14 results found
Hong SP, Lombardo Y, Chan TE, et al., 2019, Single-cell transcriptomics reveals multi-step adaptations to endocrine therapy, Nature Communications, Vol: 10, ISSN: 2041-1723
Resistant tumours are thought to arise from the action of Darwinian selection on genetically heterogenous cancer cell populations. However, simple clonal selection is inadequate to describe the late relapses often characterising luminal breast cancers treated with endocrine therapy (ET), suggesting a more complex interplay between genetic and non-genetic factors. Here, we dissect the contributions of clonal genetic diversity and transcriptional plasticity during the early and late phases of ET at single-cell resolution. Using single-cell RNA-sequencing and imaging we disentangle the transcriptional variability of plastic cells and define a rare sub population of pre-adapted (PA) cells which undergoes further transcriptomic reprogramming and copy number changes to acquire full resistance. We find evidence for sub-clonal expression of a PA signature in primary tumours and for dominant expression in clustered circulating tumour cells. We propose a multi-step model for ET resistance development and advocate the use of stage-specific biomarkers.
Law P-P, Chan P-K, McEwen K, et al., 2019, Sex differences in gene expression and proliferation are dependent on the epigenetic modifier HP1γ
<jats:title>Summary</jats:title><jats:p>Sex differences in growth rate in very early embryos have been recognized in a variety of mammals and attributed to sex-chromosome complement effects as they occur before overt sexual differentiation. We previously found that sex-chromosome complement, rather than sex hormones regulates heterochromatin-mediated silencing of a transgene and autosomal gene expression in mice. Here, sex dimorphism in proliferation was investigated. We confirm that male embryonic fibroblasts proliferate faster than female fibroblasts and show that this proliferation advantage is completely dependent upon heterochromatin protein 1 gamma (HP1γ). To determine whether this sex-regulatory effect of HP1γ was a more general phenomenon, we performed RNA sequencing on MEFs derived from males and females, with or without HP1γ. Strikingly, HP1γ was found to be crucial for regulating nearly all sexually dimorphic autosomal gene expression because deletion of the HP1γ gene in males abolished sex differences in autosomal gene expression. The identification of a key epigenetic modifier as central in defining gene expression differences between males and females has important implications for understanding physiological sex differences and sex bias in disease.</jats:p>
McEwen KR, Linnett S, Leitch HG, et al., 2018, Signalling pathways drive heterogeneity of ground state pluripotency
<jats:title>Abstract</jats:title><jats:p>Pluripotent stem cells (PSCs) can self-renew indefinitely while maintaining the ability to generate all cell types of the body. This plasticity is proposed to require heterogeneity in gene expression, driving a metastable state which may allow flexible cell fate choices. Contrary to this, naive PSC grown in fully defined ‘2i’ environmental conditions, containing small molecule inhibitors of MEK and GSK3 kinases, show homogenous pluripotency and lineage marker expression. However, here we show that 2i induces greater genome-wide heterogeneity than traditional serum-containing growth environments at the population level across both male and female PSCs. This heterogeneity is dynamic and reversible over time, consistent with a dynamic metastable equilibrium of the pluripotent state. We further show that the 2i environment causes increased heterogeneity in the calcium signalling pathway at both the population and single-cell level. Mechanistically, we identify loss of robustness regulators in the form of negative feedback to the upstream EGF receptor. Our findings advance the current understanding of the plastic nature of the pluripotent state and highlight the role of signalling pathways in the control of transcriptional heterogeneity. Furthermore, our results have critical implications for the current use of kinase inhibitors in the clinic, where inducing heterogeneity may increase the risk of cancer metastasis and drug resistance.</jats:p>
Chan TE, Pallaseni AV, Babtie AC, et al., 2018, Empirical Bayes Meets Information Theoretical Network Reconstruction from Single Cell Data
