Nuclear cloning of embryonal carcinoma cells

Extracellular production of azurin from Pseudomonas aeruginosa in the presence of Triton X-100 or Tween 80

Azurin which is a bacterial secondary metabolite has attracted much attention as potential anticancer agent in recent years. This copper-containing periplasmic redox protein supresses the tumor growth selectively. High-level secretion of proteins into the culture medium offers a significant advantage over periplasmic or cytoplasmic expression. The aim of this study was to investigate the effect of nonionic surfactants on the expression of the Pseudomonas aeruginosa azurin. Different concentrations of Triton X-100 and Tween 80 were used as supplements in growth media and extracellular azurin production was stimulated by both surfactants. According to western blot analysis results, in the presence of Triton X-100, maximum azurin expression level was achieved with 96 h of incubation at 1% concentration, and 48 h at 2% concentration. On the other hand, maximum azurin expression level was achieved in the presence of 1% Tween 80 at 72 h incubation. This study suggested for the first time a high level of azurin secretion from P. aeruginosa in the presence of Triton X-100 or Tween 80, which would be advantageous for the purification procedure.

Xist nucleates local protein gradients to propagate silencing across the X chromosome

The lncRNA Xist forms ∼50 diffraction-limited foci to transcriptionally silence one X chromosome. How this small number of RNA foci and interacting proteins regulate a much larger number of X-linked genes is unknown. We show that Xist foci are locally confined, contain ∼2 RNA molecules, and nucleate supramolecular complexes (SMACs) that include many copies of the critical silencing protein SPEN. Aggregation and exchange of SMAC proteins generate local protein gradients that regulate broad, proximal chromatin regions. Partitioning of numerous SPEN molecules into SMACs is mediated by their intrinsically disordered regions and essential for transcriptional repression. Polycomb deposition via SMACs induces chromatin compaction and the increase in SMACs density around genes, which propagates silencing across the X chromosome. Our findings introduce a mechanism for functional nuclear compartmentalization whereby crowding of transcriptional and architectural regulators enables the silencing of many target genes by few RNA molecules.

Metabolic Classification and Intervention Opportunities for Tumor Energy Dysfunction

A comprehensive view of cell metabolism provides a new vision of cancer, conceptualized as tissue with cellular-altered metabolism and energetic dysfunction, which can shed light on pathophysiological mechanisms. Cancer is now considered a heterogeneous ecosystem, formed by tumor cells and the microenvironment, which is molecularly, phenotypically, and metabolically reprogrammable. A wealth of evidence confirms metabolic reprogramming activity as the minimum common denominator of cancer, grouping together a wide variety of aberrations that can affect any of the different metabolic pathways involved in cell physiology. This forms the basis for a new proposed classification of cancer according to the altered metabolic pathway(s) and degree of energy dysfunction. Enhanced understanding of the metabolic reprogramming pathways of fatty acids, amino acids, carbohydrates, hypoxia, and acidosis can bring about new therapeutic intervention possibilities from a metabolic perspective of cancer.

Cellular reprogramming to model and study epigenetic alterations in cancer

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Cellular reprogramming to model human cancer.

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Cellular reprogramming to rewire epigenetic alterations in human cancer.

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Selective reactivation of malignancy in the cell lineage cancer is originated.

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Cellular reprogramming to recapitulate human cancer progression.

Although genetic mutations are required for cancer development, reversible non-genetic alterations also play a pivotal role in cancer progression. Failure of well-orchestrated gene regulation by chromatin states and master transcription factors can be one such non-genetic etiology for cancer development. Master transcription factor-mediated cellular reprogramming of human cancer cells allows us to model cancer progression. Here I cover the history and recent advances in reprogramming cancer cells, followed by lessons from cellular reprogramming of normal cells that may apply to cancer. Lastly, I share my perspective on cellular reprogramming for studying epigenetic alterations that have occurred in tumorigenesis, discuss the current limitations, and propose ways to overcome the obstacles in the reprogramming of cancer.

Targeting of apoptosis gene loci by reprogramming factors leads to selective eradication of leukemia cells

Applying somatic cell reprogramming strategies in cancer cell biology is a powerful approach to analyze mechanisms of malignancy and develop new therapeutics. Here, we test whether leukemia cells can be reprogrammed in vivo using the canonical reprogramming transcription factors-Oct4, Sox2, Klf4, and c-Myc (termed as OSKM). Unexpectedly, we discover that OSKM can eradicate leukemia cells and dramatically improve survival of leukemia-bearing mice. By contrast, OSKM minimally impact normal hematopoietic cells. Using ATAC-seq, we find OSKM induce chromatin accessibility near genes encoding apoptotic regulators in leukemia cells. Moreover, this selective effect also involves downregulation of H3K9me3 as an early event. Dissection of the functional effects of OSKM shows that Klf4 and Sox2 play dominant roles compared to c-Myc and Oct4 in elimination of leukemia cells. These results reveal an intriguing paradigm by which OSKM-initiated reprogramming induction can be leveraged and diverged to develop novel anti-cancer strategies.

TGFβ Family Signaling Pathways in Pluripotent and Teratocarcinoma Stem Cells' Fate Decisions: Balancing Between Self-Renewal, Differentiation, and Cancer

The transforming growth factor-β (TGFβ) family factors induce pleiotropic effects and are involved in the regulation of most normal and pathological cellular processes. The activity of different branches of the TGFβ family signaling pathways and their interplay with other signaling pathways govern the fine regulation of the self-renewal, differentiation onset and specialization of pluripotent stem cells in various cell derivatives. TGFβ family signaling pathways play a pivotal role in balancing basic cellular processes in pluripotent stem cells and their derivatives, although disturbances in their genome integrity induce the rearrangements of signaling pathways and lead to functional impairments and malignant transformation into cancer stem cells. Therefore, the identification of critical nodes and targets in the regulatory cascades of TGFβ family factors and other signaling pathways, and analysis of the rearrangements of the signal regulatory network during stem cell state transitions and interconversions, are key issues for understanding the fundamental mechanisms of both stem cell biology and cancer initiation and progression, as well as for clinical applications. This review summarizes recent advances in our understanding of TGFβ family functions in naїve and primed pluripotent stem cells and discusses how these pathways are involved in perturbations in the signaling network of malignant teratocarcinoma stem cells with impaired differentiation potential.

Epigenetic reprogramming of primary pancreatic cancer cells counteracts their in vivo tumourigenicity

Pancreatic ductal adenocarcinoma (PDAC) arises through accumulation of multiple genetic alterations. However, cancer cells also acquire and depend on cancer-specific epigenetic changes. To conclusively demonstrate the crucial relevance of the epigenetic programme for the tumourigenicity of the cancer cells, we used cellular reprogramming technology to reverse these epigenetic changes. We reprogrammed human PDAC cultures using three different techniques - (1) lentivirally via induction of Yamanaka Factors (OSKM), (2) the pluripotency-associated gene OCT4 and the microRNA mir-302, or (3) using episomal vectors as a safer alternative without genomic integration. We found that induction with episomal vectors was the most efficient method to reprogram primary human PDAC cultures as well as primary human fibroblasts that served as positive controls. Successful reprogramming was evidenced by immunostaining, alkaline phosphatase staining, and real-time PCR. Intriguingly, reprogramming of primary human PDAC cultures drastically reduced their in vivo tumourigenicity, which appeared to be driven by the cells' enhanced differentiation and loss of stemness upon transplantation. Our study demonstrates that reprogrammed primary PDAC cultures are functionally distinct from parental PDAC cells resulting in drastically reduced tumourigenicity in vitro and in vivo. Thus, epigenetic alterations account at least in part for the tumourigenicity and aggressiveness of pancreatic cancer, supporting the notion that epigenetic modulators could be a suitable approach to improve the dismal outcome of patients with pancreatic cancer.

The Making of Leukemia

Due to the clonal nature of human leukemia evolution, all leukemic cells carry the same leukemia-initiating genetic lesions, independently of the intrinsic tumoral cellular heterogeneity. However, the latest findings have shown that the mode of action of oncogenes is not homogeneous throughout the developmental history of leukemia. Studies on different types of hematopoietic tumors have shown that the contribution of oncogenes to leukemia is mainly mediated through the epigenetic reprogramming of the leukemia-initiating target cell. This driving of cancer by a malignant epigenetic stem cell rewiring is, however, not exclusive of the hematopoietic system, but rather represents a common tumoral mechanism that is also at work in epithelial tumors. Tumoral epigenetic reprogramming is therefore a new type of interaction between genes and their target cells, in which the action of the oncogene modifies the epigenome to prime leukemia development by establishing a new pathological tumoral cellular identity. This reprogramming may remain latent until it is triggered by either endogenous or environmental stimuli. This new view on the making of leukemia not only reveals a novel function for oncogenes, but also provides evidence for a previously unconsidered model of leukemogenesis, in which the programming of the leukemia cellular identity has already occurred at the level of stem cells, therefore showing a role for oncogenes in the timing of leukemia initiation.

Application of induced pluripotency in cancer studies

As soon as induced pluripotent stem cells (iPSCs) reprogramming of somatic cells were developed, the discovery attracted the attention of scientists, offering new perspectives for personalized medicine and providing a powerful platform for drug testing. The technology was almost immediately applied to cancer studies. As presented in this review, direct reprogramming of cancer cells with enforced expression of pluripotency factors have several basic purposes, all of which aim to explain the complex nature of cancer development and progression, therapy-resistance and relapse, and ultimately lead to the development of novel anti-cancer therapies. Here, we briefly present recent advances in reprogramming methodologies as well as commonalities between cell reprogramming and carcinogenesis and discuss recent outcomes from the implementation of induced pluripotency into cancer research.

Cancer reversion with oocyte extracts is mediated by cell cycle arrest and induction of tumour dormancy

Inducing stable control of tumour growth by tumour reversion is an alternative approach to cancer treatment when eradication of the disease cannot be achieved. The process requires re-establishment of normal control mechanisms that are lost in cancer cells so that abnormal proliferation can be halted. Embryonic environments can reset cellular programmes and we previously showed that axolotl oocyte extracts can reprogram breast cancer cells and reverse their tumorigenicity. In this study, we analysed the gene expression profiles of oocyte extract-treated tumour xenografts to show that tumour reprogramming involves cell cycle arrest and acquisition of a quiescent state. Tumour dormancy is associated with increased P27 expression, restoration of RB function and downregulation of mitogen-activated signalling pathways. We also show that the quiescent state is associated with increased levels of H4K20me3 and decreased H4K20me1, an epigenetic profile leading to chromatin compaction. The epigenetic reprogramming induced by oocyte extracts is required for RB hypophosphorylation and induction of P27 expression, both occurring during exposure to the extracts and stably maintained in reprogrammed tumour xenografts. Therefore, this study demonstrates the value of oocyte molecules for inducing tumour reversion and for the development of new chemoquiescence-based therapies.

Patient-derived induced pluripotent stem cells in cancer research and precision oncology

Together with recent advances in the processing and culture of human tissue, bioengineering, xenotransplantation and genome editing, Induced pluripotent stem cells (iPSCs) present a range of new opportunities for the study of human cancer. Here we discuss the main advantages and limitations of iPSC modeling, and how the method intersects with other patient-derived models of cancer, such as organoids, organs-on-chips and patient-derived xenografts (PDXs). We highlight the opportunities that iPSC models can provide beyond those offered by existing systems and animal models and present current challenges and crucial areas for future improvements toward wider adoption of this technology.

Cancer cell reprogramming to identify the genes competent for generating liver cancer stem cells

The cancer stem cell (CSC) hypothesis postulates that cancer originates from the malignant transformation of stem/progenitor cells and is considered to apply to many cancers, including liver cancer. Identification that CSCs are responsible for drug resistance, metastasis, and secondary tumor appearance suggests that these populations are novel obligatory targets for the treatment of cancer. Here, we describe our new method for identifying potential CSC candidates. The reprogramming of cancer cells via induced pluripotent stem cell (iPSC) technology is a novel therapy for the treatment and for the study of CSC-related genes. This technology has advantages for studying the interactions between CSC-related genes and the cancer niche microenvironment. This technology may also provide a useful platform for studying the genes involved in the generation of CSCs before and after reprogramming, and for elucidating the mechanisms underlying cancer initiation and progression. The present review summarizes the current understanding of transcription factors involved in the generation of liver CSCs from liver cancer cell-derived iPSCs and how these contribute to oncogenesis, and discusses the modeling of liver cancer development.

Mechanisms Regulating Stemness and Differentiation in Embryonal Carcinoma Cells

Just over ten years have passed since the seminal Takahashi-Yamanaka paper, and while most attention nowadays is on induced, embryonic, and cancer stem cells, much of the pioneering work arose from studies with embryonal carcinoma cells (ECCs) derived from teratocarcinomas. This original work was broad in scope, but eventually led the way for us to focus on the components involved in the gene regulation of stemness and differentiation. As the name implies, ECCs are malignant in nature, yet maintain the ability to differentiate into the 3 germ layers and extraembryonic tissues, as well as behave normally when reintroduced into a healthy blastocyst. Retinoic acid signaling has been thoroughly interrogated in ECCs, especially in the F9 and P19 murine cell models, and while we have touched on this aspect, this review purposely highlights how some key transcription factors regulate pluripotency and cell stemness prior to this signaling. Another major focus is on the epigenetic regulation of ECCs and stem cells, and, towards that end, this review closes on what we see as a new frontier in combating aging and human disease, namely, how cellular metabolism shapes the epigenetic landscape and hence the pluripotency of all stem cells.

