Institute of Genetics and Genomics in Geneva iGE3

Genève, Switzerland

Institute of Genetics and Genomics in Geneva iGE3

Genève, Switzerland
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Petrenko V.,University of Geneva | Petrenko V.,Institute of Genetics and Genomics in Geneva iGE3 | Gosmain Y.,University of Geneva | Dibner C.,University of Geneva | Dibner C.,Institute of Genetics and Genomics in Geneva iGE3
Frontiers in Endocrinology | Year: 2017

Circadian clocks have been developed in evolution as an anticipatory mechanism allowing for adaptation to the constantly changing light environment due to rotation of the Earth. This mechanism is functional in all light-sensitive organisms. There is a considerable body of evidence on the tight connection between the circadian clock and most aspects of physiology and metabolism. Clocks, operative in the pancreatic islets, have caught particular attention in the last years due to recent reports on their critical roles in regulation of insulin secretion and etiology of type 2 diabetes. While β-cell clocks have been extensively studied during the last years, α-cell clocks and their role in islet function and orchestration of glucose metabolism stayed unexplored, largely due to the difficulty to isolate α-cells, which represents a considerable technical challenge. Here, we provide a detailed description of an experimental approach for the isolation of separate mouse α- and β-cell population, culture of isolated primary α- and β-cells, and their subsequent long-term high-resolution circadian bioluminescence recording. For this purpose, a triple reporter ProGlucagon-Venus/RIP-Cherry/Per2:Luciferase mouse line was established, carrying specific fluorescent reporters for α- and β-cells, and luciferase reporter for monitoring the molecular clockwork. Flow cytometry fluorescence-activated cell sorting allowed separating pure α- and β-cell populations from isolated islets. Experimental conditions, developed by us for the culture of functional primary mouse α- and β-cells for at least 10 days, will be highlighted. Importantly, temporal analysis of freshly isolated α- and β-cells around-the-clock revealed preserved rhythmicity of core clock genes expression. Finally, we describe the setting to assess circadian rhythm in cultured α- and β-cells synchronized in vitro. The here-described methodology allows to analyze the functional properties of primary α- and β-cells under physiological or pathophysiological conditions and to assess the islet cellular clock properties. © 2017 Petrenko, Gosmain and Dibner.

Shi T.,Friedrich Miescher Institute for Biomedical Research | Bunker R.D.,Friedrich Miescher Institute for Biomedical Research | Mattarocci S.,Institute of Genetics and Genomics in Geneva iGE3 | Ribeyre C.,Institute of Genetics and Genomics in Geneva iGE3 | And 9 more authors.
Cell | Year: 2013

Yeast telomeres comprise irregular TG1-3 DNA repeats bound by the general transcription factor Rap1. Rif1 and Rif2, along with Rap1, form the telosome, a protective cap that inhibits telomerase, counteracts SIR-mediated transcriptional silencing, and prevents inadvertent recognition of telomeres as DNA double-strand breaks. We provide a molecular, biochemical, and functional dissection of the protein backbone at the core of the yeast telosome. The X-ray structures of Rif1 and Rif2 bound to the Rap1 C-terminal domain and that of the Rif1 C terminus are presented. Both Rif1 and Rif2 have separable and independent Rap1-binding epitopes, allowing Rap1 binding over large distances (42-110 Å). We identify tetramerization (Rif1) and polymerization (Rif2) modules that, in conjunction with the long-range binding, give rise to a higher-order architecture that interlinks Rap1 units. This molecular Velcro relies on Rif1 and Rif2 to recruit and stabilize Rap1 on telomeric arrays and is required for telomere homeostasis in vivo. © 2013 Elsevier Inc.

PubMed | Institute of Genetics and Genomics in Geneva iGE3, University of California at San Francisco and University of Geneva
Type: Journal Article | Journal: Diabetes, obesity & metabolism | Year: 2016

To determine the impact of a functional human islet clock on insulin secretion and gene transcription.Efficient circadian clock disruption was achieved in human pancreatic islet cells by small interfering RNA-mediated knockdown of CLOCK. Human islet secretory function was assessed in the presence or absence of a functional circadian clock by stimulated insulin secretion assays, and by continuous around-the-clock monitoring of basal insulin secretion. Large-scale transcription analysis was accomplished by RNA sequencing, followed by quantitative RT-PCR analysis of selected targets.Circadian clock disruption resulted in a significant decrease in both acute and chronic glucose-stimulated insulin secretion. Moreover, basal insulin secretion by human islet cells synchronized in vitro exhibited a circadian pattern, which was perturbed upon clock disruption. RNA sequencing analysis suggested alterations in 352 transcript levels upon circadian clock disruption. Among them, key regulators of the insulin secretion pathway (GNAQ, ATP1A1, ATP5G2, KCNJ11) and transcripts required for granule maturation and release (VAMP3, STX6, SLC30A8) were affected.Using our newly developed experimental approach for efficient clock disruption in human pancreatic islet cells, we show for the first time that a functional -cell clock is required for proper basal and stimulated insulin secretion. Moreover, clock disruption has a profound impact on the human islet transcriptome, in particular, on the genes involved in insulin secretion.

