Aggregating embryonic but not somatic nuclear transfer embryos increases cloning efficiency in cattle

Oct-4 activating compound 1 (OAC1) could improve the quality of somatic cell nuclear transfer embryos in the bovine

Previous studies described aberrant nuclear reprogramming in somatic cell nuclear transfer (SCNT) embryos that is distinctly different from fertilized embryos. This abnormal nuclear reprogramming hampers the proper pre- and/or post-implantation development. It has been demonstrated that SCNT blastocysts aberrantly expressed POU5F1 and POU5F1-related genes. With regard to this, it has been postulated that promoting the expression of POU5F1 in SCNT embryos may enhance reprogramming in SCNT embryos. In this study, we treated either fibroblast donor cells or SCNT embryos with OAC1 as a novel small molecule that has been reported to induce POU5F1 expression. Quantitative results from the MTS assay revealed that lower concentrations of OAC1 (1, 1.5, and 3 μM) are non-toxic after 2, 4, and 6 days, but higher concentrations (6, 8, 10, and 12 μM) are toxic and reduced the proliferation of cells after 6 days. No enhancement in the expression of endogenous POU5F1 was observed when both mouse and bovine fibroblast cells were treated with 1.5 and 3 μM OAC1 for up to 6 consecutive days. Subsequently, we treated either fibroblast as donor cells in the SCNT procedure (BFF-OAC1 group) or SCNT embryos [for 4 days (IVC-OAC1: D4-D7 group) or 7 days (IVC-OAC1: D0-D7 group)] with 1.5 μM OAC1. We observed that neither treatment of fibroblast donor cells nor SCNT embryos improved the cleavage and blastocyst rates. Interestingly, we observed that treatment of SCNT embryos all throughout the in vitro culture (IVC) (IVC-OAC1: D0-D7) with 1.5 μM OAC1 improves the quality of derived blastocyst which was indexed by morphological grading, blastomere allocation, epigenetic marks and mRNA expression of target genes. In conclusion, our results showed that supplementation of IVC medium with 1.5 μM OAC1 (D0-D7) accelerates SCNT reprogramming in bovine species.

Early Cell Specification in Mammalian Fertilized and Somatic Cell Nuclear Transfer Embryos

Early cell specification in mammalian preimplantation embryos is an intricate cellular process that leads to coordinated spatial and temporal expression of specific genes. Proper segregation into the first two cell lineages, the inner cell mass (ICM) and the trophectoderm (TE), is imperative for developing the embryo proper and the placenta, respectively. Somatic cell nuclear transfer (SCNT) allows the formation of a blastocyst containing both ICM and TE from a differentiated cell nucleus, which means that this differentiated genome must be reprogrammed to a totipotent state. Although blastocysts can be generated efficiently through SCNT, the full-term development of SCNT embryos is impaired mostly due to placental defects. In this review, we examine the early cell fate decisions in fertilized embryos and compare them to observations in SCNT-derived embryos, in order to understand if these processes are affected by SCNT and could be responsible for the low success of reproductive cloning.

Double cytoplast embryonic cloning improves in vitro but not in vivo development from mitotic pluripotent cells in cattle

Cloning multiple animals from genomically selected donor embryos is inefficient but would accelerate genetic gain in dairy cattle breeding. To improve embryo cloning efficiency, we explored the idea that epigenetic reprogramming improves when donor cells are in mitosis. We derived primary cultures from bovine inner cell mass (ICM) cells of in vitro fertilized (IVF) embryos. Cells were grown feeder-free in a chemically defined medium with increased double kinase inhibition (2i⁺). Adding recombinant bovine interleukin 6 to 2i⁺ medium improved plating efficiency, outgrowth expansion, and expression of pluripotency-associated epiblast marker genes (NANOG, FGF4, SOX2, and DPPA3). For genotype multiplication by embryonic cell transfer (ECT) cloning, primary colonies were treated with nocodazole, and single mitotic donors were harvested by mechanical shake-off. Immunofluorescence against phosphorylated histone 3 (P-H3) showed 37% of nocodazole-treated cells in metaphase compared to 6% in DMSO controls (P < 1 × 10⁻⁵), with an average of 53% of P-H3-positive cells expressing the pluripotency marker SOX2. We optimized several parameters (fusion buffer, pronase treatment, and activation timing) for ECT with mitotic embryonic donors. Sequential double cytoplast ECT, whereby another cytoplast was fused to the first cloned reconstruct, doubled cloned blastocyst development and improved morphological embryo quality. However, in situ karyotyping revealed that over 90% of mitotic ECT-derived blastocysts were tetraploid or aneuploid with extra chromosomes, compared to less than 2% in the original ICM donor cells. Following the transfer of single vs. double cytoplast embryos, there was no difference between the two methods in pregnancy establishment at D35 (1/22 = 5% vs. 4/53 = 8% for single vs. double ECT, respectively). Overall, post-implantation development was drastically reduced from embryonic mitotic clones when compared to somatic interphase clones and IVF controls. We conclude that mitotic donors cause ploidy errors during in vitro development that cannot be rescued by enhanced epigenetic reprogramming through double cytoplast cloning.