G1 cyclins link proliferation, pluripotency and differentiation of embryonic stem cells

Progression of mammalian cells through the G1 and S phases of the cell cycle is driven by the D-type and E-type cyclins. According to the current models, at least one of these cyclin families must be present to allow cell proliferation. Here, we show that several cell types can proliferate in the absence of all G1 cyclins. However, following ablation of G1 cyclins, embryonic stem (ES) cells attenuated their pluripotent characteristics, with the majority of cells acquiring the trophectodermal cell fate. We established that G1 cyclins, together with their associated cyclin-dependent kinases (CDKs), phosphorylate and stabilize the core pluripotency factors Nanog, Sox2 and Oct4. Treatment of murine ES cells, patient-derived glioblastoma tumour-initiating cells, or triple-negative breast cancer cells with a CDK inhibitor strongly decreased Sox2 and Oct4 levels. Our findings suggest that CDK inhibition might represent an attractive therapeutic strategy by targeting glioblastoma tumour-initiating cells, which depend on Sox2 to maintain their tumorigenic potential.

Cellular context-dependent consequences of Apc mutations on gene regulation and cellular behavior

The spectrum of genetic mutations differs among cancers in different organs, implying a cellular context-dependent effect for genetic aberrations. However, the extent to which the cellular context affects the consequences of oncogenic mutations remains to be fully elucidated. We reprogrammed colon tumor cells in an Apc^Min/+ (adenomatous polyposis coli) mouse model, in which the loss of the Apc gene plays a critical role in tumor development and subsequently, established reprogrammed tumor cells (RTCs) that exhibit pluripotent stem cell (PSC)-like signatures of gene expression. We show that the majority of the genes in RTCs that were affected by Apc mutations did not overlap with the genes affected in the intestine. RTCs lacked pluripotency but exhibited an increased expression of Cdx2 and a differentiation propensity that was biased toward the trophectoderm cell lineage. Genetic rescue of the mutated Apc allele conferred pluripotency on RTCs and enabled their differentiation into various cell types in vivo. The redisruption of Apc in RTC-derived differentiated cells resulted in neoplastic growth that was exclusive to the intestine, but the majority of the intestinal lesions remained as pretumoral microadenomas. These results highlight the significant influence of cellular context on gene regulation, cellular plasticity, and cellular behavior in response to the loss of the Apc function. Our results also imply that the transition from microadenomas to macroscopic tumors is reprogrammable, which underscores the importance of epigenetic regulation on tumor promotion.

Is lineage decision-making restricted during tumoral reprograming of haematopoietic stem cells?

Within the past years there have been substantial changes to our understanding of haematopoiesis and cells that initiate and sustain leukemia. Recent studies have revealed that developing haematopoietic stem and progenitor cells are much more heterogeneous and versatile than has been previously thought. This versatility includes cells using more than one route to a fate and cells having progressed some way towards a cell type retaining other lineage options as clandestine. These notions impact substantially on our understanding of the origin and nature of leukemia. An important question is whether leukemia stem cells are as versatile as their cell of origin as an abundance of cells belonging to a lineage is often a feature of overt leukemia. In this regard, we examine the coming of age of the "leukemia stem cell" theory and the notion that leukemia, like normal haematopoiesis, is a hierarchically organized tissue. We examine evidence to support the notion that whilst cells that initiate leukemia have multi-lineage potential, leukemia stem cells are reprogrammed by further oncogenic insults to restrict their lineage decision-making. Accordingly, evolution of a sub-clone of lineage-restricted malignant cells is a key feature of overt leukemia.

In vitro models of cancer stem cells and clinical applications

Cancer cells, stem cells and cancer stem cells have for a long time played a significant role in the biomedical sciences. Though cancer therapy is more effective than it was a few years ago, the truth is that still none of the current non-surgical treatments can cure cancer effectively. The reason could be due to the subpopulation called “cancer stem cells” (CSCs), being defined as those cells within a tumour that have properties of stem cells: self-renewal and the ability for differentiation into multiple cell types that occur in tumours.

The phenomenon of CSCs is based on their resistance to many of the current cancer therapies, which results in tumour relapse. Although further investigation regarding CSCs is still needed, there is already evidence that these cells may play an important role in the prognosis of cancer, progression and therapeutic strategy. Therefore, long-term patient survival may depend on the elimination of CSCs. Consequently, isolation of pure CSC populations or reprogramming of cancer cells into CSCs, from cancer cell lines or primary tumours, would be a useful tool to gain an in-depth knowledge about heterogeneity and plasticity of CSC phenotypes and therefore carcinogenesis. Herein, we will discuss current CSC models, methods used to characterize CSCs, candidate markers, characteristic signalling pathways and clinical applications of CSCs. Some examples of CSC-specific treatments that are currently in early clinical phases will also be presented in this review.

Tumorigenic potential is restored during differentiation in fusion-reprogrammed cancer cells

Detailed understanding of the mechanistic steps underlying tumor initiation and malignant progression is critical for insights of potentially novel therapeutic modalities. Cellular reprogramming is an approach of particular interest because it can provide a means to reset the differentiation state of the cancer cells and to revert these cells to a state of non-malignancy. Here, we investigated the relationship between cellular differentiation and malignant progression by the fusion of four independent mouse cancer cell lines from different tissues, each with differing developmental potentials, to pluripotent mouse embryonic stem (ES) cells. Fusion was accompanied by loss of differentiated properties of the four parental cancer cell lines and concomitant emergence of pluripotency, demonstrating the feasibility to reprogram the malignant and differentiative properties of cancer cells. However, the original malignant and differentiative phenotypes re-emerge upon withdrawal of the fused cells from the embryonic environment in which they were maintained. cDNA array analysis of the malignant hepatoma progression implicated a role for Foxa1, and silencing Foxa1 prevented the re-emergence of malignant and differentiation-associated gene expression. Our findings support the hypothesis that tumor progression results from deregulation of stem cells, and our approach provides a strategy to analyze possible mechanisms in the cancer initiation.