Stranger B.E.,Wellcome Trust Sanger Institute | Stranger B.E.,Brigham and Women's Hospital | Stranger B.E.,The Broad Institute of MIT and Harvard | Stranger B.E.,Harvard University | And 30 more authors.
PLoS Genetics | Year: 2012

The genetic basis of gene expression variation has long been studied with the aim to understand the landscape of regulatory variants, but also more recently to assist in the interpretation and elucidation of disease signals. To date, many studies have looked in specific tissues and population-based samples, but there has been limited assessment of the degree of inter-population variability in regulatory variation. We analyzed genome-wide gene expression in lymphoblastoid cell lines from a total of 726 individuals from 8 global populations from the HapMap3 project and correlated gene expression levels with HapMap3 SNPs located in cis to the genes. We describe the influence of ancestry on gene expression levels within and between these diverse human populations and uncover a non-negligible impact on global patterns of gene expression. We further dissect the specific functional pathways differentiated between populations. We also identify 5,691 expression quantitative trait loci (eQTLs) after controlling for both non-genetic factors and population admixture and observe that half of the cis-eQTLs are replicated in one or more of the populations. We highlight patterns of eQTL-sharing between populations, which are partially determined by population genetic relatedness, and discover significant sharing of eQTL effects between Asians, European-admixed, and African subpopulations. Specifically, we observe that both the effect size and the direction of effect for eQTLs are highly conserved across populations. We observe an increasing proximity of eQTLs toward the transcription start site as sharing of eQTLs among populations increases, highlighting that variants close to TSS have stronger effects and therefore are more likely to be detected across a wider panel of populations. Together these results offer a unique picture and resource of the degree of differentiation among human populations in functional regulatory variation and provide an estimate for the transferability of complex trait variants across populations. © 2012 Stranger et al.

Nikolaev S.I.,University of Geneva | Rimoldi D.,University of Lausanne | Iseli C.,University of Lausanne | Iseli C.,Swiss Institute of Bioinformatics | And 22 more authors.
Nature Genetics | Year: 2012

We performed exome sequencing to detect somatic mutations in protein-coding regions in seven melanoma cell lines and donor-matched germline cells. All melanoma samples had high numbers of somatic mutations, which showed the hallmark of UV-induced DNA repair. Such a hallmark was absent in tumor sample-specific mutations in two metastases derived from the same individual. Two melanomas with non-canonical BRAF mutations harbored gain-of-function MAP2K1 and MAP2K2 (MEK1 and MEK2, respectively) mutations, resulting in constitutive ERK phosphorylation and higher resistance to MEK inhibitors. Screening a larger cohort of individuals with melanoma revealed the presence of recurring somatic MAP2K1 and MAP2K2 mutations, which occurred at an overall frequency of 8%. Furthermore, missense and nonsense somatic mutations were frequently found in three candidate melanoma genes, FAT4, LRP1B and DSC1. © 2012 Nature America, Inc. All rights reserved.

Lukowski S.W.,University of Geneva | Lukowski S.W.,Institute of Genetics and Genomics in Geneva iGE3 | Fish R.J.,University of Geneva | Fish R.J.,Institute of Genetics and Genomics in Geneva iGE3 | And 9 more authors.
Genomics | Year: 2015

The expression of plasma proteins changes dramatically as a result of cytokine induction, particularly interleukin-6, and their levels are used as clinical markers of inflammation. miRNAs are important regulators of gene expression and play significant roles in many inflammatory diseases and processes. The interactions between miRNAs and the genes that they regulate during the acute phase response have not been investigated. We examined the effects of IL-6 stimulation on the transcriptome and miRNome of human and mouse primary hepatocytes and the HepG2 cell line. Using an integrated analysis, we identified differentially expressed miRNAs whose seed sequences are significantly enriched in the 3' untranslated regions of differentially expressed genes, many of which are involved in inflammation-related pathways. Our finding that certain miRNAs may de-repress critical acute phase proteins within acute timeframes has important biological and clinical implications. © 2015 Elsevier Inc.

