CpG Islands and Genomic Methylation Patterns

DNA methylation is not distributed uniformly throughout the genome. Its organization depends on the genomic context and the functional characteristics of different DNA regions.

CpG islands are genomic regions characterized by a relatively high frequency of CpG dinucleotides. They are frequently located near gene promoters and transcription start sites.

In many actively expressed genes, promoter-associated CpG islands remain relatively unmethylated, allowing transcriptional machinery and regulatory proteins to access DNA.

By contrast, methylation of promoter-associated CpG sites is frequently associated with transcriptional repression.

Other genomic regions, including repetitive sequences, transposable elements and gene bodies, display distinct methylation patterns.

Important genomic contexts include:

• CpG islands located near gene promoters.

• CpG shores and shelves surrounding CpG islands.

• Gene bodies and intragenic regulatory regions.

• Repetitive DNA sequences and transposable elements.

• Intergenic regions and distal regulatory elements.

The relationship between DNA methylation and gene expression depends on genomic location. Promoter methylation is commonly associated with transcriptional repression, whereas gene-body methylation can display more complex relationships with transcriptional activity.