Epigenetics At A Glance
Epigenetics Tags
The epigenome changes in response to signals. This chart on the right shows the different types of signals that can get through to the epigenome.
Gene Regulatory Proteins That Carry the Signals to the DNA Can Do One of Two Things:
Switch specific genes "on" or "off": Gene regulatory proteins attaches to a specific sequence of DNA on one or more genes. After doing so, it has the ability to turn on or switch off genes.
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Recruit enzymes that add and remove epigenetic tags: Gene Regulatory Proteins gather together enzymes that can add epigenetic tags to the DNA, histones, both or remove them. (3)
Epigenetic tags act as a kind of cellular memory. A cell's epigenetic profile - a collection of tags that tell genes whether to be on or off - is the sum of the signals it has received during its lifetime (11). It acts as a reminder to the cell, reminding the cell's genes what it is it should be doing. Factors such diet and lifestyle habits can change these tags.
Epigenetic Tags and Its Affect on Behavior
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Some drugs that areused to treat mental illness work by changing gene expression. These changes in gene expression are stabilized through epigenetic mechanisms (DNA Methylantion and Histone Modification), reversing the effects of the disease (12).
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The gene for REELIN protein has less methyl, meaning it is more active, than normal in schizophrenic brains. Reelin is important in the shaping of the brain early for development and later on for learning (12).
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One scan of epigenetic markers in the brain identified about 60 genes that are different between psychiatric patients and healthy people. Many of these genes code for proteins that are important for signaling between brain cells (12).
Epigenetic tags are believed to not only affect behavior but can be affected by behavior. Some studies being conducted to prove this include:
The bright marks on this epigenome represent the epigenetic marks.
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Drugs of abuse such as cocaine can trigger epigenetic changes in certain brain regions, affecting hundreds of genes at a time. Some of these changes remain long after the drug has been cleared from the system. Researchin this area suggests that some of the long term effects of drug abuse and addiction may be written in epigenetic code (12).
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Child abuse is an enviromental factor that leaves an epigenetic mark on the brain. In a comparison of suicide victims who were abused or not, only those abused had an epigenetic tag on the GR gene (12).
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People who commit suicide have less-active ribosomal RNA (rRNA) genes than people who die of other causes. In people who commit suicide Methyl levels are higher on rRNA genes in a part of the brain called the hippocampus, which is important for learning and memory. More methyl means less rRNA production, which means fewer ribosomes, which means less protein production (12).
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CBP, a protein that is important in the activation of genes and in learning/memory, also adds acetyl tags to histones-an epigenetic modification found on active genes. Having just one faulty copy of the CBP gene can cause Rubinstein-Taybi syndrome, a condition with a variety of characteristics, including mental disability (12).