An electrochemical protocol for CRISPR-mediated gene-editing of sheep embryonic fibroblast cells

Genetic engineering of farm animals is commonly carried out via cell-mediated transfection followed by somatic cell nuclear transfer. However, efficient transfer of exogenous DNA into ovine embryonic fibroblast (EF) cells without compromising cell viability have remained a challenging issue. Here, we aimed to develop a protocol for electrotransfection of sheep EF cells. First, we optimized the pulsing condition using an OptiMEM-GlutaMAX medium as the electroporation buffer and found two pulses of 270 V, each for 10 ms and 10 s interval, is the most efficient condition to have a high rate of transfection and cell survival. Moreover, supplementing 3 % dimethyl sulfoxide (DMSO) into the electroporation medium considerably improved the cell viability after the electroporation process. The electroporation procedure resulted in > 98% transfection efficiency and > 97 % cell survival rate using reporter plasmids. Finally, using CRISPR/Cas9-encoding vectors, we targeted BMP15 and GDF9 genes in sheep EF cells. The electroporated cells are associated with a 52 % indels rate using single gRNAs as well as a highly efficient target deletion using two gRNAs. In conclusion, we developed an electrotransfection protocol using the OptiMEM-GlutaMAX medium supplemented with 3 % DMSO for sheep EF cells. The electroporation method can be used for cell-mediated gene-editing in sheep.

Effect of Embryo Aggregation on In Vitro Development of Adipose-Derived Mesenchymal Stem Cell-Derived Bovine Clones

Somatic cell nuclear transfer (SCNT) is a method with unique ability to reprogram the epigenome of a fully differentiated cell. However, its efficiency remains extremely low. In this work, we assessed and combined two simple strategies to improve the SCNT efficiency in the bovine. These are the use of less-differentiated donor cells to facilitate nuclear reprogramming and the embryo aggregation (EA) strategy that is thought to compensate for aberrant epigenome reprogramming. We carefully assessed the optimal time of EA by using in vitro-fertilized (IVF) embryos and evaluated whether the use of adipose-derived mesenchymal stem cells (ASCs) as donor for SCNT together with EA improves the blastocyst rates and quality. Based on our results, we determined that the EA improves the preimplantation embryo development per well of IVF and SCNT embryos. We also demonstrated that day 0 (D0) is the optimal aggregation time that leads to a single blastocyst with uniform distribution of the original blastomeres. This was confirmed in bovine IVF embryos and then, the optimal condition was translated to SCNT embryos. Notably, the relative expression of the trophectoderm (TE) marker KRT18 was significantly different between aggregated and nonaggregated ASC-derived embryos. In the bovine, no effect of the donor cell is observed on the developmental rate, or the embryo quality. Therefore, no synergistic effect of the use of both strategies is observed. Our results suggest that EA at D0 is a simple and accessible strategy that improves the blastocyst rate per well in bovine SCNT and IVF embryos and influence the expression of a TE-related marker. The aggregation of two ASC-derived embryos seems to positively affect the embryo quality, which may improve the postimplantation development.

Controlled Cytoplast Arrest and Morula Aggregation Enhance Development, Cryoresilience, and In Vivo Survival of Cloned Sheep Embryos

Zona-free somatic cell transfer (SCT) and embryo aggregation increase throughput and efficiency of cloned embryo and offspring production, respectively, but both approaches have not been widely adopted. Cloning efficiency is further improved by cell cycle coordination between the interphase donor cell and metaphase-arrested recipient cytoplast. This commonly involves inclusion of caffeine and omission of calcium to maintain high mitotic cyclin-dependent kinase activity and low calcium levels, respectively, in the nonactivated cytoplast. The aim of our study was to integrate these various methodological improvements into a single work stream that increases sheep cloning success. We show that omitting calcium during zona-free SCT improved blastocyst development from 6% to 13%, while caffeine treatment reduced spontaneous oocyte activation from 17% to 8%. In a retrospective analysis, morula aggregation produced high morphological quality blastocysts with better in vivo survival to term than nonaggregated controls (15% vs. 9%), particularly after vitrification (14% vs. 0%). By combining cytoplast cell cycle control with zona-free embryo reconstruction and aggregation, this novel SCT protocol maximizes the benefits of vitrification by producing more cryoresilient blastocysts. The presented cloning methodology is relatively easy to operate and further increases throughput and efficiency of cloned embryo and offspring production. Integration of additional reprogramming steps or alternate donor cells is straightforward, providing a flexible workflow that can be adapted to changing experimental requirements.

Improves the In Vitro Developmental Competence and Reprogramming Efficiency of Cloned Bovine Embryos by Additional Complimentary Cytoplasm

Somatic cell nuclear transfer (SCNT) is a useful technology; however, its efficiency is low. In this study, we investigated the effects of cytoplasmic transfer into enucleated oocytes on the developmental competence and quality of cloned preimplantation bovine embryos via terminal deoxynucleotidyl transferase dUTP nick-end labeling, quantitative reverse transcription PCR, and immunocytochemistry. We used cytoplasm injection cloning technology (CICT), a new technique via which the cytoplasmic volume of an enucleated oocyte could be restored by injecting ∼30% of the cytoplasm of a donor oocyte. The percentages of embryos that underwent cleavage and formed a blastocyst were significantly higher (p < 0.05) in the CICT group than in the SCNT group (28.9 ± 0.8% vs. 20.2 ± 1.3%, respectively). Furthermore, the total cell number per day 8 blastocyst was significantly higher in the CICT group than in the SCNT group (176.2 ± 6.5 vs. 119.3 ± 7.7, p < 0.05). Moreover, CICT increased mitochondrial activity, as detected using MitoTracker^® Green. The mRNA levels of DNA methyltransferase 1 and DNA methyltransferase 3a were significantly lower (p < 0.05) in the CICT group than in the SCNT group. The mRNA level of DNA methyltransferase 3b was lower in the CICT group than in the SCNT group; however, this difference was not significant (p > 0.05). Taken together, these data suggest that CICT improves the in vitro developmental competence and quality of cloned bovine embryos.

