Characterization of mouse embryonic stem cell differentiation into the pancreatic lineage in vitro by transcriptional profiling, quantitative RT-PCR and immunocytochemistry

Imprinted Genes Impact Upon Beta Cell Function in the Current (and Potentially Next) Generation

Beta cell failure lies at the centre of the aetiology and pathogenesis of type 2 diabetes and the epigenetic control of the expression of critical beta cell genes appears to play a major role in this decline. One such group of epigenetically-controlled genes, termed 'imprinted' genes, are characterised by transgenerational monoallelic expression due to differential allelic DNA methylation and play key functional roles within beta cells. Here, we review the evidence for this functional importance of imprinted genes in beta cells as well as their nutritional regulation by the diet and their altered methylation and/or expression in rodent models of diabetes and in type 2 diabetic islets. We also discuss imprinted genes in the context of the next generation, where dietary overnutrition in the parents can lead to their deregulation in the offspring, alongside beta cell dysfunction and defective glucose handling. Both the modulation of imprinted gene expression and the likelihood of developing type 2 diabetes in adulthood are susceptible to the impact of nutritional status in early life. Imprinted loci, therefore, represent an excellent opportunity with which to assess epigenomic changes in beta cells due to the diet in both the current and next generation.

Molecular Characterization of Embryonic Stem Cell-Derived Cardiac Neural Crest-Like Cells Revealed a Spatiotemporal Expression of an Mlc-3 Isoform

Background and Objectives

Pluripotent embryonic stem (ES) cells represent a perfect model system for the investigation of early developmental processes. Besides their differentiation into derivatives of the three primary germ layers, they can also be differentiated into derivatives of the ‘fourth’ germ layer, the neural crest (NC). Due to its multipotency, extensive migration and outstanding capacity to generate a remarkable number of different cell types, the NC plays a key role in early developmental processes. Cardiac neural crest (CNC) cells are a subpopulation of the NC, which are of crucial importance for precise cardiovascular and pharyngeal glands’ development. CNC-associated malformations are rare, but always severe and life-threatening. Appropriate cell models could help to unravel underlying pathomechanisms and to develop new therapeutic options for relevant heart malformations.

Methods

Murine ES cells were differentiated according to a mesodermal-lineage promoting protocol. Expression profiles of ES cell-derived progeny at various differentiation stages were investigated on transcript and protein level.

Results

Comparative expression profiling of murine ES cell multilineage progeny versus undifferentiated ES cells confirmed differentiation into known cell derivatives of the three primary germ layers and provided evidence that ES cells have the capacity to differentiate into NC/CNC-like cells. Applying the NC/CNC cell-specific marker, 4E9R, an unambiguous identification of ES cell-derived NC/CNC-like cells was achieved.

Conclusions

Our findings will facilitate the establishment of an ES cell-derived CNC cell model for the investigation of molecular pathways during cardiac development in health and disease.

Comparison of Germ Cell Gene Expressions in Spontaneous Monolayer versus Embryoid Body Differentiation of Mouse Embryonic Stem Cells toward Germ Cells

Background

Genetic and morphologic similarities between mouse embryonic stem cells (ESCs) and primordial germ cells (PGCs) make it difficult to distinguish differentiation of these two cell types in vitro. Using specific GC markers expressed in low level or even not expressed in ESCs- can help recognize differentiated cells in vitro. We attempted to differentiate the mouse ESCs into Gc-like cells spontaneously in monolayer and EB culture method.

Materials and Methods

In this experimental study, we attempted to differentiate ESCs, Oct4-GFP OG2, into GC-like cells (GCLCs) spontaneously in two different ways, including: i. Spontaneous differentiation of ESCs in monolayer culture as (SP) and ii. Spontaneous differentiation of ESCs using embryoid body (EB) culture method as (EB+SP). During culture, expression level of four GC specific genes (Fkbp6, Mov10l1, Riken and Tex13) and Mvh, Scp3, Stra8, Oct4 were evaluated.

Results

In both groups, Mov10l1 was down-regulated (P=0.3), while Tex13 and Riken were up-regulated (P=0.3 and P=0.04, respectively). Fkbp6 and Stra8 were decreased in EB+SP and they were increased in SP group, while no significant difference was determined between them (P=0.1, P=0.07). Additionally, in SP group, gene expression of Mvh and Scp3 were up-regulated and they had significant differences compared to EB+SP group (P=0.00 and P=0.01, respectively). Oct4 was down-regulated in the both groups. Flow-cytometry analysis showed that mean number of Mvh-positive cells in the SP group was significantly greater compared to ESCs, EB+SP and EB7 groups (P=0.00, P=0.01, and P=0.3, respectively).

