It has been well known for many years that DNA methylation plays many roles in gene regulation and can direct different cell pathways such as apoptosis, differentiation, cancer, and aging. Although DNA methylation can be extremely stable – able to persist through multiple generations – it can also be quite dynamic and able to change in response to a cell’s internal and external environment. More recently, an additional DNA modification, hydroxymethylation, has received much attention. Methylcytosine (5mC) can be oxidized to generate hydroxymethylcytosine (5hmC), which some researchers think is an intermediate in the DNA de-methylation pathway. Unlike 5mC, which is found in approximately equal levels throughout all tissues in the body, 5hmC is most abundantly expressed in the brain and CNS compared to other tissues in the body. This has led many to speculate that 5hmC is more than just a passive mark, and may have its own unique biological functions.
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