DNA and Histones can be tagged with chemicals that modify gene expression, causing some genes to be on or off. Epigenetic processes are natural and essential to many functions, but if they occur improperly then they can lead to adverse effects.
Histone Modifications
Acetylation, phosphorylation, methylation, ubiquitination, ribosylation, and glycosylation are examples of histone modifications affecting the response of genes. The accessibility of DNA depends on the condensation of the chromatin. Condense chromatins are associated with coiled DNA, leading to repressive modifications, however, open chromatins are related to active modifications and gene expression. Examples of this can be found with the acetylation of histones.
6. Xu, J. and Yang Liu. "Probing Chromatin Compaction and Its Epigenetic States in situ with Single-Molecule Localization-Based Super-Resolution Microscopy." Cell Dev. Biol. 10 June 2021; Volume 9. https://doi.org/10.3389/fcell.2021.653077.
DNA Methylation
Most commonly occurring on cytosine or adenine bases. A methyl group is added to a cytosine residue in a cytosine-guanine sequence, also called CpG islands (cytosine-phosphate-guanine). These are sites of methylation in DNA.
DNA methylation results in DNA inhibition of transcription of some genes. Promoter regions are associated with gene silencing which prevents genes from being expressed. DNA methylation was first confirmed to occur in human cancer in 1983 and has been found in many diseases since.
8. Gartstein, M. and Michael Skinner. "Prenatal influences on temperament development: The role of environmental epigenetics." Development and Psychopathology. December 2017;30(4):1-35.
Non-Coding RNA (ncRNA)8
A type of epigenetic modification in which the non-coding RNA is transcribed but not translated to a protein product. These non-coding RNA are classified as:
- small ncRNA (micro RNA and short interfering RNA)
- long ncRNA
7. Chaturvedi. P. and Suresh Tyagi. "Epigenetic mechanisms underlying cardiac degeneration and regeneration." Int J Cardiol. 2014 Apr 15;173(1):1-11.
8. Gartstein, M. and Michael Skinner. "Prenatal influences on temperament development: The role of environmental epigenetics." Development and Psychopathology. December 2017;30(4):1-35.
