Molecular Mechanisms of synaptic vesicle recycling

Question 1

Synaptic vesicles must recycled because:

Answer 1

1. Synapses contain a limited number of synaptic vesicles and replacing them one by one by synthesis from the cell body would be too slow.

Question 2

Four pathways for retrieval of synaptic vesicle membranes

Answer 2

1. Clathrin mediated endocytosis

Question 3

explain clathrin mediated endocytosis

Answer 3

Slow (10 -20 secs)

Question 4

What are the steps in clathrin mediated synaptic vesicle endocytosis?

Answer 4

• Start with synaptic vesicle fusion with the plasma membrane and releasing neurotransmitters

Question 5

Describe clathrin heavy and light chain

Answer 5

• Self-polymerizing protein composed of three heavy and three light chains that form the clathrin triskelion

Question 6

After experimenting what was found to happen when inactivation of clathrin light chain occurs?

Answer 6

we can completely block clathrin-mediated synaptic vesicle endocytosis.

Question 7

Describe AP-2

Answer 7

• An adaptor that links the membrane of synaptic vesicle to clathrin and various accessory protein

Question 8

Describe AP180

Answer 8

Adaptive protein that is capable of binding to lipids , PIP2, and clathrin. It can also regulate synaptic vesicel endocytosis.

Question 9

How does the absence of the AP180 homolog in drosophila affect endocytosis?

Answer 9

When AP 180 is taken away there is a severe reduction in the number of synaptic vesicles and clathrin-mediated synaptic vesicles. We also see an increase in the number of cisternae/endosomes in the AP 180 mutants

Question 10

Describe Dynamin

Answer 10

• Self-polymerizing mechsnoenzyme that triggers vesicle fission and scission upon GTP hydrolysis.

Question 11

How does the absence of dynamin affect endocytosis?

Answer 11

• When there is a mutation in dynamin during high-frequency stimulation all the synaptic vesicles seem to be gone.

Question 12

Describe endophilin

Answer 12

• Important in creating the right curvature for the membrane during synaptic vesicles fission and is important in recruiting dynamin or syanptoajanin

Question 13

How does the absence of endophilin affect endocytosis?

Answer 13

We see an absence in synaptic vesicles suggesting that endophilin is required for synaptic vesicle endocytosis

Question 14

When we take away these proteins what do we generally see?

Answer 14

When you take away clathrin, some adaptor proteins, endophilin, dynamin we block synaptic vesicle endocytosis, we see fewer vesicles But in many cases we see larger cisternae/endosomal structures.

Question 15

Why is PIP 2 important?

Answer 15

PIP2 levels are important for the recruitment for proteins that regulate synaptic vesicle endocytosis like AP2 and AP180, Clathrin, endophilin, dynamic etc

Question 16

Describe synaptojanin

Answer 16

• Lipid phosphatase recruited to clathrin coated pits by AP2 and endophilin

Question 17

How does the absence of synaptojanin affect endocytosis?

Answer 17

• We see that there are very few synaptic vesicles

Question 18

Describe Kiss and run

Answer 18

• Fast<1 sec

Question 19

What is the mechanism of Kiss and Run

Answer 19

The synaptic vesicle will briefly open and release neurotransmitters and then close and the vesicle will pinch off the membrane; keeping the shape, protein and lipid

Question 20

Describe Activity dependent bulk endocytosis

Answer 20

• Relatively slow (30 secs)

Question 21

Compare endosomes and clathrin mediated endocytosis and at what frequency they take up HRP.

Answer 21

• In the lower frequencies we see primarily clathrin mediated endocytosis and they take up HRP.

Question 22

During periods of high synaptic activity we will go through clathrin mediated endocytosis but endosmes will also form (T/F)

Answer 22

TRUE

Question 23

Describe Ultrafast endocytosis

Answer 23

• After a single stimulus vesicle membrane is recovered at the sites latera to the fusion sites within 100 ms

Question 24

Compare the 4 pathways for retrieval for synaptic vesicle membrane

Answer 24

Here compare and contrast the pathways, talk about speed, stimulation frequencies, and the vesicels are kept intact.

Question 25

Synapses can differ greatly with respect to

Answer 25

1. Their firing patterns

Question 26

What are the 3 types synaptic vesicle pools in order of what they fire?

Answer 26

1. Readily releasable pool

Question 27

Compare the size, location and time taken to release for all three synaptic vesicle pools

Answer 27

1. Readily releasable pool

Question 28

Vesicular proteins exocytosed and subsequently retrieved by compensatory endocytosis are nonidentical

Answer 28

There may maybe a pool of synaptic vesicle proteins on the plasma membrane and during endocytosis there maybe pools that get mixed.

Question 29

What are the different hypothetical models for sorting of synaptic vesicle proteins

Answer 29

1. Synaptic vesicles maintain the same composition in the beginning and the end

Question 30

What are the 4 ways to trigger endocytosis?

Answer 30

1. Fused vesicles

Question 31

What are the three different states a release site can exist?

Answer 31

• Empty and accessible for a vesicle