Regulatory roles of LINE-1-encoded reverse transcriptase in cancer onset and progression

LINE-1 retrotransposons encode the reverse transcriptase (RT) enzyme, required for their own mobility, the expression of which is inhibited in differentiated tissues while being active in tumors. Experimental evidence indicate that the inhibition of LINE-1-derived RT restores differentiation in cancer cells, inhibits tumor progression and yields globally reprogrammed transcription profiles. Newly emerging data suggest that LINE-1-encoded RT modulates the biogenesis of miRNAs, by governing the balance between the production of regulatory double-stranded RNAs and RNA:DNA hybrid molecules, with a direct impact on global gene expression. Abnormally high RT activity unbalances the transcriptome in cancer cells, while RT inhibition restores ‘normal’ miRNA profiles and their regulatory networks. This RT-dependent mechanism can target the myriad of transcripts - both coding and non-coding, sense and antisense - in eukaryotic transcriptomes, with a profound impact on cell fates. LINE-1-encoded RT emerges therefore as a key regulator of a previously unrecognized mechanism in tumorigenesis

Cdx2 efficiently induces trophoblast stem-like cells in naïve, but not primed, pluripotent stem cells

Diverse pluripotent stem cell lines have been derived from the mouse, including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), embryonal carcinoma cells (ECCs), and epiblast stem cells (EpiSCs). While all are pluripotent, these cell lines differ in terms of developmental origins, morphology, gene expression, and signaling, indicating that multiple pluripotent states exist. Whether and how the pluripotent state influences the cell line's developmental potential or the competence to respond to differentiation cues could help optimize directed differentiation protocols. To determine whether pluripotent stem cell lines differ in developmental potential, we compared the capacity of mouse ESCs, iPSCs, ECCs, and EpiSCs to form trophoblast. ESCs do not readily differentiate into trophoblast, but overexpression of the trophoblast-expressed transcription factor, CDX2, leads to efficient differentiation to trophoblast and to formation of trophoblast stem cells (TSCs) in the presence of fibroblast growth factor-4 (FGF4) and Heparin. Interestingly, we found that iPSCs and ECCs could both give rise to TSC-like cells following Cdx2 overexpression, suggesting that these cell lines are equivalent in developmental potential. By contrast, EpiSCs did not give rise to TSCs following Cdx2 overexpression, indicating that EpiSCs are no longer competent to respond to CDX2 by differentiating to trophoblast. In addition, we noted that culturing ESCs in conditions that promote naïve pluripotency improved the efficiency with which TSC-like cells could be derived. This work demonstrates that CDX2 efficiently induces trophoblast in more naïve than in primed pluripotent stem cells and that the pluripotent state can influence the developmental potential of stem cell lines.

Reprogramming of human cancer cells to pluripotency for models of cancer progression

The ability to study live cells as they progress through the stages of cancer provides the opportunity to discover dynamic networks underlying pathology, markers of early stages, and ways to assess therapeutics. Genetically engineered animal models of cancer, where it is possible to study the consequences of temporal-specific induction of oncogenes or deletion of tumor suppressors, have yielded major insights into cancer progression. Yet differences exist between animal and human cancers, such as in markers of progression and response to therapeutics. Thus, there is a need for human cell models of cancer progression. Most human cell models of cancer are based on tumor cell lines and xenografts of primary tumor cells that resemble the advanced tumor state, from which the cells were derived, and thus do not recapitulate disease progression. Yet a subset of cancer types have been reprogrammed to pluripotency or near-pluripotency by blastocyst injection, by somatic cell nuclear transfer and by induced pluripotent stem cell (iPS) technology. The reprogrammed cancer cells show that pluripotency can transiently dominate over the cancer phenotype. Diverse studies show that reprogrammed cancer cells can, in some cases, exhibit early-stage phenotypes reflective of only partial expression of the cancer genome. In one case, reprogrammed human pancreatic cancer cells have been shown to recapitulate stages of cancer progression, from early to late stages, thus providing a model for studying pancreatic cancer development in human cells where previously such could only be discerned from mouse models. We discuss these findings, the challenges in developing such models and their current limitations, and ways that iPS reprogramming may be enhanced to develop human cell models of cancer progression.

The "virgin birth", polyploidy, and the origin of cancer

Recently, it has become clear that the complexity of cancer biology cannot fully be explained by somatic mutation and clonal selection. Meanwhile, data have accumulated on how cancer stem cells or stemloids bestow immortality on tumour cells and how reversible polyploidy is involved. Most recently, single polyploid tumour cells were shown capable of forming spheroids, releasing EMT-like descendents and inducing tumours in vivo. These data refocus attention on the centuries-old embryological theory of cancer. This review attempts to reconcile seemingly conflicting data by viewing cancer as a pre-programmed phylogenetic life-cycle-like process. This cycle is apparently initiated by a meiosis-like process and driven as an alternative to accelerated senescence at the DNA damage checkpoint, followed by an asexual syngamy event and endopolyploid-type embryonal cleavage to provide germ-cell-like (EMT) cells. This cycle is augmented by genotoxic treatments, explaining why chemotherapy is rarely curative and drives resistance. The logical outcome of this viewpoint is that alternative treatments may be more efficacious - either those that suppress the endopolyploidy-associated ‘life cycle’ or, those that cause reversion of embryonal malignant cells into benign counterparts. Targets for these opposing strategies are components of the same molecular pathways and interact with regulators of accelerated senescence.

Reprogramming cancer cells to pluripotency: an experimental tool for exploring cancer epigenetics

The epigenetic marks displayed by a cancer cell originate from two separate processes: The most prominent epigenetic signatures are associated with the cell of origin, i.e., the lineage and cell type identity imposed during development. The second set comprises those aberrant cancer-specific epigenetic marks that appear during tumor initiation or subsequent malignant progression. These are generally thought to associate with tumor-promoting pathways. As biochemical pathways regulating epigenetic mechanisms are potentially “druggable” and reversible, there is considerable interest in defining their roles in tumor genesis and growth, as they may represent therapeutic targets for treatment of human neoplasias.¹ However, despite the potential importance of epigenetic modifications in human cancer, it has been difficult to determine when, where and how epigenetic disruptions occur, and if they have important functional roles in sustaining the malignant state.

A morphometric screen identifies specific roles for microtubule-regulating genes in neuronal development of P19 stem cells

The first morphological change after neuronal differentiation is the microtubule-dependent initiation of thin cell protrusions called neurites. Here we performed a siRNA-based morphometric screen in P19 stem cells to evaluate the role of 408 microtubule-regulating genes during this early neuromorphogenesis step. This screen uncovered several novel regulatory factors, including specific complex subunits of the microtubule motor dynein involved in neurite initiation and a novel role for the microtubule end-binding protein EB2 in attenuation of neurite outgrowth. Epistasis analysis suggests that competition between EB1 and EB2 regulates neurite length, which links its expression to neurite outgrowth. We propose a model that explains how microtubule regulators can mediate cellular morphogenesis during the early steps of neuronal development by controlling microtubule stabilization and organizing dynein-generated forces.