Regulation and safety considerations of somatic cell nuclear transfer-cloned farm animals and their offspring used for food production

This document discusses recent developments in cloning of husbandry animals through somatic cell nuclear transfer, particularly with a view on improvements in their efficacy. Commercial developments in North and South America, Australia-New Zealand, and China are noted. The regulations and safety aspects surrounding the use of clones and their offspring for the purpose of food production are discussed. It is generally considered that foods from offspring of clones are no different than similar foods from conventional animals, yet besides safety, also ethical and animal welfare considerations come into play at the policy level. The related topic of detection and traceability of clones is discussed, which covers both molecular and documentary methods.

Effects of fusion-activation interval and embryo aggregation on in vitro and in vivo development of bovine cloned embryos

Nuclear reprogramming in somatic cell cloning is one of the key factors for proper development, with variations in the protocol appearing to improve cloning efficiency. This study aimed to determine the effects of two fusion-activation intervals and the aggregation of bovine cloned embryos on subsequent in vitro and in vivo development. Zygotes produced by handmade cloning were exposed to two fusion-activation intervals (2 h or 4 h), and then cultured in microwells either individually (1 × 100%) or after aggregation of two structures (2 × 100%). Zona-intact oocytes and zona-free oocytes and hemi-oocytes were used as parthenote controls under the same fusion-activation intervals. Day-7 cloned blastocysts were transferred to synchronous recipients. Cleavage (Day 2), blastocyst (Day 7) and pregnancy (Day 30) rates were compared by the χ² test (P < .05). Extending fusion-activation interval from 2 to 4 h reduced cleavage (91.0 vs. 74.4%) but not blastocyst (34.8 vs. 42.0%) rates. On a microwell basis, cloned embryo aggregation (2 × 100%) increased cleavage (91.5% vs. 74.4%) and blastocyst (46.0% vs. 31.3%) rates compared to controls (1 × 100%), but did not improve the overall embryo production efficiency on Day 7 (23.0% vs. 31.3%), on a per reconstructed embryo basis, respectively. Treatments had no effects on in vitro developmental kinetics, embryo quality, and in vivo development. In summary, the fusion-activation interval and/or the aggregation of cloned bovine embryos did not affect cloning efficiency based on the in vitro development to the blastocyst stage and on pregnancy outcome.

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.

Morphometric developmental pattern of bovine handmade cloned concepti in late pregnancy

Cloning procedures often interfere with conceptus growth and life ex utero, in a set of symptoms known as abnormal offspring syndrome (AOS). The aim of the present study was to compare the developmental pattern of in vivo-derived (IVD), IVF-derived and handmade cloning-derived (NT-HMC) Day 225 bovine concepti using established procedures. Pregnancy diagnosis was performed on Day 30 following blastocyst transfer on Day 7. Conceptus morphometry was assessed by ultrasonography on Day 51, and on Day 225 pregnant cows were killed for morphological examination of concepti. Pregnancy outcome was similar between groups, with greater pregnancy losses in the first trimester (70.6%) and smaller fetuses on Day 51 in the NT-HMC group than in the IVD (14.3%) and IVF (20.0%) groups. However, NT-HMC-derived concepti were twofold larger on Day 225 of gestation than controls. A higher frequency (63.5%) of placentomes larger than the largest in the IVD group was observed in the NT-HMC group, which may be relevant to placental function. Conceptus traits in the IVF group were similar to the IVD controls, with only slight changes in placentome types. Morphological changes in cloned concepti likely affected placental function and metabolism, disrupting the placental constraining mechanism on fetal growth in mid- to late pregnancy.

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.

Signal Inhibition Reveals JAK/STAT3 Pathway as Critical for Bovine Inner Cell Mass Development

The inner cell mass (ICM) of mammalian blastocysts consists of pluripotent epiblast and hypoblast lineages, which develop into embryonic and extraembryonic tissues, respectively. We conducted a chemical screen for regulators of epiblast identity in bovine Day 8 blastocysts. From the morula stage onward, in vitro fertilized embryos were cultured in the presence of cell-permeable small molecules targeting nine principal signaling pathway components, including TGFbeta1, BMP, EGF, VEGF, PDGF, FGF, cAMP, PI3K, and JAK signals. Using 1) blastocyst quality (by morphological grading), 2) cell numbers (by differential stain), and 3) epiblast (FGF4, NANOG) and hypoblast (PDGFRa, SOX17) marker gene expression (by quantitative PCR), we identified positive and negative regulators of ICM development and pluripotency. TGFbeta1, BMP, and cAMP and combined VEGF/PDGF/FGF signals did not affect blastocyst development while PI3K was important for ICM growth but did not alter lineage-specific gene expression. Stimulating cAMP specifically increased NANOG expression, while combined VEGF/PDGF/FGF inhibition up-regulated epiblast and hypoblast markers. The strongest effects were observed by suppressing JAK1/2 signaling with AZD1480. This treatment interfered with ICM formation, but trophectoderm cell numbers and markers (CDX2, KTR8) were not altered. JAK inhibition repressed both epiblast and hypoblast transcripts as well as naive pluripotency-related genes (KLF4, TFCP2L1) and the JAK substrate STAT3. We found that tyrosine (Y) 705-phosphorylated STAT3 (pSTAT3(Y705)) was restricted to ICM nuclei, where it colocalized with SOX2 and NANOG. JAK inhibition abolished this ICM-exclusive pSTAT3(Y705) signal and strongly reduced the number of SOX2-positive nuclei. In conclusion, JAK/STAT3 activation is required for bovine ICM formation and acquisition of naive pluripotency markers.

