Physiological oxygen prevents frequent silencing of the DLK1-DIO3 cluster during human embryonic stem cells culture

Imprinted small nucleolar RNAs: Missing link in development and disease?

The 14q32.2 (DLK1-DIO3) and 15q11-q13 (SNURF-SNRPN) imprinted gene loci harbor the largest known small nucleolar RNA clusters expressed from the respective maternal and paternal alleles. Recent studies have demonstrated significant roles for the 15q11-q13 located SNORD115-SNORD116 C/D box snoRNAs in Prader-Willi syndrome (PWS), a neurodevelopmental disorder. Even though the effect of SNORD116 deletion is apparent in the PWS phenotype, similar effects of a SNORD113-SNORD114 cluster deletion from the 14q32.2 locus in Kagami-Ogata syndrome (KOS14) and upregulation in Temple syndrome (TS14) remain to be explored. Moreover, apart from their probable involvement in neurodevelopmental disorders, snoRNAs from the SNORD113-SNORD114 cluster have been implicated in multiple biological processes, including pluripotency, development, cancers, and RNA modifications. Here we summarize the current understanding of the system to explore the possibility of a link between developmental disorders and C/D box snoRNA expression from the imprinted 14q32.2 locus. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA in Disease and Development > RNA in Development RNA Processing > Processing of Small RNAs.

Oxidative Stress and Assisted Reproduction: A Comprehensive Review of Its Pathophysiological Role and Strategies for Optimizing Embryo Culture Environment

Oxidative stress (OS) due to an imbalance between reactive oxygen species (ROS) and antioxidants has been established as an important factor that can negatively affect the outcomes of assisted reproductive techniques (ARTs). Excess ROS exert their pathological effects through damage to cellular lipids, organelles, and DNA, alteration of enzymatic function, and apoptosis. ROS can be produced intracellularly, from immature sperm, oocytes, and embryos. Additionally, several external factors may induce high ROS production in the ART setup, including atmospheric oxygen, CO2 incubators, consumables, visible light, temperature, humidity, volatile organic compounds, and culture media additives. Pathological amounts of ROS can also be generated during the cryopreservation-thawing process of gametes or embryos. Generally, these factors can act at any stage during ART, from gamete preparation to embryo development, till the blastocyst stage. In this review, we discuss the in vitro conditions and environmental factors responsible for the induction of OS in an ART setting. In addition, we describe the effects of OS on gametes and embryos. Furthermore, we highlight strategies to ameliorate the impact of OS during the whole human embryo culture period, from gametes to blastocyst stage.

Targeting tumor lineage plasticity in hepatocellular carcinoma using an anti-CLDN6 antibody-drug conjugate

Tumor lineage plasticity is emerging as a critical mechanism of therapeutic resistance and tumor relapse. Highly plastic tumor cells can undergo phenotypic switching to a drug-tolerant state to avoid drug toxicity. Here, we investigate the transmembrane tight junction protein Claudin6 (CLDN6) as a therapeutic target related to lineage plasticity for hepatocellular carcinoma (HCC). CLDN6 was highly expressed in embryonic stem cells but markedly decreased in normal tissues. Reactivation of CLDN6 was frequently observed in HCC tumor tissues as well as in premalignant lesions. Functional assays indicated that CLDN6 is not only a tumor-associated antigen but also conferred strong oncogenic effects in HCC. Overexpression of CLDN6 induced phenotypic shift of HCC cells from hepatic lineage to biliary lineage, which was more refractory to sorafenib treatment. The enhanced tumor lineage plasticity and cellular identity change were potentially induced by the CLDN6/TJP2 (tight junction protein 2)/YAP1 (Yes-associated protein 1) interacting axis and further activation of the Hippo signaling pathway. A de novo anti-CLDN6 monoclonal antibody conjugated with cytotoxic agent (Mertansine) DM1 (CLDN6-DM1) was developed. Preclinical data on both HCC cell lines and primary tumors showed the potent antitumor efficiency of CLDN6-DM1 as a single agent or in combination with sorafenib in HCC treatment.

