Growth RestrictedIn VitroCulture Conditions Alter the Imprinted Gene Expression Patterns of Mouse Embryonic Stem Cells

Placental scaffolds as a potential biological platform for embryonic stem cells differentiation into hepatic-like cells lineage: A pilot study

Hepatic microenvironment plays an essential role in liver regeneration, providing the necessary conditions for cell proliferation, differentiation and tissue rearrangement. One of the key factors for hepatic tissue reconstruction is the extracellular matrix (ECM), which through collagenous and non-collagenous proteins provide a three-dimensional structure that confers support for cell adhesion and assists on their survival and maintenance. In this scenario, placental ECM may be eligible for hepatic tissue reconstruction, once these scaffolds hold the major components required for cell support. Therefore, this preliminary study aimed to access the possibility of mouse embryonic stem cells differentiation into hepatocyte-like cells on placental scaffolds in a three-dimensional dynamic system using a Rotary Cell Culture System. Following a four-phase differentiation protocol that simulates liver embryonic development events, the preliminary results showed that a significant quantity of cells adhered and interacted with the scaffold through outer and inner surfaces. Positive immunolabelling for alpha fetus protein and CK7 suggest presence of hepatoblast phenotype cells, and CK18 and Albumin positive immunolabelling suggest the presence of hepatocyte-like phenotype cells, demonstrating the presence of a heterogeneous population into the recellularized scaffolds. Periodic Acid Schiff-Diastase staining confirmed the presence of glycogen storage, indicating that differentiate cells acquired a hepatic-like phenotype. In conclusion, these preliminary results suggested that mouse placental scaffolds might be used as a biological platform for stem cells differentiation into hepatic-like cells and their establishment, which may be a promissing biomaterial for hepatic tissue reconstruction.

Glia-neuron interactions in neurological diseases: Testing non-cell autonomy in a dish

For the past century, research on neurological disorders has largely focused on the most prominently affected cell types - the neurons. However, with increasing knowledge of the diverse physiological functions of glial cells, their impact on these diseases has become more evident. Thus, many conditions appear to have more complex origins than initially thought. Since neurological pathologies are often sporadic with unknown etiology, animal models are difficult to create and might only reflect a small portion of patients in which a mutation in a gene has been identified. Therefore, reliable in vitro systems to studying these disorders are urgently needed. They might be a pre-requisite for improving our understanding of the disease mechanisms as well as for the development of potential new therapies. In this review, we will briefly summarize the function of different glial cell types in the healthy central nervous system (CNS) and outline their implication in the development or progression of neurological conditions. We will then describe different types of culture systems to model non-cell autonomous interactions in vitro and evaluate advantages and disadvantages. This article is part of a Special Issue entitled SI: Exploiting human neurons.

Epigenomic disruption: the effects of early developmental exposures

Through DNA methylation, histone modifications, and small regulatory RNAs the epigenome systematically controls gene expression during development, both in utero and throughout life. The epigenome is also a very reactive system; its labile nature allows it to sense and respond to environmental perturbations to ensure survival during fetal growth. This pliability can lead to aberrant epigenetic modifications that persist into later life and induce numerous disease states. Endocrine-disrupting compounds (EDCs) are ubiquitous chemicals that interfere with growth and development. Several EDCs also interfere with epigenetic programming. The investigation of the epigenotoxic effects of bisphenol A (BPA), an EDC used in the production of plastics and resins, has further raised concern over the impact of EDCs on the epigenome. Using the Agouti viable yellow (A(vy)) mouse model, dietary BPA exposure was shown to hypomethylate both the A(vy) and the Cabp(IAP) metastable epialleles. This hypomethylating effect was counteracted with dietary supplementation of methyl donors or genistein. These results are consistent with reports of BPA and other EDCs causing epigenetic effects. Epigenotoxicity could lead to numerous developmental, metabolic, and behavioral disorders in exposed populations. The heritable nature of epigenetic changes also increases the risk for transgenerational inheritance of phenotypes. Thus, epigenotoxicity must be considered when assessing these compounds for safety.