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.

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.

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.

Expression profile of developmentally important genes between hand-made cloned buffalo embryos produced from reprogramming of donor cell with oocytes extract and selection of recipient cytoplast through brilliant cresyl blue staining and in vitro fertilized embryos

PURPOSE

To compare the expression profile of developmentally important genes between hand-made cloned buffalo embryos produced from reprogramming of donor cell with oocyte extracts and selection of recipient cytoplast through brilliant cresyl blue staining and in vitro fertilized (IVF) embryos.

METHODS

Hand-made cloned embryos were produced using oocyte extracts treated donor cells and brilliant cresyl blue (BCB) stained recipient cytoplasts. IVF embryos were produced by culturing 15-20 COCs in BO capacitated sperms from frozen thawed buffalo semen and the mRNA expression patterns of genes implicated in metabolism (GLUT1), pluripotency (OCT4), DNA methylation (DNMT1), pro- apoptosis (BAX) and anti-apoptosis (BCL2) were evaluated at 8- to16- cell stage embryos.

RESULTS

A significantly (P < 0.05) higher number of 8- to16- cell and blastocyst stages (73.9 %, 32.8 %, respectively) were reported in hand-made cloning (HMC) as compared to in vitro fertilization (49.2 %, 24.2 %, respectively). The amount of RNA recovered from 8- to 16- cell embryos of HMC and in vitro fertilization did not appear to be influenced by the method of embryo generation (3.76 ± 0.61 and 3.82 ± 0.62 ng/μl for HMC and in vitro fertilization embryos, respectively). There were no differences in the expression of the mRNA transcripts of genes (GLUT1, OCT4, DNMT1, BAX and BCL2) were analysed by real-time PCR between hand-made cloned and IVF embryos.

CONCLUSIONS

Pre-treatment of donor cells with oocyte extracts and selection of developmentally competent oocytes through BCB staining for recipient cytoplast preparations may enhance expression of developmentally important genes GLUT1, OCT4, DNMT1, BAX, and BCL2 in hand-made cloned embryos at levels similar to IVF counterparts. These results also support the notion that if developmental differences observed in HMC and in vitro fertilization produced foetuses and neonates are the results of aberrant gene expression during the pre-implantation stage, those differences in expression are subtle or appear after the maternal to zygotic transition stage of development.

Increased MAP kinase inhibition enhances epiblast-specific gene expression in bovine blastocysts

Mammalian blastocysts comprise three distinct lineages, namely, trophoblast, hypoblast, and epiblast, which develop into fetal placenta, extraembryonic yolk sac, and embryo proper, respectively. Pluripotent embryonic stem cells, capable of forming all adult cell types, can only be derived from the epiblast. In mouse and rat, this process is promoted by the double inhibition (2i) of mitogen-activated protein kinase kinase (MAP2K), which antagonizes FGF signaling, and glycogen synthase kinase 3 (GSK3), which stimulates the WNT pathway. We investigated variations of the 2i treatment on lineage segregation and pluripotency-related gene expression in bovine blastocysts. In vitro-fertilized embryos were cultured either in the presence of inhibitors of GSK3 (3 μM CHIR) and MAP2K (0.4 vs. 10 μM PD0325901, designated 2i and 2i+, respectively) or in 2i/2i+ with FGFR inhibitor (0.1 μM PD173074, designated 3i [2i and PD173074] and 3i+ [2i+ and PD173074]). Compared with 2i, both 2i+ and 3i+ potentiated the improvement in blastocyst morphology. Using an automated platform for multiplexed digital mRNA profiling, we simultaneously counted transcripts of 76 candidate genes in bovine blastocysts treated with multiple kinase inhibitors. We show that 2i+ medium specifically increased FGF4 and NANOG while reducing PDGFRalpha and SOX17 levels. The shift from a hypoblast to an epiblast gene expression signature was confirmed by quantitative PCR. A wide range of functionally related genes, including candidates involved in DNA methylation, were not significantly changed. This well-defined 2i+ effect was not observed after pharmacologically inhibiting FGF receptor or related MAP kinases (p38, JNK, and ERK5). In summary, our data suggest that increased MAP2K inhibition exerts its pluripotency-promoting effects through as yet unidentified signals.

Developmental potential and kinetics of pig embryos with different cytoplasmic volume

The effects of cytoplasmic volumes on development and developmental kinetics of in vitro produced porcine embryos were investigated. During hand-made cloning (HMC), selected cytoplasts were separated into two groups according to their size in relation to the initial oocyte: ~75% or ~50%. Following two fusion steps and activation (day 0), reconstructed embryos were cultured in vitro for 6 days. Cleavage rates on day 2 as well as blastocyst rates and cell numbers on day 6 were recorded. Results showed that embryo development was no different for ~50% versus ~75% cytoplasm at first fusion. This result was used in the following experiments, where the effect of varying cytoplasm volume in second fusion to obtain a final cytoplasm volume of ~75% to ~200% was tested. The results showed that the lowest quality was obtained when the final cytoplasm volume was ~75% and the highest quality at ~200% of the original oocyte. Similar results were observed in parthenogenetic (PA) embryos activated with different cytoplasmic volumes. A common pattern for the developmental kinetics of HMC and PA embryos was observed: the smaller group tended to have a longer time for the first two cell cycles, but subsequently a shorter time to form morula and blastocyst. In conclusion, the developmental kinetics of in vitro produced embryos was affected by the cytoplasm volume of the initial oocyte, and this further accounted for the developmental ability of the reconstructed embryos.

