Intervention with metabolites emulating endogenous cell transitions accelerates muscle regeneration in young and aged mice

Tissue regeneration following an injury requires dynamic cell-state transitions that allow for establishing the cell identities required for the restoration of tissue homeostasis and function. Here, we present a biochemical intervention that induces an intermediate cell state mirroring a transition identified during normal differentiation of myoblasts and other multipotent and pluripotent cells to mature cells. When applied in somatic differentiated cells, the intervention, composed of one-carbon metabolites, reduces some dedifferentiation markers without losing the lineage identity, thus inducing limited reprogramming into a more flexible cell state. Moreover, the intervention enabled accelerated repair after muscle injury in young and aged mice. Overall, our study uncovers a conserved biochemical transitional phase that enhances cellular plasticity in vivo and hints at potential and scalable biochemical interventions of use in regenerative medicine and rejuvenation interventions that may be more tractable than genetic ones.

The circadian clock CRY1 regulates pluripotent stem cell identity and somatic cell reprogramming

Distinct metabolic conditions rewire circadian-clock-controlled signaling pathways leading to the de novo construction of signal transduction networks. However, it remains unclear whether metabolic hallmarks unique to pluripotent stem cells (PSCs) are connected to clock functions. Reprogramming somatic cells to a pluripotent state, here we highlighted non-canonical functions of the circadian repressor CRY1 specific to PSCs. Metabolic reprogramming, including AMPK inactivation and SREBP1 activation, was coupled with the accumulation of CRY1 in PSCs. Functional assays verified that CRY1 is required for the maintenance of self-renewal capacity, colony organization, and metabolic signatures. Genome-wide occupancy of CRY1 identified CRY1-regulatory genes enriched in development and differentiation in PSCs, albeit not somatic cells. Last, cells lacking CRY1 exhibit differential gene expression profiles during induced PSC (iPSC) reprogramming, resulting in impaired iPSC reprogramming efficiency. Collectively, these results suggest the functional implication of CRY1 in pluripotent reprogramming and ontogenesis, thereby dictating PSC identity.

Transgenerational inheritance of acquired epigenetic signatures at CpG islands in mice

Transgenerational epigenetic inheritance in mammals remains a debated subject. Here, we demonstrate that DNA methylation of promoter-associated CpG islands (CGIs) can be transmitted from parents to their offspring in mice. We generated DNA methylation-edited mouse embryonic stem cells (ESCs), in which CGIs of two metabolism-related genes, the Ankyrin repeat domain 26 and the low-density lipoprotein receptor, were specifically methylated and silenced. DNA methylation-edited mice generated by microinjection of the methylated ESCs exhibited abnormal metabolic phenotypes. Acquired methylation of the targeted CGI and the phenotypic traits were maintained and transmitted across multiple generations. The heritable CGI methylation was subjected to reprogramming in parental PGCs and subsequently reestablished in the next generation at post-implantation stages. These observations provide a concrete step toward demonstrating transgenerational epigenetic inheritance in mammals, which may have implications in our understanding of evolutionary biology as well as the etiology, diagnosis, and prevention of non-genetically inherited human diseases.

Wiskott-Aldrich syndrome protein forms nuclear condensates and regulates alternative splicing

The diverse functions of WASP, the deficiency of which causes Wiskott-Aldrich syndrome (WAS), remain poorly defined. We generated three isogenic WAS models using patient induced pluripotent stem cells and genome editing. These models recapitulated WAS phenotypes and revealed that WASP deficiency causes an upregulation of numerous RNA splicing factors and widespread altered splicing. Loss of WASP binding to splicing factor gene promoters frequently leads to aberrant epigenetic activation. WASP interacts with dozens of nuclear speckle constituents and constrains SRSF2 mobility. Using an optogenetic system, we showed that WASP forms phase-separated condensates that encompasses SRSF2, nascent RNA and active Pol II. The role of WASP in gene body condensates is corroborated by ChIPseq and RIPseq. Together our data reveal that WASP is a nexus regulator of RNA splicing that controls the transcription of splicing factors epigenetically and the dynamics of the splicing machinery through liquid-liquid phase separation.

