Browsing by Author "Jordan, I. King"

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    Compound Cis-Regulatory Elements With Both Boundary and Enhancer Sequences in the Human Genome
    (Oxford University Press, 2013-10) Jjingo, Daudi; Wang, Jianrong; Conley, Andrew B.; Lunyak, Victoria V.; Jordan, I. King
    Motivation: It has been suggested that presumably distinct classes of genomic regulatory elements may actually share common sets of features and mechanisms. However, there has been no genome-wide assessment of the prevalence of this phenomenon. Results: To evaluate this possibility, we performed a bioinformatics screen for the existence of compound regulatory elements in the human genome. We identified numerous such collocated boundary and enhancer elements from human CD4þ T cells. We report evidence that such compound regulatory elements possess unique chromatin features and facilitate cell type-specific functions related to inflammation and immune response in CD4+ T cells.
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    Effect of the Transposable Element Environment of Human Genes on Gene Length and Expression
    (Oxford University Press, 2011-02-28) Jjingo, Daudi; Huda, Ahsan; Gundapuneni, Madhumati; Mariño-Ramǐrez, Leonardo; Jordan, I. King
    Independent lines of investigation have documented effects of both transposable elements (TEs) and gene length (GL) on gene expression. However, TE gene fractions are highly correlated with GL, suggesting that they cannot be considered independently. We evaluated the TE environment of human genes and GL jointly in an attempt to tease apart their relative effects. TE gene fractions and GL were compared with the overall level of gene expression and the breadth of expression across tissues. GL is strongly correlated with overall expression level but weakly correlated with the breadth of expression, confirming the selection hypothesis that attributes the compactness of highly expressed genes to selection for economy of transcription. However, TE gene fractions overall, and for the L1 family in particular, show stronger anti-correlations with expression level than GL, indicating that GL may not be the most important target of selection for transcriptional economy. These results suggest a specific mechanism, removal of TEs, by which highly expressed genes are selectively tuned for efficiency. MIR elements are the only family of TEs with gene fractions that show a positive correlation with tissue-specific expression, suggesting that they may provide regulatory sequences that help to control human gene expression. Consistent with this notion, MIR fractions are relatively enriched close to transcription start sites and associated with expression in specific sets of related tissues. Our results confirm the overall relevance of the TE environment to gene expression and point to distinct mechanisms by which different TE families may contribute to gene regulation.
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    Flow-Dependent Epigenetic DNA Methylation Regulates Endothelial Gene Expression and Atherosclerosis
    (American Society for Clinical Investigation, 2014) Dunn, Jessilyn; Qiu, Haiwei; Kim, Soyeon; Jjingo, Daudi; Hoffman, Ryan; Kim, Chan Woo; Jang, Inhwan; Son, Dong Ju; Kim, Daniel; Pan, Chenyi; Fan, Yuhong; Jordan, I. King; Jo, Hanjoong
    In atherosclerosis, plaques preferentially develop in arterial regions of disturbed blood flow (d-flow), which alters endothelial gene expression and function. Here, we determined that d-flow regulates genome-wide DNA methylation patterns in a DNA methyltransferase–dependent (DNMT-dependent) manner. Induction of d-flow by partial carotid ligation surgery in a murine model induced DNMT1 in arterial endothelium. In cultured endothelial cells, DNMT1 was enhanced by oscillatory shear stress (OS), and reduction of DNMT with either the inhibitor 5-aza-2′-deoxycytidine (5Aza) or siRNA markedly reduced OS-induced endothelial inflammation. Moreover, administration of 5Aza reduced lesion formation in 2 mouse models of atherosclerosis. Using both reduced representation bisulfite sequencing (RRBS) and microarray, we determined that d-flow in the carotid artery resulted in hyper-methylation within the promoters of 11 mechanosensitive genes and that 5Aza treatment restored normal methylation patterns. Of the identified genes, HoxA5 and Klf3 encode transcription factors that contain cAMP response elements, suggesting that the methylation status of these loci could serve as a mechanosensitive master switch in gene expression. Together, our results demonstrate that d-flow controls epigenomic DNA methylation patterns in a DNMT-dependent manner, which in turn alters endothelial gene expression and induces atherosclerosis.
