In vertebrate embryos, the earliest definitive marker for the neural plate, which will give rise to the entire central nervous system, is the transcription factor Sox2. Although some of the extracellular signals that regulate neural plate fate have been identified, we know very little about the mechanisms controlling Sox2 expression and thus neural plate identity. Here, we use electroporation for gain- and loss-of-function in the chick embryo, in combination with bimolecular fluorescence complementation, two-hybrid screens, chromatin immunoprecipitation, and reporter assays to study protein interactions that regulate expression of N2, the earliest enhancer of Sox2 to be activated and which directs expression to the largest part of the neural plate. We show that interactions between three coiled-coil domain proteins (ERNI, Geminin, and BERT), the heterochromatin proteins HP1α and HP1γ acting as repressors, and the chromatin-remodeling enzyme Brm acting as activator control the N2 enhancer. We propose that this mechanism regulates the timing of Sox2 expression as part of the process of establishing neural plate identity.

The unique properties of embryonic stem cells (ESC) rely on long-lasting self-renewal and their ability to switch in all adult cell type programs. Recent advances have shown that regulations at the chromatin level sustain both ESC properties along with transcription factors. We have focused our interest on the epigenetic modulator HP1γ (Heterochromatin Protein 1, isoform γ) that binds histones H3 methylated at lysine 9 (meH3K9) and is highly plastic in its distribution and association with the transcriptional regulation of specific genes during cell fate transitions. These characteristics of HP1γ make it a good candidate to sustain the ESC flexibility required for rapid program changes during differentiation. Using RNA interference, we describe the functional role of HP1γ in mouse ESC. The analysis of HP1γ deprived cells in proliferative and in various differentiating conditions was performed combining functional assays with molecular approaches (RT-qPCR, microarray). We show that HP1γ deprivation slows down the cell cycle of ESC and decreases their resistance to differentiating conditions, rendering the cells poised to differentiate. In addition, HP1γ depletion hampers the differentiation to the endoderm as compared with the differentiation to the neurectoderm or the mesoderm. Altogether, our results reveal the role of HP1γ in ESC self-renewal and in the balance between the pluripotent and the differentiation programs.

White adipose tissues are functionally heterogeneous and differently manage the excess of energy supply. While the expansion of subcutaneous adipose tissues (SAT) is protective in obesity, that of visceral adipose tissues (VAT) correlates with the emergence of metabolic diseases. Maintained in fat pads throughout life, adipose stem cells (ASC) are mesenchymal-like stem cells with adipogenesis and multipotent differentiation potential. ASC from distinct fat pads have long been reported to present distinct proliferation and differentiation potentials that are maintained in culture, yet the origins of these intrinsic differences are still unknown. Metabolism is central to stem cell fate decision in line with environmental changes. In this study, we performed high-resolution nuclear magnetic resonance (NMR) metabolomic analyses of ASC culture supernatants in order to characterize their metabolic phenotype in culture. We identified and quantified 29 ASC exometabolites and evaluated their consumption or secretion over 72 h of cell culture. Both ASC used glycolysis and mitochondrial metabolism, as evidenced by the high secretions of lactate and citrate, respectively, but V-ASC mostly used glycolysis. By varying the composition of the cell culture medium, we showed that glutaminolysis, rather than glycolysis, supported the secretion of pyruvate, alanine, and citrate, evidencing a peculiar metabolism in ASC cells. The comparison of the two types of ASC in glutamine-free culture conditions also revealed the role of glutaminolysis in the limitation of pyruvate routing towards the lactate synthesis, in S-ASC but not in V-ASC. Altogether, our results suggest a difference between depots in the capacity of ASC mitochondria to assimilate pyruvate, with probable consequences on their differentiation potential in pathways requiring an increased mitochondrial activity. These results highlight a pivotal role of metabolic mechanisms in the discrimination between ASC and provide new perspectives in the understanding of their functional differences.

cENS-1/cERNI genes have been shown to be expressed very early during chicken embryonic development and as well as in pluripotent chicken embryonic stem (CES) cells. We have previously identified a promoter region, which is specifically active in CES cells compared to differentiated cells. In order to understand the molecular mechanisms which regulate the cENS-1/cERNI promoter, we analyzed the cis-acting elements of this promoter in CES and differentiated cells. We identified a short sequence, named the B region, 5'-CAAG TCCAGG CAAG-3', that exhibits a strong enhancer activity in CES and differentiated cells. Mutation of the B region in the whole cENS-1 promoter strongly decreases the promoter activity in CES cells, suggesting that this region is essential for activating the promoter. The B region is similar to the previously described response element for the transcription factor CP2 and we show by supershift experiments that a protein complex containing CP2 is bound to this B response element. All these results identify a nuclear factor belonging to the CP2 transcription factor family that is crucial for the activation of the cENS-1/cERNI promoter. The pattern of expression of cCP2 in early chicken embryo before gastrulation is very similar to that of cENS-1/cERNI which strongly suggests that cCP2 also plays an essential role in gene expression early in embryonic development.