Conclusion

These findings showed that ESCs were differentiated into GCLCs in both group. But spontaneous dif- ferentiation of ESCs into GCLCs in SP group (monolayer culture) compared to EB+SP (EB culture methods) has more ability to express GCs markers.

Neuronatin deletion causes postnatal growth restriction and adult obesity in 129S2/Sv mice

OBJECTIVE

Imprinted genes are crucial for the growth and development of fetal and juvenile mammals. Altered imprinted gene dosage causes a variety of human disorders, with growth and development during these crucial early stages strongly linked with future metabolic health in adulthood. Neuronatin (Nnat) is a paternally expressed imprinted gene found in neuroendocrine systems and white adipose tissue and is regulated by the diet and leptin. Neuronatin expression is downregulated in obese children and has been associated with stochastic obesity in C57BL/6 mice. However, our recent studies of Nnat null mice on this genetic background failed to display any body weight or feeding phenotypes but revealed a defect in glucose-stimulated insulin secretion due to the ability of neuronatin to potentiate signal peptidase cleavage of preproinsulin. Nnat deficiency in beta cells therefore caused a lack of appropriate storage and secretion of mature insulin.

METHODS

To further explore the potential role of Nnat in the regulation of body weight and adiposity, we studied classical imprinting-related phenotypes such as placental, fetal, and postnatal growth trajectory patterns that may impact upon subsequent adult metabolic phenotypes.

RESULTS

Here we find that, in contrast to the lack of any body weight or feeding phenotypes on the C57BL/6J background, deletion of Nnat in mice on 129S2/Sv background causes a postnatal growth restriction with reduced adipose tissue accumulation, followed by catch up growth after weaning. This was in the absence of any effect on fetal growth or placental development. In adult 129S2/Sv mice, Nnat deletion was associated with hyperphagia, reduced energy expenditure, and partial leptin resistance. Lack of neuronatin also potentiated obesity caused by either aging or high fat diet feeding.

CONCLUSIONS

The imprinted gene Nnat plays a key role in postnatal growth, adult energy homeostasis, and the pathogenesis of obesity via catch up growth effects, but this role is dependent upon genetic background.

Cell differentiation mediated by co-culture of human umbilical cord blood stem cells with murine hepatic cells

In the present study, purified human cord blood stem cells were co-cultivated with murine hepatic alpha mouse liver 12 (AML12) cells to compare the effect on endodermal stem cell differentiation by either direct cell-cell interaction or by soluble factors in conditioned hepatic cell medium. With that approach, we want to mimic in vitro the situation of preclinical transplantation experiments using human cells in mice. Cord blood stem cells, cultivated with hepatic conditioned medium, showed a low endodermal differentiation but an increased connexin 32 (Cx32) and Cx43, and cytokeratin 8 (CK8) and CK19 expression was monitored by reverse transcription polymerase chain reaction (RT-PCR). Microarray profiling indicated that in cultivated cord blood cells, 604 genes were upregulated 2-fold, with the highest expression for epithelial CK19 and epithelial cadherin (E-cadherin). On ultrastructural level, there were no major changes in the cellular morphology, except a higher presence of phago(ly)some-like structures observed. Direct co-culture of AML12 cells with cord blood cells led to less incisive differentiation with increased sex-determining region Y-box 17 (SOX17), Cx32 and Cx43, as well as epithelial CK8 and CK19 expressions. On ultrastructural level, tight cell contacts along the plasma membranes were revealed. FACS analysis in co-cultivated cells quantified dye exchange on low level, as also proved by time relapse video-imaging of labelled cells. Modulators of gap junction formation influenced dye transfer between the co-cultured cells, whereby retinoic acid increased and 3-heptanol reduced the dye transfer. The study indicated that the cell-co-cultured model of human umbilical cord blood cells and murine AML12 cells may be a suitable approach to study some aspects of endodermal/hepatic cell differentiation induction.

