Porcine Embryonic Stem Cells: A Possible Source for Cell Replacement Therapy

Abstract

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.

Overexpression Nanog Activates Pluripotent Genes in Porcine Fetal Fibroblasts and Nuclear Transfer Embryos

“…ESCs have been considered as a useful tool for generating transgenic pig. However, the research of these potential applications progressed slowly, because no authentic porcine ESCs is available to date (Li et al, 2004;Brevini et al, 2007;Kim et al, 2007;Hall, 2008;Kim et al, 2010). Although three groups announced recently they had established iPSCs in pig by introduced human or mouse derived transcriptional factors (Oct4, Sox2, Klf4, and C-myc), none of them successfully applied the iPSCs in generating chimeras, which is the basic standard to define pluripotency (Esteban et al, 2009;Ezashi et al, 2009;Wu et al, 2009).…”

Porcine induced pluripotent stem cells may bridge the gap between mouse and human iPS

“…For example, cardiac valves and insulin have been obtained from them for years (32), and organs from transgenic pigs lacking expression of a(1,3)-galactosyltransferase gene (a major xeno-antigen) have a delayed onset of hyperacute rejection (normally occurring within minutes to hours following transplantation) (33). Pluripotent ESCs have been so far established from mice (1), humans (2), monkeys (34), and more recently rats (35,36).…”

“…Early claims of porcine ESCs were published soon after the isolation of mouse ESCs but those cell lines were characterized using poorly delineated markers. The common problem faced by laboratories worldwide has been that the putative ESCs lose their pluripotency over a relatively short number of passages (32). Unanswered questions are as follows: Have we been choosing the best embryonic stage for isolating ESCs from the developing porcine embryo?…”

“…or What are the signaling pathways that regulate pluripotency in pig and what tissue culture conditions can sustain these pathways in vitro? Regarding the former question, significant differences exist in porcine preimplantation development compared with the mouse and human (32). In pig, the epiblast (from which mouse and human ESCs are obtained) forms considerably later than in other species and is maintained for 4 days before completely differentiating.…”

“…To add further complexity, in the bovine blastocyst (another related ungulate species), expression of SSEA1, SSEA-4, TRA-1-60, and TRA-1-80 are expressed both in the inner mass and trophoectoderm, suggesting that these markers cannot be used to identify bovine ESCs exclusively (42). There is also dispute concerning the topographic and temporal expression of Sox2, Oct4, and Nanog in porcine and bovine blastocysts (32), which may indicate that unidentified transcription factors play a more relevant role in ungulates.…”