Epigenetic Mechanisms

Epigenetic mechanisms are specific mechanisms by which Epigenetic Inheritance occurs. In modern genetics the term epigenetics has come to refer to these mechanisms, and not really epigenetic inheritance overall, so it is good to separate the concept of epigenetic inheritance from the epigenetic mechanisms as discussed at the link just referenced. The focus of epigenetic research today is on the way in which epigenetic mechanisms, discussed below, are involved in the regulation of eukaryotic gene expression and so it is common to see gene regulation and epigenetics joined together.

To get started you should read the overview on the Basics of Epigenetics. Once you are familiar with this you can look at the links below. The details can get quite complex and there is a lot of active research in this area. First study the two major types of epigenetic modification and then study how the modifications can lead to structural changes that influence gene expression. The two major types of modification are:

• Histone modification


• DNA methylation

The chromatin remodeling that can result from these modifications is covered here:

• Chromatin remodeling

Putting it all together

Now that we have looked at modification and remodeling we will look at how they are involved together in gene expression and regulation. The main idea is that chromatin is structured in such a way that it either facilitates transcription by being rather open so that the DNA is accessible to Transcription Factors or it represses expression by being condensed so that the DNA is not accessible. In terms of regulation what we find is that in response to signals the cell can remodel chromatin near a promoter so that it is either more or less accessible. This will increase or decrease gene expression respectively.

Although there is quite a bit of variation from gene to gene, there are a few general epigenetic modifications that we find typically associated with genes that are actively transcribed. We also find some modifications that are typically associated with genes that have been silenced. These are illustrated at these two links:.

• Genes being actively transcribed


• Genes that are epigenetically repressed

The discussions at the links above focus on the ways in which epigenetic mechanisms affect gene expression, that is their role in regulating gene expression in eukaryotes. Epigenetic mechanisms also underlie a number of interesting phenomena such as Imprinting and Position-effect variegation. You should study both of these examples. There are many other interesting roles for epigenetic mechanisms in cell biology, developmental biology and cancer biology that we will not cover directly. In each of these areas the epigenetic mechanisms discussed above play a role through an influence on gene regulation, it is simply that the biological effects are studied within a specific context.