Epigenetics

Epigenetic (Greek: after, behind, around, in addition) refers to all processes in a cell that are considered "additional" to the processes of genetics. In contrast to the term "gene regulation", epigenetics defines all meiotically and mitotically heritable changes in gene expression that are not encoded in the DNA sequence itself, i.e. that are not based on mutation.

Epigenetic regulation includes the marking of DNA segments by means of methylation, histone modifications and non-coding micro-RNA (miRNA). DNA methylation is the best-studied epigenetic mechanism to date.

While genetic processes take many generations to become established, the epigenome can change rapidly in response to environmental stimuli. These changes can be passed on to the next generation.

The term "epigenesis" is used as an example to describe all gradual processes of embryonic morphogenesis of organs. These are based on epigenetic processes during cell division of the precursor cells, cell differentiation (see below mosaic, cutaneous).

The epigenetic processes include:

• Paramutation
• bookmarking
• imprinting
• gene silencing
• X-inactivation
• positional effects
• maternal effects
• the process of carcinogenesis (see also oncogenesis)
• many effects of teratogenic substances.

Epigenetics and other drugs: It is sometimes argued that numerous drugs have epigenetic effects. This is known from certain. Psychotropic drugs such as fluoxetine, as well as morphines. Some of these gene expression adaptations are the result of an altered DNA structure caused by chromatin remodeling: epigenetic modification of histones and gene silencing by DNA methylation due to increased expression of various methyl-binding proteins (e.g. methyl-binding proteins). Methyl-binding proteins (e.g. MeCP2 and MBD1; MeCP2 = methyl-CP-binding protein 2) are important for the normal function of mature nerve cells and belong to a group of nuclear proteins.

Epigenetic dysregulation is important for the development of immunological (investigated in systemic lupus erythematosus, atopic eczema, etc.) and various neurological diseases. Certain DNA methylation patterns are, for example, characteristic of genes that code for Il-4 and IL-5 receptors, which play a role in allergic processes. Differences in methylation patterns can be detected in patients with atopic eczema and atopic asthma compared to the non-atopic population.

Their reversibility and manipulability (e.g. in the immunotherapy of peanut allergy) is fundamentally important (also of therapeutic interest).

1. Guo Y et al(2014) Epigenetics in the treatment of systemic lupus erythematosus: potential clinical
   application. Clin Immunol 155:79-90.
2. Kabesch M (2014) Epigenetics in asthma and allergy. Curr Opin Allergy Clin Immunol 14:62-68.