222 Incomplete Reprogramming of Induced Pluripotent Stem Cells Derived From Porcine Fetal Fibroblasts

Abstract

Cellular reprogramming of committed cells into a pluripotent state can be accomplished by ectopic expression of genes such as OCT4, SOX2, KLF4, and MYC. However, during reprogramming, it has been verified that failures of reactivating endogenous genes and epigenetic remodelling lead to partially reprogrammed cells exhibiting features similar to those of fully reprogrammed cells. In this study, partially reprogrammed induced pluripotent stem cells (pre-iPSC) were derived from porcine fetal fibroblasts via drug-inducible vector carrying human transcription factors (OCT4, SOX2, KLF4, and MYC). Therefore, this study aimed to investigate characteristics of pre-iPSC and reprogramming mechanisms. The pre-iPSC were stably maintained over an extended period having in vitro differentiation ability into 3 germ layers. The pluripotent state of pre-iPSC was regulated by modulation of culture condition. They showed naive- or primed-like pluripotent state in leukemia inhibitory factor (LIF) or basic fibroblast growth factor (bFGF) supplemented culture conditions respectively. However, pre-iPSC could not be maintained without ectopic expression of transgenes. The cultured pre-iPSC expressed endogenous transcription factors (OCT4 and SOX2) except for NANOG known as gateway into complete reprogramming. In addition, endogenous genes related to mesenchymal-to-epithelial transition (DPPA2, CDH1, EPCAM, and OCLN) were not sufficiently reactivated as measured by qPCR. DNA methylation analysis for promoters of OCT4, NANOG, and XIST showed that epigenetic reprogramming did not occurred in female pre-iPSC. Given the results, we found that expression of exogenous genes could not sufficiently activate the essential endogenous genes and remodel the epigenetic milieu for achieving faithful pluripotency in pig. Accordingly, investigating pre-iPSC could help us to improve and develop reprogramming methods via understanding reprogramming mechanisms in pig. This work was supported by the Next-generation BioGreen 21 Program (PJ0113002015), Rural Development Administration, Republic of Korea.