Rat embryonic stem-like (ES-like) cells can contribute to extraembryonic tissues in vivo

Despite significant advances achieved through gene targeting in mouse embryonic stem (ES) cells, this technology is presently only available in mice. Because the rat is a species of undeniable importance to biomedical research, attempts at derivation of rat ES cell lines have been ongoing for many years; however, the putative rat ES cell lines that have been reported to date have not yet displayed the ability to contribute in vivo to developing tissues following embryo injection. In contrast to previous studies, we describe herein the successful derivation and characterization of rat ES-like cell lines that not only express markers of undifferentiated cells, alkaline phosphatase (AP) activity and stage-specific embryonic antigen-1 (SSEA-1) cell surface antigen, but also retain expression of Oct4 (also known as Pou5f1) a homeodomain transcription factor and molecular marker of pluripotent cells. Notably, these rat ES-like cells, when injected into blastocysts transferred to pseudopregnant females, can contribute to developing extraembryonic tissues. This report demonstrates for the first time that rat ES-like cells can be derived efficiently, can express a panel of pluripotent cell markers, can be genetically modified in vitro and cryopreserved, and importantly, are capable of contributing to extraembryonic tissues in vivo.

Diploid parthenogenetic embryos adopt a maternal-type methylation pattern on both sets of maternal chromosomes

Epigenetic modifications are closely associated with embryo developmental potential. One of the epigenetic modifications thought to be involved in genomic imprinting is DNA methylation. Here we show that the maternally imprinted genes Snrpn and Peg1/Mest were nearly unmethylated or heavily methylated, respectively, in their differentially methylated regions (DMRs) at the two-cell stage in parthenogenetic embryos. However, both genes were gradually de novo methylated, with almost complete methylation of all CpG sites by the morula stage in parthenogenetic embryos. Unexpectedly, another maternally imprinted gene, Peg3, showed distinct dynamics of methylation during preimplantation development of diploid parthenogenetic embryos. Peg3 showed seemingly normal methylation patterns at the two-cell and morula stages, but was also strongly de novo methylated in parthenogenetic blastocysts. In contrast, the paternally imprinted genes H19 and Rasgrf1 showed complete unmethylation of their DMRs at the morula stage in parthenogenetic embryos. These results indicate that diploid parthenogenetic embryos adopt a maternal-type methylation pattern on both sets of maternal chromosomes and that the aberrantly homogeneous status of methylation imprints may partially account for developmental failure.

Epigenetic stability of embryonic stem cells and developmental potential

Recent studies highlight the tremendous potential of human embryonic stem (ES) cells and their derivatives as therapeutic tools for degenerative diseases. However, derivation and culture of ES cells can induce epigenetic alterations, which can have long lasting effects on gene expression and phenotype. Research on human and mouse stem cells indicates that developmental, cancer-related genes, and genes regulated by genomic imprinting are particularly susceptible to changes in DNA methylation. Together with the occurrence of genetic alterations, epigenetic instability needs to be monitored when considering human stem cells for therapeutic and technological purposes. Here, we discuss the maintenance of epigenetic information in cultured stem cells and embryos and how this influences their developmental potential.

Assessment of the long-term and transgenerational consequences of perturbing preimplantation embryo development in mice

Perturbations of the development of preimplantation embryos may have long-term consequences for the health of progeny. There are no standardized methods for assessing such risks. The OECD/OCDE 416 Guideline for Testing of Chemicals (Two-Generation Reproduction Toxicity Study) is a standardized assay for detecting potential toxic effects of chemicals. The present study assessed the utility of this guideline for identifying long-term consequences of perturbing preimplantation development. Extended culturing of mammalian zygotes commonly results in retarded preimplantation development. Mouse zygotes were cultured in vitro for 96 h until the blastocyst stage (cultured blastocysts) or blastocysts were collected from the Day-3.5 uterus (in vivo blastocysts). The resulting blastocysts were transferred to the uteri of pseudopregnant recipients (P generation). Progeny from both treatments were mated for a further two generations (F1 and F2 generations). There was no effect of treatment group on gross fertility across the generations tested. Progeny of the cultured blastocysts had lower body weights to the time of weaning compared to in vivo blastocysts in the P and F1 generations, but not in the F2 generation. At maturity, there was no effect of treatment group on body weight, although thyroid weight was higher in the in vivo blastocyst group in the P generation, while the brain, pituitary, and kidneys were larger in the progeny of the cultured blastocysts of the F1 generation. The OECD/OCDE 416 assessment may have a role as a standardized test for the assessment of the biological consequences of perturbing the growth environment of the preimplantation embryo. Embryo culture influenced the somatometric parameters of the resulting progeny, some of which were maintained across a generation.

