An increase in intracellular Ca2+ concentration is essential for oocyte activation. Thus most artificial oocyte-activation methods focus on increasing the Ca2+ concentration in the oocytes. Recently, full-term development was reported in mice when oocytes were activated with no increase in intracellular Ca2+ using the Zn2+ chelator N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN). During oocyte maturation, Zn2+ is responsible for Cdc25c recognition. Once attached, the Cdc25c-zinc complex dephosphorylates maturation-promoting factor (MPF)/cyclin-dependent kinase 1 (cdk1), thus activating the Cdc25c-MPF positive feedback loop and keeping the oocyte suspended in metaphase II. The TPEN can inhibit the Cdc25c-MPF positive feedback loop, indirectly giving TPEN the power to degrade MPF, allowing the oocyte to exit metaphase II. First, we tested if incubation of porcine oocytes with TPEN could induce oocyte activation. Second, we examined whether the combination of TPEN with conventional activation methods could increase the developmental potential of activated oocytes. Last, based on the results, somatic cell nuclear transfer (SCNT) embryos were further activated with the optimum condition of TPEN to produce clones to confirm developmental competence. Frequencies of blastocyst formation were recorded and analysed by using ANOVA following arcsin transformation. Total cell numbers in blastocysts were counted and compared by using the Student's t-test. Differences at P < 0.05 were considered significant. When oocytes were incubated with a high concentration of TPEN (100–250 μM) for 10 to 120 min, blastocyst formation was comparable with conventional activation methods; however, the total cell number in the blastocysts was significantly lower (31.3 ± 3.1 v. 24.8 ± 1.9). When oocytes were activated with conventional methods and then incubated with the high concentration of TPEN, embryo development was drastically decreased; no blastocyst development was achieved from TPEN-treated oocytes. Interestingly, when activated oocytes were incubated with a low concentration of TPEN (5–10 μM), surprisingly, the TPEN-treated group showed higher developmental potential compared with the control group. Specifically, the average percent blastocyst formation of TPEN-treated oocytes (5 μM for 30 min) was 27.2 ± 1.7%, but only 10.6 ± 2.5% developed to blastocyst in the control group. Moreover, the average cell number in blastocysts was significantly higher in TPEN-treated oocytes compared with the control group (33.1 ± 2.6 v. 28.2 ± 2.1, respectively). When 290 chemically activated SCNT embryos were treated with 5 μM TPEN for 30 min and transferred into a surrogate, 2 healthy piglets were born. The results indicate that incubation of oocytes with TPEN alone can activate porcine oocytes. Also, when activated oocytes are incubated with the right concentration of TPEN, it can increase embryo quality in vitro. Embryo transfer results also show that TPEN-incubated SCNT embryos are developmentally competent. Additional studies would guide us to develop more efficient way to use TPEN in the activation of SCNT embryos.

One of the key regulators of gene expression in mammals is DNA methylation. The Tet family (Tet1–3) is suggested to be involved in regulating the level of methylation by hydroxylating a methyl group from 5-methylcytosine to form 5-hydroxymethylcystosine. This hydroxylation alters the 3-dimensional structure of the DNA and results in altered gene expression. Previous studies conducted in the mouse have shown that Tet1 is important for inner cell mass specification by regulating the apparent level of methylation on a specific promoter region in blastocysts and Tet3 is related to the apparent paternal DNA demethylation after fertilization by hydroxylating the paternal genome. The objective of this study was to investigate the expression profile of the Tet family in porcine oocytes and pre-implantation-stage embryos derived from IVF and somatic cell nuclear transfer (SCNT). The RNA was isolated from donor cells, germinal vesicle (GV), MII and 2-cell and blastocyst stage embryos (20 oocytes or embryos per group). Levels of mRNA for each Tet gene were measured by quantitative real-time RT-PCR. The levels of each mRNA transcript were compared to YWHAG, a housekeeping gene that shows a constant level of expression throughout pre-implantation embryo development and normalized to the GV stage. The analysis was repeated with 3 biological replications and 2 experimental replications. Differences in gene expression were compared by ANOVA and P < 0.05 was considered significant. No difference was found in the levels of the Tet family members between GV and MII stage oocytes. Compared with GV stage oocytes, up-regulation of Tet3 at the 2-cell stage was detected in both IVF and SCNT embryos, 4.7 and 6.2 fold, respectively. A dramatic increase in Tet1 was also observed at the blastocyst stage in IVF and SCNT embryos when compared with the GV stage, 65.7 and 79.7 fold increases, respectively. Interestingly, the level of Tet3 was down-regulated in blastocyst embryos at a 25 or more fold decrease compared with GV. The level of Tet2 remained constant throughout embryo development. Embryos (2-cell and blastocyst) compared from IVF and SCNT showed no difference in Tet expression levels. Donor cells had significantly lower levels of Tet2 and Tet3 when compared with GV. Our results indicate that the Tet family shows a dynamic expression profile during porcine pre-implantation embryo development. High expression of Tet3 in 2-cell stage embryos suggests its importance during the post-activation demethylation process. The increase of Tet1 transcript in blastocysts suggests that Tet1 is involved in regulating the type of methylation at the blastocyst stage. These results are consistent with results from previous mouse studies. There was no misregulated expression of the Tet family in SCNT embryos compared with IVF embryos, thus indicating successful reprogramming of the Tet family after SCNT. Lower levels of Tet2 and Tet3 would indicate that Tet1 is important for maintaining type of methylation in donor cells. This is the first report on the profile of the Tet family during porcine pre-implantation embryo development and further studies are needed to clarify their role during this stage.

