Epigenetics in Cell Differentiation and Development

Question 1

Steps in Neuronal development

Answer 1

Pluripotential ESCs -> Multipotential Neural SCs (NSCs) -> Neuronal (NPC) or Glial Restricted Precursor Cells (GPC) -> Neurons or Glial cells

Question 2

Neuronal Lineage Markers

Answer 2

NSCs: Nestin GFAP
NPC: Trb2
Neuron: DCX
Mature neuron: NeuN

Question 3

What are the three most crucial families of enzymes in the epigenetic control of neurogenesis

Answer 3

1. Trithorax Group of enzymes (TrxG) ~activation writers/erasers
2. Polycomb repressive group (PcG) ~ inactivation writers
3. DNA methyltransferases (DNMT) ~ inactivation/activation writers

Question 4

Describe the state of key developmental genes in ESCs

Answer 4

poised/ bivalent. They are silenced but not too much so they can quickly be activated when they have to be

Question 5

The two most crucial types of developmental genes in neurogenesis

Answer 5

Neurogenic: for neuronal division at the NSC stage
Neuronal: maturation of neurons, aka getting all the receptors , enzymes needed for functional neurons

Question 6

Epigenetic changes at the transition from ESC to NSC

Answer 6

neurogenic genes are activated (e.g. Trx proteins remove inactivation marks from them)

Neuronal genes stay poised

pluripotency genes become repressed

Question 7

Epigenetic changes at the transition from NSC to neurons

Answer 7

Inactivation of neurogenic genes

Activation of neuronal genes getting them out of the poised state

pluripotency genes stay repressed

Question 8

Why are GPCRs particularly useful to detect smell?

Answer 8

The 7-TM helix structure allows for great variability of ligand binding

Question 9

How are olfactory receptors able to express only their corresponding OR(olfactory receptors) ?

Answer 9

Monogenic and Monoallelic OR gene expression

One olfactory receptor allele from one cluster and one chromosome is expressed!
different from imprinting

Question 10

Describe how the OR choice occurs in OSN development

Answer 10

As ESC trantion to MOE (Main Olfactory Epithelium) all the OR genes in their clusters get H3K9me3 and
H4K20me3 markers for repression. Later on a as the MOE specializes in a specific OSN one OR is being chosen, its H3K9me3 and H4K20me3 are being removed and an activating H3K4me3 is added by LSD1. However, to ensure LSD1 doesnt activate other ORs a negative feedback facilitated by Acdy3 (adenylate cyclase 3) degrades LSD1 stabilising the OR choice

Question 11

What happens to the inactivated ORs in a OSN

Answer 11

The inactive ORs are clustered in an heterochromatic core in the middle of the nucleus (see image in slides)

Question 12

Barriers to reprogramming

Answer 12

DNA methylation at Oct4, Nanog, Sox2 promoters
-> circumvented by downregulating/blocking DNMT1
-> circumvented by overexpressing Tet proteins (active DNA demethylation)
- H3K27me3 at ESC-specific genes
-> circumvented by blocking methyltransferases
- miRNAs
-> circumvented by inhibiting miRNAs that target the pluripotency factors (miR
LeT-7 cluster, …)
-> circumvented by expressing miRNAs that downregulate suppressors of
cyclins.
-> etc
- H3K9me3
-> circumvented by knockdown SUV39 proteins, or increase H3K9 de-methylases

Question 13

Lineage-specific genes that are not yet expressed in ESCs (but may become active
at some point during differentiation) receive a certain name due to the chromatin
status of their promoters. How are they called? Why?

Answer 13

bivalent genes

Question 14

Hypothesise about the dynamic changes to the different histone marks present at
the Nestin and TUJ-1 promoters during the differentiation from ESCs to NSCs, and
then neurons.