blastocysts showed significantly higher total cell numbers (29.50 ± 2.10) than non-treated blastocysts (22.29 ± 1.50, P < 0.05). Next, cloned embryo quality and blastocyst formation were analyzed in aggregates. Three zona-free, reconstructed, four-cell-stage SCNT embryos were injected into the empty zona of hatched parthenogenetic (PA) blastocysts. Blastocyst formation and total cell number of cloned blastocysts increased significantly for all aggregates (76.4% and 83.18 ± 8.33) compared with non-aggregates (25.5% and 27.11 ± 1.67, P < 0.05). Finally, aggregated blastocysts were cultured on a feeder layer to examine the efficiency of porcine ES-like cell derivation. Aggregated blastocysts showed a higher primary colony formation rate than non-aggregated cloned blastocysts (17.6 ± 12.3% vs. 2.2 ± 1.35%, respectively, P < 0.05). In addition, derived ES-like cells showed typical characters of ESCs. In conclusion, the aggregation of porcine SCNT embryos at the four-cell stage could be a useful technique for improving the development rate and quality of porcine-cloned blastocysts and the derivation efficiency of porcine ntESCs.

Embryo Aggregation in Pig Improves Cloning Efficiency and Embryo Quality

In this study, we analyzed the effects of the cloned embryo aggregation on in vitro embryo development and embryo quality by measuring blastocyst diameter and cell number, DNA fragmentation levels and the expression of genes associated with pluripotency, apoptosis, trophoblast and DNA methylation in the porcine. Zona-free reconstructed cloned embryos were cultured in the well of the well system, placing one (1x non aggregated group) or three (3x group) embryos per microwell. Our results showed that aggregation of three embryos increased blastocyst formation rate and blastocyst diameter of cloned pig embryos. DNA fragmentation levels in 3x aggregated cloned blastocysts were significantly decreased compared to 1x blastocysts. Levels of Oct4, Klf4, Igf2, Bax and Dnmt 1 transcripts were significantly higher in aggregated embryos, whereas Nanog levels were not affected. Transcripts of Cdx2 and Bcl-xl were essentially non-detectable. Our study suggests that embryo aggregation in the porcine may be beneficial for cloned embryo development and embryo quality, through a reduction in apoptotic levels and an improvement in cell reprogramming.

Embryo Aggregation Promotes Derivation Efficiency of Outgrowths from Porcine Blastocysts

Porcine embryonic stem cells (pESCs) have become an advantageous experimental tool for developing therapeutic applications and producing transgenic animals. However, despite numerous reports of putative pESC lines, deriving validated pESC lines from embryos produced in vitro remains difficult. Here, we report that embryo aggregation was useful for deriving pESCs from in vitro-produced embryos. Blastocysts derived from embryo aggregation formed a larger number of colonies and maintained cell culture stability. Our derived cell lines demonstrated expression of pluripotent markers (alkaline phosphatase, Oct4, Sox2, and Nanog), an ability to form embryoid bodies, and the capacity to differentiate into the three germ layers. A cytogenetic analysis of these cells revealed that all lines derived from aggregated blastocysts had normal female and male karyotypes. These results demonstrate that embryo aggregation could be a useful technique to improve the efficiency of deriving ESCs from in vitro-fertilized pig embryos, studying early development, and deriving pluripotent ESCs in vitro in other mammals.

Factors affecting the development of somatic cell nuclear transfer embryos in Cattle

Nuclear transfer is a complex multistep procedure that includes oocyte maturation, cell cycle synchronization of donor cells, enucleation, cell fusion, oocyte activation and embryo culture. Therefore, many factors are believed to contribute to the success of embryo development following nuclear transfer. Numerous attempts to improve cloning efficiency have been conducted since the birth of the first sheep by somatic cell nuclear transfer. However, the efficiency of somatic cell cloning has remained low, and applications have been limited. In this review, we discuss some of the factors that affect the developmental ability of somatic cell nuclear transfer embryos in cattle.

Availability of empty zona pellucida for generating embryonic chimeras

In the present study we used an empty zona pellucida derived from hatched blastocysts as an alternative source for embryo aggregation and compared results with the conventional microwell method. Denuded 4-cell stage porcine embryos were aggregated by introduction into an empty zona or placement within a concave microwell. The present study showed that although the rate of aggregate formation was similar, the blastocyst rates and allocation of more cells to the inner cell mass (ICM) in the resultant aggregates were increased significantly more in the empty zona than in the microwell. Notably, using an empty zona showed no limitations with regards to the increased number of embryos aggregated or embryonic stages for aggregation, while partial or no aggregation frequently occurred in the microwell. The discrepancy may be due to the difference of microenvironments where the embryos were placed namely, the presence/absence of zona pellucida. We hypothesize the success of the empty zona in generating aggregates is due to the physical aggregation of individual embryos allowing closer contact between the blastomeres and/or embryos compared with a concave microwell. These results indicate that aggregation conditions could influence overall production efficiency and developmental potential of aggregates, suggesting physical restraint via empty zona that provide three-dimensional pressures is an important factor for successful embryo aggregation.