Skin-derived progenitors (SKP) are capable of generating both neural and mesodermal progeny in vitro: neurons, Schwann cells, adipocytes, osteocytes and chondrocytes, thus exhibiting characteristics similar to embryonic neural crest stem cells. SKP show distinct transcriptional profiles when compared with neurospheres/neural stem cells in the central nervous system (CNS) and skin-derived fibroblasts, indicating a novel type of multipotent stem cell derived from the dermis of the skin. However, it remains unclear whether SKP cells can produce ectoderm and mesoderm lineages or other germ layers in vivo, although oocyte-like structures can be induced from porcine SKP in vitro. Embryonic chimeras are a well-established tool for investigating cell lineage determination and cell potency through normal embryonic development. Thus the purpose of this study was to investigate the in vivo developmental potential of porcine SKP by chimera production. Porcine SKP cells and fibroblasts were isolated from the back skin of Day 35 to 50 GFP transgenic fetuses. Individual cells or clusters of male GFP transgenic SKP and skin-derived GFP-expressing fibroblasts were injected into pre-compact in vitro-fertilized (IVF) embryos, respectively and then transferred into corresponding surrogates 24 h post-injection. Additional injected embryos were cultured in PZM3 medium for another 2 days until the blastocyst stage and subsequently stained with Hoechst 33342. Interestingly, in some of the chimeras the injected SKP cells migrated and dispersed into different locations of the host blastocysts, whereas in others they remained as a cluster of cells within the chimeric blastocysts. In contrast, the fibroblast cells were not observed to spread around the host blastocysts. Two chimeric fetuses were recovered at the middle of gestation and a litter of viable piglets was born. Genomic DNA was extracted from various tissues of chimeric piglets and subjected to PCR amplification. Two chimeric fetuses and 2 out of 6 piglets carried the GFP transgene in SKP-derived chimeras, but GFP was not present in the fibroblast-derived chimeric fetuses (n = 6). Surprisingly, the GFP transgene was present in various tissues of two SKP-derived chimeric piglets, including lung, heart, liver, artery, kidney, brain, skin, muscle, gut, ovary, pancreas and stomach, thus representing the 3 germ layers (ectoderm, mesoderm and endoderm). In addition, SRY was detected in several tissues of the two GFP-positive female chimeric piglets, confirming the chimerism of these piglets. Therefore, it appears that porcine SKP can contribute to various cell types of the 3 germ layers and have a broader developmental potency than previously expected. Alternatively, pre-compact (4-cell and 8-cell stage) embryos may provide a unique environment for reprogramming skin-derived progenitors into a more primitive state by the process of embryonic compaction. This study was funded by NIH National Center for Research Resources (R01RR013438) and Food for the 21st Century at the University of Missouri.