Kubik S.,Institute of Genetics and Genomics in Geneva iGE3 | Bruzzone M.J.,Institute of Genetics and Genomics in Geneva iGE3 | Jacquet P.,Ecole Polytechnique Federale de Lausanne | Falcone J.-L.,University of Geneva | And 2 more authors.
Molecular Cell | Year: 2015

Previous studies indicate that eukaryotic promoters display a stereotypical chromatin landscape characterized by a well-positioned +1 nucleosome near the transcription start site and an upstream -1 nucleosome that together demarcate a nucleosome-free (or -depleted) region. Here we present evidence that there are two distinct types of promoters distinguished by the resistance of the -1 nucleosome to micrococcal nuclease digestion. These different architectures are characterized by two sequence motifs that are broadly deployed at one set of promoters where a nuclease-sensitive ("fragile") nucleosome forms, but concentrated in a narrower, nucleosome-free region at all other promoters. The RSC nucleosome remodeler acts through the motifs to establish stable +1 and -1 nucleosome positions, while binding of a small set of general regulatory (pioneer) factors at fragile nucleosome promoters plays a key role in their destabilization. We propose that the fragile nucleosome promoter architecture is adapted for regulation of highly expressed, growth-related genes. © 2015 Elsevier Inc.

Dermitzakis E.T.,University of Geneva | Dermitzakis E.T.,Institute of Genetics and Genomics in Geneva iGE3
Nature Reviews Genetics | Year: 2012

Recent developments in the collection and analysis of cellular multilayered data in large cohorts with extensive organismal phenotyping promise to reveal links between genetic variation and biological processes. The use of these cellular resources as models for human biology-known as 'cellular phenotyping'-is likely to transform our understanding of the genetic and long-term environmental influences on complex traits. I discuss the advantages and caveats of a deeper analysis of cellular phenotypes in large cohorts and assess the methodological advances, resource needs and prospects of this new approach. © 2012 Macmillan Publishers Limited. All rights reserved.

Popadin K.,University of Geneva | Popadin K.,Institute of Genetics and Genomics in Geneva iGE3 | Popadin K.,Russian Academy of Sciences | Gutierrez-Arcelus M.,University of Geneva | And 8 more authors.
American Journal of Human Genetics | Year: 2013

Large intergenic noncoding RNAs (lincRNAs) are still poorly functionally characterized. We analyzed the genetic and epigenetic regulation of human lincRNA expression in the GenCord collection by using three cell types from 195 unrelated European individuals. We detected a considerable number of cis expression quantitative trait loci (cis-eQTLs) and demonstrated that the genetic regulation of lincRNA expression is independent of the regulation of neighboring protein-coding genes. lincRNAs have relatively more cis-eQTLs than do equally expressed protein-coding genes with the same exon number. lincRNA cis-eQTLs are located closer to transcription start sites (TSSs) and their effect sizes are higher than cis-eQTLs found for protein-coding genes, suggesting that lincRNA expression levels are less constrained than that of protein-coding genes. Additionally, lincRNA cis-eQTLs can influence the expression level of nearby protein-coding genes and thus could be considered as QTLs for enhancer activity. Enrichment of expressed lincRNA promoters in enhancer marks provides an additional argument for the involvement of lincRNAs in the regulation of transcription in cis. By investigating the epigenetic regulation of lincRNAs, we observed both positive and negative correlations between DNA methylation and gene expression (expression quantitative trait methylation [eQTMs]), as expected, and found that the landscapes of passive and active roles of DNA methylation in gene regulation are similar to protein-coding genes. However, lincRNA eQTMs are located closer to TSSs than are protein-coding gene eQTMs. These similarities and differences in genetic and epigenetic regulation between lincRNAs and protein-coding genes contribute to the elucidation of potential functions of lincRNAs. © 2013 The American Society of Human Genetics.

Rivera-Rivera C.J.,University of Geneva | Rivera-Rivera C.J.,Institute of Genetics and Genomics in Geneva iGE3 | Montoya-Burgos J.I.,University of Geneva | Montoya-Burgos J.I.,Institute of Genetics and Genomics in Geneva iGE3
Molecular Biology and Evolution | Year: 2016

Phylogenetic inference artifacts can occur when sequence evolution deviates from assumptions made by the models used to analyze them. The combination of strong model assumption violations and highly heterogeneous lineage evolutionary rates can become problematic in phylogenetic inference, and lead to the well-described long-branch attraction (LBA) artifact. Here, we define an objective criterion for assessing lineage evolutionary rate heterogeneity among predefined lineages: the result of a likelihood ratio test between a model in which the lineages evolve at the same rate (homogeneous model) and a model in which different lineage rates are allowed (heterogeneous model). We implement this criterion in the algorithm Locus Specific Sequence Subsampling (LS3), aimed at reducing the effects of LBA in multi-gene datasets. For each gene, LS3 sequentially removes the fastest-evolving taxon of the ingroup and tests for lineage rate homogeneity until all lineages have uniform evolutionary rates. The sequences excluded from the homogeneously evolving taxon subset are flagged as potentially problematic. The software implementation provides the user with the possibility to remove the flagged sequences for generating a new concatenated alignment. We tested LS3 with simulations and two real datasets containing LBA artifacts: a nucleotide dataset regarding the position of Glires within mammals and an amino-acid dataset concerning the position of nematodes within bilaterians. The initially incorrect phylogenies were corrected in all cases upon removing data flagged by LS3. © 2016 The Author 2016. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

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