BackgroundLong terminal repeats (LTR) from endogenous retroviruses (ERV) are source of binding sites for transcription factors which affect the host regulatory networks in different cell types, including pluripotent cells. The embryonic epiblast is made of pluripotent cells that are subjected to opposite transcriptional regulatory networks to give rise to distinct embryonic and extraembryonic lineages. To assess the transcriptional contribution of ERV to early developmental processes, we have characterized in vitro and in vivo the regulation of ENS-1, a host adopted and developmentally regulated ERV that is expressed in chick embryonic stem cells.ResultsWe show that Ens-1 LTR activity is controlled by two transcriptional pathways that drive pluripotent cells to alternative developmental fates. Indeed, both Nanog that maintains pluripotency and Gata4 that induces differentiation toward extraembryonic endoderm independently activate the LTR. Ets coactivators are required to support Gata factors' activity thus preventing inappropriate activation before epigenetic silencing occurs during differentiation. Consistent with their expression patterns during chick embryonic development, Gata4, Nanog and Ets1 are recruited on the LTR in embryonic stem cells; in the epiblast the complementary expression of Nanog and Gata/Ets correlates with the Ens-1 gene expression pattern; and Ens-1 transcripts are also detected in the hypoblast, an extraembryonic tissue expressing Gata4 and Ets2, but not Nanog. Accordingly, over expression of Gata4 in embryos induces an ectopic expression of Ens-1.ConclusionOur results show that Ens-1 LTR have co-opted conditions required for the emergence of extraembryonic tissues from pluripotent epiblasts cells. By providing pluripotent cells with intact binding sites for Gata, Nanog, or both, Ens-1 LTR may promote distinct transcriptional networks in embryonic stem cells subpopulations and prime the separation between embryonic and extraembryonic fates.

Embryonic stem (ES) cells are important developmental cells that appear very early during development and subsequently give rise to all the cell lineages of the future adult organism. In these cells a limited subset of transcription factors is expressed that are well conserved among species and essential for the fate of the stem cell. The transcriptome analysis of ES cells from chicken has revealed a gene family, cENS, that is specifically expressed in ES cells and in early embryos and is repressed during the differentiation process. This family is characterized by displaying retroviral structures and shares no homology with other species' genes. These characteristics are probably not restricted to the chicken genome and raise the question of whether similar genes are present and have been maintained in other species. We have examined the different copies of this gene in the sequenced chicken genome to investigate its dynamics and its evolution. We have distinguished two groups of cENS-related copies. The first group, resulting from recent transposition events, contains the transcribed ENS-1 and ENS-3 plus copies subjected to negative selection pressures. The second group contains degenerate copies that were integrated into the genome earlier. Comparison with copies previously isolated from three Galliformes showed that they are also subjected to selection pressures. We also detected numerous solo-LTRs containing the ENS-1 promoter that may control the expression of host genes. Taken together, these findings suggest a function sustained by a neogene of retroviral origin during the early stages of chicken development.

P rotein-energy wasting (PEW) and cachexia, a severe form of PEW, are associated with poor survival in chronic kidney disease (CKD) and may occur in 20% to 80% of hemodialysis (HD) patients. 1,2 However, the mechanisms involved in uremic PEW are complex and remain poorly understood. PEW is different from malnutrition as it cannot be overcome by nutritional supplementation. 3 To date, there are few, if any, effective therapies to improve PEW associated with CKD. 4 Whether there is an increase in resting energy expenditure (REE), and its role in PEW during CKD, remain topics of

Mesenchymal stem cells from healthy adipose tissue are adipocytes progenitors with immunosuppressive potential that are used for years in cell therapy. Whether adipose stem cells (ASC) may prevent inflammation in early obesity is not known. To address this question, we performed a kinetic study of high-fat (HF) diet induced obesity in mice to follow the immune regulating functions of adipose stem cells (ASC) isolated from the subcutaneous (SAT) and the visceral adipose tissue (VAT).Our results show that, early in obesity and before inflammation was detected, HF diet durably and differently activated ASC from SAT and VAT. Subcutaneous ASC from HF-fed mice strongly inhibited the proliferation of activated T lymphocytes, whereas visceral ASC selectively inhibited TNFα expression by macrophages and simultaneously released higher concentrations of IL6. These depot specific differences may contribute to the low-grade inflammation that develops with obesity in VAT while inflammation in SAT is delayed. The mechanisms involved differ from those already described for naïve cells activation with inflammatory cytokines and probably engaged metabolic activation. These results evidence that adipose stem cells are metabolic sensors acquiring an obesity-primed immunocompetent state in answer to depot-specific intrinsic features with overnutrition, placing these cells ahead of inflammation in the local dialog with immune cells.