Abstract
Not all genes are expressed in all tissues at all times. While many molecular mechanisms regulating gene expression (in space and over time) are coded in the DNA sequence (e.g. enhancers, repressors, transcription factors), there is a number of so-called epigenetic mechanisms that can regulate gene expression by other means. In this chapter, we will first review the basics of epigenetics and then describe the two most common epigenetic mechanisms, DNA methylation and histone modification. We will conclude by touching upon a few issues relevant to the integration of genomic and epigenomic information in population-based studies.
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Notes
- 1.
Gametogenesis refers to the production of gametes (eggs and sperm) in gonads, through meiosis (see Sect. 4.1.)
- 2.
Epialleles differ in their epigenetic modifications (whereas alleles differ in nucleotides).
- 3.
Retrotransposon is a form of the transposable elements that first copy themselves from DNA to RNA (transcription), then back to DNA (reversed transcription), before inserting themselves into the genome in a new position. In this way, they generate insertions, deletions and translocations.
- 4.
Note the nomenclature: CG refers to cytosine located on one DNA strand and guanine on the other (complementary) strand. On the other hand, CpG refers to the two nucleotides being located side by side on the same DNA strand.
- 5.
Methyl-CpG binding-domain proteins.
- 6.
Acetylation, methylation, phosphorylation, sumoylation and ubiquitylation.
- 7.
For example, trimethylation of lysine 27 in H3 histone (H3K27me3) is associated with gene silencing (e.g. Soshnikova and Duboule 2008). As described above, deficiencies in another of the histone-trimethylation complexes (H3K4me3) influence the lifespan of C. elegans and that epigenetic modifications (demethylation) of this complex, when located in the vicinity of certain genes, are transmitted across four generations, together with the phenotype. In other words, it influences expression of these genes and longevity (Greer et al. 2011).
- 8.
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Paus, T. (2013). Epigenomics. In: Population Neuroscience. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-36450-1_5
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DOI: https://doi.org/10.1007/978-3-642-36450-1_5
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