Porcine embryonic stem cells: a possible source for cell replacement therapy.

The development of porcine embryonic stem cell lines (pESC) has received renewed interest given the advances being made in the production of immunocompatible transgenic pigs. However, difficulties are evident in the production of pESCs in-vitro. This may largely be attributable to differences in porcine pre-implantation development compared to the mouse and human. Expression of oct4, nanog and sox2 differs in the zona-enclosed porcine blastocyst compared to its mouse and human counterparts, which may suggest that other factors may be responsible for maintaining porcine pluripotency in the early blastocyst. In addition, the epiblast forms considerably later, at days 7 to 8 when the porcine blastocyst begins to hatch and is maintained for 4 days before completely differentiating. This review covers an outline of the known molecular profile during porcine pre-implantation development and provides a history in the development of putative pESCs to date. Greater knowledge on the molecular mechanisms that underlie porcine pluripotency and pre-implantation development may aid in improving the development of pESCs.