Abstract

The term epigenetics defines heritable changes of gene expression that are not driven by the primary nucleotide sequence of a gene, but rather by the reorganisation of chromatin structures. In eukaryotes, chromatin allows the compaction of DNA into the nucleus via its basic structural subunit, the nucleosome, in which DNA is wrapped around histone octamers. This structure is timely and spatially remodeled to fit the needs of DNA replication and chromosome segregation during cell division processes, RNA transcription and DNA repair. In this chapter, we describe the two major mechanisms of epigenetic regulation: DNA methylation and covalent modifications of nucleosomal histone proteins, their crosstalk, and how their combinations switch on and off gene expression.