Introduction:
Epigenetics is the study of heritable variations in gene activity and expression without alternation in DNA sequence, this kind of stable alternations can be passed down to progeny in short term, however, in some broader definitions, heritability is not necessary condition, for example, in the overview of the Roadmap Epigenomics Project, epigenetics is regarded as ‘also stable, long-term, alterations in the transcriptional potential of a cell that are not necessarily heritable’. Patterns of epigenetic modifications are thought to include: (1) methylation on cytosine (DNA methylation); (2) modification of histone proteins and chromatin architecture; (3) small and non-coding RNA-based mechanisms. Two major epigenetic modifications: DNA methylation and histone modifications have been focused in studies of development and cell proliferation over the past few years [1,2]. Recently, the epigenetic modifications are found associating with memory, behaviour and environment. For instance, memories formation, dynamic regulation in behaviour changes …show more content…
Ten-eleven translocation (TET) family of enzymes are found responsible in hydroxylating 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) or further make 5hmC oxidized to 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC) (Fig.2), whereas in plant, it has different way by directly removing 5mC from DNA by glycosylase pathway [9,10,11]. This leaves a question to us, why the process of demethylation in mammal can be so different from plants’ by using the oxidation-demethylation cycle instead of direct demethylation. In the process of evolution, the more effective and efficient biological systems would be retained and pass on to the next generations. We can assume that 5hmC, 5fC and 5caC are not only the intermediate products in mammalian DNA