Lecture 10: NMJ formation

Question 1

what is the strucutural backbbone of axons

Answer 1

microtubules

Question 2

descrbie microtubules in axons

Answer 2

hundreds of microm
unusually stable
unipolar bundles

Question 3

what are the tip of axons like

Answer 3

migratory cells

Question 4

how are axons established

Answer 4

migratory growth cone at tip

as migrate leave behind axon

Question 5

what are growth cones

Answer 5

the migratory tip of each axon

Question 6

what is the property of severed growht cone

Answer 6

continue to navigate

Question 7

what is the principle for spatial preferences with eg

Answer 7

key in lock = certain cells have the relevant receptor for the signal
eg the extension of neurons in the retina of frogs
the rught retina connect to the left tectum and vice versa

Question 8

give the moleculr details of spatial prefernce example of neurons and retina in frogs

Answer 8

gradient of EphA3 in retina highest in temporal lowest in nasal
gradient of EphrinA2 A5 in tectum highest in posterior
repel eachother
neurons from the temporal (high Eph) to the anterior (low ephirn)
and nasal (lowEph) to posterior (high ephrin)

Question 9

what are growth cones composed of

Answer 9

mt (stop at neck)
actin (rich at the peripery/sgl fibres)
receptors

Question 10

how does guidance signalling of axon work

Answer 10

key lock

receptors-singlas

Question 11

give examples of receptor-signal combination invovled in grwoth cone migration

Answer 11

signal - rec
slit -robo (repel)
sema3A - neuropilin
ephrinB2 - EphB
ephrinA - EphA

Question 12

what ssignal receptors are differentially expressed in the lateral and medial lateral medial column (LMC)

Answer 12

ephrin b2 in medial

ephrin a in lateral

Question 13

describe how slit-robo controls motor axon establishment

Answer 13

slit is expressed in the floor plate

repel the robo2 positive motor neurones but not the commisural neurones

Question 14

describe robo1 and robo 3 action

Answer 14

expressed in the commisural neurones
robo1 can repel
robo3 dom negative - couples up with robo1 - makes complex not repel therefore can cross midline
loss of robo3 - preventss midline crossing of the commisural neurones

Question 15

what diseases have robo3 mutation

Answer 15

HGPPS (horizontal gaze pulsy with progressive scollosis)
cant look left anf right
lots of neruones dont cross midline

Question 16

what does Sma£A singalling mediate

Answer 16

split into dorsal and ventral nerve branches
expr in the middle of limb bud
repels growth cones (collapse on exposure) = create d/v paths

Question 17

what other development example in unit has Sema3A

Answer 17

neural crest cells migrating

Question 18

what creates the dorsoventral paths of neurons

Answer 18

diff tf code

induces diffenetial expression of eph/ephrin

Question 19

examples of tf od the motor neuron translating to eph/ephrin

Answer 19

Lim1 - Eph A4 (in lmc lateral)

Isl - EphB (in lmc medial)

Question 20

what is the effect of the Eph/ephrin singals on growth cone

Answer 20

morphogenetic changes
F-actin - give cone directionality = open up space for MT and mdiate signalling
MT - give cone advance - poly/depoly
ko F-actin - no directionality but can still advance

Question 21

how is the morthogenetic changes of the growth cone different to the migratory cell

Answer 21

use guidance cues to favour poly and stabilisation of MT depending whether attractive or repel cue

Question 22

what are chanracteristics of actin and mt

Answer 22

actin = unidirectional growth treadmill, proflin inh growht, forminenh of poly , also rewuire enz inc WASP/SCAR
MT - grow and depoly from the + end = why can groqw and collapse back

Question 23

what cotnrols the activation of Rho in growth cone

Answer 23

Slit and ROBO assembles the GEFS and GAPS

promote

Question 24

what is the role of Rho

Answer 24

promote distinct morphogenetic events (rac1 - lamellipodia, cdc42 - filopodia, RhoA - contractility) coordiate actin binding regulators (ABPS and MTBPS)

Question 25

summary for how signal pathway interact with actin

Answer 25

signal pathways interact with GAPS and GEFS - act on actinn binding pr - actin singal = refines actin activity

Question 26

what is nmj

Answer 26

a highly specialised synaptic cell junction between two tissues

Question 27

what cell component crucial for nmj formation and maintenance

Answer 27

ECM inc basement mbn pr (agrin,perlecan,laminin,collagen IV and ColQ)

Question 28

desrcibe role of agrin

Answer 28

is presyn released
required for post synaptic AChR clusters
how - z-agrin released from neuron - anchors to b.mbn - where maintains AChR at post syn sites

Question 29

describe the molecular detail for how agrin works

Answer 29

agrin instruct the assembly of postsyn machinery
agrin complex with MuSK and LRP4
then binds with raspyn
raspyn scaffold for clustering of AChR (but can not mediate localisation at NMJ)

Question 30

what laminins are expr at NMJ

Answer 30

all have B2 and Y1

Question 31

what seen in B2 KO mice

Answer 31

no presyn active zones (a4)
dispersion of presyn vesicles
glial invasion of syn cleft (b2)
lack of postsyn folds

Question 32

descibe the role of a4 laminin in pre syn active zone

Answer 32

norm expr everywhere but the synaptic areas

= controls the alignment

Question 33

what is the wt role of b2 laminin in glial invasion

Answer 33

repels glial cells from the invading cleft

Question 34

what the role of laminin 421

Answer 34

binds to extracellular loop of calcium channels
this links it to the activ zone
the laminin holds the active zone in place

Question 35

what two broad dev mechanisms does nmj formation use

Answer 35

contact formation between gc and target muscle

reciprocal signalling events using basement mbn as a hub