In vivo partial cellular reprogramming enhances liver plasticity and regeneration

Mammals have limited regenerative capacity, whereas some vertebrates, like fish and salamanders, are able to regenerate their organs efficiently. The regeneration in these species depends on cell dedifferentiation followed by proliferation. We generate a mouse model that enables the inducible expression of the four Yamanaka factors (Oct-3/4, Sox2, Klf4, and c-Myc, or 4F) specifically in hepatocytes. Transient in vivo 4F expression induces partial reprogramming of adult hepatocytes to a progenitor state and concomitantly increases cell proliferation. This is indicated by reduced expression of differentiated hepatic-lineage markers, an increase in markers of proliferation and chromatin modifiers, global changes in DNA accessibility, and an acquisition of liver stem and progenitor cell markers. Functionally, short-term expression of 4F enhances liver regenerative capacity through topoisomerase2-mediated partial reprogramming. Our results reveal that liver-specific 4F expression in vivo induces cellular plasticity and counteracts liver failure, suggesting that partial reprogramming may represent an avenue for enhancing tissue regeneration.

Myc Supports Self-Renewal of Basal Cells in the Esophageal Epithelium

It is widely believed that cellular senescence plays a critical role in both aging and cancer, and that senescence is a fundamental, permanent growth arrest that somatic cells cannot avoid. Here we show that Myc plays an important role in self-renewal of esophageal epithelial cells, contributing to their resistance to cellular senescence. Myc is homogeneously expressed in basal cells of the esophageal epithelium and Myc positively regulates their self-renewal by maintaining their undifferentiated state. Indeed, Myc knockout induced a loss of the undifferentiated state of esophageal epithelial cells resulting in cellular senescence while forced MYC expression promoted oncogenic cell proliferation. A superoxide scavenger counteracted Myc knockout-induced senescence, therefore suggesting that a mitochondrial superoxide takes part in inducing senescence. Taken together, these analyses reveal extremely low levels of cellular senescence and senescence-associated phenotypes in the esophageal epithelium, as well as a critical role for Myc in self-renewal of basal cells in this organ. This provides new avenues for studying and understanding the links between stemness and resistance to cellular senescence.

In vivo partial reprogramming alters age-associated molecular changes during physiological aging in mice

Partial reprogramming by expression of reprogramming factors (Oct4, Sox2, Klf4 and c-Myc) for short periods of time restores a youthful epigenetic signature to aging cells and extends the life span of a premature aging mouse model. However, the effects of longer-term partial reprogramming in physiologically aging wild-type mice are unknown. Here, we performed various long-term partial reprogramming regimens, including different onset timings, during physiological aging. Long-term partial reprogramming lead to rejuvenating effects in different tissues, such as the kidney and skin, and at the organismal level; duration of the treatment determined the extent of the beneficial effects. The rejuvenating effects were associated with a reversion of the epigenetic clock and metabolic and transcriptomic changes, including reduced expression of genes involved in the inflammation, senescence and stress response pathways. Overall, our observations indicate that partial reprogramming protocols can be designed to be safe and effective in preventing age-related physiological changes. We further conclude that longer-term partial reprogramming regimens are more effective in delaying aging phenotypes than short-term reprogramming.

Precise in vivo genome editing via single homology arm donor mediated intron-targeting gene integration for genetic disease correction

In vivo genome editing represents a powerful strategy for both understanding basic biology and treating inherited diseases. However, it remains a challenge to develop universal and efficient in vivo genome-editing tools for tissues that comprise diverse cell types in either a dividing or non-dividing state. Here, we describe a versatile in vivo gene knock-in methodology that enables the targeting of a broad range of mutations and cell types through the insertion of a minigene at an intron of the target gene locus using an intracellularly linearized single homology arm donor. As a proof-of-concept, we focused on a mouse model of premature-aging caused by a dominant point mutation, which is difficult to repair using existing in vivo genome-editing tools. Systemic treatment using our new method ameliorated aging-associated phenotypes and extended animal lifespan, thus highlighting the potential of this methodology for a broad range of in vivo genome-editing applications.

Mutations in foregut SOX2+ cells induce efficient proliferation via CXCR2 pathway

Identification of the precise molecular pathways involved in oncogene-induced transformation may help us gain a better understanding of tumor initiation and promotion. Here, we demonstrate that SOX2⁺ foregut epithelial cells are prone to oncogenic transformation upon mutagenic insults, such as Kras^G12D and p53 deletion. GFP-based lineage-tracing experiments indicate that SOX2⁺ cells are the cells-of-origin of esophagus and stomach hyperplasia. Our observations indicate distinct roles for oncogenic KRAS mutation and P53 deletion. p53 homozygous deletion is required for the acquisition of an invasive potential, and Kras^G12D expression, but not p53 deletion, suffices for tumor formation. Global gene expression analysis reveals secreting factors upregulated in the hyperplasia induced by oncogenic KRAS and highlights a crucial role for the CXCR2 pathway in driving hyperplasia. Collectively, the array of genetic models presented here demonstrate that stratified epithelial cells are susceptible to oncogenic insults, which may lead to a better understanding of tumor initiation and aid in the design of new cancer therapeutics.