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.

Exposure to DNA is insufficient for in vitro transgenesis of live bovine sperm and embryos

Transgenic mammals have been produced using sperm as vectors for exogenous DNA (sperm-mediated gene transfer (SMGT)) in combination with artificial insemination. Our study evaluated whether SMGT could also be achieved in combination with IVF to efficiently produce transgenic bovine embryos. We assessed binding and uptake of fluorescently labelled plasmids into sperm in the presence of different concentrations of dimethyl sulphoxide or lipofectamine. Live motile sperm displayed a characteristic punctuate fluorescence pattern across their entire surface, while uniform postacrosomal fluorescence was only apparent in dead sperm. Association with sperm or lipofection reagent protected exogenous DNA from DNase I digestion. Following IVF, presence and expression of episomal and non-episomal green fluorescent protein (GFP)-reporter plasmids was monitored in oocytes and embryos. We found no evidence of intracellular plasmid uptake and none of the resulting zygotes (n=96) and blastocysts were GFP positive by fluorescence microscopy or genomic PCR (n=751). When individual zona-free oocytes were matured, fertilised and continuously cultured in the presence of episomal reporter plasmids until the blastocyst stage, most embryos (38/68=56%) were associated with the exogenous DNA. Using anti-GFP immunocytochemistry (n=48) or GFP fluorescence (n=94), no GFP expression was detected in blastocysts. By contrast, ICSI resulted in 18% of embryos expressing the GFP reporter. In summary, exposure to DNA was an inefficient technique to produce transgenic bovine sperm or blastocysts in vitro.

A virus-free poly-promoter vector induces pluripotency in quiescent bovine cells under chemically defined conditions of dual kinase inhibition

Authentic induced pluripotent stem cells (iPSCs), capable of giving rise to all cell types of an adult animal, are currently only available in mouse. Here, we report the first generation of bovine iPSC-like cells following transfection with a novel virus-free poly-promoter vector. This vector contains the bovine cDNAs for OCT4, SOX2, KLF4 and c-MYC, each controlled by its own independent promoter. Bovine fibroblasts were cultured without feeders in a chemically defined medium containing leukaemia inhibitory factor (LIF) and inhibitors of MEK1/2 and glycogen synthase kinase-3 signaling (‘2i’). Non-invasive real-time kinetic profiling revealed a different response of bovine vs human and mouse cells to culture in 2i/LIF. In bovine, 2i was necessary and sufficient to induce the appearance of tightly packed alkaline phosphatase-positive iPSC-like colonies. These colonies formed in the absence of DNA synthesis and did not expand after passaging. Following transfection, non-proliferative primary colonies expressed discriminatory markers of pluripotency, including endogenous iPSC factors, CDH1, DPPA3, NANOG, SOCS3, ZFP42, telomerase activity, Tra-1-60/81 and SSEA-3/4, but not SSEA-1. This indicates that they had initiated a self-sustaining pluripotency programme. Bovine iPSC-like cells maintained a normal karyotype and differentiated into derivatives of all three germ layers in vitro and in teratomas. Our study demonstrates that conversion into induced pluripotency can occur in quiescent cells, following a previously undescribed route of direct cell reprogramming. This identifies a major species-specific barrier for generating iPSCs and provides a chemically defined screening platform for factors that induce proliferation and maintain pluripotency of embryo-derived pluripotent stem cells in livestock.

Production of bovine hand-made cloned embryos by zygote-oocyte cytoplasmic hemi-complementation

The aim of this study was to evaluate the effect of the cytoplast type and activation process on development of cloned embryos. Bovine oocytes (MII) or zygotes at the one-cell stage (IVF) were manually bisected and segregated in MII or IVF hemi-cytoplasts or hemi-karyoplasts. Adult skin cells from a bovine female were used as nucleus donors (SC). Experimental groups were composed of IVF embryos; parthenogenetic embryos; hand-made cloned (HMC) embryos; and reconstructed HMC embryos using IVF hemi-cytoplast + MII hemi-cytoplast + SC (G-I); IVF hemi-cytoplast + IVF hemi-cytoplast + SC (G-II); MII hemi-cytoplast + IVF hemi-karyoplast (G-III); and IVF hemi-cytoplast + IVF hemi-karyoplast (G-IV). Embryos from G-I to G-IV were allocated to subgroups as sperm-activated (SA) or were further chemically activated (SA + CA). Embryos from all groups and subgroups were in vitro cultured in the WOW system. Blastocyst development in subgroup G-I SA (28.2%) was similar to IVF (27.0%) and HMC (31.4%) controls, perhaps due to a to a more suitable activation process and/or better complementation of cytoplasmic reprogramming factors, with the other groups and subgroups having lower levels of development. No blastocyst development was observed when using IVF hemi-karyoplasts (G-III and G-IV), possibly due to the manipulation process during a sensitive biological period. In summary, the presence of cytoplasmic factors from MII hemi-oocytes and the sperm activation process from hemi-zygotes appear to be necessary for adequate in vitro development, as only the zygote-oocyte hemi-complementation was as efficient as controls for the generation of bovine cloned blastocysts.

