Isolation and characterization of trophoblast-derived stem-like cells from peri-implantation porcine embryos

In mammals, the trophoblast lineage of the embryo is specified before attachment/implantation to become the fetal portion of the placenta. Trophoblast-derived cells were isolated and cultured from day 10 and day 13 porcine embryos and were grown in vitro in a defined, serum-free culture medium for over 2 years without showing any signs of senescence. However, trophoblast-derived cells placed into serum-containing medium rapidly senesce and fail to proliferate. Semiquantitative and quantitative gene expression analyses of cells in culture from 0 to 30 days confirmed the presence (and relative abundance) of mRNA transcripts from genes involved in trophoblast function (CDX2, TEAD4, CYP17A1, HSD17B1, FGFR2, PLET, HAND1) as well as some genes known to mediate pluripotency (POU5F1, KLF4, CMYC). Protein immunolocalization demonstrated expression of both trophoblast and mesenchymal cell markers. DNA methylation patterns in promoters of three critical developmental genes (HAND1, KLF4, TEAD4) did not change appreciably over 4 months of culture in vitro. It was demonstrated that these trophoblast-derived cells are easily stably transfected with an exogenous transgene (eGFP) by a variety of methods, and show the ability to survive and to be passaged repeatedly after transfection. In summary, early embryonic porcine trophoblast-derived cells have demonstrated unique characteristics, which means they could be used as valuable tools for laboratory work. Anticipated applications include the study of trophoblast physiology as well as possible solutions for improving efficiency of transgenesis by somatic cell nuclear transfer and for pluripotency reprogramming of cells.