Gimelbrant, Alexander

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Gimelbrant, Alexander

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Gimelbrant

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Alexander

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Gimelbrant, Alexander

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Lung Stem Cell Self-Renewal Relies on BMI1-Dependent Control of Expression at Imprinted Loci
(Elsevier BV, 2011-09-02) Zacharek, Sima J.; Fillmore, Christine M.; Lau, Allison N.; Gludish, David W.; Chou, Alan; Ho, Joshua W.K.; Zamponi, Raffaella; Gazit, Roi; Bock, Christoph; Jäger, Natalie; Smith, Zachary; Kim, Tae-min; Saunders, Arven H.; Wong, Janice; Lee, Joo-Hyeon; Roach, Rebecca R.; Rossi, Derrick; Meissner, Alexander; Gimelbrant, Alexander; Park, Peter; Kim, Carla
Bmi1 is required for the self-renewal of stem cells in many tissues including the lung epithelial stem cells, Bronchioalveolar Stem Cells (BASCs). Imprinted genes, which exhibit expression from only the maternally- or paternally-inherited allele, are known to regulate developmental processes but their role in adult cells remains a fundamental question. Many imprinted genes were de-repressed in Bmi1 knockout mice, and knockdown of Cdkn1c (p57) and other imprinted genes partially rescued the self-renewal defect of Bmi1 mutant lung cells. Expression of p57 and other imprinted genes was required for lung cell self-renewal in culture and correlated with repair of lung epithelial cell injury in vivo. Our data suggest that Bmi1-dependent regulation of expressed alleles at imprinted loci, distinct from imprinting per se, is required for control of lung stem cells. We anticipate that the regulation and function of imprinted genes is crucial for self-renewal in diverse adult tissue-specific stem cells.
Allele-Specific Methylation Occurs at Genetic Variants Associated with Complex Disease
(Public Library of Science, 2014) Hutchinson, John; Raj, Towfique; Fagerness, Jes; Stahl, Eli; Viloria, Fernando T.; Gimelbrant, Alexander; Seddon, Johanna; Daly, Mark; Chess, Andrew; Plenge, Robert
We hypothesize that the phenomenon of allele-specific methylation (ASM) may underlie the phenotypic effects of multiple variants identified by Genome-Wide Association studies (GWAS). We evaluate ASM in a human population and document its genome-wide patterns in an initial screen at up to 380,678 sites within the genome, or up to 5% of the total genomic CpGs. We show that while substantial inter-individual variation exists, 5% of assessed sites show evidence of ASM in at least six samples; the majority of these events (81%) are under genetic influence. Many of these cis-regulated ASM variants are also eQTLs in peripheral blood mononuclear cells and monocytes and/or in high linkage-disequilibrium with variants linked to complex disease. Finally, focusing on autoimmune phenotypes, we extend this initial screen to confirm the association of cis-regulated ASM with multiple complex disease-associated variants in an independent population using next-generation bisulfite sequencing. These four variants are implicated in complex phenotypes such as ulcerative colitis and AIDS progression disease (rs10491434), Celiac disease (rs2762051), Crohn's disease, IgA nephropathy and early-onset inflammatory bowel disease (rs713875) and height (rs6569648). Our results suggest cis-regulated ASM may provide a mechanistic link between the non-coding genetic changes and phenotypic variation observed in these diseases and further suggests a route to integrating DNA methylation status with GWAS results.
Chromatin signature of widespread monoallelic expression
(eLife Sciences Publications, Ltd, 2013) Nag, Anwesha; Savova, Virginia; Fung, Ho-Lim; Miron, Alexander; Yuan, Guo-Cheng; Zhang, Kun; Gimelbrant, Alexander
In mammals, numerous autosomal genes are subject to mitotically stable monoallelic expression (MAE), including genes that play critical roles in a variety of human diseases. Due to challenges posed by the clonal nature of MAE, very little is known about its regulation; in particular, no molecular features have been specifically linked to MAE. In this study, we report an approach that distinguishes MAE genes in human cells with great accuracy: a chromatin signature consisting of chromatin marks associated with active transcription (H3K36me3) and silencing (H3K27me3) simultaneously occurring in the gene body. The MAE signature is present in ∼20% of ubiquitously expressed genes and over 30% of tissue-specific genes across cell types. Notably, it is enriched among key developmental genes that have bivalent chromatin structure in pluripotent cells. Our results open a new approach to the study of MAE that is independent of polymorphisms, and suggest that MAE is linked to cell differentiation. DOI: http://dx.doi.org/10.7554/eLife.01256.001