Effect of microinjection of a single IVF-derived blastomere on the development of cloned embryos at the eight-cell stage in bovine

This study was conducted to determine the effect of microinjection of a single blastomere from in vitro fertilization (IVF)-derived eight-cell embryo into eight-cell cloned embryos harboring the gene encoding recombinant human lactoferrin (rhLF), GFP, and NEO markers in bovine. The reconstructed chimeric embryos were assessed for their development to blastocyst, or to term after transfer, and tissues of offspring were evaluated by polymerase chain reaction (PCR) for the presence of nuclear transfer (NT)-derived transgenic cells, and the cloned embryos without microinjection were used as controls. The chimeric embryos showed slightly higher blastocyst rate than that for controls. The single IVF-derived blastomere appeared to preferential contribute to inner cell mass (ICM) in the chimeric blastocysts. After transfer, the rates of development of chimeric embryos to day 60, to term, and to weaning were significantly higher than those of controls. Sixty-three chimeric blastocysts were transferred and 11 calves were born: 7 calves of them were dead, and the remaining 4 calves are apparently normal and healthy. Most of the tissues collected from dead fetus were transgenic, whereas NT-derived transgenic cells were not detected in some tissues of the living calves. Our results indicated that a single blastomere from IVF-derived eight-cell embryo improves the in vivo developmental potential of transgenic cloned eight-cell embryos in bovine; however, the single IVF-derived blastomere appears to be better able to populate the ICM and many tissues of offspring than NT-derived blastomeres.

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.

DNA methylation patterns in tissues from mid-gestation bovine foetuses produced by somatic cell nuclear transfer show subtle abnormalities in nuclear reprogramming

BACKGROUND

Cloning of cattle by somatic cell nuclear transfer (SCNT) is associated with a high incidence of pregnancy failure characterized by abnormal placental and foetal development. These abnormalities are thought to be due, in part, to incomplete re-setting of the epigenetic state of DNA in the donor somatic cell nucleus to a state that is capable of driving embryonic and foetal development to completion. Here, we tested the hypothesis that DNA methylation patterns were not appropriately established during nuclear reprogramming following SCNT. A panel of imprinted, non-imprinted genes and satellite repeat sequences was examined in tissues collected from viable and failing mid-gestation SCNT foetuses and compared with similar tissues from gestation-matched normal foetuses generated by artificial insemination (AI).

RESULTS

Most of the genomic regions examined in tissues from viable and failing SCNT foetuses had DNA methylation patterns similar to those in comparable tissues from AI controls. However, statistically significant differences were found between SCNT and AI at specific CpG sites in some regions of the genome, particularly those associated with SNRPN and KCNQ1OT1, which tended to be hypomethylated in SCNT tissues. There was a high degree of variation between individuals in methylation levels at almost every CpG site in these two regions, even in AI controls. In other genomic regions, methylation levels at specific CpG sites were tightly controlled with little variation between individuals. Only one site (HAND1) showed a tissue-specific pattern of DNA methylation. Overall, DNA methylation patterns in tissues of failing foetuses were similar to apparently viable SCNT foetuses, although there were individuals showing extreme deviant patterns.

CONCLUSION

These results show that SCNT foetuses that had developed to mid-gestation had largely undergone nuclear reprogramming and that the epigenetic signature at this stage was not a good predictor of whether the foetus would develop to term or not.

Developmental potential of bovine hand-made clone embryos reconstructed by aggregation or fusion with distinct cytoplasmic volumes

Animal cloning has been associated with developmental abnormalities, with the level of heteroplasmy caused by the procedure being one of its potential limiting factors. The aim of this study was to determine the effect of the fusion of hemicytoplasts or aggregation of hemiembryos, varying the final cytoplasmic volume, on development and cell density of embryos produced by hand-made cloning (HMC), parthenogenesis or by in vitro fertilization (IVF). One or two enucleated hemicytoplasts were paired and fused with one skin somatic cell. Activated clone and zona-free parthenote embryos and hemiembryos were in vitro cultured in the well-of-the-well (WOW) system, being allocated to one of six experimental groups, on a per WOW basis: single clone or parthenote hemiembryos (1 x 50%); aggregation of two (2 x 50%), three (3 x 50%), or four (4 x 50%) clone or parthenote hemiembryos; single clone or parthenote embryos (1 x 100%); or aggregation of two clone or parthenote embryos (2 x 100%). Control zona-intact parthenote or IVF embryos were in vitro cultured in four-well dishes. Results indicated that the increase in the number of aggregated structures within each WOW was followed by a linear increase in cleavage, blastocyst rate, and cell density. The increase in cytoplasmic volume, either by fusion or by aggregation, had a positive effect on embryo development, supporting the establishment of pregnancies and the birth of a viable clone calf after transfer to recipients. However, embryo aggregation did not improve development on a hemicytoplast basis, except for the aggregation of two clone embryos.

Cloning from stem cells: different lineages, different species, same story

Following nuclear transfer (NT), the most stringent measure of extensive donor cell reprogramming is development into viable offspring. This is referred to as cloning efficiency and quantified as the proportion of cloned embryos transferred into surrogate mothers that survive into adulthood. Cloning efficiency depends on the ability of the enucleated recipient cell to carry out the reprogramming reactions (‘reprogramming ability’) and the ability of the nuclear donor cell to be reprogrammed (‘reprogrammability’). It has been postulated that reprogrammability of the somatic donor cell epigenome is inversely proportional to its differentiation status. In order to test this hypothesis, reprogrammability was compared between undifferentiated stem cells and their differentiated isogenic progeny. In the mouse, cells of divergent differentiation status from the neuronal, haematopoietic and skin epithelial lineage were tested. In cattle and deer, skeletal muscle and antler cells, respectively, were used as donors. No conclusive correlation between differentiation status and cloning efficiency was found, indicating that somatic donor cell type may not be the limiting factor for cloning success. This may reflect technical limitations of the NT-induced reprogramming assay. Alternatively, differentiation status and reprogrammability may be unrelated, making all cells equally difficult to reprogramme once they have left the ground state of pluripotency.