The FOXO signaling axis displays conjoined functions in redox homeostasis and stemness

Previous views of reactive oxygen species (ROS) depicted them as harmful byproducts of metabolism as uncontrolled levels of ROS can lead to DNA damage and cell death. However, recent studies have shed light into the key role of ROS in the self-renewal or differentiation of the stem cell. The interplay between ROS levels, metabolism, and the downstream redox signaling pathways influence stem cell fate. In this review we will define ROS, explain how they are generated, and how ROS signaling can influence transcription factors, first and foremost forkhead box-O transcription factors, that shape not only the cellular redox state, but also stem cell fate. Now that studies have illustrated the importance of redox homeostasis and the role of redox signaling, understanding the mechanisms behind this interplay will further shed light into stem cell biology.

Identification of prognostic claudins signature in hepatocellular carcinoma from a hepatocyte differentiation model

BACKGROUND

Loss of terminal differentiation markers and gain of stem cell-like properties are a major hallmark of cancer malignant progression. Identification of novel biomarkers representing tumor developmental progeny and predictive of patients' prognosis would greatly benefit clinical cancer management.

METHODS

Human embryonic stem cells were induced to differentiate into hepatocytes along hepatic lineages. Transcriptomic data from different liver developmental stages were analyzed combining with the RNA-seq data from The Cancer Genome Atlas (TCGA) project. Kaplan-Meier survival analysis and Cox regression analyses were used to analyze the clinical significance in HCC patients.

RESULTS

A shifted expression pattern of claudin (CLDN) family genes were identified to be closely associated with liver development and tumor progression. Claudins with hepatic features were found to be significantly down-regulated and predicted better prognosis in HCC patients. Conversely, another set of claudins with embryonic stem cell features were found to be significantly up-regulated and predicted worse prognosis in HCC patients. A claudin signature score system was further established by combining the two sets of claudin genes. The newly established claudins signature could robustly predict HCC patients' prognosis in the training, testing, and independent validation cohorts.

CONCLUSIONS

In the present study, we developed a novel embryonic developmental claudins signature to monitor the extent of tumor dedifferentiation in HCC from an in vitro hepatocyte differentiation model. The claudins signature might present a great potential in predicting prognostic significance in HCC as cell surface biomarkers, and provide novel therapeutic targets for precision oncology further in the clinic.

A hepatocyte differentiation model reveals two subtypes of liver cancer with different oncofetal properties and therapeutic targets

Clinical observation of the association between cancer aggressiveness and embryonic development stage implies the importance of developmental signals in cancer initiation and therapeutic resistance. However, the dynamic gene expression during organogenesis and the master oncofetal drivers are still unclear, which impeded the efficient elimination of poor prognostic tumors, including human hepatocellular carcinoma (HCC). In this study, human embryonic stem cells were induced to differentiate into adult hepatocytes along hepatic lineages to mimic liver development in vitro. Combining transcriptomic data from liver cancer patients with the hepatocyte differentiation model, the active genes derived from different hepatic developmental stages and the tumor tissues were selected. Bioinformatic analysis followed by experimental assays was used to validate the tumor subtype-specific oncofetal signatures and potential therapeutic values. Hierarchical clustering analysis revealed the existence of two subtypes of liver cancer with different oncofetal properties. The gene signatures and their clinical significance were further validated in an independent clinical cohort and The Cancer Genome Atlas database. Upstream activator analysis and functional screening further identified E2F1 and SMAD3 as master transcriptional regulators. Small-molecule inhibitors specifically targeting the oncofetal drivers extensively down-regulated subtype-specific developmental signaling and inhibited tumorigenicity. Liver cancer cells and primary HCC tumors with different oncofetal properties also showed selective vulnerability to their specific inhibitors. Further precise targeting of the tumor initiating steps and driving events according to subtype-specific biomarkers might eliminate tumor progression and provide novel therapeutic strategy.

