DNA demethylation

DNA demethylation is the process of removal of a methyl group from nucleotides in DNA. Both DNA demethylation and methylation play important roles in mammalian development and differentiation, as well as in cognition and neuroregeneration (after injury to peripheral nerves in mammals). DNA methylation on cytosine at CpG sites on a gene promoter leads to the silencing of gene expression, while DNA demethylation of a gene promoter is linked to transcriptional activation and gene expression. These are called epigenetic changes. The DNA methylation status that controls gene expression is copied during DNA replication and is transmitted to daughter cells along with the DNA sequence. This area is currently being investigated for its role in disease progression and for potential treatments, such as cancer therapy. DNA demethylation is the process of removal of a methyl group from nucleotides in DNA. Both DNA demethylation and methylation play important roles in mammalian development and differentiation, as well as in cognition and neuroregeneration (after injury to peripheral nerves in mammals). DNA methylation on cytosine at CpG sites on a gene promoter leads to the silencing of gene expression, while DNA demethylation of a gene promoter is linked to transcriptional activation and gene expression. These are called epigenetic changes. The DNA methylation status that controls gene expression is copied during DNA replication and is transmitted to daughter cells along with the DNA sequence. This area is currently being investigated for its role in disease progression and for potential treatments, such as cancer therapy. DNA demethylation can occur through passive or active mechanisms. The passive process takes place in the absence of methylation of newly synthesised DNA strands by DNMT1 during several replication rounds (for example, upon 5-Azacytidine treatment), leading to dilution of the methylation signal. Active DNA demethylation is mediated by multiple enzymes and can occur independent of DNA replication. All the cases of DNA demethylation can be classified as global (genome wide) or locus-specific (when just specific sequences are demethylated).The genome-wide DNA demethylation occurs: