Molecular Roadblocks for Cellular Reprogramming

Institute for Stem Cell Biology and Regenerative Medicine, Department of Pathology, and Cancer Biology Program, Stanford University School of Medicine, 265 Campus Drive, Stanford, CA 94305, USA.
Molecular cell (Impact Factor: 14.46). 09/2012; 47(6):827-38. DOI: 10.1016/j.molcel.2012.09.008
Source: PubMed

ABSTRACT During development, diverse cellular identities are established and maintained in the embryo. Although remarkably robust in vivo, cellular identities can be manipulated using experimental techniques. Lineage reprogramming is an emerging field at the intersection of developmental and stem cell biology in which a somatic cell is stably reprogrammed into a distinct cell type by forced expression of lineage-determining factors. Lineage reprogramming enables the direct conversion of readily available cells from patients (such as skin fibroblasts) into disease-relevant cell types (such as neurons and cardiomyocytes) or into induced pluripotent stem cells. Although remarkable progress has been made in developing novel reprogramming methods, the efficiency and fidelity of reprogramming need to be improved in order increase the experimental and translational utility of reprogrammed cells. Studying the mechanisms that prevent successful reprogramming should allow for improvements in reprogramming methods, which could have significant implications for regenerative medicine and the study of human disease. Furthermore, lineage reprogramming has the potential to become a powerful system for dissecting the mechanisms that underlie cell fate establishment and terminal differentiation processes. In this review, we will discuss how transcription factors interface with the genome and induce changes in cellular identity in the context of development and reprogramming.

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    • "This new direct reprograming method featuring defined factors indicates that transdifferentiation can occur across germ layers. Transdifferentiation can be controlled through epigenetic regulation and gene activation [57], [58]. In 2012, Ladewig et al. reported that inhibiting GSK-3β and SMAD signaling during reprogramming increased the efficiency of human iN generation as well as the purity of the resulting iNs [59]. "
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    ABSTRACT: Wnts were previously shown to regulate the neurogenesis of neural stem or progenitor cells. Here, we explored the underlying molecular mechanisms through which Wnt signaling regulates neurotrophins (NTs) in the NT-induced neuronal differentiation of human mesenchymal stem cells (hMSCs). NTs can increase the expression of Wnt1 and Wnt7a in hMSCs. However, only Wnt7a enables the expression of synapsin-1, a synaptic marker in mature neurons, to be induced and triggers the formation of cholinergic and dopaminergic neurons. Human recombinant (hr)Wnt7a and general neuron makers were positively correlated in a dose- and time-dependent manner. In addition, the expression of synaptic markers and neurites was induced by Wnt7a and lithium, a glycogen synthase kinase-3β inhibitor, in the NT-induced hMSCs via the canonical/β-catenin pathway, but was inhibited by Wnt inhibitors and frizzled-5 (Frz5) blocking antibodies. In addition, hrWnt7a triggered the formation of cholinergic and dopaminergic neurons via the non-canonical/c-jun N-terminal kinase (JNK) pathway, and the formation of these neurons was inhibited by a JNK inhibitor and Frz9 blocking antibodies. In conclusion, hrWnt7a enhances the synthesis of synapse and facilitates neuronal differentiation in hMSCS through various Frz receptors. These mechanisms may be employed widely in the transdifferentiation of other adult stem cells.
    PLoS ONE 08/2014; 9(8):e104937. DOI:10.1371/journal.pone.0104937 · 3.23 Impact Factor
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    • "The transformation of differentiated somatic cells to induced pluripotent cells (iPSCs) has opened a new horizon of regenerative medicine in cell transplantation therapies; however, there are several limitations in using iPSCs as a valuable tool for studying disease modeling. For example, not all clones that appear in the induced process are fully reprogramminged (Hanna et al., 2009; Vierbuchen and Wernig, 2012). In addition , the difficulty of picking clones and the generation of Oct4 promoter–labeled iPSCs are processes that are too expensive for use by researchers. "
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    ABSTRACT: Abstract Induced pluripotent stem cells (iPSCs) are usually generated by reprogramming somatic cells through transduction with a transcription factor cocktail. However, the low efficiency of this procedure has kept iPSCs away from the study of the clinical application of stem cell biology. Our research shows that continuous passage increases the efficiency of reprogramming. Compared with conventional method of establishment of iPSCs, more embryonic stem cell (ESC)-like clones are generated by continuous passage during early reprogramming. These inchoate clones, indistinguishable from genuine ESC clones, are closer to fully reprogrammed cells compared with those derived from classical iPSC induction, which increased the expression of pluripotent gene markers and the levels of demethylation of Oct4 and Nanog. These results suggested that full reprogramming is a gradual process that does not merely end at the point of the activation of endogenous pluripotency-associated genes. Continuous passage could increase the pluripotency of induced cells and accelerate the process of reprogramming by epigenetic modification. In brief, we have provided an advanced strategy to accelerate the reprogramming and generate more nearly fully reprogrammed iPSCs efficiently and rapidly.
    01/2014; DOI:10.1089/cell.2013.0067
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    • "The observed initial mistargeting of the reprogramming factors is a plausible explanation for the low efficiencies and slow kinetics of iPS cell reprogramming. By analogy, it could be assumed that other types of lineage reprogramming also involve transcription factor cooperativity and positive feedback activation (Vierbuchen and Wernig, 2012). "
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    ABSTRACT: Direct lineage reprogramming is a promising approach for human disease modeling and regenerative medicine, with poorly understood mechanisms. Here, we reveal a hierarchical mechanism in the direct conversion of fibroblasts into induced neuronal (iN) cells mediated by the transcription factors Ascl1, Brn2, and Myt1l. Ascl1 acts as an "on-target" pioneer factor by immediately occupying most cognate genomic sites in fibroblasts. In contrast, Brn2 and Myt1l do not access fibroblast chromatin productively on their own; instead, Ascl1 recruits Brn2 to Ascl1 sites genome wide. A unique trivalent chromatin signature in the host cells predicts the permissiveness for Ascl1 pioneering activity among different cell types. Finally, we identified Zfp238 as a key Ascl1 target gene that can partially substitute for Ascl1 during iN cell reprogramming. Thus, a precise match between pioneer factors and the chromatin context at key target genes is determinative for transdifferentiation to neurons and likely other cell types.
    Cell 10/2013; 155(3):621-35. DOI:10.1016/j.cell.2013.09.028 · 33.12 Impact Factor
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