GSE49389
Genome-wide analysis of the rat colon reveals site-specific differences in histone modifications and proto-oncogene expression
Goal: Since disease susceptibility of the intestine exhibits an anatomical bias, we propose that the chromatin landscape, especially the site-specific epigenetic differences in histone modification patterns throughout the longitudinal axis, contributes to a differential response to chemoprotective agents. Method: We assessed the chromatin structure associated with gene expression profiles in the rat proximal and distal colon by globally correlating chromatin immunoprecipitation next-generation sequencing analysis (ChIP-Seq) with mRNA transcription (RNA-Seq) data. Crypts were isolated from the proximal and distal colonic regions from rats maintained on a semi-purified diet, and mRNA gene expression profiles were generated using RNA-Seq. The remaining isolated crypts were paraformaldehyde-crosslinked and chromatin immunoprecipitated using antibodies against H3K4me3, H3K9me3, and RNA Polymerase II. Results/Conclusion: Globally, RNA-Seq results indicated that 9,866 genes were actively expressed, of which 540 genes were differentially expressed between the proximal and distal colon. With regard to differentially expressed genes, a high correlation was observed between H3K4me3-Seq and RNA-Seq data, with 96% of the canonical pathways being similarly affected in the H3K4me3-Seq and RNA-Seq data sets. Gene ontology analysis indicated that colonic crypt location significantly impacted both chromatin and transcriptional regulation of genes involved in cell transformation, lipid metabolism, lymphatic development and immune cell trafficking. Gene function analysis indicated that the PI3-Kinase signaling pathway was regulated in a site-specific manner, e.g., pathway proto-oncogenes, c-Jun, c-Fos and ATF, were up-regulated in the distal colon. Middle and long non-coding RNAs (lncRNAs) were also detected in the colon, including select lncRNAs formerly only detected in the rat nervous system. In summary, distinct combinatorial patterns of histone modifications exist in the proximal versus distal colon. These site-specific differences may explain the differential effects of chemoprotective agents on cell transformation in the ascending (proximal) and descending (distal) colon. Overall design: Examination of mRNA profiles and 2 different histone modifications (H3K4me3 and H3K9me3) in 2 tissue types (proximal and distal colon).