Project description:Eukaryotic genome is compartmentalized into structural and functional domains. One of the concepts of higher order organization of chromatin posits that the DNA is organized in constrained loops that behave as independent functional domains. A predominantly ribo-proteinaceous nucleoskeleton, termed as Nuclear Matrix (NuMat) is proposed to provide the structural platform for attachment of these loops. The DNA sequence located at the base of the loops are known as the Matrix Attachment Regions (MARs). NuMat relates to all nuclear processes and has been shown to be cell type specific in composition. It is a biochemically defined structure and several protocols have been used to isolate the NuMat where some of the steps have been critically evaluated. In the present study we have looked into the dynamics of MARs when the isolation process is varied and also during embryonic development of D. melanogaster. Our results show that a subset of MARs termed here as “Core-MARs” are fixed and unalterable anchor points in the Drosophila genome as they remain associated with NuMat at all developmental stages and do not depend on the isolation procedure used. Core-MARs are abundant in the pericentromeric heterochromatin. On the other hand, MARs in the euchromatin are dynamic and reflect the transcriptomic profile of the developmental stage of the host cell. New MARs are generated by nuclear stabilization (a critical step in the isolation procedure), and during development, mostly at the paused RNA polymerase II (Pol II) promoters. Paused Pol II MARs depend on RNA transcription for NuMat association. RNase A treatment leads to collapse of the NuMat and loss of paused Pol II promoter MARs. Our data reveals the role of MARs in functional compartmentalization of D. melanogaster genome and adds to the current understanding of nuclear architecture and 3D organization of a functionally dynamic nucleus.
Project description:Experimental approaches to define the relationship between gene expression and nuclear matrix attachment regions (MARs) have given contrasting and method-specific results. We have developed a next generation sequencing strategy to identify MARs across the human genome (MAR-Seq). The method is based on crosslinking chromatin to its nuclear matrix attachment sites to minimize changes during biochemical processing. We used this method to compare nuclear matrix organization in MCF-10A mammary epithelial-like cells and MDA-MB-231 breast cancer cells and evaluated the results in the context of global gene expression (array analysis) and positional enrichment of gene-regulatory histone modifications (ChIP-Seq). In the normal-like cells, nuclear matrix–attached DNA was enriched in expressed genes, while in the breast cancer cells, it was enriched in non-expressed genes. In both cell lines, the chromatin modifications that mark transcriptional activation or repression were appropriately associated with gene expression. Using this new MAR-Seq approach, we provide the first genome-wide characterization of nuclear matrix attachment in mammalian cells and reveal that the nuclear matrix–associated genome is highly cell-context dependent.
Project description:Experimental approaches to define the relationship between gene expression and nuclear matrix attachment regions (MARs) have given contrasting and method-specific results. We have developed a next generation sequencing strategy to identify MARs across the human genome (MAR-Seq). The method is based on crosslinking chromatin to its nuclear matrix attachment sites to minimize changes during biochemical processing. We used this method to compare nuclear matrix organization in MCF-10A mammary epithelial-like cells and MDA-MB-231 breast cancer cells and evaluated the results in the context of global gene expression (array analysis) and positional enrichment of gene-regulatory histone modifications (ChIP-Seq). In the normal-like cells, nuclear matrix–attached DNA was enriched in expressed genes, while in the breast cancer cells, it was enriched in non-expressed genes. In both cell lines, the chromatin modifications that mark transcriptional activation or repression were appropriately associated with gene expression. Using this new MAR-Seq approach, we provide the first genome-wide characterization of nuclear matrix attachment in mammalian cells and reveal that the nuclear matrix–associated genome is highly cell-context dependent.
Project description:Experimental approaches to define the relationship between gene expression and nuclear matrix attachment regions (MARs) have given contrasting and method-specific results. We have developed a next generation sequencing strategy to identify MARs across the human genome (MAR-Seq). The method is based on crosslinking chromatin to its nuclear matrix attachment sites to minimize changes during biochemical processing. We used this method to compare nuclear matrix organization in MCF-10A mammary epithelial-like cells and MDA-MB-231 breast cancer cells and evaluated the results in the context of global gene expression (array analysis) and positional enrichment of gene-regulatory histone modifications (ChIP-Seq). In the normal-like cells, nuclear matrix–attached DNA was enriched in expressed genes, while in the breast cancer cells, it was enriched in non-expressed genes. In both cell lines, the chromatin modifications that mark transcriptional activation or repression were appropriately associated with gene expression. Using this new MAR-Seq approach, we provide the first genome-wide characterization of nuclear matrix attachment in mammalian cells and reveal that the nuclear matrix–associated genome is highly cell-context dependent.
Project description:Transcription of genes residing within constitutive heterochromatin is paradoxical to the tenets of epigenetic code. Regulatory mechanisms of Drosophila melanogaster heterochromatic gene transcription remain largely unknown. We investigated the contribution of pericentromeric genome organization and heterochromatic factors in orchestrating heterochromatic gene expression. Using 5C-seq, we characterized the pericentromeric TADs in Drosophila melanogaster. Het TAD borders are enriched in nuclear matrix attachment regions while the intra-TAD interactions are mediated by various insulator binding proteins. Heterochromatic genes of similar expression levels cluster into Het TADs, indicating transcriptional co-regulation. HP1a or Su(var)3-9 RNAi results in perturbation of global pericentromeric TAD organization but the expression of the heterochromatic genes is minimally affected. A subset of active heterochromatic genes has been shown to have combination of HP1a/H3K9me3 with H3K36me3 at their exons. Consequently, knock-down of dMES-4 (H3K36 methyl transferase) downregulates expression of the heterochromatic genes. Furthermore, dADD1, present near the TSS of the active heterochromatic genes, is likely to regulate the heterochromatic gene expression in the presence of HP1a or H3K9me3 marks. Therefore, our findings provide mechanistic insights into the interplay of chromatin interactions and the combination of heterochromatic factors (HP1a, H3K9me3, dMES-4 and dADD1) in regulating heterochromatic gene expression.
Project description:Transcription of genes residing within constitutive heterochromatin is paradoxical to the tenets of epigenetic code. Regulatory mechanisms of Drosophila melanogaster heterochromatic gene transcription remain largely unknown. We investigated the contribution of pericentromeric genome organization and heterochromatic factors in orchestrating heterochromatic gene expression. Using 5C-seq, we characterized the pericentromeric TADs in Drosophila melanogaster. Het TAD borders are enriched in nuclear matrix attachment regions while the intra-TAD interactions are mediated by various insulator binding proteins. Heterochromatic genes of similar expression levels cluster into Het TADs, indicating transcriptional co-regulation. HP1a or Su(var)3-9 RNAi results in perturbation of global pericentromeric TAD organization but the expression of the heterochromatic genes is minimally affected. A subset of active heterochromatic genes has been shown to have combination of HP1a/H3K9me3 with H3K36me3 at their exons. Consequently, knock-down of dMES-4 (H3K36 methyl transferase) downregulates expression of the heterochromatic genes. Furthermore, dADD1, present near the TSS of the active heterochromatic genes, is likely to regulate the heterochromatic gene expression in the presence of HP1a or H3K9me3 marks. Therefore, our findings provide mechanistic insights into the interplay of chromatin interactions and the combination of heterochromatic factors (HP1a, H3K9me3, dMES-4 and dADD1) in regulating heterochromatic gene expression.