Climbing Mount Efficiency--small steps, not giant leaps towards higher cloning success in farm animals

Despite more than a decade of research efforts, farm animal cloning by somatic cell nuclear transfer (SCNT) is still frustratingly inefficient. Inefficiency manifests itself at different levels, which are currently not well integrated. At the molecular level, it leads to widespread genetic, epigenetic and transcriptional aberrations in cloned embryos. At the organismal level, these genome-wide abnormalities compromise development of cloned foetuses and offspring. Specific molecular defects need to be causally linked to specific cloned phenotypes, in order to design specific treatments to correct them. Cloning efficiency depends on the ability of the nuclear donor cell to be fully reprogrammed into an embryonic state and the ability of the enucleated recipient cell to carry out the reprogramming reactions. It has been postulated that reprogrammability of the somatic donor cell epigenome is influenced by its differentiation status. However, direct comparisons between cells of divergent differentiation status within several somatic lineages have found no conclusive evidence for this. Choosing somatic stem cells as donors has not improved cloning efficiency, indicating that donor cell type may be less critical for cloning success. Different recipient cells, on the other hand, vary in their reprogramming ability. In bovine, using zygotes instead of oocytes has increased cloning success. Other improvements in livestock cloning efficiency include better coordinating donor cell type with cell cycle stage and aggregating cloned embryos. In the future, it will be important to demonstrate if these small increases at every step are cumulative, adding up to an integrated cloning protocol with greatly improved efficiency.

Epigenetic regulation of foetal development in nuclear transfer animal models

Somatic cell nuclear transfer (SCNT, 'cloning') holds great potential for agricultural applications, generation of medical model animals, transgenic farm animals or by 'therapeutic cloning' for generating human embryonic stem cells for the treatment of human diseases. However, the low survival rate of SCNT-derived pregnancies represents a serious limitation of the current technology. In order to overcome this hurdle, a deeper understanding of the epigenetic reprogramming of the somatic cell nuclei and its effect on the pregnancy is needed. Here we review the literature on nuclear reprogramming by SCNT, including studies of gene expression, DNA methylation, chromatin remodelling, genomic imprinting and X chromosome inactivation. Reprogramming of genes expressed in the inner cell mass, from which the body of the foetus is formed, seems to be highly efficient. Defects in the extra-embryonic tissues are probably the major cause of the low success rate of reproductive cloning. Methods to partially overcome such problems exist, yet more future research is needed to find practical and efficient methods to remedy this problem. Improvement of the survival of foetuses is a central issue for the future of agricultural SCNT not only for its economic viability, but also because in lack of improvements in animal welfare current regulations can block the use of the method in the EU and several other countries.

Aggregation of bovine cloned embryos at the four-cell stage stimulated gene expression and in vitro embryo development

Pre-implantation embryos produced by somatic cell nuclear transfer (SCNT) have varied developmental potentials. The majority of SCNT blastocysts do not develop to term, and the mechanisms inhibiting development are still largely unknown. Aggregation of cloned embryos has been attempted to compensate for the developmental deficiency of individual cloned embryos. In this report, we investigated the impact of aggregation of bovine cloned embryos at the four-cell stage on in vitro development and gene expression of the embryos. Cell numbers and development rate of aggregated (NTagg) and non-aggregated (NT) blastocysts were characterized and compared. The blastocyst formation after aggregation was modeled using the binominal distribution. The results indicate that aggregation enhances the blastocyst formation but does not increase the overall blastocyst rate. Additionally, utilizing microarray gene chip analysis 8.8% of 8,059 genes analyzed were differentially expressed between NTagg and NT blastocysts, with more than 80% of the differentially expressed genes up-regulated in the NTagg blastocysts. Up-regulated genes include those involved in transcription, biosynthesis and signaling such as TDGF1, HNFA, CAV1, GLU5, and CD81. Our results indicate that aggregation of bovine cloned embryos at an early stage promotes the in vitro development of the resulting pre-implantation embryos.

Regulation of blastocyst stage gene expression and outgrowth interferon tau activity of somatic cell clone aggregates

The inefficiency of mammalian somatic cell cloning is associated with abnormal gene expression presumably caused by errors in reprogramming of the transplanted genome. In the mouse, aggregation of four-cell stage clones leads to an improvement of both gene expression and development. To determine whether clone-clone aggregation at postgenomic activation stages influences gene expression in bovine clones, we profiled, in single and aggregated embryos at the blastocyst stage, expression of developmentally relevant genes namely Oct4, Dnmt1, Dnmt3, Glut1, Glut3, and a housekeeping gene, Poly(A) polymerase (PolyA) by real-time RT-PCR. Compared to embryos generated by in vitro fertilization (IVF), individual clones more frequently exhibited transcript levels that were more than twofold higher or lower than the average value of IVF embryos. This was observed less often in clone aggregates for Oct4, Dnmt1, Dnmt3, and PolyA, but not for Glut1 and Glut3. The analysis of interferon tau bioactivity as a marker of trophectoderm function in blastocyst outgrowths showed that both single clones and clone aggregates have less extraembryonic potential in vitro compared to IVF embryos, with no apparent consequence of aggregation. These findings indicate that aggregation of bovine clones with each other at later cleavage stages can change gene expression patterns at preimplantation stages, but does not rescue trophectoderm function in vitro.