In vivo reprogramming of wound-resident cells generates skin epithelial tissue

Large cutaneous ulcers are, in severe cases, life threatening^1,2. As the global population ages, non-healing ulcers are becoming increasingly common^1,2. Treatment currently requires the transplantation of pre-existing epithelial components, such as skin grafts, or therapy using cultured cells². Here we develop alternative supplies of epidermal coverage for the treatment of these kinds of wounds. We generated expandable epithelial tissues using in vivo reprogramming of wound-resident mesenchymal cells. Transduction of four transcription factors that specify the skin-cell lineage enabled efficient and rapid de novo epithelialization from the surface of cutaneous ulcers in mice. Our findings may provide a new therapeutic avenue for treating skin wounds and could be extended to other disease situations in which tissue homeostasis and repair are impaired.

Abstract 1990: Aberrant cell surface expression of GRP78 in breast cancer cells marks a stem-like population that has increased metastatic potential in vivo

Reliable approaches to identify and target stem-cell mechanisms that mediate aggressive cancer could have great therapeutic value, based on the growing evidence of embryonic signatures in metastatic cancers. However, how to best identify and target stem-like mechanisms aberrantly utilized by cancer cells has been challenging. We harnessed the power of induced pluripotent stem cells (iPSCs) to identify embryonic mechanisms exploited by cancer. A screen comparing the cell surface proteome of iPSCs and breast cancer cells identified GRP78, a heat shock protein that is normally ER-restricted, but has been shown to be aberrantly expressed on the cell surface of several cancers, where it can act as a signaling molecule by poorly understood mechanisms. Although cell surface GRP78 (sGRP78) has emerged as an attractive chemotherapeutic target, understanding how sGRP78 is functioning in cancer has been complicated by the fact that GRP78 can function to regulate a variety of cellular responses, using a diverse array of reported binding partners, which can vary by cell type. Therefore, without insight into the specific GRP78-dependent mechanisms that are responsible for mediating aggressive cancer, it will be difficult to determine how to best target GRP78. We have discovered that (1) sGRP78 is expressed on iPSCs (but not their somatic parental populations) and plays an important role in reprogramming, (2) sGRP78 promotes cellular functions such as proliferation/survival and migration in both stem cells and breast cancer cells (3) overexpression of GRP78 in breast cancer cells leads to an induction of a previously established CD24-/CD44+ 'cancer stem cell' (CSC) population (4) sGRP78+ breast cancer cell populations are enriched for genes involved in stemness and appear to be a subset of previously established CSCs (5) sGRP78+ breast cancer cell populations show a significantly enhanced ability to seed metastatic organ sites in vivo (6) GRP78 interacts with Dermcidin (DCD) at the cell surface of cancer cells and iPSCs, where it is important in regulating stem cell and cancer cell migration and survival/proliferation. These collective findings suggest that sGRP78 marks a stem-like population in breast cancer cells that has increased metastatic potential in vivo, and that sGRP78 and DCD cooperate to regulate key cellular functions important in mediating tumorigenesis. Overall, this work has implications for understanding how cancer cells exploit embryonic-like mechanisms, which could provide novel strategies for chemotherapeutic targeting of aggressive breast cancer cell populations.

Citation Format: Tyson W. Lager, Henry C. Conner, Ian H. Guldner, Michael Z. Wu, Yuriko Hishida, Tomoaki Hishida, Sergio Ruiz, Amanda E. Yamasaki, Juan Carlos Izpisua Belmonte, Peter C. Gray, Jonathan A. Kelber, Siyuan Zhang, Athanasia D. Panopoulos. Aberrant cell surface expression of GRP78 in breast cancer cells marks a stem-like population that has increased metastatic potential in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1990.

