Question

Under the interplay of epigenetic regulators:

1.In your own words, what is Dnmt1 and what does it do?

2.In your own words, what is Dnmt3a and 3b, and what do they do?

3.Identify two distinct ways that DNA methylation regulates gene expression. One way is related to histone modifications, the other way is not.

Under Regulating X Inactivation

4.Describe how DNA-methylation and histone modifications play a role in X-chromosome inactivation.

Answer 1

Q1)Dnmt1 is an enzyme produced by DNMT1 gene. DNA(Cytosine-5-)-methyltransferase 1 are the enzymes responsible for the catalyzing the transfer of methyl group to a specific CpG structures in DNA and this process is called DNA methylation. The function of these enzyme is maintenance of DNA methylation which inturn ensures the fidelity of replication of inherited epigenetic pattern , change in methylation pattern is linked to certain tumors and developmental abnormalities.

Q2) DNA(Cytosine-5-)-methyltransferase 3A is an enzymes responsible for de novo DNA methylation. It's function is DNA methylation maintenance as well as. In case change in DNMT1 methylation occures and causes tumor formation , these cells were found to have retained their inherited methylation pattern.

DNA(Cytosine-5)-methytransferase 3Beta is an enzyme important for embryonic development , imprinting and X-chromosome inactivation. It functions in de novo methylation rather than maintenance of DNA methylation. The protien is found localised to nucleus.Mutation in it's gene causes  immunodeficiency-centromeric instability-facial anomalies (ICF) syndrome

Q4)For transcription to occure, gene promoters should be readily accessible to transcription factors and other regulatory unites. However DNA methylation can prevent transcription factor binding directly and can cause changes in chromatin structure that restricts access of transcription factor to the gene promoter.Histone modification takes place when methylated CpG attracts methyl CpG binding domain protiens that recruite repressor complexes . The modification of histone due to recruitment of repressor complexes results in a more condensed chromatin structure which is opposed to the required open and active chromatin structure. Which renders more than 3/4 th genes of one of the X chromosomes genetically silent causing X-chromosome inactivation.