Chromatin Signature Identifies Monoallelic Gene Expression Across Mammalian Cell Types
(Genetics Society of America, 2015) Nag, Anwesha; Vigneau, Sebastien; Savova, Virginia; Zwemer, Lillian M.; Gimelbrant, Alexander
Monoallelic expression of autosomal genes (MAE) is a widespread epigenetic phenomenon which is poorly understood, due in part to current limitations of genome-wide approaches for assessing it. Recently, we reported that a specific histone modification signature is strongly associated with MAE and demonstrated that it can serve as a proxy of MAE in human lymphoblastoid cells. Here, we use murine cells to establish that this chromatin signature is conserved between mouse and human and is associated with MAE in multiple cell types. Our analyses reveal extensive conservation in the identity of MAE genes between the two species. By analyzing MAE chromatin signature in a large number of cell and tissue types, we show that it remains consistent during terminal cell differentiation and is predominant among cell-type specific genes, suggesting a link between MAE and specification of cell identity.
Genes with monoallelic expression contribute disproportionately to genetic diversity in humans
(2016) Savova, Virginia; Chun, Sung; Sohail, Mashaal; McCole, Ruth; Witwicki, Robert; Gai, Lisa; Lenz, Tobias L.; Wu, C.-ting; Sunyaev, Shamil; Gimelbrant, Alexander
An unexpectedly large number of human autosomal genes are subject to monoallelic expression (MAE). Our analysis of 4,227 such genes reveals surprisingly high genetic variation across human populations. This increased diversity is unlikely to reflect relaxed purifying selection. Remarkably, MAE genes exhibit elevated recombination rate and increased density of hypermutable sequence contexts. However, these factors do not fully account for the increased diversity. We find that the elevated nucleotide diversity of MAE genes is also associated with greater allelic age: their variants tend to be older and are enriched in polymorphisms shared with Neanderthals and chimpanzees. Both synonymous and nonsynonymous alleles in MAE genes have elevated average population frequencies. We also observed strong enrichment of the MAE signature among genes reported to evolve under balancing selection. We propose that an important biological function of widespread MAE might be generation of cell-to-cell heterogeneity; the increased genetic variation contributes to this heterogeneity.
dbMAE: the database of autosomal monoallelic expression
(Oxford University Press, 2016) Savova, Virginia; Patsenker, Jon; Vigneau, Sebastien; Gimelbrant, Alexander
Recently, data on ‘random’ autosomal monoallelic expression has become available for the entire genome in multiple human and mouse tissues and cell types, creating a need for better access and dissemination. The database of autosomal monoallelic expression (dbMAE; https://mae.hms.harvard.edu) incorporates data from multiple recent reports of genome-wide analyses. These include transcriptome-wide analyses of allelic imbalance in clonal cell populations based on sequence polymorphisms, as well as indirect identification, based on a specific chromatin signature present in MAE gene bodies. Currently, dbMAE contains transcriptome-wide chromatin identification calls for 8 human and 21 mouse tissues, and describes over 16 000 murine and ∼700 human cases of directly measured biased expression, compiled from allele-specific RNA-seq and genotyping array data. All data are manually curated. To ensure cross-publication uniformity, we performed re-analysis of transcriptome-wide RNA-seq data using the same pipeline. Data are accessed through an interface that allows for basic and advanced searches; all source references, including raw data, are clearly described and hyperlinked. This ensures the utility of the resource as an initial screening tool for those interested in investigating the role of monoallelic expression in their specific genes and tissues of interest.
Tumor suppressor genes that escape from X-inactivation contribute to cancer sex bias
(2016) Dunford, Andrew; Weinstock, David; Savova, Virginia; Schumacher, Steven E.; Cleary, John P.; Yoda, Akinori; Sullivan, Timothy J.; Hess, Julian M.; Gimelbrant, Alexander; Beroukhim, Rameen; Lawrence, Michael; Getz, Gad; Lane, Andrew
