20. Cell interactions In neural development

Question 1

briefly describe the process of neurulation

Answer 1

dorsal most-ectoderm thickens and evaginates

neural folds fuse creating neural tube

notochord under the tube made of underlying mesoderm

Question 2

what is the purpose of lateral inhibition

Answer 2

once one cell adopts a fate - it sends signals to prevent other cells from doing the same

Question 3

what is the purpose of Notch in drosophila

Answer 3

inhibits the neural fate in the neurectoderm

Question 4

describe the different notch mutants in drosophila

• normal notch
• too much notch
• not enough notch

Answer 4

• normal notch = wild-type
• too much notch = missing bristles
• not enough notch = extra bristles

Question 5

what is SOP

Answer 5

sensory organ precursor

Question 6

what happens once a SOP is specified

what does this require?

Answer 6

adjacent imaginal disc cells and laterally inhibited from doing the same

requires notch

Question 7

describe the process of notch signalling

Answer 7

notch binds its receptor via epidermal growth factor repeats

notch conformational change = cleaves the intracellular domain

translocates to the nucleus and binds to CSL family proteins
= target gene transcription

Question 8

what binds to the notch receptor

Answer 8

DSL proteins

Question 9

what do DSL stand for

Answer 9

delta/ serrate/ lag2

Question 10

describe DSL proteins

Answer 10

large membrane proteins
many EGF repeats
involved in lateral inhibitoon

Question 11

what is a proneural cluster

Answer 11

a cluster of cells that all have the potential to form a SOP = only one SOP per cluster

Question 12

what 3 proteins do all pro neural cluster cells express

Answer 12

acheate-scute proteins
delta
notch

Question 13

describe the positive feedback loop of acheate scute

Answer 13

acheate-scute over expression = expression of delta

notch binds on neighbour = activates split proteins that repress acheate-scute expression on neighbouring cells

ALLOWS ONE CELL TO OVEREXPRESS ACHEATE-SCUTE = commits it to SOP future

Question 14

where are pro neural clusters found

Answer 14

in the imaginal disc

Question 15

what happens once committed as an SOP

Answer 15

asymmetrical divisions = forms a shaft, socket, neuron or sheath

Question 16

how do neurons outgrow

Answer 16

cell body sends out axonal processes - direction is determined by actin polymerisation/ depolymerisation

Question 17

what is the purpose of the growth cone

Answer 17

dynamic structure at the end of the axon

able to migrate towards target tissue via chemotaxis

Question 18

describe the structure of the growth cone

Answer 18

contains filopodia - these are fingers that drive movement via actin polymerisation/ depolymerisation

Question 19

how do growth cones move

Answer 19

via chemotaxis

Question 20

what molecule is involved in chemoattraction

Answer 20

netrins

Question 21

what molecule is involved in chemorepulsion

Answer 21

semaphorins

Question 22

describe an example of chemoattraction

Answer 22

commissural neurons axons migrate ventrally through the floor plate

they are attracted to the floor plate which produces netrin 1

Question 23

name 2 netrin receptors

Answer 23

Unc-40

Unc-5

Question 24

what is the main differences between Unc-40 and Unc-5

Answer 24

Unc-40 binds directly and strongly to netrin

Unc-5 does not bind directly

Question 25

what is the effect of Unc-5 on Unc-40

Answer 25

modifies the response of Unc-40

Question 26

what does expression of Unc-5 cause in retinal neurons

Answer 26

causes retinal neurons to move away from netrin

Question 27

what happens once the neuron has crossed the floor plate

Answer 27

it stops responding to netrin and changes chemotactic behaviour

Question 28

what happens when the axon reaches a target neuromuscular junction

Answer 28

it branches and swells to form axon terminals. these terminals mature to contain vesicles with neurotransmitters inside

Question 29

what is the effect of agrin at neuromuscular junction

Answer 29

causes clustering of acetylcholine receptors

Question 30

what releases agrin

Answer 30

axon terminals on motor neurons

Question 31

one molecule of agrin can aggregate how many acetylcholine receptors

Answer 31

200

Question 32

what is MUSK

Answer 32

a muscle specific tyrosine kinase

Question 33

what does agrin bind to

Answer 33

LRP4/Musk

Question 34

what happens once agrin binds to LRP4/Musk

Answer 34

activates raspyn by action of Rho/Rac raspyn binds to Ach receptors causing aggregation

Question 35

what is the function of Aria

Answer 35

binds to ErbB and activates expression of acetylcholine receptor genes in adjacent cells