Proximal Regulatory Elements with Emphasis on CpG Rich Regions

Abstract

Transcriptional regulation in eukaryotes is a multi-step procedure which the DNA template is transcribed into RNA by RNA polymerase II in a combinatorial manner, where specific proteins (general transcription factors, activators and co-activators) are binding to regulatory elements on the DNA (core and proximal promoters, CpG islands, enhancers, silencers, locus control regions). More than 50 % of the mammalian genes initiate transcription from short regions in DNA that contains high frequency of CpG sites referred to as CpG islands. CpG islands are generally non-methylated and associated with the majority of gene promoters. Many studies have identified examples of CpG island methylation in CpG promoters that lead to abnormal gene silencing in cancer cells. CpG island methylation is also function in X-inactivation and genomic imprinting. Differential CpG island methylation is also shown in embryonic stem cells but also in somatic cells indicating their role in gene expression during cellular differentiation and cell type determination. CpG islands, therefore illustrate the complex role played by DNA methylation in the regulation of transcription.