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Distribution of CpG dinucleotide in the human genome and differences in methylation patterns between normal and tumor cells. In the majority of the
mammalian genome, depicted as exons 2 and 3 of a sample gene (numbered boxes), introns of the gene (line between the exons), and regions outside
the gene, the CpG dinucleotide has been depleted over evolution as shown by the sparse number of such sites (lollipops). Small regions of DNA,
approximately 0.5-4.0 kb in size, harbor the expected number of CpG sites and are termed CpG islands. Many of these are associated with promoter
regions of approximately half of the genes in the genome (frequent lollipops surrounding exon 1 of the sample gene). In normal cells, most CpG sites
outside CpG islands are methylated (yellow lollipops) while most gene promoter CpG island sites are unmethylated (open lollipops). This unmethylated
Source: Cancer, The Online Metabolic and Molecular Bases of Inherited Disease
state of the promoter CpG islands is a permissive state for active gene transcription (arrow, top panel). In cancer cells, the DNA methylation and chromatin
Valle CpG
D, Beaudet
B, Kinzler
KW, Antonarakis
SE, that
Ballabio
A, Gibson
K, Mitchell
G. The
Online Metabolic
Molecular
patterns are Citation:
shifted. Many
sites inAL,
theVogelstein
bulk genome
and coding
region of genes
should
be methylated
become
unmethylated,
and aand
growing
list
Bases
of
Inherited
Disease;
2014
Available
at:
http://mhmedical.com/
Accessed:
May
12,
2017
of genes have abnormal methylation of CpG island-containing promoters with associated transcriptional silencing (X at transcription start site).
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