Question

Discuss the molecular model for inheritance of DNA methylation

can u tell me plzz in brief

Answer 1

DNA methylation is a heritable epigenetic mark involving the covalent transfer of a methyl group to the C-5 position of the cytosine ring of DNA by DNA methyltransferases (DNMTs).

DNA methylation is regulated by a family of DNMTs: DNMT1, DNMT2, DNMT3A, DNMT3B, and DNMT3L. DNMT1 preferentially methylates hemimethylated DNA in vitro and is localized to replication foci during S phase.

Methylation of cytosine bases in plant genomes is one mechanism associated with variation in gene expression. DNA methylation is covalently attached to cytosines and, as a result, is inherited through mitosis and/or meiosis.

There is limited evidence that the methylation status of genes is altered and inherited to the next generation as a result of the environment, but there is strong evidence that spontaneous methylation variants arise and do not always adhere to Mendel’s law.

Cytosine residues are methylated in three sequence contexts, CG, CHG, and CHH (where H = A, T, or C). The molecular pathways that induce and maintain them further differentiate each of these three types of methylation. For example, CG methylation is maintained by the MET1 DNA methyltransferase, CHG methylation is maintained in Arabidopsis by the methyltransferase CMT3, whereas CHH is targeted by the activities of either DRM1/DRM2 or CMT2 methyltransferases.

The However, more than 98% of DNA methylation occurs in a CpG dinucleotide context in somatic cells, while as much as a quarter of all methylation appears in a non-CpG context in embryonic stem cells (ESCs).

When CG methylation is lost in met1 mutants, expression of DNA demethylases is reduced in addition to regathering of H3K9 methylation to heterochromatin in a methylation-independent manner.

RNAi mechanisms also appear to play a role in restoring and correcting errors in DNA methylation induced by loss of ddm1.