182 Establishment of expanded potential embryonic stem cell lines from porcine embryos
Authors: Nowak-Imialek M. , Gao X. , Liu P. , Niemann H. 
Published: December 2018

The domestic pig is an excellent large animal in biomedical medicine and holds great potential for testing the clinical safety and efficacy of stem cell therapies. Previously, numerous studies reported the derivation of porcine embryonic stem cell (ESC)-like lines, but none of these lines fulfilled the stringent criteria for true pluripotent germline competent ESC. Here, we report the first establishment of porcine expanded potential stem cells (pEPSC) from parthenogenetic and in vivo-derived blastocysts. A total of 12 cell lines from parthenogenetic blastocysts from Day 7 (12/24) and 26 cell lines from in vivo-derived blastocysts from Day 5 (26/27) were established using defined stem cell culture conditions. These cells closely resembled mouse ESC with regard to morphology, formed compact colonies with high nuclear/cytoplasmic ratios, and could be maintained in vitro for more than 40 passages with a normal karyotype. The pEPSC expressed key pluripotency genes, including OCT4, NANOG, SOX2, and SALL4 at similar levels as porcine blastocysts. Immunostaining analysis confirmed expression of critical cell surface markers SSEA-1 and SSEA-4 in pEPSC. The EPSC differentiated in vitro into tissues expressing markers of the 3 germ layers: SOX7, AFP, T, DES, CRABP2, α-SMA, β-tubulin, PAX6, and, notably, the trophoblast markers HAND1, GATA3, PGF, and KRT7. After injection into immunocompromised mice, the pEPSC formed teratomas with derivatives of the 3 germ layers and placental lactogen-1 (PL-1)-positive trophoblast-like cells. Additionally, pEPSC cultured in vitro under conditions specific for germ cells formed embryoid bodies, which contained ~9% primordial germ cell (PGC)-like cells (PGCLC) that expressed PGC-specific genes, including NANOS3, BLIMP1, TFAP2C, CD38, DND1, KIT, and OCT4 as detected by quantitative RT-PCR and immunostaining. Next, we examined the in vivo differentiation potential of pEPSC and injected pEPSC stably expressing the CAG-H2B-mCherry transgene reporter into porcine embryos. The donor cells proliferated and were localised in both the trophectoderm and inner cell mass of the blastocysts cultured in vitro. After transfer to 3 recipient sows, chimeric embryos implanted and a total of 45 fetuses were recovered on Days 26 to 28. Flow cytometry of single cells collected from embryonic and extraembryonic tissues of the fetuses revealed mCherry+ cells in 7 conceptuses, in both the placenta and embryonic tissues; in 3 chimeric conceptuses, mCherry+ cells were exclusively found in embryonic tissues; and in 2 conceptuses, mCherry+ cells were exclusively localised in the placenta. The contribution of the mCherry+ cells was low (0.4-1.7%), but they were found and co-detected in multiple porcine embryonic tissues using tissue lineage-specific markers, including SOX2, TUJ1, GATA4, SOX17, AFP, α-SMA, and trophoblast markers PL-1 and KRT7 in the placental cells. The successful establishment of pEPSC represents a major step forward in stem cell research and provides cell lines with the unique state of cellular potency useful for genetic engineering and unravelling pluripotency regulation in pigs.