tailieunhanh - Báo cáo y học: " Contrasting chromatin organization of CpG islands and exons in the human genome"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Wertheim cung cấp cho các bạn kiến thức về ngành y đề tài: Contrasting chromatin organization of CpG islands and exons in the human genome. | Choi Genome Biology 2010 11 R70 http 2010 11 7 R70 w Genome Biology RESEARCH Open Access Contrasting chromatin organization of CpG islands and exons in the human genome Jung Kyoon Choi 1 2 Abstract Background CpG islands and nucleosome-free regions are both found in promoters. However their association has never been studied. On the other hand DNA methylation is absent in promoters but is enriched in gene bodies. Intragenic nucleosomes and their modifications have been recently associated with RNA splicing. Because the function of intragenic DNA methylation remains unclear I explored the possibility of its involvement in splicing regulation. Results Here I show that CpG islands were associated not only with methylation-free promoters but also with nucleosome-free promoters. Nucleosome-free regions were observed only in promoters containing a CpG island. However the DNA sequences of CpG islands predicted the opposite pattern implying a limitation of sequence programs for the determination of nucleosome occupancy. In contrast to the methylation-and nucleosome-free states of CpG-island promoters exons were densely methylated at CpGs and packaged into nucleosomes. Exon-enrichment of DNA methylation was specifically found in spliced exons and in exons with weak splice sites. The enrichment patterns were less pronounced in initial exons and in non-coding exons potentially reflecting a lower need for their splicing. I also found that nucleosomes DNA methylation and H3K36me3 marked the exons of transcripts with low medium and high gene expression levels respectively. Conclusions Human promoters containing a CpG island tend to remain nucleosome-free as well as methylation-free. In contrast exons demonstrate a high degree of methylation and nucleosome occupancy. Exonic DNA methylation seems to function together with exonic nucleosomes and H3K36me3 for the proper splicing of transcripts with different expression levels. Background A CpG island CGI is a .