Abstract
We investigated whether sequential reprogramming via porcine induced pluripotent stem cells (piPSCs) or exposure to oocyte cytoplasm following nuclear transfer could generate nuclear transfer-derived ESCs (piPSCs-ntESCs). Nuclear transfer embryos were reconstructed with piPSCs possessing a ZsGreen fluorescent marker for expression of exogenous Nanog and Lin28. Reconstructed oocytes developed to morphologically normal 8-cell/morulae (35/93, 37.6%) and blastocysts (12/93, 12.9%). Although most green fluorescent protein-positive blastocysts showed efficient outgrowth (8/10, 80%), none formed primary colonies and all cultures degenerated. Conversely, 15% of fluorescent positive 8-cell/morula stage embryos showed outgrowth (6/40), with three forming primary colonies (7.5%). All three were expanded and maintained as piPSC-ntESC lines. These cell lines expressed stem cell marker genes and proteins. Despite inactivation of one X chromosome, all piPSC-ntESC lines formed teratomas comprising derivatives from all three embryonic germ layers. Strong SSEA1, 3, and 4 expression was detected at the 8-cell/morula stage in embryos reconstructed from both piPSCs and porcine embryonic fibroblasts (PEFs). SSEA3 was notably absent from IVF controls at pre-implantation embryo stages. Finally, we attempted to establish ntESCs from 8-cell/morulae reconstructed with PEFs using the same culture conditions as those for piPSC-ntESC derivation. Although eight primary colonies arose from 107 embryos (7.5%), they all degenerated after the first passage culture. Early and sustained expression of key reprogramming regulatory factors may be critical for pluripotent stem cell derivation to derive piPSC-ntESCs from 8-cell/morula stages, while the expression of SSEAs may be involved in the initial stem cell colony formation phases.