miR-412-5p targets Xpo1 to regulate angiogenesis in hemorrhoid tissue

Hemorrhoid is a common and recurrent proctological disease, which is often accompanied by angiogenesis and edema. MicroRNAs in the DLK1-DIO3 imprinted clusters are involved in the development and pathogenesis of mammalian hemorrhoids. Results of the present study indicated multiple, differential expression of DLK1-DIO3 imprinted cluster microRNA between hemorrhoid and normal tissues, where miR-412-5p expression in hemorrhoid tissue was significantly decreased. Fluorescein reporter assays showed that miR-412-5p silenced Xpo1 mRNA expression by targeting its 3'-UTR. Overexpression of miR-412-5p in human umbilical vein endothelial cells (HUVECs) indicated that proliferation, migration and formation of vascular structures in HUVECs were inhibited in vitro. In addition, overexpression of miR-412-5p significantly inhibited Xpo1 expression and promoted upregulation of the p53 protein and its retention in the nucleus. Simultaneously, expression of p66SHC and p16 proteins was activated. In summary, downregulation of endogenous miR-412-5p expression in hemorrhoid vascular endothelial cells leads to high expression of the target gene Xpo1 and translocation of the p53 protein out of the nucleus, rendering it unable to activate p66SHC and p16. This ultimately weakens regulation of the vascular endothelial cell cycle, thereby accelerating the division of hemorrhoid vascular endothelial cells, leading to angiogenesis.

Long Noncoding RNA: Function and Mechanism on Differentiation of Mesenchymal Stem Cells and Embryonic Stem Cells

Background:

Long suspected as transcriptional noise, recently recognized, long non-coding RNAs (lncRNAs) are emerging as an indicator, biomarker and therapy target in the physiologic and pathologic process. Mesenchymal stem cells and embryonic stem cells are important source for normal and therapeutic tissue repair. However, the mechanism of stem cell differentiation is not completely understood. Research on lncRNAs may provide novel insights into the mechanism of differentiation process of the stem cell which is important for the application of stem cell therapy. The lncRNAs field is still very young, new insights into lncRNAs function are emerging to a greater understanding of biological processes.

Objective:

In this review, we summarize the recent researches studying lncRNAs and illustrate how they act in the differentiation of the mesenchymal stem cells and embryonic stem cells, and discuss some future directions in this field.

Results:

Numerous lncRNAs were differentially expressed during differentiation of mesenchymal stem cells and embryonic stem cells. LncRNAs were able to regulate the differentiation processes through epigenetic regulation, transcription regulation and post-transcription regulation.

Conclusion:

LncRNAs are involved in the differentiation process of mesenchymal stem cells and embryonic stem cells, and they could become promising indicator, biomarker and therapeutic targets in the physiologic and pathologic process. However, the mechanisms of the role of lncRNAs still require further investigation.

Defining Physiological Normoxia for Improved Translation of Cell Physiology to Animal Models and Humans

The extensive oxygen gradient between the air we breathe (Po₂ ~21 kPa) and its ultimate distribution within mitochondria (as low as ~0.5-1 kPa) is testament to the efforts expended in limiting its inherent toxicity. It has long been recognized that cell culture undertaken under room air conditions falls short of replicating this protection in vitro. Despite this, difficulty in accurately determining the appropriate O₂ levels in which to culture cells, coupled with a lack of the technology to replicate and maintain a physiological O₂ environment in vitro, has hindered addressing this issue thus far. In this review, we aim to address the current understanding of tissue Po₂ distribution in vivo and summarize the attempts made to replicate these conditions in vitro. The state-of-the-art techniques employed to accurately determine O₂ levels, as well as the issues associated with reproducing physiological O₂ levels in vitro, are also critically reviewed. We aim to provide the framework for researchers to undertake cell culture under O₂ levels relevant to specific tissues and organs. We envisage that this review will facilitate a paradigm shift, enabling translation of findings under physiological conditions in vitro to disease pathology and the design of novel therapeutics.

