Epigenetique 1.0: Class

Question 1

What is Chromatine?

Answer 1

ADN + échaffaudage de protéines, incluant:
- facteurs de transcription
- histones

Question 2

True or False,
La différenciation épigénétique est irréversible

Answer 2

True

But

cancer can activate/innactivate in order to promote survival

Dans le cancer:
Réactivation de gènes normalement inactifs
+
Inhibition de gènes normalement transcrits

Question 3

Normally, epigenetics -> Marque transmise d’une cellule à toutes ses
descendantes. When is this not true?

Answer 3

Marque effacée dans l’embryon précoce
- déméthylation globale de l’ADN de la morule-> starting over from this point!

The parental imprented cells are not affected

Question 4

True or False
Marque épigénétique est une altération au niveau de la ADN, contrôlant la
transcription

Answer 4

Altération au niveau de la chromatine, contrôlant la
transcription sans changer la séquence d’ADN

Question 5

Trithorax vs Polycomb

Answer 5

Histone epigenetic markers

Trithorax: Gene activator
TTX: fonction topoïsomérase
-> Peuvent faire glisser les nucléosomes sur l’ADN (page 38)

Polycomb: Gene inhibitor

TTX active et Pc inhibe la transcription

Question 6

DNA
Méthyle transférase (DNMT) will methylate what? What is the efect of this PRECISELY??

Answer 6

Méthylation des CG
cytosine guanine

méthylation des CpG peut empêcher la
liaison des facteurs de transcription
avec l’ADN

pg13

Question 7

acetylation vs deacetylation and DNA transcription

Answer 7

Acetylation is a process where an acetyl functional group is transferred from one molecule to another1. When histones are acetylated, it removes the positive charge on the histones, thereby decreasing the interaction of the N termini of histones with the negatively charged phosphate groups of DNA1. This transforms the condensed chromatin into a more relaxed structure, referred to as euchromatin, that is associated with greater levels of gene transcription1.

On the other hand, deacetylation is the reverse reaction where an acetyl group is removed from a molecule1. This can be catalyzed by enzymes with “histone deacetylase” (HDAC) activity1. Deacetylation increases the interaction of the N termini of histones with the negatively charged phosphate groups of DNA, leading to a more condensed chromatin structure, referred to as heterochromatin1. This is associated with lower levels of gene transcription

Question 8

MeCP2 clinical relevance

Answer 8

The MECP2 gene is located on the X chromosome, and Rett syndrome is classified as an X-linked dominant disorder2. As a result, males are more severely affected and rarely survive infancy, while females, due to X chromosome inactivation, have a mixture of cells that express either the wild-type or mutant version of MeCP2

Syndrome lié au X, dominant,
♀ : seules les filles sont atteintes
♂ : presque toujours létal chez les hommes

The X is:
hypo-acétylé
hypermethylated
->overactivation of MeCP

Question 9

role of Histone DeAcetylase (HDAC)?

Answer 9

Recruited by MeCP
It reduces the amount of acetyl

Les histones sont
dé-acétylées par
HDAC, ce qui
inhibe la
transcription

Low Acetyl -> condensed DNA -> hétérochromatine

Question 10

Met1?

Answer 10

Met1 is an DNA
Méthyle transférase (DNMTequivalent)

however this is recruited via ncRNAs. Specifically, double branded RNA
recognizes a part of the complementary DNA and leads to methylation (via Met1) and thus the inhibition of those genes until death do us appart.

Question 11

Contrôle
post-transcriptionnel

Answer 11

Dégradation de l’ARN par siRNA

microRNA (from Dicer) leads to the cutting of the RNA and inhibition

RISC takes the segmented RNA that was done by DICER and then binds any complementary RNA found in the cytoplasm and cuts it down

Question 12

What is the role of dicer?

Answer 12

Cut messengerRNA in small fragments (in the cytoplasm)

(dice your onion)

Question 13

What is the role of RISC?

Answer 13

Takes the segmented RNA that was done by DICER and then binds any complementary RNA found in the cytoplasm and cuts it down

Question 14

True or False,

For non coding RNAs to have an effect they must first be translated to proteins.

Answer 14

FASLE,
ARN non-transcrits they can have effect without being proteins

Question 15

ESCC vs Let-7?

Answer 15

ESCC -> leads to a cellule souche!! (stem cell)

LET-7 -> innactivates molecules in order to keep cell as differentiated

un miRNA peut à lui-seul
transformer une cellule différenciée en
cellule souche.