20. Cell interactions In neural development Flashcards
briefly describe the process of neurulation
dorsal most-ectoderm thickens and evaginates
neural folds fuse creating neural tube
notochord under the tube made of underlying mesoderm
what is the purpose of lateral inhibition
once one cell adopts a fate - it sends signals to prevent other cells from doing the same
what is the purpose of Notch in drosophila
inhibits the neural fate in the neurectoderm
describe the different notch mutants in drosophila
- normal notch
- too much notch
- not enough notch
- normal notch = wild-type
- too much notch = missing bristles
- not enough notch = extra bristles
what is SOP
sensory organ precursor
what happens once a SOP is specified
what does this require?
adjacent imaginal disc cells and laterally inhibited from doing the same
requires notch
describe the process of notch signalling
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
what binds to the notch receptor
DSL proteins
what do DSL stand for
delta/ serrate/ lag2
describe DSL proteins
large membrane proteins
many EGF repeats
involved in lateral inhibitoon
what is a proneural cluster
a cluster of cells that all have the potential to form a SOP = only one SOP per cluster
what 3 proteins do all pro neural cluster cells express
acheate-scute proteins
delta
notch
describe the positive feedback loop of acheate scute
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
where are pro neural clusters found
in the imaginal disc
what happens once committed as an SOP
asymmetrical divisions = forms a shaft, socket, neuron or sheath
how do neurons outgrow
cell body sends out axonal processes - direction is determined by actin polymerisation/ depolymerisation
what is the purpose of the growth cone
dynamic structure at the end of the axon
able to migrate towards target tissue via chemotaxis
describe the structure of the growth cone
contains filopodia - these are fingers that drive movement via actin polymerisation/ depolymerisation
how do growth cones move
via chemotaxis
what molecule is involved in chemoattraction
netrins
what molecule is involved in chemorepulsion
semaphorins
describe an example of chemoattraction
commissural neurons axons migrate ventrally through the floor plate
they are attracted to the floor plate which produces netrin 1
name 2 netrin receptors
Unc-40
Unc-5
what is the main differences between Unc-40 and Unc-5
Unc-40 binds directly and strongly to netrin
Unc-5 does not bind directly
what is the effect of Unc-5 on Unc-40
modifies the response of Unc-40
what does expression of Unc-5 cause in retinal neurons
causes retinal neurons to move away from netrin
what happens once the neuron has crossed the floor plate
it stops responding to netrin and changes chemotactic behaviour
what happens when the axon reaches a target neuromuscular junction
it branches and swells to form axon terminals. these terminals mature to contain vesicles with neurotransmitters inside
what is the effect of agrin at neuromuscular junction
causes clustering of acetylcholine receptors
what releases agrin
axon terminals on motor neurons
one molecule of agrin can aggregate how many acetylcholine receptors
200
what is MUSK
a muscle specific tyrosine kinase
what does agrin bind to
LRP4/Musk
what happens once agrin binds to LRP4/Musk
activates raspyn by action of Rho/Rac
raspyn binds to Ach receptors causing aggregation
what is the function of Aria
binds to ErbB and activates expression of acetylcholine receptor genes in adjacent cells