Reprogramming of MLL-AF9 leukemia cells into pluripotent stem cells

The 'Yamanaka factors' (Oct4, Sox2, Klf4 and c-Myc) are able to generate induced pluripotent stem (iPS) cells from different cell types. However, to what degree primary malignant cells can be reprogrammed into a pluripotent state has not been vigorously assessed. We established an acute myeloid leukemia (AML) model by overexpressing the human mixed-lineage leukemia-AF9 (MLL-AF9) fusion gene in mouse hematopoietic cells that carry Yamanaka factors under the control of doxycycline (Dox). On addition of Dox to the culture, the transplantable leukemia cells were efficiently converted into iPS cells that could form teratomas and produce chimeras. Interestingly, most chimeric mice spontaneously developed the same type of AML. Moreover, both iPS reprogramming and leukemia reinitiation paths could descend from the same leukemia-initiating cell. RNA-seq analysis showed reversible global gene expression patterns between these interchangeable leukemia and iPS cells on activation or reactivation of MLL-AF9, suggesting a sufficient epigenetic force in driving the leukemogenic process. This study represents an important step for further defining the potential interplay between oncogenic molecules and reprogramming factors during MLL leukemogenesis. More importantly, our reprogramming approach may be expanded to characterize a range of hematopoietic malignancies in order to develop new strategies for clinical diagnosis and treatment.

Modelling human disease with pluripotent stem cells

Recent progress in the field of cellular reprogramming has opened up the doors to a new era of disease modelling, as pluripotent stem cells representing a myriad of genetic diseases can now be produced from patient tissue. These cells can be expanded and differentiated to produce a potentially limitless supply of the affected cell type, which can then be used as a tool to improve understanding of disease mechanisms and test therapeutic interventions. This process requires high levels of scrutiny and validation at every stage, but international standards for the characterisation of pluripotent cells and their progeny have yet to be established. Here we discuss the current state of the art with regard to modelling diseases affecting the ectodermal, mesodermal and endodermal lineages, focussing on studies which have demonstrated a disease phenotype in the tissue of interest. We also discuss the utility of pluripotent cell technology for the modelling of cancer and infectious disease. Finally, we spell out the technical and scientific challenges which must be addressed if the field is to deliver on its potential and produce improved patient outcomes in the clinic.

An iPSC line from human pancreatic ductal adenocarcinoma undergoes early to invasive stages of pancreatic cancer progression

Pancreatic ductal adenocarcinoma (PDAC) carries a dismal prognosis and lacks a human cell model of early disease progression. When human PDAC cells are injected into immunodeficient mice, they generate advanced-stage cancer. We hypothesized that if human PDAC cells were converted to pluripotency and then allowed to differentiate back into pancreatic tissue, they might undergo early stages of cancer. Although most induced pluripotent stem cell (iPSC) lines were not of the expected cancer genotype, one PDAC line, 10-22 cells, when injected into immunodeficient mice, generated pancreatic intraepithelial neoplasia (PanIN) precursors to PDAC that progressed to the invasive stage. The PanIN-like cells secrete or release proteins from many genes that are known to be expressed in human pancreatic cancer progression and that predicted an HNF4α network in intermediate-stage lesions. Thus, rare events allow iPSC technology to provide a live human cell model of early pancreatic cancer and insights into disease progression.

Function of oncogenes in cancer development: a changing paradigm

Tumour-associated oncogenes induce unscheduled proliferation as well as genomic and chromosomal instability. According to current models, therapeutic strategies that block oncogene activity are likely to selectively target tumour cells. However, recent evidences have revealed that oncogenes are only essential for the proliferation of some specific tumour cell types, but not all. Indeed, the latest studies of the interactions between the oncogene and its target cell have shown that oncogenes contribute to cancer development not only by inducing proliferation but also by developmental reprogramming of the epigenome. This provides the first evidence that tumorigenesis can be initiated by stem cell reprogramming, and uncovers a new role for oncogenes in the origin of cancer. Here we analyse these evidences and propose an updated model of oncogene function that can explain the full range of genotype-phenotype associations found in human cancer. Finally, we discuss how this vision opens new avenues for developing novel anti-cancer interventions.

Recent advancements in cloning by somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) cloning is the sole reproductive engineering technology that endows the somatic cell genome with totipotency. Since the first report on the birth of a cloned sheep from adult somatic cells in 1997, many technical improvements in SCNT have been made by using different epigenetic approaches, including enhancement of the levels of histone acetylation in the chromatin of the reconstructed embryos. Although it will take a considerable time before we fully understand the nature of genomic programming and totipotency, we may expect that somatic cell cloning technology will soon become broadly applicable to practical purposes, including medicine, pharmaceutical manufacturing and agriculture. Here we review recent progress in somatic cell cloning, with a special emphasis on epigenetic studies using the laboratory mouse as a model.

The cellular memory disc of reprogrammed cells

The crucial facts underlying the low efficiency of cellular reprogramming are poorly understood. Cellular reprogramming occurs in nuclear transfer, induced pluripotent stem cell (iPSC) formation, cell fusion, and lineage-switching experiments. Despite these advances, there are three fundamental problems to be addressed: (1) the majority of cells cannot be reprogrammed, (2) the efficiency of reprogramming cells is usually low, and (3) the reprogrammed cells developed from a patient's own cells activate immune responses. These shortcomings present major obstacles for using reprogramming approaches in customised cell therapy. In this Perspective, the author synthesises past and present observations in the field of cellular reprogramming to propose a theoretical picture of the cellular memory disc. The current hypothesis is that all cells undergo an endogenous and exogenous holographic memorisation such that parts of the cellular memory dramatically decrease the efficiency of reprogramming cells, act like a barrier against reprogramming in the majority of cells, and activate immune responses. Accordingly, the focus of this review is mainly to describe the cellular memory disc (CMD). Based on the present theory, cellular memory includes three parts: a reprogramming-resistance memory (RRM), a switch-promoting memory (SPM) and a culture-induced memory (CIM). The cellular memory arises genetically, epigenetically and non-genetically and affects cellular behaviours. [corrected].

