B1 SINE-binding ZFP266 impedes reprogramming through suppression of chromatin opening by pioneering factors

Successful generation of induced pluripotent stem cells (iPSCs) via the overexpression of Oct4 (Pou5f1), Sox2, Klf4 and c-Myc (OSKM) highlights the power of transcription factor (TF)-mediated cellular conversions. Nevertheless, iPSC reprogramming is inherently inefficient and understanding the molecular mechanisms underlying this inefficiency holds the key to control cellular identity successfully. Here, we report 16 novel reprogramming roadblock genes identified by CRISPR/Cas9-mediated genome-wide knockout (KO) screening. Of these, disruption of KRAB zinc finger protein (KRAB-ZFP) Zfp266 strongly and consistently enhanced iPSC generation in several iPSC reprogramming settings, emerging as the most robust roadblock. Further analyses revealed that ZFP266 bound Short Interspersed Nuclear Elements (SINEs) adjacent to OSK binding sites and impedes chromatin opening. This work serves as a resource for better understanding reprogramming mechanisms and proposes SINEs as a critical genetic element that regulates chromatin accessibility at enhancers for efficient pluripotency induction.

Generation of Functional Cardiomyocytes from Human Gastric Fibroblast-Derived Induced Pluripotent Stem Cells

Coronary artery diseases are major problems of the world. Coronary artery disease patients frequently suffer from peptic ulcers when they receive aspirin treatment. For diagnostic and therapeutic purposes, the implementation of panendoscopy (PES) with biopsy is necessary. Some biopsy samples are wasted after the assay is completed. In the present study, we established a protocol for human gastric fibroblast isolation and induced pluripotent stem cell (iPSC) generation from gastric fibroblasts via PES with biopsy. We showed that these iPSCs can be differentiated into functional cardiomyocytes in vitro. To our knowledge, this is the first study to generate iPSCs from gastric fibroblasts in vitro.

AKT signaling is associated with epigenetic reprogramming via the upregulation of TET and its cofactor, alpha-ketoglutarate during iPSC generation

Background Phosphoinositide-3 kinase (PI3K)/AKT signaling participates in cellular proliferation, survival and tumorigenesis. The activation of AKT signaling promotes the cellular reprogramming including generation of induced pluripotent stem cells (iPSCs) and dedifferentiation of primordial germ cells (PGCs). Previous studies suggested that AKT promotes reprogramming by activating proliferation and glycolysis. Here we report a line of evidence that supports the notion that AKT signaling is involved in TET-mediated DNA demethylation during iPSC induction. Methods AKT signaling was activated in mouse embryonic fibroblasts (MEFs) that were transduced with OCT4, SOX2 and KLF4. Multiomics analyses were conducted in this system to examine the effects of AKT activation on cells undergoing reprogramming. Results We revealed that cells undergoing reprogramming with artificially activated AKT exhibit enhanced anabolic glucose metabolism and accordingly increased level of cytosolic α-ketoglutarate (αKG), which is an essential cofactor for the enzymatic activity of the 5-methylcytosine (5mC) dioxygenase TET. Additionally, the level of TET is upregulated. Consistent with the upregulation of αKG production and TET, we observed a genome-wide increase in 5-hydroxymethylcytosine (5hmC), which is an intermediate in DNA demethylation. Moreover, the DNA methylation level of ES-cell super-enhancers of pluripotency-related genes is significantly decreased, leading to the upregulation of associated genes. Finally, the transduction of TET and the administration of cell-permeable αKG to somatic cells synergistically enhance cell reprogramming by Yamanaka factors. Conclusion These results suggest the possibility that the activation of AKT during somatic cell reprogramming promotes epigenetic reprogramming through the hyperactivation of TET at the transcriptional and catalytic levels.

MYCL promotes iPSC-like colony formation via MYC Box 0 and 2 domains

Induced pluripotent stem cells (iPSCs) have the potential to differentiate into any cell in the body and thus have attractive regenerative medicine potential. Current iPSC generation protocols, however, have low efficiency and show variable quality among clones. This variability influences the efficiency and reproducibility of iPSC differentiation. Our previous study reported that MYC proteins (c-MYC and MYCL) are important for the reprogramming efficiency and germline transmission of iPSCs, but that MYCL can generate iPSC colonies more efficiently than c-MYC. However, why c-MYC and MYCL cause different reprogramming efficiencies is unknown. In this study, we found that MYC Box 0 (MB0) and MB2, two functional domains conserved in the MYC protein family, contribute to the phenotypic difference and promote iPSC generation in MYCL-induced reprogramming. Proteome analysis suggested that in MYCL-induced reprogramming, cell adhesion-related cytoskeletal proteins are regulated by the MB0 domain, while RNA processes are regulated by the MB2 domain. These findings provide a molecular explanation for why MYCL has higher reprogramming efficiency than c-MYC.

