Author
Alexandre Wagschal
Other affiliations: Centre national de la recherche scientifique, University of Montpellier
Bio: Alexandre Wagschal is an academic researcher from Harvard University. The author has contributed to research in topics: DNA methylation & Genomic imprinting. The author has an hindex of 14, co-authored 19 publications receiving 6505 citations. Previous affiliations of Alexandre Wagschal include Centre national de la recherche scientifique & University of Montpellier.
Papers
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TL;DR: It is proposed that bivalent domains silence developmental genes in ES cells while keeping them poised for activation, highlighting the importance of DNA sequence in defining the initial epigenetic landscape and suggesting a novel chromatin-based mechanism for maintaining pluripotency.
5,131 citations
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TL;DR: Study of the Kcnq1 domain on mouse distal chromosome 7 underscores the importance of histone methylation in placental imprinting and identifies mechanistic similarities with X-chromosome inactivation in extraembryonic tissues, suggesting that the two epigenetic mechanisms are evolutionarily linked.
Abstract: Imprinted genes are clustered in domains, and their allelic repression is mediated by imprinting control regions1,2,3. These imprinting control regions are marked by DNA methylation, which is essential to maintain imprinting in the embryo4. To explore how imprinting is regulated in placenta, we studied the Kcnq1 domain on mouse distal chromosome 7. This large domain is controlled by an intronic imprinting control region5,6 and comprises multiple genes that are imprinted in placenta, without the involvement of promoter DNA methylation7,8,9,10. We found that the paternal repression along the domain involves acquisition of trimethylation at Lys27 and dimethylation at Lys9 of histone H3. Eed-Ezh2 Polycomb complexes are recruited to the paternal chromosome and potentially regulate its repressive histone methylation. Studies on embryonic stem cells and early embryos support our proposal that chromatin repression is established early in development and is maintained in the placenta. In the embryo, however, imprinting is stably maintained only at genes that have promoter DNA methylation. These data underscore the importance of histone methylation in placental imprinting and identify mechanistic similarities with X-chromosome inactivation in extraembryonic tissues, suggesting that the two epigenetic mechanisms are evolutionarily linked.
428 citations
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TL;DR: Findings support the notion that altered expression of miRNAs may contribute to abnormal blood lipid levels, predisposing individuals to human cardiometabolic disorders.
Abstract: Genome-wide association studies (GWASs) have linked genes to various pathological traits. However, the potential contribution of regulatory noncoding RNAs, such as microRNAs (miRNAs), to a genetic predisposition to pathological conditions has remained unclear. We leveraged GWAS meta-analysis data from >188,000 individuals to identify 69 miRNAs in physical proximity to single-nucleotide polymorphisms (SNPs) associated with abnormal levels of circulating lipids. Several of these miRNAs (miR-128-1, miR-148a, miR-130b, and miR-301b) control the expression of key proteins involved in cholesterol-lipoprotein trafficking, such as the low-density lipoprotein (LDL) receptor (LDLR) and the ATP-binding cassette A1 (ABCA1) cholesterol transporter. Consistent with human liver expression data and genetic links to abnormal blood lipid levels, overexpression and antisense targeting of miR-128-1 or miR-148a in high-fat diet-fed C57BL/6J and Apoe-null mice resulted in altered hepatic expression of proteins involved in lipid trafficking and metabolism, and in modulated levels of circulating lipoprotein-cholesterol and triglycerides. Taken together, these findings support the notion that altered expression of miRNAs may contribute to abnormal blood lipid levels, predisposing individuals to human cardiometabolic disorders.
215 citations
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TL;DR: A role for miR-148a is uncovered as a key regulator of hepatic LDL-C clearance through direct modulation of LDLR expression and the therapeutic potential of inhibiting miR -148a to ameliorate an elevated LDL/HDL-C ratio, a prominent risk factor for cardiovascular disease is demonstrated.
Abstract: The hepatic low-density lipoprotein receptor (LDLR) pathway is essential for clearing circulating LDL cholesterol (LDL-C). Whereas the transcriptional regulation of LDLR is well characterized, the post-transcriptional mechanisms that govern LDLR expression are just beginning to emerge. Here we develop a high-throughput genome-wide screening assay to systematically identify microRNAs (miRNAs) that regulate LDLR activity in human hepatic cells. From this screen we identified and characterized miR-148a as a negative regulator of LDLR expression and activity and defined a sterol regulatory element-binding protein 1 (SREBP1)-mediated pathway through which miR-148a regulates LDL-C uptake. In mice, inhibition of miR-148a increased hepatic LDLR expression and decreased plasma LDL-C. Moreover, we found that miR-148a regulates hepatic expression of ATP-binding cassette, subfamily A, member 1 (ABCA1) and circulating high-density lipoprotein cholesterol (HDL-C) levels in vivo. These studies uncover a role for miR-148a as a key regulator of hepatic LDL-C clearance through direct modulation of LDLR expression and demonstrate the therapeutic potential of inhibiting miR-148a to ameliorate an elevated LDL-C/HDL-C ratio, a prominent risk factor for cardiovascular disease.
212 citations
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TL;DR: In the embryo and placenta, the differential DNA methylation at ICRs and imprinted genes is maintained in the absence of G9a, and this provides the first evidence for the involvement of an HMT and suggests that histone methylation contributes to imprinted gene repression in the trophoblast.
