Chromatin/Epigenetic

Epigenetics is the study of heritable changes in gene expression  that do not involve changes to the underlying DNA sequence which in turn affects how cells read the genes. Epigenetic change is a regular and natural occurrence but can also be influenced by several factors including age, the environment/lifestyle, and disease state. Epigenetic modifications can manifest as commonly as the manner in which cells terminally differentiate to end up as skin cells, liver cells, brain cells, etc. Or, epigenetic change can have more damaging effects that can result in diseases like cancer. At least three systems including DNA methylation, histone modification and non-coding RNA (ncRNA)-associated gene silencing are currently considered to initiate and sustain epigenetic change.
Many different DNA and histone modifications have been identified to determine the epigenetic landscape. DNA methylation is mainly mediated by DNA-methyl transferase (DNMT), there are two known types of DNMT, namely DNMT1 and DNMT3A/B. Histone modifications mainly include acetylation, methylation, phosphorylation, and ubiquitination. The acetylation of histones can be mediated by histone acetyltransferases (HATs) and histone deacetyltransferases (HDACs), while Histhone demethylation is performed by two classes of histone demethylases: lysine-specific demethylase (LSD) family proteins (LSD1 and LSD2) and JmjC domaincontaining histone demethylase (JHDM).

References:

1.Roloff TC, Nuber UA.Eur J Cell Biol. 2005 Mar;84(2-3):123-35.