There is a striking and unexplained male predominance across many cancer types. A subset of X chromosome (chrX) genes can escape X-inactivation, which would protect females from complete functional loss by a single mutation. To identify putative “Escape from X-Inactivation Tumor Suppressor” (EXITS) genes, we compared somatic alterations from >4100 cancers across 21 tumor types for sex bias. Six of 783 non-pseudoautosomal region (PAR) chrX genes (ATRX, CNKSR2, DDX3X, KDM5C, KDM6A, and MAGEC3) more frequently harbored loss-of-function mutations in males (based on false discovery rate <0.1), compared to zero of 18,055 autosomal and PAR genes (P<0.0001). Male-biased mutations in genes that escape X-inactivation were observed in combined analysis across many cancers and in several individual tumor types, suggesting a generalized phenomenon. We conclude that biallelic expression of EXITS genes in females explains a portion of the reduced cancer incidence compared to males across a variety of tumor types.
Autosomal Monoallelic Expression in the Mouse
(BioMed Central, 2012) Zwemer, Lillian M; Zak, Alexander; Thompson, Benjamin R; Kirby, Andrew; Daly, Mark; Chess, Andrew; Gimelbrant, Alexander
Background: Random monoallelic expression defines an unusual class of genes displaying random choice for expression between the maternal and paternal alleles. Once established, the allele-specific expression pattern is stably maintained and mitotically inherited. Examples of random monoallelic genes include those found on the X-chromosome and a subset of autosomal genes, which have been most extensively studied in humans. Here, we report a genome-wide analysis of random monoallelic expression in the mouse. We used high density mouse genome polymorphism mapping arrays to assess allele-specific expression in clonal cell lines derived from heterozygous mouse strains. Results: Over 1,300 autosomal genes were assessed for allele-specific expression, and greater than 10% of them showed random monoallelic expression. When comparing mouse and human, the number of autosomal orthologs demonstrating random monoallelic expression in both organisms was greater than would be expected by chance. Random monoallelic expression on the mouse autosomes is broadly similar to that in human cells: it is widespread throughout the genome, lacks chromosome-wide coordination, and varies between cell types. However, for some mouse genes, there appears to be skewing, in some ways resembling skewed X-inactivation, wherein one allele is more frequently active. Conclusions: These data suggest that autosomal random monoallelic expression was present at least as far back as the last common ancestor of rodents and primates. Random monoallelic expression can lead to phenotypic variation beyond the phenotypic variation dictated by genotypic variation. Thus, it is important to take into account random monoallelic expression when examining genotype-phenotype correlation.
Risk alleles of genes with monoallelic expression are enriched in gain-of-function variants and depleted in loss-of-function variants for neurodevelopmental disorders
(2017) Savova, Virginia; Vinogradova, Svetlana; Pruss, Danielle; Gimelbrant, Alexander; Weiss, Lauren A.
Over 3,000 human genes can be expressed from a single allele in one cell, and from the other allele – or both – in neighboring cells. Little is known about the consequences of this epigenetic phenomenon, monoallelic expression (MAE). We hypothesized that MAE increases expression variability, with potential impact on human disease. Here, we use a chromatin signature to infer MAE for genes in lymphoblastoid cell lines and human fetal brain tissue. We confirm that across clones, MAE status correlates with expression level, and that in human tissue datasets, MAE genes show increased expression variability. We then compare mono- and biallelic genes at three distinct scales. In the human population, we observe that genes with polymorphisms influencing expression variance are more likely to be MAE (P < 1.1 × 10−6). At the trans-species level, we find gene expression differences and directional selection between humans and chimpanzees more common among MAE genes (P < 0.05). Extending to human disease, we show that MAE genes are underrepresented in neurodevelopmental CNVs (P < 2.2×10−10) suggesting that pathogenic variants acting via expression level are less likely to involve MAE genes. Using neuropsychiatric SNP and SNV data, we see that genes with pathogenic expression-altering or loss-of-function variants are less likely MAE (P < 7.5×10−11) and genes with only missense or gain-of-function variants are more likely MAE (P < 1.4×10−6). Together, our results suggest that MAE genes tolerate a greater range of expression level than BAE genes and this information may be useful in prediction of pathogenicity.