<jats:title>Abstract</jats:title><jats:p>Gene expression is controlled by networks of transcription factors and regulators, but the structure of these networks is as yet poorly understood and is thus inferred from data. Recent work has shown the efficacy of information theoretical approaches for network reconstruction from single cell transcriptomic data. Such methods use information to estimate dependence between every pair of genes in the dataset, then edges are inferred between top-scoring pairs. Dependence, however, does not indicate significance, and the definition of “top-scoring” is often arbitrary and a <jats:italic>priori</jats:italic> related to expected network size. This makes comparing networks across datasets difficult, because networks of a similar size are not necessarily similarly accurate. We present a method for performing formal hypothesis tests on putative network edges derived from information theory, bringing together empirical Bayes and work on theoretical null distributions for information measures. Thresholding based on empirical Bayes allows us to control network accuracy according to how we intend to use the network. Using single cell data from mouse pluripotent stem cells, we recover known interactions and suggest several new interactions for experimental validation (using a stringent threshold) and discover high-level interactions between sub-networks (using a more relaxed threshold). Furthermore, our method allows for the inclusion of prior information. We use <jats:italic>in-silico</jats:italic> data to show that even relatively poor quality prior information can increase the accuracy of a network, and demonstrate that the accuracy of networks inferred from single cell data can sometimes be improved by priors from population-level ChIP-Seq and qPCR data.</jats:p>
Strogantsev R, Krueger F, Yamazawa K, et al., 2015, Allele-specific binding of ZFP57 in the epigenetic regulation of imprinted and non-imprinted monoallelic expression, GENOME BIOLOGY, Vol: 16, ISSN: 1474-760X
Amouroux R, McEwen KR, Hajkova P, 2014, Current technological advances in mapping new DNA modifications, Drug Discovery Today: Disease Models, Vol: 12, Pages: 15-26, ISSN: 1740-6757
McEwen KR, Leitch HG, Amouroux R, et al., 2013, The impact of culture on epigenetic properties of pluripotent stem cells and pre-implantation embryos, BIOCHEMICAL SOCIETY TRANSACTIONS, Vol: 41, Pages: 711-719, ISSN: 0300-5127
Aziz A, Baxter EJ, Edwards C, et al., 2013, Cooperativity of imprinted genes inactivated by acquired chromosome 20q deletions, JOURNAL OF CLINICAL INVESTIGATION, Vol: 123, Pages: 2169-2182, ISSN: 0021-9738
Leitch HG, McEwen KR, Turp A, et al., 2013, Naive pluripotency is associated with global DNA hypomethylation, NATURE STRUCTURAL & MOLECULAR BIOLOGY, Vol: 20, Pages: 311-316, ISSN: 1545-9993
Radford EJ, Isganaitis E, Jimenez-Chillaron J, et al., 2012, An unbiased assessment of the role of imprinted genes in an intergenerational model of developmental programming., PLoS Genet, Vol: 8
Environmental factors during early life are critical for the later metabolic health of the individual and of future progeny. In our obesogenic environment, it is of great socioeconomic importance to investigate the mechanisms that contribute to the risk of metabolic ill health. Imprinted genes, a class of functionally mono-allelic genes critical for early growth and metabolic axis development, have been proposed to be uniquely susceptible to environmental change. Furthermore, it has also been suggested that perturbation of the epigenetic reprogramming of imprinting control regions (ICRs) may play a role in phenotypic heritability following early life insults. Alternatively, the presence of multiple layers of epigenetic regulation may in fact protect imprinted genes from such perturbation. Unbiased investigation of these alternative hypotheses requires assessment of imprinted gene expression in the context of the response of the whole transcriptome to environmental assault. We therefore analyse the role of imprinted genes in multiple tissues in two affected generations of an established murine model of the developmental origins of health and disease using microarrays and quantitative RT-PCR. We demonstrate that, despite the functional mono-allelicism of imprinted genes and their unique mechanisms of epigenetic dosage control, imprinted genes as a class are neither more susceptible nor protected from expression perturbation induced by maternal undernutrition in either the F1 or the F2 generation compared to other genes. Nor do we find any evidence that the epigenetic reprogramming of ICRs in the germline is susceptible to nutritional restriction. However, we propose that those imprinted genes that are affected may play important roles in the foetal response to undernutrition and potentially its long-term sequelae. We suggest that recently described instances of dosage regulation by relaxation of imprinting are rare and likely to be highly regulated.
