Mechanisms underlying the formation of induced pluripotent stem cells

Abstract

Human pluripotent stem cells (hPSCs) offer unique opportunities for studying human biology, modeling diseases and for therapeutic applications. The simplest approach so far to generate human PSCs lines is through reprogramming of somatic cells from an individual by defined factors, referred to simply as reprogramming. Reprogramming circumvents the ethical issues associated with human embryonic stem cells (hESCs) and nuclear transfer hESCs (nt-hESCs), and the resulting induced pluripotent stem cells (hiPSCs) retain the same basic genetic makeup as the somatic cell used for reprogramming. Since the first report of iPSCs by Takahashi and Yamanaka, the molecular mechanisms of reprogramming have been extensively investigated. A better mechanistic understanding of reprogramming is fundamental not only to iPSC biology and improving the quality of iPSCs for therapeutic use, but also to our understanding of the molecular basis of cell identity, pluripotency and plasticity. Here we summarize the genetic, epigenetic and cellular events during reprogramming, and the roles of various factors identified thus far in the reprogramming process.

Exogenous human OKSM factors maintain pluripotency gene expression of bovine and porcine iPS-like cells obtained with STEMCCA delivery system

“…Moreover, they could not be manually expanded. At this time point, mouse iPSC reach the stabilization phase of the reprogramming process characterized by the independence of exogenous factors and can be expanded without losing the stem cell characteristic morphology [ 23 ]. With this approach, although we achieved a good delivery system, we couldn’t maintain the expression of endogenous pluripotency genes.…”

Ten years of progress and promise of induced pluripotent stem cells: historical origins, characteristics, mechanisms, limitations, and potential applications

“…During the reprogramming process, the epigenetic signature of the somatic cell must be erased to adopt a stem cell-like epigenome. These epigenetic changes include chromatin remodeling, DNA demethylation of promoter regions of pluripotency genes, reactivation of the somatically silenced X chromosome and histone post-translational modifications ( Takahashi et al, 2007 ; Wernig et al, 2007 ; Maherali et al, 2007 ; Fussner et al, 2011 ; Buganim, Faddah & Jaenisch, 2013 ; Gonzalez & Huangfu, 2016 ).…”

“…DNA methylation is an epigenetic barrier of iPSC generation ( Nishino et al, 2011 ; Doege et al, 2012 ; Gao et al, 2013 ). The methylation occurs at the C5 position of cytosine on the target gene promoters in mammalian somatic cells ( Gonzalez & Huangfu, 2016 ). Promoter DNA methylation is inversely associated with gene expression ( Bird, 2002 ).…”

What is a stem cell?

“…A subclass consists of the somatic cell nuclear transfer (SCNT) lines where the embryo was created by SCNT into an oocyte and the resulting embryos are used to establish the cell lines (Tachibana et al, 2013). iPSCs are created by expressing key pluripotency-associated transcription factors in differentiated cell types such as fibroblasts, leukocytes, or epithelial cells (González, Boué, & Belmonte, 2011;González & Huangfu, 2016). The best quality iPSC lines are very similar to ESCs and the best mouse lines can form germ line chimeras when injected in mouse blastocysts, and can even form a complete mouse embryo using the technique of tetraploid complementation (Boland et al, 2009;Zhao et al, 2009).…”