As you might have read in an earlier post, the epigenome is composed of chemical markers that affect gene expression. These mechanisms do not alter a DNA molecule's nucleotide sequence, but they do affect the arrangement of chromatin (which is the complex of DNA, protein and RNA found in the nucleus) and accessibility to genes. An important function of chromatin is to pack DNA to a small volume, but it is also involved in gene expression.
Epigenetic modifications can be temporal, reversible, heritable, and affected by environmental factors. A common type of modification is DNA methylation, which is the addition of a methyl group to the nucleic acid cytosine found in DNA. DNA methylation is associated with gene silencing. In other words, this modification is commonly found in genes that are not being actively transcribed.
A very important category of epigenetic modifications is the histone tail modification. These modifications include methylation, acetylation, phosphorylation, ubiquitination, and SUMOylation. This list may seem overwhelming, but these are all simply additions of groups to specific residues (amino acids) found in the tails of the histone proteins that wrap DNA to form the chromatin structure. While acetylation, methylation, and phosphorylation involve the addition of relatively small groups, ubiquitination and SUMOylation add proteins, which are much larger.
Both DNA methylation and the modification of histone tails play important roles in gene expression, and the consequences of certain patterns have already been studied. Scientists are trying to uncover the mechanisms by which these modifications and their specific combinations affect gene expression. They are also interested in how these modifications occur and which are their triggers. This blog focuses on findings about the relationship between substance abuse by a woman and modifications to her fetus' epigenome. If you are interested in learning more about this fascinating subject, make sure to check in weekly!
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