Putative porcine embryonic stem cell lines derived from aggregated four-celled cloned embryos produced by oocyte bisection cloning

We attempted to isolate ES cell lines using inner cell masses from high-quality cloned porcine blastocysts. After being seeded onto feeders, embryos had better (P < 0.05) attachment, outgrowth formation and primary colonization in both 2× and 3× aggregated cloned embryos (62.8, 42.6 and12.8% vs. 76.2, 55.2 and 26.2%, respectively) compared to the non-aggregated group (41.6, 23.4 and 3.9%). Effects of feeder types (STO vs. MEF) and serum sources (FBS vs. KSR) on extraction of cloned embryo-derived porcine ES cells were examined. More (17.1%) ntES cell lines over Passage 3 were generated in the MEF/KSR group. However, ntES cells cultured in KSR-supplemented medium had a low proliferation rate with defective morphology, and eventually underwent differentiation or apoptosis subsequently. Approximately 26.1, 22.7 and 35.7% of primary colonies were formed after plating embryos in DMEM, DMEM/F12 and α-MEM media, respectively. Survival rates of ntES cells cultured in α-MEM, DMEM and DMEM/F12 were 16.7, 4.3 and 6.8%, respectively (P > 0.05). We further examined the beneficial effect of TSA treatment of 3× aggregated cloned embryos on establishment of ntES cell lines. Primary colony numbers and survival rates of ntES cells beyond passage 3 were higher (P < 0.05) in those derived from TSA-treated 3× blastocysts (36.7 and 26.7%) than from the non-treated aggregated group (23.1 and 11.5%). These cells, remaining undifferentiated over 25 passages, had alkaline phosphatase activity and expressed ES specific markers Oct4, Nanog, Sox2, and Rex01. Moreover, these ntES cells successfully differentiated into embryoid bodies (EBs) that expressed specific genes of all three germ layers after being cultured in LIF-free medium. In conclusion, we have successfully derived putative porcine ntES cells with high efficiency from quality cloned embryos produced by embryo aggregation, and optimized the ES cell culture system suitable for establishing and maintaining ntES cell lines in undifferentiated state.

Production of viable cloned miniature pigs by aggregation of handmade cloned embryos at the 4-cell stage

The aim of the present study was to improve the quality of handmade cloned porcine embryos by multiple embryo aggregations. Embryos derived from aggregation of three cloned embryos (3×) had a better blastocyst rate than cloned control (1×) embryos (73.6% vs 35.1%, respectively; P<0.05), but did not differ from those produced by aggregation of two cloned embryos (2×; 63.0%). Total cell numbers differed among treatments (P<0.05), with the greatest cell numbers (126) in the 3× group and the lowest (55) in the control group. The ratio of inner cell mass:total cell number was comparable in the 2× and 3× groups (25.1% vs 26.1%, respectively) and was significantly better than that in the control group (15.3%). The proportion of apoptotic cells in 2× and 3× groups was lower than that in the control group (2.7% and 2.2% vs 4.7%, respectively; P<0.05). Expression of Oct4 and Cdx2 was higher, whereas that of Bax was lower (P<0.05), in the 3× compared with non-aggregate group. Seven piglets were born to two surrogate mothers after embryo transfer of 3× aggregated blastocysts. In conclusion, aggregated embryos had greater total cell numbers and better pluripotency gene expression, with reduced expression of the pro-apoptosis gene Bax. Collectively, these improvement may be associated with the development of cloned embryos to term.

Eventual proapoptotic or anti-apoptotic impact of aberrantly expressed Cx43 and Cx26 can depend on ER-alpha overexpression in human endometrioid adenocarcinoma