Global gene expression analysis of bovine blastocysts produced by multiple methods

Reproductive efficiency using somatic cell nuclear transfer (SCNT) technology remains suboptimal. Of the various efforts to improve the efficiency, chromatin transfer (CT) and clone-clone aggregation (NTagg) have been reported to produce live cloned animals. To better understand the molecular mechanisms of somatic cell reprogramming during SCNT and assess the various SCNT methods on the molecular level, we performed gene expression analysis on bovine blastocysts produced via standard nuclear transfer (NT), CT, NTagg, in vitro fertilization (IVF), and artificial insemination (AI), as well as on somatic donor cells, using bovine genome arrays. The expression profiles of SCNT (NT, CT, NTagg) embryos were compared with IVF and AI embryos as well as donor cells. NT and CT embryos have indistinguishable gene expression patterns. In comparison to IVF or AI embryos, the number of differentially expressed genes in NTagg embryos is significantly higher than in NT and CT embryos. Genes that were differentially expressed between all the SCNT embryos and IVF or AI embryos are identified. Compared to AI embryos, more than half of the genes found deregulated between SCNT and AI embryos appear to be the result of in vitro culture alone. The results indicate that although SCNT methods have altered differentiated somatic nuclei gene expression to more closely resemble that of embryonic nuclei, combination of insufficient reprogramming and in vitro culture condition compromise the developmental potential of SCNT embryos. This is the first set of comprehensive data for analyzing the molecular impact of various nuclear transfer methods on bovine pre-implantation embryos.

Cattle Cloned from Increasingly Differentiated Muscle Cells1

It has been postulated that mammalian nuclear transfer (NT) cloning efficiency is inversely correlated with donor cell differentiation status. To test this hypothesis, we compared genetically identical and increasingly differentiated donors within the myogenic lineage. Bovine male fetal muscle cells were cultured for 1-6 days in vitro. The proportion of cells displaying the following antigens was quantified by immunofluorescence microscopy: MYOD1, MYF5, PAX7, MYOG, DES, MYH, and 5-Bromo-2-deoxyuridine. Based on the antigen profile of both bulk populations and individually size-selected cells prepared for NT, donors serum-starved for 1, 4, and 5 days were classified as myogenic precursors (MPCs), myotubes (MTs), and muscle-derived fibroblasts (MFs) with purities of 92%, 85%, and 99%, respectively. Expression of the following transcripts was measured by RT-PCR in 1) cells selected for NT, 2) metaphase II oocytes, 3) NT couplets, 4) NT reconstructs, 5) NT two-cell embryos, and 6) NT blastocysts: MYOD1, MYF5, PAX7, MYOG, MYF6, ACTB, and 18S rRNA. Muscle-specific genes were silenced and remained undetectable up to the blastocyst stage, whereas housekeeping genes 18S and ACTB continued to be expressed. Differentiation status affected development to transferable embryos (118 [23%] of 520 vs. 93 [11%] of 873 vs. 66 [38%] of 174 for MPC vs. MT vs. MF, respectively, P < 0.001). However, there were no significant differences in pregnancy rate and development to weaning between the cell types (pregnancy rate: 14 [64%] of 22 vs. 8 [35%] of 23 vs. 10 [45%] of 22, and development: 4 [18%] of 22 vs. 2 [9%] of 23 vs. 3 [14%] of 22 for MPC vs. MT vs. MF, respectively).

Red Deer Cloned from Antler Stem Cells and Their Differentiated Progeny1

The significance of donor cell differentiation status for successful cloning by somatic cell nuclear transfer (SCNT) is unclear. Here, we cloned a new species, red deer (Cervus elaphus), from multipotent antler stem cells and their differentiated progeny. Cultured donor cell lines from male antlerogenic periosteum (AP) were left undifferentiated or chemically induced to initiate osteogenesis or adipogenesis. Based on their morphology and marker gene expression profile, donor cells were classified as undifferentiated AP cells, presumptive osteoblasts, or adipocytes. Adipocytes upregulated adipogenic markers procollagen type I alpha 2 (COL1A2), peroxisome proliferator-activated receptor gamma 2 (PPARG), and gylceraldehyde-3-phosphate dehydrogenase (GAPDH), and downregulated antlerogenic transcripts POU-domain class 5 transcription factor (POU5F1) and parathyroid hormone (PTH)-like hormone (PTHLH). Despite differences prior to NT, transcript abundance of donor-specific markers COL1A2, PPARG, GAPDH, and POU5F1 did not differ significantly in cloned blastocysts (P = 0.10, 0.50, 0.61, and 0.16, respectively). However, donor cell and blastocyst expression levels were completely different for most genes analyzed, indicating their successful reprogramming. The type of donor cell used for NT (AP, bone, and fat cells), had no effect on in vitro development to blastocysts (93 [38%] of 248 vs. 32 [44%] of 73 vs. 59 [32%] of 183, respectively). Likewise, development to weaning was not significantly different between the three cell types (2 [4%] of 46 vs. 2 [29%] of 7 vs. 4 [13%] of 31, for AP vs. bone vs. fat, respectively). Microsatellite DNA analysis confirmed that the eight cloned red deer calves were genetically identical to the cells used for NT.