Integration of CpG-free DNA induces de novo methylation of CpG islands in pluripotent stem cells

CpG islands (CGIs) are primarily promoter-associated genomic regions and are mostly unmethylated within highly methylated mammalian genomes. The mechanisms by which CGIs are protected from de novo methylation remain elusive. Here we show that insertion of CpG-free DNA into targeted CGIs induces de novo methylation of the entire CGI in human pluripotent stem cells (PSCs). The methylation status is stably maintained even after CpG-free DNA removal, extensive passaging, and differentiation. By targeting the DNA mismatch repair gene MLH1 CGI, we could generate a PSC model of a cancer-related epimutation. Furthermore, we successfully corrected aberrant imprinting in induced PSCs derived from an Angelman syndrome patient. Our results provide insights into how CpG-free DNA induces de novo CGI methylation and broaden the application of targeted epigenome editing for a better understanding of human development and disease.

In Vivo Amelioration of Age-Associated Hallmarks by Partial Reprogramming

Aging is the major risk factor for many human diseases. In vitro studies have demonstrated that cellular reprogramming to pluripotency reverses cellular age, but alteration of the aging process through reprogramming has not been directly demonstrated in vivo. Here, we report that partial reprogramming by short-term cyclic expression of Oct4, Sox2, Klf4, and c-Myc (OSKM) ameliorates cellular and physiological hallmarks of aging and prolongs lifespan in a mouse model of premature aging. Similarly, expression of OSKM in vivo improves recovery from metabolic disease and muscle injury in older wild-type mice. The amelioration of age-associated phenotypes by epigenetic remodeling during cellular reprogramming highlights the role of epigenetic dysregulation as a driver of mammalian aging. Establishing in vivo platforms to modulate age-associated epigenetic marks may provide further insights into the biology of aging.

Interspecies Chimerism with Mammalian Pluripotent Stem Cells

Interspecies blastocyst complementation enables organ-specific enrichment of xenogenic pluripotent stem cell (PSC) derivatives. Here, we establish a versatile blastocyst complementation platform based on CRISPR-Cas9-mediated zygote genome editing and show enrichment of rat PSC-derivatives in several tissues of gene-edited organogenesis-disabled mice. Besides gaining insights into species evolution, embryogenesis, and human disease, interspecies blastocyst complementation might allow human organ generation in animals whose organ size, anatomy, and physiology are closer to humans. To date, however, whether human PSCs (hPSCs) can contribute to chimera formation in non-rodent species remains unknown. We systematically evaluate the chimeric competency of several types of hPSCs using a more diversified clade of mammals, the ungulates. We find that naïve hPSCs robustly engraft in both pig and cattle pre-implantation blastocysts but show limited contribution to post-implantation pig embryos. Instead, an intermediate hPSC type exhibits higher degree of chimerism and is able to generate differentiated progenies in post-implantation pig embryos.

In vivo genome editing via CRISPR/Cas9 mediated homology-independent targeted integration

Targeted genome editing via engineered nucleases is an exciting area of biomedical research and holds potential for clinical applications. Despite rapid advances in the field, in vivo targeted transgene integration is still infeasible because current tools are inefficient, especially for non-dividing cells, which compose most adult tissues. This poses a barrier for uncovering fundamental biological principles and developing treatments for a broad range of genetic disorders. Based on clustered regularly interspaced short palindromic repeat/Cas9 (CRISPR/Cas9) technology, here we devise a homology-independent targeted integration (HITI) strategy, which allows for robust DNA knock-in in both dividing and non-dividing cells in vitro and, more importantly, in vivo (for example, in neurons of postnatal mammals). As a proof of concept of its therapeutic potential, we demonstrate the efficacy of HITI in improving visual function using a rat model of the retinal degeneration condition retinitis pigmentosa. The HITI method presented here establishes new avenues for basic research and targeted gene therapies.

Loss of MAX results in meiotic entry in mouse embryonic and germline stem cells

Meiosis is a unique process that allows the generation of reproductive cells. It remains largely unknown how meiosis is initiated in germ cells and why non-germline cells do not undergo meiosis. We previously demonstrated that knockdown of Max expression, a gene encoding a partner of MYC family proteins, strongly activates expression of germ cell-related genes in ESCs. Here we find that complete ablation of Max expression in ESCs results in profound cytological changes reminiscent of cells undergoing meiotic cell division. Furthermore, our analyses uncovers that Max expression is transiently attenuated in germ cells undergoing meiosis in vivo and its forced reduction induces meiosis-like cytological changes in cultured germline stem cells. Mechanistically, Max depletion alterations are, in part, due to impairment of the function of an atypical PRC1 complex (PRC1.6), in which MAX is one of the components. Our data highlight MAX as a new regulator of meiotic onset.

The mechanisms that trigger meiosis in germ cells and halt this process in non-germline cells are unclear. Here, the authors show that knockout of Max in embryonic stem cells results in meiotic onset in a mechanism that involves the PRC1 complex.

