Stem Cell Signalling

Question 1

What is a stem cell?

Answer 1

A cell which can differentiate and self renew

Question 2

What cells are able to differentiate into any cell type in the body?

Answer 2

Embryonic stem (ES) cells and induced pluripotent stem (iPS) cells

Question 3

What are the medical applications of ES and iPS cells?

Answer 3

Regenerative therapies
Disease remodelling
Remodelling organ toxicities

Question 4

What are iPS cells?

Answer 4

They are embryonic like cells but they can be taken from any tissue (somatic cells)

Question 5

Example of a regenerative therapy this could be used for?

Answer 5

Neurodegenerative disease - make new neurons

Question 6

Where are ES cells derived from?

Answer 6

Blastocytes (pre-implantation embryos)

Question 7

What does pluripotent mean?

Answer 7

All germ layers - ectoderm, mesoderm and endoderm

Question 8

Why can ES and iPS be maintained indefinitely in vitro?

Answer 8

because of their ability to self renew

Question 9

What type of cell cycle do ES and iPS cells have?

Answer 9

Fast cycling due to their constant self-renewal and therefore do not have all the checkpoints found in normal cells

Question 10

What extracellular signals control stem cell self-renewal and differentiation?

Answer 10

GFs
Cytokines
Cell-Matrix and Cell-cell interactions

Question 11

What signalling pathways control stem cell self-renewal and differentiation?

Answer 11

Protein kinases
E3 Ub ligases
Post translational modifications

Question 12

What cell specific gene expression programmes control stem cell self-renewal and differentiation?

Answer 12

Transcription factors
Epigenetic modifiers
Non-coding RNAs

Question 13

What are the 3 main pathways in Stem cell signal transduction?

Answer 13

The LIF pathway
A differentiation switch - ERK1/2 signalling
ERK5 pathway

Question 14

What does LIF stand for?

Answer 14

Leukaemia inhibitory factor pathway

Question 15

What does the LIF pathway promote?

Answer 15

Pluripotency and self renewal

Question 16

What does ERK1/2 signalling promote?

Answer 16

Differentiation, not self renewal

Question 17

What does ERK5 signalling promote?

Answer 17

Self renewal

Question 18

What is LIF?

Answer 18

A cytokine which activates IL-6 family receptors (LIFR and IL-6R)

Question 19

What were ES cells originally cultured on?

Answer 19

MEF ‘feeders’ layer - they secrete LIF

Question 20

How does LIF induce self renewal?

Answer 20

LIF bind to LIFR -> dimers of LIFR and gp130 join together through a conformational change -> There is a JAK on LIFR and gp130 which are brought together -> JAKs phosphorylate each other -> JAK on LIFR phosphorylates the gp130 -> provides a tyrosine docking site -> STAT3 recruitment via its SH2 domain -> STAT3 tyrosine phosphorylation -> STAT3 forms a homodimer -> detaches from the receptor and translocates to the nucleus -> binds to DNA and recruits transcriptional activation components -> drive gene expression

Question 21

What activates ERK1/2 signalling in ES cells?

Answer 21

Fibroblast growth factor (FGF) 4

Question 22

What does ERK1/2 do in the ES cells?

Answer 22

Switches off the stem cell genes and induces expression of lineage specific factors

Question 23

Name a TF which promotes self renewal

Answer 23

Nanog

Question 24

Name a TF which promotes differentiation into neurons

Answer 24

Sox1

Question 25

How does ERK1/2 activation induce differentiation?

Answer 25

The FGF receptor is stimulated -> SOS1 activates Ras -> Ras converted into GTP bound form -> Recruit Raf -> Raf is phosphorylated by other kinases -> Raf phosphorylates and activates MEK1/2 -> MEK1/2 phosphorylate and activate ERK1/2 -> ERK1/2 phosphorylates TFs to shut down stem cell genes, can phosphorylate other transcriptional regulators and epigenetic modifiers to induce chromatin remodelling

Question 26

How is SOS regulated?

Answer 26

It is autoinhibited in unstimulated cells

Question 27

What is SOS in a complex with in unstimulated cells?

Answer 27

DH PH REM:CDC25 GRB2

Question 28

What do DH domains have and what do they bind?

Answer 28

Lipid binding domains | Phospholipids in the membrane

Question 29

What do PH domains bind to?

Answer 29

Phospholipids in the membrane

Question 30

What does REM:CDC25 contain?

Answer 30

The catalytic activity

Question 31

What part of the SOS unstimulated complex is autoinhibited?

Answer 31

REM:CDC25

Question 32

What happens to the SOS inhibitory complex when FGFR is activated?

Answer 32

GRB2 binds to the phospho-tyrosine binding sites on the receptor REM:CDC25 associates with the Ras and the other components associate with the phospholipids in the membrane

Question 33

How do ERK5 induce self renewal?

Answer 33

Do not know what stimulates it -> Activation of MEKK2 and 3 through dimerisation and phosphorylation of each other -> Phosphorylation and activation of MEK5 -> Phosphorylation and activation of ERK5 -> ERK5 phosphorylates itself on the C-terminal region -> switches on stem cell gene transcription