Treatment of reconstructed pig clones with the histone deacetylase inhibitor (HDACi) Scriptaid immediately after nuclear transfer (NT) and activation results in increased cloning efficiency. Aberrant gene expression examined in NT blastocyst stage embryos is only partially corrected by Scriptaid use; therefore, 2 other HDACi were examined in this study including the class I and II HDACi, suberoylanilide hydroxamic acid (SAHA) and its hydrophobic derivative 4-iodo-SAHA (I-SAHA). Blastocyst rates and total cell numbers were examined across 6 treatment groups (1 μM SAHA, 10 μM SAHA, 1 μM I-SAHA, 10 μM I-SAHA, 0.5 μM Scriptaid and no HDACi treatment). Nuclear transfer was performed on enucleated MII oocytes using 3 different cell lines. Clones were electrically fused and activated, treated with HDACi for 14 to 16 h and cultured to the blastocyst stage in PZM3 under low oxygen tension for 7 days. Blastocyst number was calculated from the total number of fused oocytes. Blastocysts were then fixed in 4% paraformaldehyde and total cell number was determined by Hoechst staining of nuclei. The results from all 3 cell lines were pooled and 782 embryos were examined for blastocyst development from 7 replicates. All statistical analysis was performed by SAS 9.1 and means were separated by least significant difference (P < 0.05). The treatment group 10 μM SAHA had the highest blastocyst rate of 41.9% (n = 124) and was significantly different than no HDACi treatment (29.2%, n = 161; P < 0.003). There was no significant difference in blastocyst rates between 1 μM SAHA, 10 μM SAHA, 1 μM I-SAHA and 0.5 μM Scriptaid with blastocyst rates of 31.6% (n = 168), 41.9% (n = 124) 34.2% (n = 76) and 40.2% (n = 179), respectively (P < 0.05). Treatment with 10 μM I-SAHA significantly decreased development when compared with the other HDACi treatments (17.6%, n = 74, P < 0.05). There was no interaction between treatment and cell line for blastocyst rates (P > 0.45). Total cell number was significantly higher in blastocysts from the 1 μM I-SAHA (37.9, n = 20) treatment group when compared with Scriptaid (29.9, n = 50) and no HDACi treatment (29.4, n = 42; P < 0.04). There were no significant improvements in total cell number between the other concentrations (P > 0.05). Additionally, there was also a significant interaction between cell line used for nuclear transfer and the total cell number (P < 0.002). Two treatments were selected to determine if 10 μM SAHA and 1 μM I-SAHA treatment postnuclear transfer was compatible with term development. Six embryo transfers were performed and 5 recipient pigs became pregnant and developed to term. The results of this study show that treatment with the HDACi, SAHA and I-SAHA postnuclear transfer has the same blastocyst rates as the commonly used HDACi, Scriptaid. Additionally, treatment with 1 μM I-SAHA improves total cell number when compared with Scriptaid or no HDACi treatment. Funding was provided by Food for the 21st Century.

There have been significant improvements in the culture of porcine embryos in vitro; however, it is still suboptimal. Improvements in porcine embryo culture would benefit utilisation of porcine embryos for a variety of purposes. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is known to be expressed in the female reproductive tract and the level of its expression is high between conception and implantation. Previous studies show supplementing GM-CSF in embryo culture promotes embryonic development in human and bovine embryos. The aim of this study was to investigate the effect of GM-CSF on the culture of porcine embryos derived from somatic cell nuclear transfer (SCNT) and IVF. Different concentrations of recombinant porcine GM-CSF (0, 2, 10 ng mL–1) were introduced into Porcine Zygote Medium 3 from Day 1 to 6. Frequencies of cleaved embryos and blastocyst formation were recorded and analysed by using ANOVA following arcsin transformation. Total cell number in blastocysts from each group were counted and compared by using the Student's t-test. Differences at P < 0.05 were considered significant. A total of 563 SCNT embryos from 6 different donor cell lines on 11 different days were produced for the study. Incubation of SCNT embryos with GM-CSF did not affect the frequency of cleaved embryos. Frequencies of cleaved embryos in control (0 ng mL–1), 2 ng mL–1 GM-CSF and 10 ng mL–1 GM-CSF were 64.2%, 68.1% and 65.0%, respectively. Interestingly, both concentrations of GM-CSF significantly increased the frequency of blastocyst formation as compared with the control. In 2 ng mL–1 and 10 ng mL–1 