Ferron SR, Charalambous M, Radford E, et al., 2011, Postnatal loss of Dlk1 imprinting in stem cells and niche astrocytes regulates neurogenesis, Nature, Vol: 475, Pages: 381-U136, ISSN: 0028-0836
McEwen KR, Ferguson-Smith AC, 2010, Distinguishing epigenetic marks of developmental and imprinting regulation., Epigenetics & Chromatin, Vol: 3, ISSN: 1756-8935
BACKGROUND: The field of epigenetics is developing rapidly, however we are only beginning to comprehend the complexity of its influence on gene regulation. Using genomic imprinting as a model we examine epigenetic profiles associated with different forms of gene regulation. Imprinting refers to the expression of a gene from only one of the chromosome homologues in a parental-origin-specific manner. This is dependent on heritable germline epigenetic control at a cis-acting imprinting control region that influences local epigenetic states. Epigenetic modifications associated with imprinting regulation can be compared to those associated with the more canonical developmental regulation, important for processes such as differentiation and tissue specificity. Here we test the hypothesis that these two mechanisms are associated with different histone modification enrichment patterns. RESULTS: Using high-throughput data extraction with subsequent analysis, we have found that particular histone modifications are more likely to be associated with either imprinting repression or developmental repression of imprinted genes. H3K9me3 and H4K20me3 are together enriched at imprinted genes with differentially methylated promoters and do not show a correlation with developmental regulation. H3K27me3 and H3K4me3, however, are more often associated with developmental regulation. We find that imprinted genes are subject to developmental regulation through bivalency with H3K4me3 and H3K27me3 enrichment on the same allele. Furthermore, a specific tri-mark signature comprising H3K4me3, H3K9me3 and H4K20me3 has been identified at all imprinting control regions. CONCLUSION: A large amount of data is produced from whole-genome expression and epigenetic profiling studies of cellular material. We have shown that such publicly available data can be mined and analysed in order to generate novel findings for categories of genes or regulatory elements. Comparing two types of gene regulation, impri
McEwen KR, Ferguson-Smith AC, 2009, Genomic Imprinting – A Model for Roles of Histone Modifications in Epigenetic Control, Epigenomics, Editors: Ferguson-Smith, Greally, Martienssen, Netherlands, Publisher: Springer Publishing Company, Pages: 235-258
Hong SP, Chan TE, Lombardo Y, et al., Single-cell Transcriptomics reveals multi-step adaptations to endocrine therapy
<jats:title>Abstract</jats:title><jats:p>Resistant tumours are thought to arise from the action of Darwinian selection on genetically heterogenous cancer cell populations. However, simple clonal selection is inadequate to describe the late relapses often characterising luminal breast cancers treated with endocrine therapy (ET), suggesting a more complex interplay between genetic and non-genetic factors. Partially, this is due to our limited understanding on the effect of ET at the single cell level. In the present study, we dissect the contributions of clonal genetic diversity and transcriptional plasticity during the early and late phases of ET at single-cell resolution. Using single-cell RNA-sequencing and imaging we disentangle the transcriptional variability of plastic cells and define a rare sub-population of pre-adapted (PA) cells which undergoes further transcriptomic reprogramming and copy number changes to acquire full resistance. PA cells show reduced oestrogen receptor α activity but increased features of quiescence and migration. We find evidence for sub-clonal expression of this PA signature in primary tumours and for dominant expression in clustered circulating tumour cells. We propose a multi-step model for ET resistance development and advocate the use of stage-specific biomarkers.</jats:p>
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