Analysis of the Paternally-Imprinted DLK1-MEG3 and IGF2-H19 Tandem Gene Loci in NT2 Embryonal Carcinoma Cells Identifies DLK1 as a Potential Therapeutic Target

The paternally-imprinted genes insulin-like growth factor 2 (IGF2), H19, delta-like homologue 1 (DLK1), and maternally-expressed gene 3 (MEG3) are expressed from the tandem gene loci IGF2-H19 and DLK1-MEG3, which play crucial roles in initiating embryogenesis and development. The erasure of imprinting (EOI) at differentially methylated regions (DMRs) which regulate the expression of these genes maintains the developmental quiescence of primordial germ cells (PGCs) migrating through the embryo proper during embryogenesis and prevents them from forming teratomas. To address the potential involvement of the IGF2-H19 and DLK1-MEG3 loci in the pathogenesis of embryonal carcinoma (EC), we investigated their genomic imprinting at DMRs in the human PGC-derived EC cell line NTera-2 (NT2). We observed EOI at the IGF2-H19 locus and, somewhat to our surprise, a loss of imprinting (LOI) at the DLK1-MEG3 locus. As a result, NT2 cells express imprinted gene ratios from these loci such that there are i) low levels of the proliferation-promoting IGF2 relative to ii) high levels of the proliferation-inhibiting long noncoding RNA (lncRNA) H19 and iii) high levels of proliferation-promoting DLK1 relative to iv) low levels of the proliferation-inhibiting lncRNA MEG3. Consistent with this pattern of expression, the knockdown of DLK1 mRNA by shRNA resulted in decreased in vitro cell proliferation and in vivo tumor growth as well as decreased in vivo organ seeding by NT2 cells. Furthermore, treatment of NT2 cells with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-azaD) inhibited their proliferation. This inhibition was accompanied by changes in expression of both tandem gene sets: a decrease in the expression of DLK1 and upregulation of the proliferation-inhibiting lncRNA MEG3, and at the same time upregulation of IGF2 and downregulation of the lncRNA H19. These results suggest that the DLK1-MEG3 locus, and not the IGF2-H19 locus, drives the tumorigenicity of NT2 cells. Based on these results, we identified DLK1 as a novel treatment target for EC that could be downregulated by 5-azaD.

An integrated chromatin accessibility and transcriptome landscape of human pre-implantation embryos

Human pre-implantation embryonic development involves extensive changes in chromatin structure and transcriptional activity. Here, we report on LiCAT-seq, a technique that enables simultaneous profiling of chromatin accessibility and gene expression with ultra-low input of cells, and map the chromatin accessibility and transcriptome landscapes for human pre-implantation embryos. We observed global difference in chromatin accessibility between sperm and all stages of embryos, finding that the accessible regions in sperm tend to occur in gene-poor genomic regions. Integrative analyses between the two datasets reveals strong association between the establishment of accessible chromatin and embryonic genome activation (EGA), and uncovers transcription factors and endogenous retrovirus (ERVs) specific to EGA. In particular, a large proportion of the early activated genes and ERVs are bound by DUX4 and become accessible as early as the 2- to 4-cell stages. Our results thus offer mechanistic insights into the molecular events inherent to human pre-implantation development.

miR-758 mediates oxLDL-dependent vascular endothelial cell damage by suppressing the succinate receptor SUCNR1

Atherosclerosis is a vascular disease associated with ageing, and its occurrence and development are closely related to the vascular inflammatory response. Oxidized low-density lipoprotein (oxLDL) has distinct effects in atherosclerosis. We aimed to determine the mechanisms underlying these effects. microRNAs including miR-758 were differentially expressed in oxLDL-treated HUVECs or HAECs. Luciferase reporter assay results indicated that SUCNR1 is an important target of miR-758. Expression of SUCNR1 and its downstream components was decreased significantly in ApoE-/- mice. Overexpression of miR-758 could suppress HUVEC proliferation by cell cycle arrest at the G0/G1 phase. miR-758 was overexpressed on HUVECs with markedly reduced capillary tubule formation capacity. Overexpression of miR-758 on HUVECs or HAECs could significantly reduce SUCNR1 (GPR91), SATA3, phosphorylated STAT3 (p-STAT3), and EVGF levels. Thus, oxLDL likely damages vascular endothelial cells by modulating the DLK1-DIO3 genomic imprinted microRNA cluster component miR-758, thereby suppressing expression of SUCNR1/GPR91 and its downstream components.

