Project description:Methods: mRNA profiles of untransfected HeLa cells (wild-type; wt) were compared with mRNA profiles of HeLa cells stably maintaining an S/MAR-based episome. Results: We here report for the first time that episomally maintained S/MAR-based vectors do not alter gene expression profile of the host cell's genome. No global changes in gene expression in episome maintaining cells, compared to non-transfected cells could be observed. To identify differentially expressed genes, false discovery rate (FDR; q-value) cut off was set to 0.01. Significantly differentially expressed genes with q<0.01 and an absolute fold-change of 2 were not detected. For verification, we chose five genes with high fold-change and low q-values (q<0.05) and compared expression levels between untransfected HeLa and HeLa stably maintaining an S/MAR-based within three replicates in qPCR. Conclusions: S/MAR-based replicons used in this study do not code for viral proteins but tend to co-localise with promoter sequences and transcription start sites. Recent observations that cooperatively transcribed promoters can influence each other raise concerns that S/MAR-based replicons have the potential to alter endogenous gene expression. Therefore, we compared the transcriptome of untransfected HeLa cells with HeLa cells stably maintaining an S/MAR-based episome. Setting the FDR to <0.01, we found no significantly differentially expressed genes. This finding is of utmost importance for potential gene therapeutic application of S/MAR-based replicons.
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.