Reciprocal regulation of Akt and Oct4 promotes the self-renewal and survival of embryonal carcinoma cells

Signaling via the Akt serine/threonine protein kinase plays critical roles in the self-renewal of embryonic stem cells and their malignant counterpart, embryonal carcinoma cells (ECCs). Here we show that in ECCs, Akt phosphorylated the master pluripotency factor Oct4 at threonine 235, and that the levels of phosphorylated Oct4 in ECCs correlated with resistance to apoptosis and tumorigenic potential. Phosphorylation of Oct4 increased its stability and facilitated its nuclear localization and its interaction with Sox2, which promoted the transcription of the core stemness genes POU5F1 and NANOG. Furthermore, in ECCs, unphosphorylated Oct4 bound to the AKT1 promoter and repressed its transcription. Phosphorylation of Oct4 by Akt resulted in dissociation of Oct4 from the AKT1 promoter, which activated AKT1 transcription and promoted cell survival. Therefore, a site-specific, posttranslational modification of the Oct4 protein orchestrates the regulation of its stability, subcellular localization, and transcriptional activities, which collectively promotes the survival and tumorigenicity of ECCs.

microRNA-based cancer cell reprogramming technology

Epigenetic modifications play crucial roles in cancer initiation and development. Complete reprogramming can be achieved through the introduction of defined biological factors such as Oct4, Sox2, Klf4, and cMyc into mouse and human fibroblasts. Introduction of these transcription factors resulted in the modification of malignant phenotype behavior. Recent studies have shown that human and mouse somatic cells can be reprogrammed to become induced pluripotent stem cells using forced expression of microRNAs, which completely eliminates the need for ectopic protein expression. Considering the usefulness of RNA molecules, microRNA-based reprogramming technology may have future applications in regenerative and cancer medicine.

Reprogramming of gastrointestinal cancer cells

Cell reprogramming reverts cells to multipotent, preprogrammed states by re-establishing epigenetic markers. It can also induce considerable malignant phenotype modification. Because key events in cancer relapse and metastasis, including epithelial-mesenchymal transition phenotypes, are regulated primarily by reversible and transient epigenetic modifications rather than the accumulation of irreversible and stable genetic abnormalities, studying dynamic mechanisms regulating these biological processes is important. Transcription factors for induced pluripotent stem cells and non-coding microRNAs allow pluripotent phenotype induction. We present the current knowledge of the possible applications of cell reprogramming in reducing aggressive phenotype expression, which can induce tumor cell hibernation and maintain appropriate phenotypes, thereby minimizing relapse and metastasis after surgical resection of gastrointestinal cancer.

Nuclear transfer to eggs and oocytes

We review experiments in which somatic cell nuclei are transplanted singly to enucleated eggs (metaphase II) in amphibia and mammals and as multiple nuclei to the germinal vesicle of amphibian oocytes (prophase I). These experiments have shown the totipotency of some somatic cell nuclei, as well as switches in cell type and changes in gene expression. Abnormalities of nuclear transplant embryo development increase greatly as nuclei are taken from progressively more differentiated donor cells. The molecular changes that accompany the reprogramming of transplanted nuclei help to indicate the mechanisms used by eggs and oocytes to reprogram gene expression. We discuss the importance of chromosomal protein exchange, of transcription factor supply, and of chromatin access in reprogramming.

Epigenetic reprogramming of breast cancer cells with oocyte extracts

BACKGROUND

Breast cancer is a disease characterised by both genetic and epigenetic alterations. Epigenetic silencing of tumour suppressor genes is an early event in breast carcinogenesis and reversion of gene silencing by epigenetic reprogramming can provide clues to the mechanisms responsible for tumour initiation and progression. In this study we apply the reprogramming capacity of oocytes to cancer cells in order to study breast oncogenesis.

RESULTS

We show that breast cancer cells can be directly reprogrammed by amphibian oocyte extracts. The reprogramming effect, after six hours of treatment, in the absence of DNA replication, includes DNA demethylation and removal of repressive histone marks at the promoters of tumour suppressor genes; also, expression of the silenced genes is re-activated in response to treatment. This activity is specific to oocytes as it is not elicited by extracts from ovulated eggs, and is present at very limited levels in extracts from mouse embryonic stem cells. Epigenetic reprogramming in oocyte extracts results in reduction of cancer cell growth under anchorage independent conditions and a reduction in tumour growth in mouse xenografts.

CONCLUSIONS

This study presents a new method to investigate tumour reversion by epigenetic reprogramming. After testing extracts from different sources, we found that axolotl oocyte extracts possess superior reprogramming ability, which reverses epigenetic silencing of tumour suppressor genes and tumorigenicity of breast cancer cells in a mouse xenograft model. Therefore this system can be extremely valuable for dissecting the mechanisms involved in tumour suppressor gene silencing and identifying molecular activities capable of arresting tumour growth. These applications can ultimately shed light on the contribution of epigenetic alterations in breast cancer and advance the development of epigenetic therapies.

Efficiencies and mechanisms of nuclear reprogramming

The differentiated state of somatic cells is highly stable, but it can be experimentally reversed. The resulting cells can then be redirected into many different pathways. Nuclear reprogramming has been achieved by nuclear transfer to eggs, cell fusion, and overexpression of transcription factors. The mechanisms of nuclear reprogramming are not understood, but some insight into them is provided by comparing the efficiencies of different reprogramming strategies. Here, we compare these efficiencies by describing the frequency and rapidity with which reprogramming is induced and by the proportion of cells and level of expression in which reprogramming is achieved. We comment on the mechanisms that lead to successful somatic-cell reprogramming and on those that resist in helping to maintain the differentiated state of somatic cells.

Comparative proteomics of human embryonic stem cells and embryonal carcinoma cells

Pluripotent human embryonic stem cells (ESCs) can be differentiated in vitro into a variety of cells which hold promise for transplantation therapy. Human embryonal carcinoma cells (ECCs), stem cells of human teratocarcinomas, are considered a close but malignant counterpart to human ESCs. In this study, a comprehensive quantitative proteomic analysis of ESCs and ECCs was carried out using the iTRAQ method. Using two-dimensional LC and MS/MS analyses, we identified and quantitated approximately 1800 proteins. Among these are proteins associated with pluripotency and development as well as tight junction signaling and TGFbeta receptor pathway. Nearly approximately 200 proteins exhibit more than twofold difference in abundance between ESCs and ECCs. Examples of early developmental markers high in ESCs include beta-galactoside-binding lectin, undifferentiated embryonic cell transcription factor-1, DNA cytosine methyltransferase 3beta isoform-B, melanoma antigen family-A4, and interferon-induced transmembrane protein-1. In contrast, CD99-antigen (CD99), growth differentiation factor-3, cellular retinoic acid binding protein-2, and developmental pluripotency associated-4 were among the highly expressed proteins in ECCs. Several proteins that were highly expressed in ECCs such as heat shock 27 kDa protein-1, mitogen-activated protein kinase kinase-1, nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor like-2, and S100 calcium-binding protein-A4 have also been attributed to malignancy in other systems. Importantly, immunocytochemistry was used to validate the proteomic analyses for a subset of the proteins. In summary, this is the first large-scale quantitative proteomic study of human ESCs and ECCs, which provides critical information about the regulators of these two closely related, but developmentally distinct, stem cells.

