CpG island

Regions of DNA with a high frequency of CpG sites

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CpG islands are regions of DNA that have a high frequency of cytosine and guanine nucleotides linked by a phosphodiester bond. These regions are often located near or at the promoter regions of genes and are typically 300 to 3,000 base pairs in length. CpG islands are important in the regulation of gene expression and are often associated with housekeeping genes.

Structure and Function

CpG islands are characterized by a high GC content and a high ratio of observed to expected CpG dinucleotides. In the human genome, CpG dinucleotides are underrepresented due to the tendency of methylated cytosines to mutate to thymines over evolutionary time. However, in CpG islands, this methylation is often suppressed, allowing these regions to maintain a high density of CpG sites.

Role in Gene Regulation

CpG islands are often found in the promoter regions of genes, where they play a crucial role in the regulation of gene expression. The methylation status of CpG islands can influence the binding of transcription factors and other proteins that regulate transcription. When CpG islands are methylated, the associated gene is typically silenced. Conversely, unmethylated CpG islands are associated with active gene expression.

Epigenetic Modifications

The methylation of CpG islands is a key epigenetic modification that can affect gene expression without altering the underlying DNA sequence. This methylation is carried out by DNA methyltransferases, which add a methyl group to the cytosine residue of CpG dinucleotides. Changes in the methylation patterns of CpG islands are associated with various diseases, including cancer, where abnormal methylation can lead to the silencing of tumor suppressor genes.

Biological Significance

CpG islands are important for maintaining the normal function of the genome. They are involved in the regulation of gene expression, genomic imprinting, and X-chromosome inactivation. The presence of CpG islands in promoter regions is a common feature of many genes, particularly those that are ubiquitously expressed across different tissues.

Clinical Implications

Abnormal methylation of CpG islands is implicated in several diseases, most notably cancer. Hypermethylation of CpG islands in the promoter regions of tumor suppressor genes can lead to their silencing, contributing to the development and progression of cancer. Conversely, hypomethylation of CpG islands can lead to genomic instability and the activation of oncogenes.

Research and Applications

CpG islands are a focus of research in the field of epigenetics. Techniques such as bisulfite sequencing are used to study the methylation patterns of CpG islands. Understanding these patterns can provide insights into the mechanisms of gene regulation and the development of diseases.

Also see

• DNA methylation
• Epigenetics
• Gene expression
• Promoter (genetics)
• Transcription factor