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    Mammalian-Wide Interspersed Repeat (MIR)-Derived Enhancers and the Regulation of Human Gene Expression
    (BioMed Central, 2014) Jjingo, Daudi; Conley, Andrew B.; Wang, Jianrong; Mariño-Ramírez, Leonardo; Lunyak, Victoria V.; Jordan, I. King
    Background: Mammalian-wide interspersed repeats (MIRs) are the most ancient family of transposable elements (TEs) in the human genome. The deep conservation of MIRs initially suggested the possibility that they had been exapted to play functional roles for their host genomes. MIRs also happen to be the only TEs whose presence in-and-around human genes is positively correlated to tissue-specific gene expression. Similar associations of enhancer prevalence within genes and tissue-specific expression, along with MIRs’ previous implication as providing regulatory sequences, suggested a possible link between MIRs and enhancers. Results: To test the possibility that MIRs contribute functional enhancers to the human genome, we evaluated the relationship between MIRs and human tissue-specific enhancers in terms of genomic location, chromatin environment, regulatory function, and mechanistic attributes. This analysis revealed MIRs to be highly concentrated in enhancers of the K562 and HeLa human cell-types. Significantly more enhancers were found to be linked to MIRs than would be expected by chance, and putative MIR-derived enhancers are characterized by a chromatin environment highly similar to that of canonical enhancers. MIR-derived enhancers show strong associations with gene expression levels, tissue-specific gene expression and tissue-specific cellular functions, including a number of biological processes related to erythropoiesis. MIR-derived enhancers were found to be a rich source of transcription factor binding sites, underscoring one possible mechanistic route for the element sequences co-option as enhancers. There is also tentative evidence to suggest that MIR-enhancer function is related to the transcriptional activity of non-coding RNAs. Conclusions: Taken together, these data reveal enhancers to be an important cis-regulatory platform from which MIRs can exercise a regulatory function in the human genome and help to resolve a long-standing conundrum as to the reason for MIRs’ deep evolutionary conservation.
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    On the Presence and Role of Human Gene-Body DNA Methylation
    (International Multidisciplinary Publishing Academy for Computational Technologies, 2012-05-09) Jjingo, Daudi; Conley, Andrew B.; Yi, Soojin V.; Lunyak, Victoria V.; Jordan, I. King
    DNA methylation of promoter sequences is a repressive epigenetic mark that down-regulates gene expression. However, DNA methylation is more prevalent within gene-bodies than seen for promoters, and gene-body methylation has been observed to be positively correlated with gene expression levels. This paradox remains unexplained, and accordingly, the role of DNA methylation in gene-bodies is poorly understood. We addressed the presence and role of human gene-body DNA methylation using a meta-analysis of human genome-wide methylation, expression and chromatin data sets. Methylation is associated with transcribed regions as genic sequences have higher levels of methylation than intergenic or promoter sequences. We also find that the relationship between gene-body DNA methylation and expression levels is non-monotonic and bell-shaped. Mid-level expressed genes have the highest levels of gene-body methylation, whereas the most lowly and highly expressed sets of genes both have low levels of methylation. While gene-body methylation can be seen to efficiently repress the initiation of intragenic transcription, the vast majority of methylated sites within genes are not associated with intragenic promoters. In fact, highly expressed genes initiate the most intragenic transcription, which is inconsistent with the previously held notion that gene-body methylation serves to repress spurious intragenic transcription to allow for efficient transcriptional elongation. These observations lead us to propose a model to explain the presence of human gene-body methylation. This model holds that the repression of intragenic transcription by gene-body methylation is largely epiphenomenal, and suggests that gene-body methylation levels are predominantly shaped via the accessibility of the DNA to methylating enzyme complexes.
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    Transcriptional Activity, Chromosomal Distribution and Expression Effects of Transposable Elements in Coffea Genomes
    (PLoS ONE (Public Library of Science), 2013-11-11) Lopes, Fabrício R.; Jjingo, Daudi; R. M. da Silva, Carlos; Andrade, Alan C.; Marraccini, Pierre; Teixeira, Joaõ B.; Carazzolle, Marcelo F.; A. G. Pereira, Gonçalo; Pereira, Luiz Filipe P.; Vanzela, André L. L.; Wang, Lu; Jordan, I. King; Carareto, Claudia M. A.
    Plant genomes are massively invaded by transposable elements (TEs), many of which are located near host genes and can thus impact gene expression. In flowering plants, TE expression can be activated (de-repressed) under certain stressful conditions, both biotic and abiotic, as well as by genome stress caused by hybridization. In this study, we examined the effects of these stress agents on TE expression in two diploid species of coffee, Coffea canephora and C. eugenioides, and their allotetraploid hybrid C. arabica. We also explored the relationship of TE repression mechanisms to host gene regulation via the effects of exonized TE sequences. Similar to what has been seen for other plants, overall TE expression levels are low in Coffea plant cultivars, consistent with the existence of effective TE repression mechanisms. TE expression patterns are highly dynamic across the species and conditions assayed here are unrelated to their classification at the level of TE class or family. In contrast to previous results, cell culture conditions per se do not lead to the de-repression of TE expression in C. arabica. Results obtained here indicate that differing plant drought stress levels relate strongly to TE repression mechanisms. TEs tend to be expressed at significantly higher levels in non-irrigated samples for the drought tolerant cultivars but in drought sensitive cultivars the opposite pattern was shown with irrigated samples showing significantly higher TE expression. Thus, TE genome repression mechanisms may be finely tuned to the ideal growth and/or regulatory conditions of the specific plant cultivars in which they are active. Analysis of TE expression levels in cell culture conditions underscored the importance of nonsense-mediated mRNA decay (NMD) pathways in the repression of Coffea TEs. These same NMD mechanisms can also regulate plant host gene expression via the repression of genes that bear exonized TE sequences.