Neuronatin gene: Imprinted and misfolded: Studies in Lafora disease, diabetes and cancer may implicate NNAT-aggregates as a common downstream participant in neuronal loss

Neuronatin (NNAT) is a ubiquitous and highly conserved mammalian gene involved in brain development. Its mRNA isoforms, chromosomal location, genomic DNA structure and regulation have been characterized. More recently there has been rapid progress in the understanding of its function in physiology and human disease. In particular there is fairly direct evidence implicating neuronatin in the causation of Lafora disease and diabetes. Neuronatin protein has a strong predisposition to misfold and form cellular aggregates that cause cell death by apoptosis. Aggregation of Neuronatin within cortical neurons and resulting cell death is the hallmark of Lafora disease, a progressive and fatal neurodegenerative disease. Under high glucose conditions simulating diabetes, neuronatin protein also accumulates and destroys pancreatic beta cells. The neuronatin gene is imprinted and only the paternal allele is normally expressed in the adult. However, changes in DNA methylation may cause the maternal allele to lose imprinting and trigger cell proliferation and metastasis. Neuronatin has also been shown to be translated peripherally within the dendrites of neurons, a finding of relevance in synaptic plasticity. The current understanding of the function of neuronatin raises the possibility that this gene may participate in the common downstream mechanisms associated with aberrant neuronal growth and death. A better understanding of these mechanisms may open new therapeutic targets to help modify the progression of devastating neurodegenerative conditions such as Alzheimer's and anterior horn cell disease.

Transcription factor lbx1 expression in mouse embryonic stem cell-derived phenotypes

Transcription factor Lbx1 is known to play a role in the migration of muscle progenitor cells in limb buds and also in neuronal determination processes. In addition, involvement of Lbx1 in cardiac neural crest-related cardiogenesis was postulated. Here, we used mouse embryonic stem (ES) cells which have the capacity to develop into cells of all three primary germ layers. During in vitro differentiation, ES cells recapitulate cellular developmental processes and gene expression patterns of early embryogenesis. Transcript analysis revealed a significant upregulation of Lbx1 at the progenitor cell stage. Immunofluorescence staining confirmed the expression of Lbx1 in skeletal muscle cell progenitors and GABAergic neurons. To verify the presence of Lbx1 in cardiac cells, triple immunocytochemistry of ES cell-derived cardiomyocytes and a quantification assay were performed at different developmental stages. Colabeling of Lbx1 and cardiac specific markers troponin T, α-actinin, GATA4, and Nkx2.5 suggested a potential role in early myocardial development.

The embryonic stem cell test combined with toxicogenomics as an alternative testing model for the assessment of developmental toxicity

One of the most studied in vitro alternative testing methods for identification of developmental toxicity is the embryonic stem cell test (EST). Although the EST has been formally validated, the applicability domain as well as the predictability of the model needs further study to allow successful implementation of the EST as an alternative testing method in regulatory toxicity testing. Genomics technologies have already provided a proof of principle of their value in identification of toxicants such as carcinogenic compounds. Also within the EST, gene expression profiling has shown its value in the identification of developmental toxicity and in the evaluation of factors critical for risk assessment, such as dose and time responses. It is expected that the implementation of genomics into the EST will provide a more detailed end point evaluation as compared to the classical morphological scoring of differentiation cultures. Therefore, genomics may contribute to improvement of the EST, both in terms of definition of its applicability domain as well as its predictive capacity. In the present review, we present the progress that has been made with regard to the prediction of developmental toxicity using the EST combined with transcriptomics. Furthermore, we discuss the developments of additional aspects required for further optimization of the EST, including kinetics, the use of human embryonic stem cells (ESC) and computational toxicology. Finally, the current and future use of the EST model for prediction of developmental toxicity in testing strategies and in regulatory toxicity evaluations is discussed.

The FunGenES database: a genomics resource for mouse embryonic stem cell differentiation

Embryonic stem (ES) cells have high self-renewal capacity and the potential to differentiate into a large variety of cell types. To investigate gene networks operating in pluripotent ES cells and their derivatives, the “Functional Genomics in Embryonic Stem Cells” consortium (FunGenES) has analyzed the transcriptome of mouse ES cells in eleven diverse settings representing sixty-seven experimental conditions. To better illustrate gene expression profiles in mouse ES cells, we have organized the results in an interactive database with a number of features and tools. Specifically, we have generated clusters of transcripts that behave the same way under the entire spectrum of the sixty-seven experimental conditions; we have assembled genes in groups according to their time of expression during successive days of ES cell differentiation; we have included expression profiles of specific gene classes such as transcription regulatory factors and Expressed Sequence Tags; transcripts have been arranged in “Expression Waves” and juxtaposed to genes with opposite or complementary expression patterns; we have designed search engines to display the expression profile of any transcript during ES cell differentiation; gene expression data have been organized in animated graphs of KEGG signaling and metabolic pathways; and finally, we have incorporated advanced functional annotations for individual genes or gene clusters of interest and links to microarray and genomic resources. The FunGenES database provides a comprehensive resource for studies into the biology of ES cells.