Project description: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 (Nag et al. Elife. 2013 Dec 31;2:e01256). Here, we use murine cells to establish that this chromatin signature is conserved between mouse and human, and is associated with MAE in every tested cell type. Our analyses reveal extensive conservation in the identity of MAE genes between the two species. By applying MAE chromatin signature analysis to a large number of cell and tissue types, we show that the MAE state remains consistent during terminal cell differentiation and is predominant among cell-type specific genes, suggesting a link between MAE and specification of cell identity. Chromatin immunoprecipitation with antibodies specific for histone modifications H3K27me3 and H3K36me3 and subsequent high-throughput sequencing were performed on fixed chromatin from a B-lymphoid clonal cell line, derived from 129S1/SvImJ x CAST/EiJ F1 mice and immortalized with Abelson murine leukemia virus.
Project description:In diploid eukaryotic organisms, both alleles of each autosomal gene are usually assumed to be simultaneously expressed at similar levels. However, some genes can be expressed preferentially or strictly from a single allele, a process known as monoallelic expression. Classic monoallelic expression of X-chromosome-linked genes, olfactory receptor genes and developmentally imprinted genes is the result of epigenetic modifications. Genetic-origin-dependent monoallelic expression, however, is caused by cis-regulatory differences between the alleles. There is a paucity of systematic study to investigate these phenomena across multiple tissues, and the mechanisms underlying such monoallelic expression are not yet fully understood. Here we provide a detailed portrait of monoallelic gene expression across multiple tissues/cell lines in a hybrid mouse cross between the Mus musculus strain C57BL/6J and the Mus spretus strain SPRET/EiJ. We observed pervasive tissue-dependent allele-specific gene expression: in total, 1,839 genes exhibited monoallelic expression in at least one tissue, and 410 genes in at least two tissues. Among these 88 are monoallelic genes with different active alleles between tissues, probably representing genetic-origin-dependent monoallelic expression. We also identified six autosomal monoallelic genes with the active allele being identical in all eight tissues, which are likely novel candidates of imprinted genes. To depict the underlying regulatory mechanisms at the chromatin layer, we performed ATAC-seq in two different cell lines derived from the F1 mouse. Consistent with the global expression pattern, cell-type dependent monoallelic peaks were found, and a higher proportion of C57BL/6J-active peaks were observed in both cell types, implying possible species-specific regulation. Finally, only a small part of monoallelic gene expression could be explained by allelic differences in chromatin organization in promoter regions, suggesting that other distal elements may play important roles in shaping the patterns of allelic gene expression across tissues.
Project description:Analysis of Allelic bias in clonal lymphoblastoid cells. Abstract: 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. Here 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. Poly A purified total RNA was used for library construction using a method described by Parkhomchuk et. al. NAR 2009. The library was strand-specific but the pipeline for data analysis does not assume the library is strand-specific.
Project description:Random monoallelic expression is defined by the allele-specific expression of genes, and by the fact that for an individual cell this monoallelic expression is neither obligate nor necessarily coordinated with the allelic expression in other cells. In order to find novel examples of random monoallelic expression in mouse, we did a transcriptome-wide survey of allele-specific gene expression in two different immortalized cell types. Lymphoblast cell lines and fibroblast cell lines were established (both clonal and nonclonal) and were used as a source of both nuclear RNA and genomic DNA. These samples were assessed for allele-specific gene expression using a custom-designed Mouse SNP Chip. A large number of genes (over 10% of those that were assessed in lymphoblast clones) displayed random monoallelic expression. For each cell line, two replicate samples of ds-cDNA were assessed for monoallelic expression, while genomic DNA was assessed as a control for possible LOH events. Nonclonal samples were used as controls for cis-acting allelic bias.
Project description: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 (Nag et al. Elife. 2013 Dec 31;2:e01256). Here, we use murine cells to establish that this chromatin signature is conserved between mouse and human, and is associated with MAE in every tested cell type. Our analyses reveal extensive conservation in the identity of MAE genes between the two species. By applying MAE chromatin signature analysis to a large number of cell and tissue types, we show that the MAE state remains consistent during terminal cell differentiation and is predominant among cell-type specific genes, suggesting a link between MAE and specification of cell identity. PolyA RNA purification and subsequent high-throughput sequencing were performed on two independent B-lymphoid clonal cell line, derived from 129S1/SvImJ x CAST/EiJ F1 mice and immortalized with Abelson murine leukemia virus, and on two independent fibroblast clonal cell lines, derived from 129S1/Sv x CAST/EiJ F1 and immortalized with SV40.
Project description:Distant enhancer elements are a major source of specificity in mammalian gene expression. Although enhancers that regulate broad developmental decisions and inducible gene expression have been studied extensively, little is known about regulatory elements that govern monogenic and monoallelic expression. Here, using high throughput epigenetic and genetic techniques we identified a plethora of distant enhancers that regulate monoallelic olfactory receptor (OR) gene expression. Potential OR enhancers have unique, cell type specific epigenetic marks that distinguish them from other neuronal enhancers and correlate with enhancer activity in vivo. Using sequence capture to enrich for these sequences we identified Dnase-protected footprints that reveal novel regulatory sequences and transcription factors required for OR gene activation. Our experiments provide insight to the regulation of OR expression, and describe novel principles and methodologies towards the understanding of transcriptional mechanisms that generate cellular diversity. In vivo examination of H3K79me3 enrichment and DNAse protected footprints on olfactory receptor enhancer sequences. We performed ChIP-seq on native chromatin isolated from the mouse olfactory epithelium using antibodies against H3K79me3. To sequence accessible regions of the genome we treated nuclei with limiting amounts of DNAse I to digest accessible chromatin and perform Dnase Hypersensitivity (DHS)-seq. In the olfactory epithelium, the H enhancer – the first described enhancer for olfactory receptors has a well-defined DNAse I hypersensitivity peak and is flanked by high levels of H3K79me3. We find other intergenic sequences nearby olfactory receptor genes that share the same chromatin signature, and test their function in vivo. TO uncover transcription factor footprints on olfactory receptor enhancers we performed sequence capture of the DHS-seq library to enrich for these sequences. We find multiple DNAse-protected sequences and perform motif analysis on transcription factor footprints to reveal factors involved in olfactory receptor gene regulation.
Project description:Analysis of Allelic bias in clonal lymphoblastoid cells. Abstract: 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. Here 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.