Inhibition of mouse embryonic carcinoma cell growth by lidamycin through down-regulation of embryonic stem cell-like genes Oct4, Sox2 and Myc

Lidamycin (LDM, also known as C-1027) as an anti-cancer agent inhibits growth in a variety of cancer cells by inducing apoptosis and cell cycle arrest. In this study we demonstrated that inhibition of mouse embryonic carcinoma (EC) cell growth using LDM at low concentrations can be attributed to a loss of the cell's self-renewal capability but not to apoptosis or cell death, which can be correlated to the down-regulation of embryonic stem (ES) cell-like genes Oct4, Sox2 and c-Myc. MTT assays showed that LDM inhibited the growth of mouse P19 EC cells in a time- and dose-dependent manner. The EC cells exposed to a low dose (0.01 nM) of LDM lost their capability to generate colonies, as evidenced by the colony forming assay. Flow cytometer analyses demonstrated that LDM induced G1 arrest in exposed EC cells without apoptosis. Real-time qPCR, Western blotting and immunocytochemistry revealed that Oct4, Sox2 and c-Myc were down-regulated in LDM-exposed EC cells, but not adriamycin (ADM)-exposed cells. Furthermore, a combination of the low dose of LDM and ADM significantly reduced the proliferation of the cancer cells than single-agent treatment. This suggested that synergy of ADM and LDM improved chemotherapy. Taking together, our results indicate that LDM can reduce the capability for self-renewal that mouse EC cells possess through the repression of ES cell-like genes, thereby inhibiting carcinoma cell growth. This data also suggests that LDM might have potential for application in CSC-based therapy and be a useful tool for studying ES cell pluripotency and differentiation.

Linking incomplete reprogramming to the improved pluripotency of murine embryonal carcinoma cell-derived pluripotent stem cells

Somatic cell nuclear transfer (SCNT) has been proved capable of reprogramming various differentiated somatic cells into pluripotent stem cells. Recently, induced pluripotent stem cells (iPS) have been successfully derived from mouse and human somatic cells by the over-expression of a combination of transcription factors. However, the molecular mechanisms underlying the reprogramming mediated by either the SCNT or iPS approach are poorly understood. Increasing evidence indicates that many tumor pathways play roles in the derivation of iPS cells. Embryonal carcinoma (EC) cells have the characteristics of both stem cells and cancer cells and thus they might be the better candidates for elucidating the details of the reprogramming process. Although previous studies indicate that EC cells cannot be reprogrammed into real pluripotent stem cells, the reasons for this remain unclear. Here, nuclei from mouse EC cells (P19) were transplanted into enucleated oocytes and pluripotent stem cells (P19 NTES cells) were subsequently established. Interestingly, P19 NTES cells prolonged the development of tetraploid aggregated embryos compared to EC cells alone. More importantly, we found that the expression recovery of the imprinted H19 gene was dependent on the methylation state in the differential methylation region (DMR). The induction of Nanog expression, however, was independent of the promoter region DNA methylation state in P19 NTES cells. A whole-genome transcriptome analysis further demonstrated that P19 NTES cells were indeed the intermediates between P19 cells and ES cells and many interesting genes were uncovered that may be responsible for the failed reprogramming of P19 cells. To our knowledge, for the first time, we linked incomplete reprogramming to the improved pluripotency of EC cell-derived pluripotent stem cells. The candidate genes we discovered may be useful not only for understanding the mechanisms of reprogramming, but also for deciphering the transition between tumorigenesis and pluripotency.

H3K27 trimethylation is an early epigenetic event of p16INK4a silencing for regaining tumorigenesis in fusion reprogrammed hepatoma cells

Stable epigenetic silencing of p16(INK4a) is a common event in hepatocellular carcinoma (HCC) cells, which is associated with abnormal cell proliferation and liberation from cell cycle arrest. Understanding the early epigenetic events in silencing p16(INK4a) expression may illuminate a prognostic strategy to block HCC development. Toward this end, we created a reprogram cell model by the fusion mouse HCC cells with mouse embryonic stem cells, in which the ES-Hepa hybrids forfeited HCC cell characteristics along with reactivation of the silenced p16(INK4a). HCC characteristics, in terms of gene expression pattern and tumorigenic potential, was restored upon induced differentiation of these reprogrammed ES-Hepa hybrids. The histone methylation pattern relative to p16(INK4a) silencing during differentiation of the ES-Hepa hybrids was analyzed. H3K27 trimethylation at the p16(INK4a) promoter region, occurring in the early onset of p16(INK4a) silencing, was followed by H3K9 dimethylation at later stages. During the induced differentiation of the ES-Hepa hybrids, H3K4 di- and trimethylations were maintained at high levels during the silencing of p16(INK4a), strongly suggesting that H3K4 methylation events did not cause the silencing of p16(INK4a). Our results suggested that the enrichment of H3K27 trimethylation, independent of H3K9 dimethylation, trimethylation, and DNA methylation, was an early event in the silencing of p16(INK4a) during the tumor development. This unique chromatin pattern may be a heritable marker of epigenetic regulation for p16(INK4a) silencing during the developmental process of hepatocellular carcinogenesis.

Zscan4 regulates telomere elongation and genomic stability in ES cells

Exceptional genomic stability is one of the hallmarks of mouse embryonic stem (ES) cells. However, the genes contributing to this stability remain obscure. We previously identified Zscan4 as a specific marker for 2-cell embryo and ES cells. Here we show that Zscan4 is involved in telomere maintenance and long-term-genomic stability in ES cells. Only 5% of ES cells express Zscan4 at a given time, but nearly all ES cells activate Zscan4 at least once within nine passages. The transient Zscan4-positive state is associated with rapid telomere extension by telomere recombination and upregulation of meiosis-specific homologous recombination genes, which encode proteins that are colocalized with ZSCAN4 on telomeres. Furthermore, Zscan4 knockdown shortens telomeres, increases karyotype abnormalities and spontaneous sister chromatid exchange, and slows down cell proliferation until reaching crisis by eight passages. Together, our data reveal a unique mode of genome maintenance in ES cells.

Epigenetic reprogramming and induced pluripotency

The cloning of animals from adult cells has demonstrated that the developmental state of adult cells can be reprogrammed into that of embryonic cells by uncharacterized factors within the oocyte. More recently, transcription factors have been identified that can induce pluripotency in somatic cells without the use of oocytes, generating induced pluripotent stem (iPS) cells. iPS cells provide a unique platform to dissect the molecular mechanisms that underlie epigenetic reprogramming. Moreover, iPS cells can teach us about principles of normal development and disease, and might ultimately facilitate the treatment of patients by custom-tailored cell therapy.