Abstract: Whereas DNA methylation is essential for genomic imprinting, the importance of histone methylation in the allelic expression of imprinted genes is unclear. Imprinting control regions (ICRs), however, are marked by histone H3-K9 methylation on their DNA-methylated allele. In the placenta, the paternal silencing along the Kcnq1 domain on distal chromosome 7 also correlates with the presence of H3-K9 methylation, but imprinted repression at these genes is maintained independently of DNA methylation. To explore which histone methyltransferase (HMT) could mediate the allelic H3-K9 methylation on distal chromosome 7, and at ICRs, we generated mouse conceptuses deficient for the SET domain protein G9a. We found that in the embryo and placenta, the differential DNA methylation at ICRs and imprinted genes is maintained in the absence of G9a. Accordingly, in embryos, imprinted gene expression was unchanged at the domains analyzed, in spite of a global loss of H3-K9 dimethylation (H3K9me2). In contrast, the placenta-specific imprinting of genes on distal chromosome 7 is impaired in the absence of G9a, and this correlates with reduced levels of H3K9me2 and H3K9me3. These findings provide the first evidence for the involvement of an HMT and suggest that histone methylation contributes to imprinted gene repression in the trophoblast.
193 citations
Cited by
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TL;DR: High-resolution maps for the genome-wide distribution of 20 histone lysine and arginine methylations as well as histone variant H2A.Z, RNA polymerase II, and the insulator binding protein CTCF across the human genome using the Solexa 1G sequencing technology are generated.
6,488 citations
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TL;DR: The reprogramming of gene expression during EMT, as well as non-transcriptional changes, are initiated and controlled by signalling pathways that respond to extracellular cues, and the convergence of signalling pathways is essential for EMT.
Abstract: The transdifferentiation of epithelial cells into motile mesenchymal cells, a process known as epithelial-mesenchymal transition (EMT), is integral in development, wound healing and stem cell behaviour, and contributes pathologically to fibrosis and cancer progression. This switch in cell differentiation and behaviour is mediated by key transcription factors, including SNAIL, zinc-finger E-box-binding (ZEB) and basic helix-loop-helix transcription factors, the functions of which are finely regulated at the transcriptional, translational and post-translational levels. The reprogramming of gene expression during EMT, as well as non-transcriptional changes, are initiated and controlled by signalling pathways that respond to extracellular cues. Among these, transforming growth factor-β (TGFβ) family signalling has a predominant role; however, the convergence of signalling pathways is essential for EMT.
6,036 citations
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TL;DR: It is proposed that bivalent domains silence developmental genes in ES cells while keeping them poised for activation, highlighting the importance of DNA sequence in defining the initial epigenetic landscape and suggesting a novel chromatin-based mechanism for maintaining pluripotency.
5,131 citations
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Ewan Birney, John A. Stamatoyannopoulos1, Anindya Dutta2, Roderic Guigó3 +317 more•Institutions (44)
TL;DR: Functional data from multiple, diverse experiments performed on a targeted 1% of the human genome as part of the pilot phase of the ENCODE Project are reported, providing convincing evidence that the genome is pervasively transcribed, such that the majority of its bases can be found in primary transcripts.
Abstract: We report the generation and analysis of functional data from multiple, diverse experiments performed on a targeted 1% of the human genome as part of the pilot phase of the ENCODE Project. These data have been further integrated and augmented by a number of evolutionary and computational analyses. Together, our results advance the collective knowledge about human genome function in several major areas. First, our studies provide convincing evidence that the genome is pervasively transcribed, such that the majority of its bases can be found in primary transcripts, including non-protein-coding transcripts, and those that extensively overlap one another. Second, systematic examination of transcriptional regulation has yielded new understanding about transcription start sites, including their relationship to specific regulatory sequences and features of chromatin accessibility and histone modification. Third, a more sophisticated view of chromatin structure has emerged, including its inter-relationship with DNA replication and transcriptional regulation. Finally, integration of these new sources of information, in particular with respect to mammalian evolution based on inter- and intra-species sequence comparisons, has yielded new mechanistic and evolutionary insights concerning the functional landscape of the human genome. Together, these studies are defining a path for pursuit of a more comprehensive characterization of human genome function.
5,091 citations
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Massachusetts Institute of Technology1, Broad Institute2, University of California, Los Angeles3, University of British Columbia4, Baylor College of Medicine5, Howard Hughes Medical Institute6, University of Washington7, Ludwig Institute for Cancer Research8, University of California, San Francisco9, University of Connecticut10, University of Zagreb11, University of Texas at Austin12, Washington University in St. Louis13, University of Queensland14, Harvard University15, Cold Spring Harbor Laboratory16, University of Southern California17, University of California, Santa Cruz18, Simon Fraser University19, Morgridge Institute for Research20, University of Texas at Dallas21, National Institutes of Health22
TL;DR: It is shown that disease- and trait-associated genetic variants are enriched in tissue-specific epigenomic marks, revealing biologically relevant cell types for diverse human traits, and providing a resource for interpreting the molecular basis of human disease.
Abstract: The reference human genome sequence set the stage for studies of genetic variation and its association with human disease, but epigenomic studies lack a similar reference. To address this need, the NIH Roadmap Epigenomics Consortium generated the largest collection so far of human epigenomes for primary cells and tissues. Here we describe the integrative analysis of 111 reference human epigenomes generated as part of the programme, profiled for histone modification patterns, DNA accessibility, DNA methylation and RNA expression. We establish global maps of regulatory elements, define regulatory modules of coordinated activity, and their likely activators and repressors. We show that disease- and trait-associated genetic variants are enriched in tissue-specific epigenomic marks, revealing biologically relevant cell types for diverse human traits, and providing a resource for interpreting the molecular basis of human disease. Our results demonstrate the central role of epigenomic information for understanding gene regulation, cellular differentiation and human disease.
5,037 citations