Estrogen receptor (ER) and progesterone receptor (PgR) accumulations lead to impairment of gap junctional intercellular communication in endometrial cancer. The task of this study was to explore relationships of Cx26 and Cx43 with anti-apoptotic protein Bcl-xL and proapoptotic agent Bak in ER-alpha and PgR negative or variably positive endometrioid adenocarcinomas. Cx26, Cx43, Bak, Bcl-xL, PgR and ER-alpha were detected in 78 endometrioid adenocarcinomas with immunohistochemistry. There was a remarkable cellular re-distribution of Cx26 and Cx43 from normally membranous location in normal endometrium to aberrantly cytoplasmic expression in endometrioid adenocarcinomas, thus suggesting the decrease of functional membranous gap junctions in the malignancy. Bak failed to correlate with Cx43 regardless of either PgR or ER-alpha status of tumors, while Bcl-xL positively correlated with Cx43 in ER-alpha positive tumors (p = 0.001, r = 0.427) and both PgR positive (p = 0.019, r = 0.312) and negative (p = 0.015, r = 0.509) cancers. Similarly, Bcl-xL significantly associated with Cx26 in ER-alpha positive tumors (p = 0.036, r = 0.267) and both PgR positive (p = 0.026, r = 0.297) and negative (p = 0.046, r = 0.429) cancers. On the contrary, Bak exclusively correlated with Cx26 only in ER-alpha negative tumors (p = 0.027, r = 0.551). ER-alpha status of endometrioid adenocarcinomas could restrict eventual proapoptotic or anti-apoptotic impact of aberrantly expressed Cx43 and Cx26 in these tumors.

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.

Generation and developmental characteristics of porcine tetraploid embryos and tetraploid/diploid chimeric embryos

The aim of this study was to optimize electrofusion conditions for generating porcine tetraploid (4n) embryos and produce tetraploid/diploid (4n/2n) chimeric embryos. Different electric field intensities were tested and 2 direct current (DC) pulses of 0.9 kV/cm for 30 μs was selected as the optimum condition for electrofusion of 2-cell embryos to produce 4n embryos. The fusion rate of 2-cell embryos and the development rate to blastocyst of presumably 4n embryos, reached 85.4% and 28.5%, respectively. 68.18% of the fused embryos were found to be 4n as demonstrated by fluorescent in situ hybridization (FISH). Although the number of blastomeres in 4n blastocysts was significantly lower than in 2n blastocysts (P<0.05), there was no significant difference in developmental rates of blastocysts between 2n and 4n embryos (P>0.05), suggesting that the blastocyst forming capacity in 4n embryos is similar to those in 2n embryos. Moreover, 4n/2n chimeric embryos were obtained by aggregation of 4n and 2n embryos. We found that the developmental rate and cell number of blastocysts of 4-cell (4n)/4-cell (2n) chimeric embryos were significantly higher than those of 2-cell (4n)/4-cell (2n), 4-cell (4n)/8-cell (2n), 4-cell (4n)/2-cell (2n) chimeric embryos (P<0.05). Consistent with mouse chimeras, the majority of 4n cells contribute to the trophectoderm (TE), while the 2n cells are mainly present in the inner cell mass (ICM) of porcine 4n/2n chimeric embryos. Our study established a feasible and efficient approach to produce porcine 4n embryos and 4n/2n chimeric embryos.

Epigenetic changes of lentiviral transgenes in porcine stem cells derived from embryonic origin

Because of the physiological and immunological similarities that exist between pigs and humans, porcine pluripotent cell lines have been identified as important candidates for preliminary studies on human disease as well as a source for generating transgenic animals. Therefore, the establishment and characterization of porcine embryonic stem cells (pESCs), along with the generation of stable transgenic cell lines, is essential. In this study, we attempted to efficiently introduce transgenes into Epiblast stem cell (EpiSC)-like pESCs. Consequently, a pluripotent cell line could be derived from a porcine-hatched blastocyst. Enhanced green fluorescent protein (EGFP) was successfully introduced into the cells via lentiviral vectors under various multiplicities of infection, with pluripotency and differentiation potential unaffected after transfection. However, EGFP expression gradually declined during extended culture. This silencing effect was recovered by in vitro differentiation and treatment with 5-azadeoxycytidine. This phenomenon was related to DNA methylation as determined by bisulfite sequencing. In conclusion, we were able to successfully derive EpiSC-like pESCs and introduce transgenes into these cells using lentiviral vectors. This cell line could potentially be used as a donor cell source for transgenic pigs and may be a useful tool for studies involving EpiSC-like pESCs as well as aid in the understanding of the epigenetic regulation of transgenes.

Recent progress in bovine somatic cell nuclear transfer

Bovine somatic cell nuclear transfer (SCNT) embryos can develop to the blastocyst stage at a rate similar to that of embryos produced by in vitro fertilization. However, the full-term developmental rate of SCNT embryos is very low, owing to the high embryonic and fetal losses after embryo transfer. In addition, increased birth weight and postnatal mortality are observed at high rates in cloned calves. The low efficiency of SCNT is probably attributed to incomplete reprogramming of the donor nucleus and most of the developmental problems of clones are thought to be caused by epigenetic defects. Applications of SCNT will depend on improvement in the efficiency of production of healthy cloned calves. In this review, we discuss problems and recent progress in bovine SCNT.