Application of Modified mRNA in Somatic Reprogramming to Pluripotency and Directed Conversion of Cell Fate

Modified mRNA (modRNA)-based somatic reprogramming is an effective and safe approach that overcomes the genomic mutation risk caused by viral integrative methods. It has improved the disadvantages of conventional mRNA and has better stability and immunogenicity. The modRNA molecules encoding multiple pluripotent factors have been applied successfully in reprogramming somatic cells such as fibroblasts, mesenchymal stem cells, and amniotic fluid stem cells to generate pluripotent stem cells (iPSCs). Moreover, it also can be directly used in the terminal differentiation of stem cells and fibroblasts into functional therapeutic cells, which exhibit great promise in disease modeling, drug screening, cell transplantation therapy, and regenerative medicine. In this review, we summarized the reprogramming applications of modified mRNA in iPSC generation and therapeutic applications of functionally differentiated cells.

iPSC Preparation and Epigenetic Memory: Does the Tissue Origin Matter?

The production of induced pluripotent stem cells (iPSCs) represent a breakthrough in regenerative medicine, providing new opportunities for understanding basic molecular mechanisms of human development and molecular aspects of degenerative diseases. In contrast to human embryonic stem cells (ESCs), iPSCs do not raise any ethical concerns regarding the onset of human personhood. Still, they present some technical issues related to immune rejection after transplantation and potential tumorigenicity, indicating that more steps forward must be completed to use iPSCs as a viable tool for in vivo tissue regeneration. On the other hand, cell source origin may be pivotal to iPSC generation since residual epigenetic memory could influence the iPSC phenotype and transplantation outcome. In this paper, we first review the impact of reprogramming methods and the choice of the tissue of origin on the epigenetic memory of the iPSCs or their differentiated cells. Next, we describe the importance of induction methods to determine the reprogramming efficiency and avoid integration in the host genome that could alter gene expression. Finally, we compare the significance of the tissue of origin and the inter-individual genetic variation modification that has been lightly evaluated so far, but which significantly impacts reprogramming.

Dot1L interaction partner AF10 safeguards cell identity during the acquisition of pluripotency

ABSTRACTHistone-modifying enzymes function as part of protein complexes that alter the accessibility of chromatin to elicit differential gene expression patterns. Dot1L, the sole histone H3 lysine (K) 79 (H3K79) methyltransferase, is associated with proteins that recognize specific histone modifications and target Dot1L to particular chromatin contexts. Here we find that depletion of the Dot1L interacting protein AF10, which recognizes unmodified H3K27, mimics Dot1L catalytic inhibition to increase the efficiency of reprogramming somatic cells to induced pluripotent stem cells (iPSCs). AF10 deletion results in almost no steady state transcriptional changes yet is responsible for half of the Dot1L iPSC reprogramming phenotype. In contrast, reduced levels of Dot1L interactors AF9 and ENL that recognize H3 acetylation decrease iPSC generation. Despite the opposite effects in reprogramming of Dot1L interacting proteins with differing histone reader specificity, we find that the AF10-histone interaction domain is dispensable for increased iPSC generation. Instead, the AF10-Dot1L interaction domain that potentiates H3K79 di- and tri-methylation is a barrier to pluripotency acquisition. Taken together we reveal a key role for higher order gene body histone methylation in safeguarding cell identity.

Identification of potential transcription factors that enhance human iPSC generation

Although many factors have been identified and used to enhance the iPSC reprogramming process, its efficiency remains quite low. In addition, reprogramming efficacy has been evidenced to be affected by disease mutations that are present in patient samples. In this study, using RNA-seq platform we have identified and validated the differential gene expression of five transcription factors (TFs) (GBX2, NANOGP8, SP8, PEG3, and ZIC1) that were associated with a remarkable increase in the number of iPSC colonies generated from a patient with Parkinson's disease. We have applied different bioinformatics tools (Gene ontology, protein–protein interaction, and signaling pathways analyses) to investigate the possible roles of these TFs in pluripotency and developmental process. Interestingly, GBX2, NANOGP8, SP8, PEG3, and ZIC1 were found to play a role in maintaining pluripotency, regulating self-renewal stages, and interacting with other factors that are involved in pluripotency regulation including OCT4, SOX2, NANOG, and KLF4. Therefore, the TFs identified in this study could be used as additional transcription factors that enhance reprogramming efficiency to boost iPSC generation technology.