Generation of a luciferase-expressing human embryonic stem cell line: NERCe002-A-2

The human embryonic stem cell line NERCe002-A-2 was generated by transduction of NERCe002-A cells with an expression vector carrying the luciferase gene. The stem cells labelled with luciferase can be transplanted into animals and detected by the bioluminescence imaging technology. This provides optimal prospects of application to in vivo stem cell tracing. Luciferin served as a substrate to detect the activity of luciferase, and luciferase expression was measured by quantitative PCR. Characterization assays suggested that the NERCe002-A-2 cell line expresses typical markers of pluripotency and can form the 3 germ layers in vivo.

Establishment and characterization of a human embryonic stem cell line, NERCe002-A-3, with inducible 14-3-3ζ overexpression

NERCe002-A-3 cells were generated from the normal human embryonic stem cell line NERCe002-A. NERCe002-A-3 cells overexpressed 14-3-3ζ after exposure to doxycycline. 14-3-3ζ protein have the ability to bind a multitude of functionally diverse signalling proteins. The NERCe002-A-3 cell line is considered a model for functional studies of the 14-3-3ζ protein in hESC self-renewal and cell differentiation. Doxycycline-treated NERCe002-A-3 cells showed a>27-fold increase in relative expression of 14-3-3ζ as compared with un-induced cells. Characterization assays proved that NERCe002-A-3 cells express typical markers of pluripotency and have the ability to form the three germ layers in vivo.

Generation of a human embryonic stem cell line expressing tetrameric Zoanthus sp. green fluorescent protein: NERCe002-A-1

The human embryonic stem cell (hESC) line NERCe002-A-1 was generated through lentiviral transduction of the original NERCe002-A-1 hESC line with Zoanthus sp. green fluorescent protein (ZsGreen). Cells that expressed ZsGreen showed a >8.6-fold increase in fluorescence intensity compared with that of cells that expressed enhanced green fluorescent protein. The fluorescent hESC line can aid in identification of biological characteristics in vitro and in vivo by tracking cell growth, migration, and differentiation. Characteristic tests confirmed that the NERCe002-A-1 cell line expressed typical markers of pluripotency and had the capability to form the three germ layers in vivo.

Spheroid-cultured human umbilical cord-derived mesenchymal stem cells attenuate hepatic ischemia-reperfusion injury in rats

Mesenchymal stem cell (MSC) transplantation is a promising treatment for ischemia-reperfusion injury (IRI). However, its effects on hepatic IRI were not consistent in the previous studies. 3D spheroid-cultured MSCs enhance their production of trophic and anti-inflammatory properties, but their effects on hepatic IRI remain unclear. In this study, we compared the 3D spheroid-cultured human umbilical derived MSCs (3D UC-MSCs) with 2D-cultured UC-MSCs (2D UC-MSCs) on treating hepatic IRI. The RNA sequencing data showed that suppression of cell mitosis, response to hypoxia, inflammation, and angiogenesis were the top genetic changes in 3D UC-MSCs compared with 2D UC-MSCs. Although both pro-inflammatory and anti-inflammatory genes were upregulated in the 3D UC-MSCs, the mRNA and protein of an RNase (ZC3H12A), which turnovers the mRNA of pro-inflammatory genes at the post-transcript level, were significantly upregulated in 3D UC-MSCs. 3D UC-MSCs reduced the secretion of many chemokines and growth factors, but increased the secretion of vascular endothelial growth factor. Compared with the vehicle and 2D UC-MSCs, 3D UC-MSCs significantly reduced hepatic IRI in rats, based on the plasma aminotransferase levels, liver damage scores, neutrophil infiltration, hepatocyte apoptosis and expression of inflammation-associated genes. These findings suggest that 3D UC-MSCs therapy is a promising treatment for hepatic IRI.