Primed pluripotent cell lines derived from various embryonic origins and somatic cells in pig

Since pluripotent embryonic stem cell (ESC) lines were first derived from the mouse, tremendous efforts have been made to establish ESC lines in several domestic species including the pig; however, authentic porcine ESCs have not yet been established. It has proven difficult to maintain an ESC-like state in pluripotent porcine cell lines due to the frequent occurrence of spontaneous differentiation into an epiblast stem cell (EpiSC)-like state during culture. We have been able to derive EpiSC-like porcine ESC (pESC) lines from blastocyst stage porcine embryos of various origins, including in vitro fertilized (IVF), in vivo derived, IVF aggregated, and parthenogenetic embryos. In addition, we have generated induced pluripotent stem cells (piPSCs) via plasmid transfection of reprogramming factors (Oct4, Sox2, Klf4, and c-Myc) into porcine fibroblast cells. In this study, we analyzed characteristics such as marker expression, pluripotency and the X chromosome inactivation status in female of our EpiSC-like pESC lines along with our piPSC line. Our results show that these cell lines demonstrate the expression of genes associated with the Activin/Nodal and FGF2 pathways along with the expression of pluripotent markers Oct4, Sox2, Nanog, SSEA4, TRA 1–60 and TRA 1–81. Furthermore all of these cell lines showed in vitro differentiation potential, the X chromosome inactivation in female and a normal karyotype. Here we suggest that the porcine species undergoes reprogramming into a primed state during the establishment of pluripotent stem cell lines.

Equine cloning: in vitro and in vivo development of aggregated embryos

The production of cloned equine embryos remains highly inefficient. Embryo aggregation has not yet been tested in the equine, and it might represent an interesting strategy to improve embryo development. This study evaluated the effect of cloned embryo aggregation on in vitro and in vivo equine embryo development. Zona-free reconstructed embryos were individually cultured in microwells (nonaggregated group) or as 2- or 3-embryo aggregates (aggregated groups). For in vitro development, they were cultured until blastocyst stage and then either fixed for Oct-4 immunocytochemical staining or maintained in in vitro culture where blastocyst expansion was measured daily until Day 17 or the day on which they collapsed. For in vivo assays, Day 7-8 blastocysts were transferred to synchronized mares and resultant vesicles, and cloned embryos were measured by ultrasonography. Embryo aggregation improved blastocyst rates on a per well basis, and aggregation did not imply additional oocytes to obtain blastocysts. Embryo aggregation improved embryo quality, nevertheless it did not affect Day 8 and Day 16 blastocyst Oct-4 expression patterns. Equine cloned blastocysts expanded and increased their cell numbers when they were maintained in in vitro culture, describing a particular pattern of embryo growth that was unexpectedly independent of embryo aggregation, as all embryos reached similar size after Day 7. Early pregnancy rates were higher using blastocysts derived from aggregated embryos, and advanced pregnancies as live healthy foals also resulted from aggregated embryos. These results indicate that the strategy of aggregating embryos can improve their development, supporting the establishment of equine cloned pregnancies.

Methylation status of differentially methylated regions at Igf2/H19 locus in porcine gametes and preimplantation embryos

The aim of this study was to demonstrate how differential methylation imprints are established during porcine preimplantation embryo development. For the methylation analysis, the primers for the three Igf2/H19 DMRs were designed and based upon previously published sequences. The methylation marks of Igf2/H19 DMRs were analysed in sperm and MII oocytes with our results showing that these regions are fully methylated in sperm but remain unmethylated in MII oocytes. In order to identify the methylation pattern at the pronuclear stage, we indirectly compared the methylation profile of Igf2/H19 DMR3 in each zygote derived by in vitro fertilization, parthenogenesis, and androgenesis. Interestingly, this region was found to be differently methylated according to parental origins; DMR3 was hemimethylated in in vitro fertilized zygotes, fully methylated in parthenogenetic zygotes, and demethylated in androgenetic zygotes. These results indicate that the methylation mark of the paternal allele is erased by active demethylation, and that of the maternal one is de novo methylated. We further examined the methylation imprints of Igf2/H19 DMR3 during early embryonic development. The hemimethylated pattern as seen in zygotes fertilized in vitro was observed up to the 4-cell embryo stage. However, this mark was exclusively demethylated at the 8-cell stage and then restored at the morula stage. These results suggest that methylation imprints are established via dynamic changes during early embryonic development in porcine embryos.