of GM-CSF groups, 30.8% and 32.3% of embryos reached blastocyst respectively, whereas only 22.4% of embryos reached blastocyst in the control group. A significant increase in total cell number in blastocysts was observed when GM-CSF was introduced into embryo culture. An average of 28.8 ± 0.9 cells was recorded in the control group, whereas 31.9 ± 1.1 and 31.8 ± 1.1 were observed in 2 ng mL–1 and 10 ng mL–1 of GM-CSF groups, respectively. Similar effects were observed when GM-CSF was introduced to the culture of IVF embryos. For IVF study, 525 embryos were generated on 10 different days and embryos cultured in the presence of GM-CSF tended to show higher blastocyst formation (P = 0.1). Frequencies of blastocyst per cleaved in the 3 groups were 55.7% (control), 65.7% (2 ng mL–1 GM-CSF) and 66.7% (10 ng mL–1 GM-CSF). In addition, culture of IVF embryos with GM-CSF significantly increased total cell number in Day 6 blastocysts. Total cell number in blastocysts in 2 ng mL–1 GM-CSF (34.2 ± 0.8) and 10 ng mL–1 GM-CSF (34.4 ± 1.2) were significantly higher compared with control (27.3 ± 1.2). Our results indicate that introducing GM-CSF into embryo culture media can increase the quality of blastocyst stage embryos. An increase in the frequency of blastocyst formation and total cell number in blastocysts suggests that GM-CSF can be used to produce better-quality embryos in vitro. Currently, effects of GM-CSF on implantation of SCNT embryos are under investigation. Further studies would elucidate the specific mechanism of GM-CSF on porcine embryos.

Somatic cell nuclear transfer (SCNT) efficiency in pigs and other species is still very low. This low efficiency and the occurrence of developmental abnormalities in offspring has been attributed to incomplete or incorrect reprogramming. Cytoplasmic extracts from both mammalian and amphibian oocytes can alter the epigenetic state of mammalian somatic nuclei as well as gene expression to more resemble that of pluripotent cells. Rathbone et al. (2010) has showed that pretreating somatic donor cells with frog oocyte extract (FOE) increased live birth in ovine. Liu et al. (2011) also reported that treating donor cells with FOE enhanced handmade clone embryo development in pigs. The aim of this study was to evaluate the early development of cloned embryos produced with porcine GFP fibroblasts pre-treated with a permeabilizing agent, digitonin and matured frog oocyte extract. Frog egg cytoplasmic extract was prepared from one frog's oocytes after being matured in vitro to MII stage. The experiment included 2 groups. In the FOE-treated group, GFP-tagged fetal fibroblasts were permeabilized by digitonin (15 ng mL–1) and incubated in FOE containing an ATP-regenerating system (2.5 mM ATP, 125 μM GTP, 62.5 μg mL–1 of creatine kinase, 25 mM phosphocreatine and 1 mM NTP) at room temperature (24°C) for 2 h; cell membranes were re-sealed by culturing in 10% FBS in DMEM media for 2.5 h at 38.5°C before used as donor cells. In the control group, the same donor cells were treated with digitonin, but without frog oocyte extract incubation. The SCNT embryos were produced by using the 2 groups of donor cells as described above. In total, 305 control and 492 FOE oocytes were enucleated from 8 biological replicates. Two hundred fifty control and 370 FOE couplets were fused and cultured in porcine zygote medium 3. Percent cleavage was recorded on Day 2 and the percent blastocyst formation was determined on Day 7 (SCNT day = 0). In addition, the number of nuclei in the blastocysts was recorded on Day 7. Percent fusion, cleavage, blastocyst formation and number of nuclei in blastocysts were analysed by using SAS software (v9.2), with day and treatment class as main effects. There was no difference in percent fusion (FOE, 76.2 ± 2.5% vs control, 80.8 ± 2.8%) or in cleavage (FOE: 74.8 ± 2.5% vs control: 74.6 ± 2.9%). Only green blastocysts with 16 or more nuclei were considered to be a true SCNT blastocyst. The percent blastocyst was higher in the FOE group than that in the control (13.9 ± 0.8% vs 9.5 ± 0.9%, P < 0.05), whereas the number of nuclei in the blastocysts was not different between the 2 groups (39.7 ± 2.4, 35.9 ± 3.8 for FOE and control, respectively). In conclusion, our study demonstrated that pre-treatment of donor cells with digitonin and Xenopus MII oocyte extract increased porcine SCNT embryo development to blastocyst and cloning efficiency. Funded by the National Natural Science Foundation of China (NO. 31071311), Natural Science Foundation of Fujian Province of China (No. 2009J06017) and NIH U42 RR18877.