Evaluation of porcine stem cell competence for somatic cell nuclear transfer and production of cloned animals

Molecular Mechanisms of Somatic Cell Cloning and Other Assisted Reproductive Technologies in Mammals: Which Determinants Have Been Unraveled Thus Far?-Current Status, Further Progress and Future Challenges

Taking into consideration recent reports on the successful creation of cloned rhesus monkeys [...].

Stem Cells as Nuclear Donors for Mammalian Cloning

Mammals are routinely cloned by introducing somatic nuclei into enucleated oocytes. Cloning contributes to propagating desired animals, to germplasm conservation efforts, among other applications. A challenge to more broader use of this technology is the relatively low cloning efficiency, which inversely correlates with donor cell differentiation status. Emerging evidence suggests that adult multipotent stem cells improve cloning efficiency, while the greater potential of embryonic stem cells for cloning remains restricted to the mouse. The derivation of pluripotent or totipotent stem cells from livestock and wild species and their association with modulators of epigenetic marks in donor cells should increase cloning efficiency.

OCT6 inhibits differentiation of porcine-induced pluripotent stem cells through MAPK and PI3K signaling regulation

As a transcription factor of the Pit-Oct-Unc (POU) domain family, octamer-binding transcription factor 6 ( OCT6) participates in various aspects of stem cell development and differentiation. At present, however, its role in porcine-induced pluripotent stem cells (piPSCs) remains unclear. Here, we explored the function of OCT6 in piPSCs. We found that piPSCs overexpressing OCT6 maintained colony morphology and pluripotency under differentiation conditions, with a similar gene expression pattern to that of non-differentiated piPSCs. Functional analysis revealed that OCT6 attenuated the adverse effects of extracellular signal-regulated kinase (ERK) signaling pathway inhibition on piPSC pluripotency by activating phosphatidylinositol 3-kinase-protein kinase B (PI3K-AKT) signaling activity. Our research sheds new light on the mechanism by which OCT6 promotes PSC maintenance.

A Dystrophin Exon-52 Deleted Miniature Pig Model of Duchenne Muscular Dystrophy and Evaluation of Exon Skipping

Duchenne muscular dystrophy (DMD) is a lethal X-linked recessive disorder caused by mutations in the DMD gene and the subsequent lack of dystrophin protein. Recently, phosphorodiamidate morpholino oligomer (PMO)-antisense oligonucleotides (ASOs) targeting exon 51 or 53 to reestablish the DMD reading frame have received regulatory approval as commercially available drugs. However, their applicability and efficacy remain limited to particular patients. Large animal models and exon skipping evaluation are essential to facilitate ASO development together with a deeper understanding of dystrophinopathies. Using recombinant adeno-associated virus-mediated gene targeting and somatic cell nuclear transfer, we generated a Yucatan miniature pig model of DMD with an exon 52 deletion mutation equivalent to one of the most common mutations seen in patients. Exon 52-deleted mRNA expression and dystrophin deficiency were confirmed in the skeletal and cardiac muscles of DMD pigs. Accordingly, dystrophin-associated proteins failed to be recruited to the sarcolemma. The DMD pigs manifested early disease onset with severe bodywide skeletal muscle degeneration and with poor growth accompanied by a physical abnormality, but with no obvious cardiac phenotype. We also demonstrated that in primary DMD pig skeletal muscle cells, the genetically engineered exon-52 deleted pig DMD gene enables the evaluation of exon 51 or 53 skipping with PMO and its advanced technology, peptide-conjugated PMO. The results show that the DMD pigs developed here can be an appropriate large animal model for evaluating in vivo exon skipping efficacy.

FGF2 Signaling Plays an Important Role in Maintaining Pluripotent State of Pig Embryonic Germ Cells

Germ cells are alternative sources for deriving pluripotent stem cells. Because embryonic germ cells (EGCs) possess physiological and developmental features similar to those of embryonic stem cells, pig EGCs are considered a potential tool for generating transgenic animals for agricultural usage. Therefore, in this study, we attempted to establish and characterize pig EGCs from fetal gonads. EGC lines were derived from the genital ridges of porcine fetuses in media containing leukemia inhibitory factor (LIF), fibroblast growth factor 2 (FGF2), and stem cell factor. After establishment, these cells were cultured and stabilized in LIF- or FGF2-containing media. The cell lines were maintained under both conditions over an extended time period and spontaneously differentiated into the three germ layers in vitro. Interestingly, expression of pluripotency markers showed different patterns between cell lines cultured in LIF or FGF2. SSEA4 was only expressed in FGF2-treated pig EGCs (FGF2-pEGCs), not LIF-treated pig EGCs (LIF-pEGCs). Pluripotency genes were upregulated in FGF2-pEGCs, and germline markers were highly expressed, indicating that FGF2 supplements are more efficient in supporting the pluripotency of pEGCs. In conclusion, we verified that FGF2 signaling plays an important role in reprogramming and maintaining pEGCs from fetal gonads.

Bone marrow mesenchymal stem cells as nuclear donors improve viability and health of cloned horses

Introduction

Cell plasticity is crucial in cloning to allow an efficient nuclear reprogramming and healthy offspring. Hence, cells with high plasticity, such as multipotent mesenchymal stem cells (MSCs), may be a promising alternative for horse cloning. In this study, we evaluated the use of bone marrow-MSCs (BM-MSCs) as nuclear donors in horse cloning, and we compared the in vitro and in vivo embryo development with respect to fibroblasts.

Materials and methods

Zona-free nuclear transfer was performed using BM-MSCs (MSC group, n=3432) or adult fibroblasts (AF group, n=4527). Embryos produced by artificial insemination (AI) recovered by uterine flushing and transferred to recipient mares were used as controls (AI group).

Results

Blastocyst development was higher in the MSC group than in the AF group (18.1% vs 10.9%, respectively; p<0.05). However, pregnancy rates and delivery rates were similar in both cloning groups, although they were lower than in the AI group (pregnancy rates: 17.7% [41/232] for MSC, 12.5% [37/297] for AF and 80.7% [71/88] for AI; delivery rates: 56.8% [21/37], 41.5% [17/41] and 90.1% [64/71], respectively). Remarkably, the gestation length of the AF group was significantly longer than the control (361.7±10.9 vs 333.9±8.7 days), in contrast to the MSC group (340.6±8.89 days). Of the total deliveries, 95.2% (20/21) of the MSC-foals were viable, compared to 52.9% (9/17) of the AF-foals (p<0.05). In addition, the AF-foals had more physiological abnormalities at birth than the MSC-foals; 90.5% (19/21) of the MSC-delivered foals were completely normal and healthy, compared to 35.3% (6/17) in the AF group. The abnormalities included flexural or angular limb deformities, umbilical cord enlargement, placental alterations and signs of syndrome of neonatal maladjustment, which were treated in most cases.

Conclusion

In summary, we obtained 29 viable cloned foals and found that MSCs are suitable donor cells in horse cloning. Even more, these cells could be more efficiently reprogrammed compared to fibroblasts.