Chicagoland Jewish High School, IL
Teacher: Robert Taylor
Epigenetic modifications are heritable changes in chromosomal structure that modify gene expression without altering the DNA sequence. While genetic mutations are
permanent, epigenetic modifications are potentially reversible (Sainani, 2010). This is exciting to scientists who once thought that diseases caused by abnormal gene expression
were set in stone, or rather, base pairs.
A diverse field, epigenetics includes DNA methylation, histone modification and RNA-associated silencing (Egger et al., 2004). While these processes are often interrelated, DNA
methylation stands out as an integral regulator of gene expression. Errors in DNA methylation abnormally repress or express genes. When errors affect genes essential to normal cell
function, diseases often arise. Armed with knowledge of DNA methylationís role in malfunctioning cells, scientists have the potential not only to understand but also to reverse
abnormal methylation, thus curing the diseases it causes. Prominent among these diseases is cancer.
. . . DNA methylation typically targets CpG dinucleotides, which occur when a cytosine directly precedes a guanine on one strand of DNA (Das and Singal, 2004). CpG dinucleotides
are highly concentrated in CpG islands, stretches of DNA between .5 and 5 kilobases that are made up of 60-80% GC base pairs. CpG islands are normally upstream of gene promoter
regions. When CpG islands become methylated, transcription is repressed. Methylated DNA can physically prevent transcription factors from binding to the promoter and can recruit
histone deacytelases (HDACs), which cause DNA to wrap more tightly around histones, thus preventing transcription (Licht, 2011). If CpG islands remain unmethylated, RNA polymerase
II is free to attach to the promoter and begin transcription.