2. Outlines
CpG island
CpG sites
Relation between CpG island and gene
Where they occur
Methylation
3. CpG Islands
CpG islands (CGI) are genomic
regions that contain a high
concentration of CpG sites.
4. CpG sites
CpG sites are regions of DNA where a cytosine
nucleotide occurs next to a guanine nucleotide in the
linear sequence of bases along its length.
"CpG" is shorthand for "—C—phosphate—G—", that
is, cytosine and guanine separated by only one
phosphate; phosphate links any two nucleosides
together in DNA
5. CpG sites
The "CpG" notation is used
to distinguish this linear
sequence from the CG basepairing of cytosine and
guanine. The CpG notation
can also be interpreted as the
cytosine being 5 prime to the
guanine base.
6. CpG islands & Genes
CpG islands located in the promoter regions of genes can
play important roles in gene silencing
Housekeeping genes
Almost all housekeeping genes are associated with at least one CpG
island
Tissue specific genes
About 40 % tissue specific genes are associated with islands
7. Where they occurs?
In mammalian genomes, CpG islands are typically
300-3,000 base pairs in length, and have been found in
or near approximately 40% of promoters of
mammalian genes. About 70% of human promoters
have a high CpG content.
Based on an extensive search on the complete
sequences of human chromosomes 21 and 22, DNA
regions greater than 500 bp were found more likely to
be the "true" CpG islands associated with the 5'
regions of genes.
8. Where they occurs?
CpG islands typically occur at or near the transcription
start site of genes, particularly housekeeping genes, in
vertebrates.
Normally a C (cytosine) base followed immediately by
a G (guanine) base (a CpG) is rare in vertebrate DNA
because the cytosines in such an arrangement tend to
be methylated. This methylation helps distinguish the
newly synthesized DNA strand from the parent strand,
which aids in the final stages of DNA proofreading
after duplication
9. Epigenetic
Epigenetic is the study of
heritable changes in gene activity
which are not caused by changes in
the DNA sequence.
e.g. DNA methylation
10. DNA methylation
DNA Methylation is a
biochemical process
involving the addition of a
methyl group to the cytosine
or adenine DNA nucleotides.
DNA Methylation stably
alters the expression of genes
in cells.
11. DNA methylation
A DNA molecule that is
methylated at the two center
cytosine. DNA Methylation
plays an important role for
epigenetic gene regulation in
development and disease.
12. Methylation & Silencing
Mechanism
One way cells differentiate is
Methylation
Addition of CH3 in Cnucleotides
Silences genes in region
Methylation is inherited during
cell division…….