Nutri-epigenomics: lifelong remodelling of our epigenomes by nutritional and metabolic factors and beyond

The phenotype of an individual is the result of complex interactions between genotype, epigenome and current, past and ancestral environment, leading to lifelong remodelling of our epigenomes. Various replication-dependent and -independent epigenetic mechanisms are involved in developmental programming, lifelong stochastic and environmental deteriorations, circadian deteriorations, and transgenerational effects. Several types of sequences can be targets of a host of environmental factors and can be associated with specific epigenetic signatures and patterns of gene expression. Depending on the nature and intensity of the insult, the critical spatiotemporal windows and developmental or lifelong processes involved, these epigenetic alterations can lead to permanent changes in tissue and organ structure and function, or to reversible changes using appropriate epigenetic tools. Given several encouraging trials, prevention and therapy of age- and lifestyle-related diseases by individualised tailoring of optimal epigenetic diets or drugs are conceivable. However, these interventions will require intense efforts to unravel the complexity of these epigenetic, genetic and environment interactions and to evaluate their potential reversibility with minimal side effects.

Transcriptional and post-transcriptional regulation of retrotransposons IAP and MuERV-L affect pluripotency of mice ES cells

BACKGROUND

In the mouse, culture of embryonic stem (ES) cells may decrease their pluripotency and give rise to foetal abnormalities in recipient embryos. These abnormalities are frequently associated with both, chromosome abnormalities or epigenetic alteration of imprinting genes; however, little is known about the epigenetic stability of endogenous retrotransposable elements (REs). In our laboratory, we came across a R1 ES cell line, which at passage 27, lost the ability of germline transmission and started inducing the kinky tail phenotype in all chimeric animals produced with it.

METHODS

In order to investigate whether this phenotype was associated with chromosome alteration, inadvertent differentiation, or epigenetic modification, we characterized and compared this R1 ES cell line at passage 27 with an early passage and with a second ES cell line C57/CBAF1 generated in our laboratory. We assessed: i) karyotype; ii) expression of pluripotent and differentiation markers, iii) mRNA transcription by qRT-PCR of two REs, intracisternal-A particle (IAP) and murine endogenous-retrovirus-L (MuERV-L), and iv) methylation of IAP and MuERV-L.

RESULTS

The R1 ES cell at passage 27, presented normal morphology, karyotype, and expression of genetic markers characteristic of pluripotent; however, it was detected an altered mRNA transcription of sense and antisense RNA strands of both REs, concomitantly with an altered methylation pattern for the IAP element but not for MuERV-L. These results indicate that besides methylation, other post-transcriptional processes are involved in gene silencing of some REs; and that culture of ES cells may decrease their pluripotency by producing inadvertent alterations in the expression of REs without significantly affecting the morphology, chromosome structure, and expression of pluripotent or differentiation markers.

CONCLUSION

Inadvertent REs instability may have important consequences for the use of ES cells in transgenesis (chimera formation) or in cell therapy.

Inhibitors of histone deacetylases and DNA methyltransferases alter imprinted gene regulation in embryonic stem cells

Pluripotent embryonic stem cells are able to differentiate into a variety of cell types, thereby making them a valuable source for transplantation medicine. Recent studies have reported the use of pharmacological agents, namely 5-Aza-Cytidine (5AzaC) and Trichostatin A (TSA), to guide embryonic stem (ES) cells to differentiate into specific cellular lineages. However, those drugs are known to be potent inhibitors of DNA methyltransferases and/or histone deacetylases. Since both epigenetic mechanisms are involved in the expression of imprinted genes in fetal and adult somatic tissues, it is essential to investigate further the role of these agents in regulating imprinted gene expression in embryonic cells. Embryonic stem cells were exposed to 5AzaC and TSA and analyzed for transcript abundance of a number of imprinted and non-imprinted marker genes. Most imprinted gene transcripts increased following exposure to 5AzaC or TSA alone and responded in either an additive or synergistic manner when exposed to both drugs together. Interestingly, transcript levels of several imprinted genes remained high and in some cases, increased further after drug removal or even after passaging the cells, indicating a long lasting and retarded effect on gene expression. Together, our results suggest that DNA methylation and histone acetylation play jointly an important epigenetic role in governing imprinted gene expression in embryonic stem cells. Moreover, these results describe the sensitivity and irreversibility of embryonic stem cells to epigenetic modifiers, highlighting potential risks for their use in therapeutic applications.