Role of telomeric repeat-containing RNA in telomeric chromatin remodeling during the early expansion of human embryonic stem cells

This study aimed to explore the role of telomeric repeat-containing RNA (TERRA) in telomeric chromatin remodeling during the early expansion of human embryonic stem cells (hESCs). During the derivation of hESCs, histone demethylation in the telomeric region facilitates telomerase-mediated telomere elongation. An adequate telomere repeat is essential for hESCs to acquire and/or maintain the unlimited symmetric division, which suggests that there is a link between pluripotency and telomere maintenance. The present study found that the gradual decrease in TERRA levels and related TERRA foci were correlated with telomeric length elongation in the early expansion of hESCs. In addition, TERRA participated in telomeric chromatin remodeling by cooperating with SUV39H1 (suppressor of variegation 3-9 homolog 1/2) to propagate telomeric heterochromatin marker, histone H3 trimethylation of lysine 9. Moreover, the fibroblast growth factor signaling pathway, which is activated in hESCs, could suppress TERRA levels via telomeric repeat factor 1, which results in reduced SUV39H1 recruitment by TERRA at the telomere. Taken together, these results highlight the role of TERRA in hESC telomere elongation and homeostasis in the acquisition and/or maintenance of stem cell pluripotency.-Zeng, S., Liu, L., Sun, Y., Lu, G., Lin, G. Role of telomeric repeat-containing RNA in telomeric chromatin remodeling during the early expansion of human embryonic stem cells.

Pluripotent Stem Cell Metabolism and Mitochondria: Beyond ATP

Metabolism is central to embryonic stem cell (ESC) pluripotency and differentiation, with distinct profiles apparent under different nutrient milieu, and conditions that maintain alternate cell states. The significance of altered nutrient availability, particularly oxygen, and metabolic pathway activity has been highlighted by extensive studies of their impact on preimplantation embryo development, physiology, and viability. ESC similarly modulate their metabolism in response to altered metabolite levels, with changes in nutrient availability shown to have a lasting impact on derived cell identity through the regulation of the epigenetic landscape. Further, the preferential use of glucose and anaplerotic glutamine metabolism serves to not only support cell growth and proliferation but also minimise reactive oxygen species production. However, the perinuclear localisation of spherical, electron-poor mitochondria in ESC is proposed to sustain ESC nuclear-mitochondrial crosstalk and a mitochondrial-H₂O₂ presence, to facilitate signalling to support self-renewal through the stabilisation of HIFα, a process that may be favoured under physiological oxygen. The environment in which a cell is grown is therefore a critical regulator and determinant of cell fate, with metabolism, and particularly mitochondria, acting as an interface between the environment and the epigenome.

A reporter model to visualize imprinting stability at the Dlk1 locus during mouse development and in pluripotent cells

Genomic imprinting results in the monoallelic expression of genes that encode important regulators of growth and proliferation. Dysregulation of imprinted genes, such as those within the Dlk1-Dio3 locus, is associated with developmental syndromes and specific diseases. Our ability to interrogate causes of imprinting instability has been hindered by the absence of suitable model systems. Here, we describe a Dlk1 knock-in reporter mouse that enables single-cell visualization of allele-specific expression and prospective isolation of cells, simultaneously. We show that this ‘imprinting reporter mouse’ can be used to detect tissue-specific Dlk1 expression patterns in developing embryos. We also apply this system to pluripotent cell culture and demonstrate that it faithfully indicates DNA methylation changes induced upon cellular reprogramming. Finally, the reporter system reveals the role of elevated oxygen levels in eroding imprinted Dlk1 expression during prolonged culture and in vitro differentiation. The possibility to study allele-specific expression in different contexts makes our reporter system a useful tool to dissect the regulation of genomic imprinting in normal development and disease.

Summary: A Dlk1 knock-in reporter mouse reports allele- and tissue-specific Dlk1 expression in developing embryos that can be used to study changes in genomic imprinting during cellular reprogramming.

microRNAs and Prostate Cancer

microRNAs are noncoding RNAs that are important for embryonic stem cell development and epithelial to mesenchymal transition (EMT). Tumor cells hijack EMT and stemness to grow and metastasize to distant organs including bone. In the tumor microenvironment, tumor cells interact with the stromal fibroblasts at the primary and metastatic sites and this interaction leads to tumor growth, EMT, and bone metastasis. Tumor-stromal interactions are a dynamic process that involves both cell-cell communications and extracellular vesicles and soluble factors. Growing body of evidence suggests that microRNAs are part of the payload that comprises the extracellular vesicles. microRNAs induce reactive stroma and thus convert normal stroma into tumor-associated stroma to promote aggressive tumorigenicity in vitro and in vivo. Landmark published studies demonstrate that expression of specific microRNAs of DLK1-DIO3 stem cell cluster correlates with patient survival in metastatic prostate cancer. Thus, microRNAs mediate tumor growth, EMT, and metastasis through cell intrinsic mechanisms and extracellular communications and could be novel biomarkers and therapeutic targets in bone metastatic prostate cancer.

