Lewin - Neuron death, growth, and neurotrophins

Question 1

What model system was used to study naturally occurring cell death in the dorsal root ganglia (DRG)?

A. male mice
B. female mice
C. chick embryo
D. drosophila

Answer 1

C. chick embryo

Question 2

What was found via chick embryos regarding cell death and the DRG?

Answer 2

• The amount of target tissue influences neuron survival

- there was less cell death in ganglia that are innervating limbs

Question 3

What is the neurotrophin hypothesis?

Answer 3

• theres a factor that neurons must take up to survive
• there is a limiting amount of this factor –> some will live, some will die
• match innervating cells to size of the target tissue
• the number of growth factors produced by the cell will determine if it lives or dies

Question 4

What is Nerve Growth Factor (NGF) and how was it discovered?

Answer 4

• a target-derived soluble factor that can support neuron survival
• implanted tumor cells into the chorion allantoic membrane - compared when tumor cells were placed in embryo (only simulated cell growth in side it was implanted) or directly in the membrane (stimulated cell growth everywhere)

Question 5

NGF was determined to be some kind of protein. What was used to better understand the nature of this factor?

Answer 5

• snake venom was used to exclude that the factor was nucleic acid (snake venom digests nucleic acid)
• can also use mouse saliva to purify the factor

Question 6

Neurons can survive without NGF.

A. true
B. false

Answer 6

B. false

Neurons can survive in very low concentrations of NGF, but can’t survive without it

Question 7

What of the following are true about NGF? (more than one may be true)

A. it is a dimer
B. active form is 15kD Beta-NGF dimer
C. NGF is synthesized as pro NGF
D. NGF serves as a survival factor for a large proportion of peripheral neurons

Answer 7

B. active form is 15kD Beta-NGF dimer
C. NGF is synthesized as pro NGF
D. NGF serves as a survival factor for a large proportion of peripheral neurons

Question 8

NGF is the only growth factor.

A. true
B. false

Answer 8

B. false

there are 4: NGF, BDNF, NT-3, NT-4

Question 9

What is TrkA?

Answer 9

• a membrane protein which, when comes together w another TrkA subunit, becomes active an phosphorylates itself
• is a receptor for NGF anf NT3
• has a high affinity (doesn’t need a high concentration)

Question 10

What is P75?

Answer 10

• a protein that can bind to all GFs, but has a low affinity (requires a high concentration)
• with NGF –> is a survival enhancer
• with proNGF –> promotes cell death

Question 11

What receptor does BDNF bind to?

Answer 11

TrkB only

Question 12

What receptor does NT3 bind to?

Answer 12

Trk A,B,C, but has a high affinity to TrkC

Question 13

What is the interaction between Neurotrophin and Trk receptor?

Answer 13

• when Trk binds to the ligand it dimerises and the receptor can auto-phosphorylate
• these phosphate residues make the proteins recognizable –> signal cascade of activation
• each receptor has a different combination of phosphate residues –> allows for specificity and selectivity

Question 14

What receptors are involved in cell survival?

A. TrkA
B. TrkB
C. TrkC
D. P75

Answer 14

A. TrkA
B. TrkB
C. TrkC

Question 15

What receptors are involved in cell death?

A. TrkA
B. TrkB
C. TrkC
D. P75

Answer 15

D. P75

Question 16

What is apoptosis?

Answer 16

• an active mechanism that requires new gene transcription and protein synthesis in order to deliberately kill the cell
• requires signalling

Question 17

What is necrosis?

Answer 17

• non-actively regulated cell death due to cell damage (pathological cell death)
• dying cells swell and become lysed

Question 18

How can apoptosis be delayed?

Answer 18

by blocking protein synthesis

-ex. presence of cycloheximide blocks -NGF –> neurons can survive

Question 19

What are caspases?

Answer 19

• a family of proteins that initiate and promote apoptosis

- there are two types: initial cascade, and executionary cascade

Question 20

What is CED3?

Answer 20

• a mutagen in nematodes that leads to cell death

- similar genes are highly conserved across evolution

Question 21

In mammals what are the regulators involved in apoptosis?

Answer 21

• BaX = pro apoptosis
• BCL-2 = anti-apoptosis. Activates mitochondria to become more active and produce more ATP (prevents Cyt C from activating)
• Cyt C = initiates caspase activation

Question 22

How is Trk signalling linked to apoptosis?

Answer 22

Trk binds to the ligand (phosphorylates) –> binds protein –> CREB can bind to the complex –> enters the nucleus (after phosphor.) –> enhanced BCL-2 transcription which blocks apoptosis

Question 23

How is MAPKinase signalling linked to apoptosis?

Answer 23

through phosphorylation and mitochondria, this pathway blocks the activation of Cyt C and delays apoptosis

Question 24

-NGF with ERK leads to…

A. cell death
B. no cell death

Answer 24

B. no cell death

ERK bipasses the effect of -NGF

Question 25

NGF + JNK leads to... A. cell death B. no cell death

Answer 25

A. cell death JNK leads to apoptosis

Question 26

What are two roles of NGF?

Answer 26

- prevention of cell death (MAPK, ERK) | - promoting neurite outgrowth (P13K/Act pathway)

Question 27

Based on mouse KO studies, it was found that... A. Bax is required for apoptosis B. Bax prevents cells from undergoing apoptosis C. in the presence of Bax and NGF, cells grow normally D. signaling happens at neurite endings

Answer 27

A. Bax is required for apoptosis C. in the presence of Bax and NGF, cells grow normally D. signaling happens at neurite endings

Question 28

Neurotrophins are not required for long distance growth but are required for fine tuned innervations and local branching. A. true B. false

Answer 28

A. true

Question 29

Which of the following are involved in local branching? A. NGF B. NT3 C. NT4 D. CREB-mediated gene

Answer 29

A. NGF | B. NT3

Question 30

Which of the following are involved in long range axon growth? A. NGF B. NT3 C. NT4 D. CREB-mediated gene

Answer 30

D. CREB-mediated gene

Question 31

What type of sensory neurons do the first cells that arrive to the DRG give rise to?

Answer 31

-the first cells give rise to postmitotic cells that divide very few times --> give rise to large mechanoreceptors

Question 32

What type of sensory neurons do the late migrating cells that arrive to the DRG give rise to?

Answer 32

-the late cells divide and proliferate many times and give rise to large and small nociceptors

Question 33

The expression of different neurotrophic receptors will determine cell type. In what cells are TrKB and TrKA present in?

Answer 33

- TrKB is present in all proliferating cells | - TrKA is present in all postmitotic cells

Question 34

NTFs are involved in defining the identity of neurons. A. true B. false

Answer 34

A. true -all mechanosensory cells are dependent on embryonic NGF

Question 35

NGF is the most present neurotrophin when it comes to synaptic plasticity. A. true B. false

Answer 35

B. false BDNF is the most present NT when it comes to synaptic plasticity.

Question 36

What is the role of NGF in pain and inflammation?

Answer 36

- NGF induces pain - it is an acute inclusion of inflammation --> leads to hypersensitvity of nociceptors - by making inflammation in the skin - production of NGF is increased