The molecular programme of tumour reversion: the steps beyond malignant transformation

How cells become malignant has preoccupied scientists for over a century. However, the converse question is also valid: are tumour cells capable of reverting from their malignant state? Askanazy's studies in 1907 indicated that teratoma cells could differentiate into normal somatic tissues and current evidence indicates that some tumour cells have acquired the molecular circuitry that results in the negation of chromosomal instability, translocations, oncogene activation and loss of tumour suppressor genes. Studying these extremely rare events of tumour reversion and deciphering these pathways, which involve SIAH1, presenilin 1, TSAP6 and translationally controlled tumour protein (TCTP), could lead to new avenues in cancer treatment.

Cellular reprogramming and pluripotency induction

INTRODUCTION

Cellular reprogramming is the process of directing mature cells to a primitive state of gene expression.

SOURCES OF DATA

Medline searches using the keywords 'pluripotency', 'induce' (and derivatives), and/or 'stem' limited to the years 2006 to the present and other selected literature known to the author.

AREAS OF AGREEMENT

Since 2006, there has been a cavalcade of scientific works describing so-called 'direct reprogramming' wherein somatic cells are forced into a state of gene expression very similar to embryonic stem cells. These findings build upon prior research using nuclear transfer (cloning) and even older efforts to understand developmental processes.

AREAS OF CONTROVERSY

While already of tremendous research value, it remains to be seen how (if) direct reprogramming methodologies will be refined for clinical use.

AREAS TIMELY FOR DEVELOPING RESEARCH

A greater understanding of epigenetics, the process by which different patterns of gene expression are established, maintained and redirected, will continue to be enlightened by advances in cellular reprogramming.

Epigenetic modifications of embryonic stem cells: current trends and relevance in developing regenerative medicine

Epigenetics is a growing field not only in the area of cancer research but recently in stem cells including human embryonic stem cell (hESC) research. The hallmark of profiling epigenetic changes in stem cells lies in maintaining pluripotency or multipotency and in attaining lineage specifications that are relevant for regenerative medicine. Epigenetic modifications including DNA methylation, histone acetylation and methylation, play important roles in regulating gene expressions. Other epigenetic modifications include X chromosome silencing, genomic stability and imprinting and mammalian development. This review attempts to elucidate the mechanism(s) behind epigenetic modifications and review techniques scientists use for identifying each modification. We also discuss some of the trends of epigenetic modifications in the fields of directed differentiation of embryonic stem cells and de-differentiation of somatic cells.

MiR-92b and miR-9/9* are specifically expressed in brain primary tumors and can be used to differentiate primary from metastatic brain tumors

A recurring challenge for brain pathologists is to diagnose whether a brain malignancy is a primary tumor or a metastasis from some other tissue. The accurate diagnosis of brain malignancies is essential for selection of proper treatment. MicroRNAs are a class of small non‐coding RNA species that regulate gene expression; many exhibit tissue‐specific expression and are misregulated in cancer. Using microRNA expression profiling, we found that hsa‐miR‐92b and hsa‐miR‐9/hsa‐miR‐9* are over‐expressed, specifically in brain primary tumors, as compared to primary tumors from other tissues and their metastases to the brain. By considering the expression of only these two microRNAs, it is possible to distinguish between primary and metastatic brain tumors with very high accuracy. These microRNAs thus represent excellent biomarkers for brain primary tumors. Previous reports have found that hsa‐miR‐92b and hsa‐miR‐9/hsa‐miR‐9* are expressed more strongly in developing neurons and brain than in adult brain. Thus, their specific over‐expression in brain primary tumors supports a functional role for these microRNAs or a link between neuronal stem cells and brain tumorigenesis.

DGCR8 is essential for microRNA biogenesis and silencing of embryonic stem cell self-renewal

The molecular controls that govern the differentiation of embryonic stem (ES) cells remain poorly understood. DGCR8 is an RNA-binding protein that assists the RNase III enzyme Drosha in the processing of microRNAs (miRNAs), a subclass of small RNAs. Here we study the role of miRNAs in ES cell differentiation by generating a Dgcr8 knockout model. Analysis of mouse knockout ES cells shows that DGCR8 is essential for biogenesis of miRNAs. On the induction of differentiation, DGCR8-deficient ES cells do not fully downregulate pluripotency markers and retain the ability to produce ES cell colonies; however, they do express some markers of differentiation. This phenotype differs from that reported for Dicer1 knockout cells, suggesting that Dicer has miRNA-independent roles in ES cell function. Our findings indicate that miRNAs function in the silencing of ES cell self-renewal that normally occurs with the induction of differentiation.

Nuclear transfer reprogramming does not improve the low developmental potency of embryonic stem cells induced by long-term culture

Epigenetic states of embryonic stem (ES) cells are easily altered by long-term cultivation and lose their developmental potential. To rescue this reduced developmental capacity, nuclear transfer (NT) of ES cells was carried out, and original ES and ES cells from cloned blastocysts (ntES) cells established after NT were compared with in vitro differentiation ability and developmental potential by embryoid body formation and tetraploid aggregation respectively. In the establishment of ntES cell lines, the oocytes fused with the ES cell were activated, and further cultured to cloned blastocysts. When in vitro differentiation ability was examined between original and ntES cell lines derived from ES cells with extensive passages (ES-ep), the day of appearance of simple embryoid body, cystic embryoid body, and spontaneous beating was almost similar. The developmental rates of ES-ep cells, that aggregated with tetraploid embryos to term, ranged from 3 to 6%. Moreover, the majority of live pups died soon after birth. In the ntES cell lines derived from ES-ep cells, developmental rates ranged from 0 to 5%. Those pups also died soon after birth, similar to the ES-ep-derived pups. These results suggest that profound epigenetic modifications of ES cells were retained in the re-established cell lines by NT.

Reprogramming efficiency following somatic cell nuclear transfer is influenced by the differentiation and methylation state of the donor nucleus

Reprogramming of a differentiated cell nucleus by somatic cell nuclear transplantation is an inefficient process. Following nuclear transfer, the donor nucleus often fails to express early embryonic genes and establish a normal embryonic pattern of chromatin modifications. These defects correlate with the low number of cloned embryos able to produce embryonic stem cells or develop into adult animals. Here, we show that the differentiation and methylation state of the donor cell influence the efficiency of genomic reprogramming. First, neural stem cells, when used as donors for nuclear transplantation, produce embryonic stem cells at a higher efficiency than blastocysts derived from terminally differentiated neuronal donor cells, demonstrating a correlation between the state of differentiation and cloning efficiency. Second, using a hypomorphic allele of DNA methyltransferase-1, we found that global hypomethylation of a differentiated cell genome improved cloning efficiency. Our results provide functional evidence that the differentiation and epigenetic state of the donor nucleus influences reprogramming efficiency.