The effects of chemical and physical factors on mammalian embryo culture and their importance for the practice of assisted human reproduction

BACKGROUND

Although laboratory procedures, along with culture media formulations, have improved over the past two decades, the issue remains that human IVF is performed in vitro (literally 'in glass').

METHODS

Using PubMed, electronic searches were performed using keywords from a list of chemical and physical factors with no limits placed on time. Examples of keywords include oxygen, ammonium, volatile organics, temperature, pH, oil overlays and incubation volume/embryo density. Available clinical and scientific evidence surrounding physical and chemical factors have been assessed and presented here.

RESULTS AND CONCLUSIONS

Development of the embryo outside the body means that it is constantly exposed to stresses that it would not experience in vivo. Sources of stress on the human embryo include identified factors such as pH and temperature shifts, exposure to atmospheric (20%) oxygen and the build-up of toxins in the media due to the static nature of culture. However, there are other sources of stress not typically considered, such as the act of pipetting itself, or the release of organic compounds from the very tissue culture ware upon which the embryo develops. Further, when more than one stress is present in the laboratory, there is evidence that negative synergies can result, culminating in significant trauma to the developing embryo. It is evident that embryos are sensitive to both chemical and physical signals within their microenvironment, and that these factors play a significant role in influencing development and events post transfer. From the viewpoint of assisted human reproduction, a major concern with chemical and physical factors lies in their adverse effects on the viability of embryos, and their long-term effects on the fetus, even as a result of a relatively brief exposure. This review presents data on the adverse effects of chemical and physical factors on mammalian embryos and the importance of identifying, and thereby minimizing, them in the practice of human IVF. Hence, optimizing the in vitro environment involves far more than improving culture media formulations.

Transcriptional activation of human CDCA8 gene regulated by transcription factor NF-Y in embryonic stem cells and cancer cells

The cell division cycle associated 8 (CDCA8) gene plays an important role in mitosis. Overexpression of CDCA8 was reported in some human cancers and is required for cancer growth and progression. We found CDCA8 expression was also high in human ES cells (hESCs) but dropped significantly upon hESC differentiation. However, the regulation of CDCA8 expression has not yet been studied. Here, we characterized the CDCA8 promoter and identified its cis-elements and transcription factors. Three transcription start sites were identified. Reporter gene assays revealed that the CDCA8 promoter was activated in hESCs and cancer cell lines. The promoter drove the reporter expression specifically to pluripotent cells during early mouse embryo development and to tumor tissues in tumor-bearing mice. These results indicate that CDCA8 is transcriptionally activated in hESCs and cancer cells. Mechanistically, two key activation elements, bound by transcription factor NF-Y and CREB1, respectively, were identified in the CDCA8 basic promoter by mutation analyses and electrophoretic motility shift assays. NF-Y binding is positively correlated with promoter activities in different cell types. Interestingly, the NF-YA subunit, binding to the promoter, is primarily a short isoform in hESCs and a long isoform in cancer cells, indicating a different activation mechanism of the CDCA8 transcription between hESCs and cancer cells. Finally, enhanced CDCA8 promoter activities by NF-Y overexpression and reduced CDCA8 transcription by NF-Y knockdown further verified that NF-Y is a positive regulator of CDCA8 transcription. Our study unearths the molecular mechanisms underlying the activation of CDCA8 expression in hESCs and cancer cells, which provides a better understanding of its biological functions.

Ascorbic acid improves pluripotency of human parthenogenetic embryonic stem cells through modifying imprinted gene expression in the Dlk1-Dio3 region

Introduction

Human parthenogenetic embryonic stem cells (hpESCs) are generated from artificially activated oocytes, however, the issue of whether hpESCs have equivalent differentiation ability to human fertilized embryonic stem cells remains controversial.