Environmental and nutritional effects on the epigenetic regulation of genes

Major efforts have been directed towards the identification of genetic mutations, their use as biomarkers, and the understanding of their consequences on human health and well-being. There is an emerging interest, however, in the possibility that environmentally-induced changes at levels other than the genetic information could have long-lasting consequences as well. This review summarises our current knowledge of how the environment, nutrition, and ageing affect the way mammalian genes are organised and transcribed, without changes in the underlying DNA sequence. Admittedly, the link between environment and epigenetics remains largely to be explored. However, recent studies indicate that environmental factors and diet can perturb the way genes are controlled by DNA methylation and covalent histone modifications. Unexpectedly, and not unlike genetic mutations, aberrant epigenetic alterations and their phenotypic effects can sometimes be passed on to the next generation.

Temporal and parental-specific expression of imprinted genes in a newly derived Chinese human embryonic stem cell line and embryoid bodies

Although the study of imprinted genes in human development is very important, little is known about their expression and regulation in the early differentiation of human tissues due to lack of an appropriate model. In this study, a Chinese human embryonic stem (hES) cell line, SHhES1, was derived and fully characterized. Expression profiles of human imprinted genes were determined by Affymetrix Oligo micro-array in undifferentiated SHhES1 cells and SHhES1-derived embryoid bodies (EBs) at day 3, 8, 13 and 18. Thirty-two known human imprinted genes were detected in undifferentiated ES cells. Significantly, differential expression was found in nine genes at different stages of EB formation. Expression profile changes were confirmed by quantitative real-time reverse transcriptase-polymerase chain reaction in SHhES1 cells as well as in another independently derived hES cell line, HUES-7. In addition, the monoallelic expressions of four imprinted genes were examined in three different passages of undifferentiated ES cells and EBs of both hES cell lines. The monoallelic expressions of imprinted genes, H19, PEG10, NDNL1 and KCNQ1 were maintained in both undifferentiated hES cells and derived EBs. More importantly, with the availability of maternal peripheral blood lymphocyte sample, we demonstrated that the maternal expression of KCNQ1 and the paternal expression of NDNL1 and PEG10 were maintained in SHhES1 cells. These data provide the first demonstration that the parental-specific expression of imprinted genes is stable in EBs after extensive differentiation, also indicating that in vitro fertilization protocol does not disrupt the parental monoallelic expression of the imprinted genes examined.

Global loss of imprinting leads to widespread tumorigenesis in adult mice

Loss of imprinting (LOI), commonly observed in human tumors, refers to loss of monoallelic gene regulation normally conferred by parent-of-origin-specific DNA methylation. To test the function of LOI in tumorigenesis, we developed a model by using transient demethylation to generate imprint-free mouse embryonic stem cells (IF-ES cells). Embryonic fibroblasts derived from IF-ES cells (IF-MEFs) display TGFbeta resistance and reduced p19 and p53 expression and form tumors in SCID mice. IF-MEFs exhibit spontaneous immortalization and cooperate with H-Ras in cellular transformation. Chimeric animals derived from IF-ES cells develop multiple tumors arising from the injected IF-ES cells within 12 months. These data demonstrate that LOI alone can predispose cells to tumorigenesis and identify a pathway through which immortality conferred by LOI lowers the threshold for transformation.

Combined effects of MatrigelTM and growth factors on maintaining undifferentiated murine embryonic stem cells for embryotoxicity testing

Undifferentiated, murine embryonic stem (mES) cells have shown promise as a substrate for identifying embryotoxic chemicals and for studying mechanisms of early developmental injury. However, long-term maintenance of mES cells in an undifferentiated state is problematic. The present study evaluates the combination of Matrigel matrix and three growth factors for this purpose. Biomarkers of mES cell pluripotency, apoptosis, chromosome number and cardiomyocyte differentiation were monitored over 119 population doublings. D3 mES cells retained undifferentiated characteristics, including sustained expression of alkaline phosphatase and stage specific embryonic antigen-1 (SSEA-1) and continued transcription of Pou5f1 (Oct-4). Cell viability remained at > or=95% and population-doubling times averaged 14.3 h over 10 weeks of observation. Caspase-3 activation, a marker of cellular death by apoptosis, was measured in early- and late-passage mES cells. Early-passage cells showed dose-responsive caspase-3 activation following exposure to sodium arsenite, whereas caspase-3 activation of late-passage cells dropped to background levels at toxicant dosages above 50 ppb. Aneuploidy and impaired differentiation into beating cardiomyocytes were noted for late-passage mES cells. Matrigel, combined with growth factors, may sustain undifferentiated mES cells. However, aneuploidy, reduced caspase-3 activation, and inability to differentiate suggests further modifications to the culture system may be needed for long-term propagation of cells for embryotoxicity endpoints.

Review: Genetic and Epigenetic Aspects of Cloning and Potential Effects on Offspring of Cloned Mammals

Although the biological mechanisms by which host cytoplasm and donor nuclei interact to produce a developmentally competent reconstructed embryo remain largely unknown, some advances have been made to our understanding of the genetic and epigenetic factors involved in the of reprogramming of the donor nucleus. Genetic alterations, which comprise changes to the genetic information in both the nuclear and cytoplasm compartments, are passed on to subsequent generations at fertilization and are a potential source of variation among cloned animals and their offspring. Apart from the major chromosomal anomalies found in developmentally arrested embryos and fetuses, less detrimental rearrangements and/or mutations are likely to go unnoticed in most donor cell karyotypes, suggesting that such problems could lead to inheritable anomalies among clones and their offspring. Mitochondrial DNA is also relevant to cloning because most animals inherit most or all of their mitochondria from the host oocyte. Epigenetic alterations to the DNA or to the histone packaging proteins are independent of gene sequences. Aberrant epigenetic events may lead to variable gene expression or mitosis and consequent effects on development and phenotype. Although much of the epigenetic marking is reset during embryogenesis and development, the impact of epimutations on progeny remains unexplored.

Embryonic Stem Cells Expressing Both Platelet Endothelial Cell Adhesion Molecule-1 and Stage-Specific Embryonic Antigen-1 Differentiate Predominantly into Epiblast Cells in a Chimeric Embryo1

We examined the expression of cell-surface markers on subpopulations of mouse embryonic stem (ES) cells to identify those that were associated with cells that had the highest pluripotency. Flow cytometry analysis revealed a wide variation in the expression of platelet endothelial cell adhesion molecule 1 (PECAM-1) and stage-specific embryonic antigen (SSEA)-1 in ES cells. Almost all SSEA-1+ cells expressed a high level of PECAM- 1, and reversible repopulation was observed between PECAM- 1+SSEA-1+ and PECAM-1+SSEA-1- cells. The ES cells carrying the lacZ gene were sorted into three subpopulations: PECAM- 1-SSEA-1-, PECAM-1+SSEA-1-, and PECAM-1+SSEA-1+. Quantitative reverse transcription-polymerase chain reaction revealed a low level of Oct3/4 mRNA expression and an elevation in differentiation maker gene expression in PECAM-1- cells. To compare the pluripotency of these three subpopulations, a single cell from each was injected into eight-cell embryo and ES cells identified at later stages by X-gal staining. At the blastocyst stage, PECAM-1+ SSEA-1+/- cells were found to have differentiated into epiblast cells in high numbers. In contrast, PECAM- 1- cell derivatives localized in the primitive endoderm or trophectoderm. At 6.0-7.0 days post coitum, many PECAM-1+SSEA- 1+ cells were found in the epiblast, but few beta-gal+ cells were detected in any regions of embryos that were injected with cells from the other two populations. These results showed that the expression levels of PECAM-1 and SSEA-1 in ES cells correlated closely with their pluripotency and/or their ability to incorporate into the epiblast of chimeric embryos.