Establishment of human iPSC-based models for the study and targeting of glioma initiating cells

Glioma tumour-initiating cells (GTICs) can originate upon the transformation of neural progenitor cells (NPCs). Studies on GTICs have focused on primary tumours from which GTICs could be isolated and the use of human embryonic material. Recently, the somatic genomic landscape of human gliomas has been reported. RTK (receptor tyrosine kinase) and p53 signalling were found dysregulated in ∼90% and 86% of all primary tumours analysed, respectively. Here we report on the use of human-induced pluripotent stem cells (hiPSCs) for modelling gliomagenesis. Dysregulation of RTK and p53 signalling in hiPSC-derived NPCs (iNPCs) recapitulates GTIC properties in vitro. In vivo transplantation of transformed iNPCs leads to highly aggressive tumours containing undifferentiated stem cells and their differentiated derivatives. Metabolic modulation compromises GTIC viability. Last, screening of 101 anti-cancer compounds identifies three molecules specifically targeting transformed iNPCs and primary GTICs. Together, our results highlight the potential of hiPSCs for studying human tumourigenesis.

Glioma can originate from the transformation of neural progenitor cells into glioma initiating cells. Here, the authors demonstrate the use of induced pluripotent stem cells as a suitable model for generating neural progenitor cells, which can be subsequently transformed to glioma initiating cells that are able to the generate human glioma-like tumours in mice.

Identification of novel long noncoding RNAs underlying vertebrate cardiovascular development

BACKGROUND

Long noncoding RNAs (lncRNAs) have emerged as critical epigenetic regulators with important functions in development and disease. Here, we sought to identify and functionally characterize novel lncRNAs critical for vertebrate development.

METHODS AND RESULTS

By relying on human pluripotent stem cell differentiation models, we investigated lncRNAs differentially regulated at key steps during human cardiovascular development with a special focus on vascular endothelial cells. RNA sequencing led to the generation of large data sets that serve as a gene expression roadmap highlighting gene expression changes during human pluripotent cell differentiation. Stage-specific analyses led to the identification of 3 previously uncharacterized lncRNAs, TERMINATOR, ALIEN, and PUNISHER, specifically expressed in undifferentiated pluripotent stem cells, cardiovascular progenitors, and differentiated endothelial cells, respectively. Functional characterization, including localization studies, dynamic expression analyses, epigenetic modification monitoring, and knockdown experiments in lower vertebrates, as well as murine embryos and human cells, confirmed a critical role for each lncRNA specific for each analyzed developmental stage.

CONCLUSIONS

We have identified and functionally characterized 3 novel lncRNAs involved in vertebrate and human cardiovascular development, and we provide a comprehensive transcriptomic roadmap that sheds new light on the molecular mechanisms underlying human embryonic development, mesodermal commitment, and cardiovascular specification.

In vivo activation of a conserved microRNA program induces mammalian heart regeneration

Heart failure is a leading cause of mortality and morbidity in the developed world, partly because mammals lack the ability to regenerate heart tissue. Whether this is due to evolutionary loss of regenerative mechanisms present in other organisms or to an inability to activate such mechanisms is currently unclear. Here we decipher mechanisms underlying heart regeneration in adult zebrafish and show that the molecular regulators of this response are conserved in mammals. We identified miR-99/100 and Let-7a/c and their protein targets smarca5 and fntb as critical regulators of cardiomyocyte dedifferentiation and heart regeneration in zebrafish. Although human and murine adult cardiomyocytes fail to elicit an endogenous regenerative response after myocardial infarction, we show that in vivo manipulation of this molecular machinery in mice results in cardiomyocyte dedifferentiation and improved heart functionality after injury. These data provide a proof of concept for identifying and activating conserved molecular programs to regenerate the damaged heart.