Methods

hpESCs were injected into male severe combined immunodeficiency (SCID) mice and the efficiency of teratoma formation was calculated. Then the gene expression and methylation modification were detected by real time-PCR and bisulfate methods.

Results

Comparison of five hpESCs with different differentiation abilities revealed that levels of paternal genes in the Dlk1-Dio3 region on chromosome 14 in the hpESCs with high differentiation potential are enhanced, but strictly methylated and silenced in the hpESCs with lower differentiation potential. Treatment with ascorbic acid, rescued their ability to support teratoma formation and altered the expression profiles of paternally expressed genes in hpESCs that could not form teratoma easily. No differences in the expression of other imprinting genes were evident between hpESCs with higher and lower differentiation potential, except for those in the Dlk1-Dio3 region.

Conclusions

The Dlk1-Dio3 imprinting gene cluster distinguishes the differentiation ability of hpESCs. Moreover, modification by ascorbic acid may facilitate application of hpESCs to clinical settings in the future by enhancing their pluripotency.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0054-9) contains supplementary material, which is available to authorized users.

Loss of non-coding RNA expression from the DLK1-DIO3 imprinted locus correlates with reduced neural differentiation potential in human embryonic stem cell lines

INTRODUCTION

Pluripotent stem cells are increasingly used to build therapeutic models, including the transplantation of neural progenitors derived from human embryonic stem cells (hESCs). Recently, long non-coding RNAs (lncRNAs), including delta-like homolog 1 gene and the type III iodothyronine deiodinase gene (DLK1-DIO3) imprinted locus-derived maternally expressed gene 3 (MEG3), were found to be expressed during neural development. The deregulation of these lncRNAs is associated with various neurological diseases. The imprinted locus DLK1-DIO3 encodes abundant non-coding RNAs (ncRNAs) that are regulated by differential methylation of the locus. We aim to study the correlation between the DLK1-DIO3-derived ncRNAs and the capacity of hESCs to differentiate into neural lineages.

METHODS

We classified hESC sublines into MEG3-ON and MEG3-OFF based on the expression levels of MEG3 and its downstream microRNAs as detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). A cDNA microarray was used to analyze the gene expression profiles of hESCs. To investigate the capacity of neural differentiation in MEG3-ON and MEG3-OFF hESCs, we performed neural lineage differentiation followed by neural lineage marker expression and neurite formation analyses via qRT-PCR and immunocytochemistry, respectively. MEG3-knockdown via small interfering RNA (siRNA) and small hairpin RNA (shRNA) was used to investigate the potential causative effect of MEG3 in regulating neural lineage-related gene expression.

RESULTS

DLK1-DIO3-derived ncRNAs were repressed in MEG3-OFF hESCs compared with those in the MEG3-ON hESCs. The transcriptome profile indicated that many genes related to nervous system development and neural-type tumors were differentially expressed in MEG3-OFF hESCs. Three independent MEG3-knockdown assays using different siRNA and shRNA constructs consistently resulted in downregulation of some neural lineage genes. Lower expression levels of stage-specific neural lineage markers and reduced neurite formation were observed in neural lineage-like cells derived from MEG3-OFF-associated hESCs compared with those in the MEG3-ON groups at the same time points after differentiation.

CONCLUSIONS

Repression of ncRNAs derived from the DLK1-DIO3 imprinted locus is associated with reduced neural lineage differentiation potential in hESCs.

DLK1-DIO3 imprinted cluster in induced pluripotency: landscape in the mist

DLK1-DIO3 represents an imprinted cluster which genes are involved in physiological cell biology as early as the stem cell level and in the pathogenesis of several diseases. Transcription factor-mediated induced pluripotent cells (iPSCs) are considered an unlimited source of patient-specific hematopoietic stem cells for clinical application in patient-tailored regenerative medicine. However, to date there is no marker established able to distinguish embryonic stem cell-equivalent iPSCs or safe human iPSCs. Recent findings suggest that the DLK1-DIO3 locus possesses the potential to represent such a marker but there are also contradictory data. This review aims to report the current data on the topic describing both sides of the coin.