The molecular mechanism of epigenetic variation is as follows:
1, DNA methylation;
2.RNA interference;
3. Histone modification and chromatin remodeling; Details are as follows:
1.DNA methylation and demethylation:
DNA methylation is an effective means for organisms to shut down gene expression, and it is also one of the main mechanisms of imprinting inheritance. Demethylation of genes may lead to the loss of imprinting, over-expression of genes, and even the occurrence of tumors or cancers, such as the over-expression of tumor growth factor IGF2 gene leading to colorectal cancer. DNA methylation and demethylation is one of the important mechanisms of epigenetics.
2.RNA interference (RNAi)
It is a phenomenon that the expression of specific genes in normal organisms is suppressed. It refers to the phenomenon that double-stranded RNA(dsRNA) homologous to a specific mRNA coding region is introduced (or produced endogenously) into cells, and the degradation or translation of the mRNA is blocked, resulting in gene expression silencing. This phenomenon occurs at the post-transcriptional level, also known as post-transcriptional gene silencing. This is one of the important mechanisms of epigenetics.
3. Histone modification and chromatin remodeling
Histones (H 1, H2A, H2B, H3, H4) can be modified by methylation, acetylation, etc. The modified histone changes the affinity with DNA double strand, thus changing the loose or agglutinative state of chromatin, or regulating the gene by affecting the affinity between transcription factors and promoters.
The core histone of nucleosome can undergo many post-translational modifications, including methylation, acetylation, phosphorylation, ubiquitination and ADP ribosylation. These modifications change the structure of chromatin by affecting the interaction between histone and DNA and between histone and histone.
A single modification of histone can't work independently, and the combination of several different modifications (different types of modifications and modifications at different sites) is often recognized as a sign or language by a series of specific protein, thus changing the chromatin state and realizing the regulation of specific gene expression. Therefore, these combinatorial modifications are also called histone codes.