Abstract 1932: Parallel functions of the endoplasmic reticulum chaperone protein GRP78 in tumorigenesis and the induction of pluripotency

Increasing evidence supports the concept that instances of cancer recurrence may be due to a subpopulation of cells within a tumor that behave as stem cells. Previous studies have demonstrated that pathways critical in oncogenesis parallel those necessary for the induction of pluripotency, suggesting that similar mechanisms regulate both processes. By therefore understanding the mechanisms that govern reprogramming, we may gain insight into the methods by which cancer cells acquire and exploit stem cell properties, and enable more strategic targeting of these cell populations to prevent malignant relapse. Members of the TGF-beta superfamily (e.g. activin/Nodal), which regulate many important normal cellular responses including cell growth and differentiation, have also been shown to promote tumorigenesis. Cripto, a regulator of TGF-beta superfamily ligand signaling expressed on human embryonic stem cells, is overexpressed in many types of cancer, and has also been shown to promote tumor growth and metastasis. Previous work has demonstrated that Cripto regulates TGF-beta function in tumor cell lines by forming a complex with GRP78, a protein generally restricted to the endoplasmic reticulum in normal tissues, but expressed at the cell surface in many types of tumors. Targeting GRP78 in mouse models suppresses tumor growth, and cell surface GRP78 has been shown to be a molecular target on human tumor samples. Although these studies have suggested an important role for GRP78 in promoting tumorigenesis, the mechanisms are not yet fully understood. We have discovered that GRP78 expression is induced during reprogramming, and becomes localized to the cell surface in pluripotent cells, where it co-localizes with Cripto. Overexpression of GRP78 in somatic cells induced their reprogramming efficiency. We further found that a GRP78 antibody, that disrupts cell surface GRP78/Cripto binding and Cripto-mediated TGF-beta superfamily signaling, inhibited reprogramming. Treatment of pluripotent stem cell populations with this GRP78 antibody also decreased proliferation, but did not impact pluripotency. These combined findings suggest that GRP78 may be localized to the cell surface during reprogramming where it functions to inhibit TGF-beta signaling and promote stem cell proliferation and/or survival. Interestingly, overexpression of GRP78 in human breast cancer cell lines caused an increased resistance to cisplatin. Furthermore, inhibiting cell surface function of GRP78 in these breast cancer lines resulted in a higher susceptibility to cisplatin treatment, demonstrating a specific function for cell surface GRP78 in cisplatin resistance. These combined stem cell functions of GRP78 therefore parallel many of the functions of GRP78 for cancer cells, and thus provide insight into understanding how cancer cells acquire and exploit stem cell properties.

Citation Format: Athanasia D. Panopoulos, Yuriko Hishida, Min-Zu Wu, Sergio Ruiz, Erika Batchelder, Tomoaki Hishida, Jonathan A. Kelber, Peter C. Gray, Juan Carlos Izpisua Belmonte. Parallel functions of the endoplasmic reticulum chaperone protein GRP78 in tumorigenesis and the induction of pluripotency. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1932. doi:10.1158/1538-7445.AM2014-1932

Direct conversion of human fibroblasts into retinal pigment epithelium-like cells by defined factors

The generation of functional retinal pigment epithelium (RPE) is of great therapeutic interest to the field of regenerative medicine and may provide possible cures for retinal degenerative diseases, including age-related macular degeneration (AMD). Although RPE cells can be produced from either embryonic stem cells or induced pluripotent stem cells, direct cell reprogramming driven by lineage-determining transcription factors provides an immediate route to their generation. By monitoring a human RPE specific Best1::GFP reporter, we report the conversion of human fibroblasts into RPE lineage using defined sets of transcription factors. We found that Best1::GFP positive cells formed colonies and exhibited morphological and molecular features of early stage RPE cells. Moreover, they were able to obtain pigmentation upon activation of Retinoic acid (RA) and Sonic Hedgehog (SHH) signaling pathways. Our study not only established an ideal platform to investigate the transcriptional network regulating the RPE cell fate determination, but also provided an alternative strategy to generate functional RPE cells that complement the use of pluripotent stem cells for disease modeling, drug screening, and cell therapy of retinal degeneration.

Identification of Ccr4-not complex components as regulators of transition from partial to genuine induced pluripotent stem cells

Somatic cells can be reprogrammed to induced pluripotent stem cells (iPSCs) by defined factors. However, substantial cell numbers subjected to iPSC induction stray from the main reprogramming route and are immortalized as partial iPSCs. These partial iPSCs can become genuine iPSCs by exposure to the ground state condition. However, such conversion is only possible for mouse partial iPSCs, and it is not applicable to human cells. Moreover, the molecular basis of this conversion is completely unknown. Therefore, we performed genome-wide screening with a piggyBac vector to identify genes involved in conversion from partial to genuine iPSCs. This screening led to identification of Cnot2, one of the core components of the Ccr4-Not complex. Subsequent analyses revealed that other core components, Cnot1 and Cnot3, also contributed to the conversion. Thus, our data have uncovered a novel role of core components of the Ccr4-Not complex as regulators of transition from partial to genuine iPSCs.