lecture 19: epigenetics

define epigentics

heritable changes in gene expression that do not alter the DNA sequence

explain why the residue is methylated and what other residue needs to be adjacent

DNMT (DNA methyltransferase) adds methylated group to C; There will always be an adjacent G to the methylated C.

name two mechanisms by which methylation inhibits gene expression. include in your answer heterochromatin formation

how can methylation activate gene expression

it will prevent insulators from working; When an insulator is methylated it won’t be able to bind to the silencer site and this will activate gene expression.

how does imprinting get erased during the life cycle and when does it get established again? is it completely erased?

in general, methylation is erased early in making germs cells and then it gets establish as the sperm and eggs mature; DNA methylation is erased genome-wide and then reestablished, with differentially methylated regions getting methylated according to the sex of the individual

how do cells manage dosage compensation in humans compared to C. elegans and Drophoshila?

Our cells are equipped to handle one X chromosome being expressed. The second one gets activated through epigenetics and a long non-coding RNA called Xist.

how does Xist cause X inactivation?

Xist RNA is expressed from one chromosome and coats it; RNA Xist then recruits methylation enzymes and histone deactylation factors; eventually chromosome turns into heterochromatin - Barr Body (inactivated X chromosome)

What is the role of Tsix

an antisense RNA that is expressed from the same region in the opposite direction and it prevents Xist from working (net result is only one X chromosome is inactivated

How are chromosomes counted? (Xist)

how could you show the Xist is necessary and sufficient for chromosomal inactivation?

to show it’s necessary: can have deletion of Xist and not see any inactivation X inactivation

to show it’s sufficient: put Xist on another chromosome (Chr 18) and show that chromosome’s get inactivated