Optimization of Culture Conditions for Maintaining Porcine Induced Pluripotent Stem Cells

Ground state porcine induced pluripotent stem cells (piPSCs), which retain the potential to generate chimeric animal and germline transmission, are difficult to produce. This study investigated morphological and biological progression at the early stage of porcine somatic cell reprogramming, and explored suitable conditions to increase the induction efficiency of piPSCs. A cocktail of defined transcription factors was used to generate piPSCs. The amphotropic retrovirus, which carried human OCT4 (O), SOX2 (S), KLF4 (K), C-MYC (M), TERT (T), and GFP, were used to infect porcine embryonic fibroblasts (PEFs). The number of clones derived from OSKM (4F) and OSKMT (4F+T) was significantly higher than that from SKM (3F) and SKMT (3F+T), suggesting that OCT4 played a critical role in regulating porcine cell reprogramming. The number of alkaline phosphatase-positive clones from a medium with leukemia inhibitory factor (LIF) and basic fibroblast growth factor (bFGF) (M1 medium) was significantly higher than that with insulin and 2i PD0325901/CHIR99021 (M2 medium), indicating that insulin and 2i could not effectively maintain piPSC propagation. In the M1 medium, piPSC lines could not maintain the typical self-renewal morphology on gelatin-coated and Matrigel-coated plates. Without the mouse embryonic fibroblast (MEF) feeder, piPSCs started to simultaneously differentiate. Based on the potential for self-renewal and activation of pluripotent markers, we found that the culture condition of 4F+T plus LIF and bFGF plus MEF feeder promoted PEF reprogramming more efficiently than the other conditions tested here. Two piPSC lines (IB-1 and IB-2) were derived and maintained for up to 20 passages in vitro.