Abstract
Genetic reprogramming of somatic cells to a pluripotent state (induced pluripotent stem cells or iPSCs) by over-expression of specific genes has been accomplished using mouse and human cells. However, it is still unclear how similar human iPSCs are to human Embryonic Stem Cells (hESCs). Here, we describe the transcriptional profile of human iPSCs generated without viral vectors or genomic insertions, revealing that these cells are in general similar to hESCs but with significant differences. For the generation of human iPSCs without viral vectors or genomic insertions, pluripotent factors Oct4 and Nanog were cloned in episomal vectors and transfected into human fetal neural progenitor cells. The transient expression of these two factors, or from Oct4 alone, resulted in efficient generation of human iPSCs. The reprogramming strategy described here revealed a potential transcriptional signature for human iPSCs yet retaining the gene expression of donor cells in human reprogrammed cells free of viral and transgene interference. Moreover, the episomal reprogramming strategy represents a safe way to generate human iPSCs for clinical purposes and basic research.
Highlights
Genetic reprogramming to a pluripotent state of mouse somatic cells was first achieved by ectopic expression of four factors (Oct4, Sox2, Klf4 and c-Myc) using retroviruses [1]
IPSC colonies with a mature morphology similar to human Embryonic Stem Cells (hESCs) were distinguished from the original neural stem cells (NSCs) population (Fig. 1E–F)
Human induced pluripotent stem cells (iPSCs) were achieved using transient episomal vectors carrying the cDNAs for Oct4 and Nanog in a cell type that was likely more prone to genetic reprogramming, such as NSCs
Summary
Genetic reprogramming to a pluripotent state of mouse somatic cells was first achieved by ectopic expression of four factors (Oct, Sox, Klf and c-Myc) using retroviruses [1] Such cells were named induced pluripotent stem cells (iPSCs). This method was applied to human cells using the same factors or a different combination in a lentivirus vector (Oct, Sox, Lin and Nanog) [2,3,4,5]. Both mouse and human iPSCs are similar to embryonic stem cells (ESCs) with respect to their morphology, cell behavior, gene expression, epigenetic status and differentiation potential both in culture and in vivo. One reason is that the technology used to derived iPSCs is not ‘‘footprint-free’’ and subjected to transcriptional interference
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