Neural Induction 2

Question 1

Where did the search for the neural inducer start?

Answer 1

activin

Question 2

activin

Answer 2

member of TGFb family
indices mesoderm
found in mesoderm of early embryos and brain/notochord later

Question 3

Activin in ectodermal cells

Answer 3

bind receptor, dimerises, activates cytoplasmic c kinase domain = signal

Question 4

activin in ectoderm explants

Answer 4

activin bind receptor, signalling occurs

secondary signal from mesoderm converts ectodermal fate to neuonal fate

Question 5

activin receptor with no signalling domain

Answer 5

still bind activin and dimerise but no signal

Question 6

Experiment - activin receptor

Answer 6

mRNA encoding mutant receptor injected into both cells of 2 cell embryo - neural tissue?? would expect epidermal tissue as no signal

Question 7

finding of truncated activin receptor - neural tissue

Answer 7

neural tissue when to active signalling and no secondary signalling from mesoderm

Question 8

conclusion from truncated activin receptor experiment

Answer 8

activin inhibition leads to formation of neural tissue

Question 9

3 endogenous activin inhibitors

Answer 9

follistatin
noggin
chordin

Question 10

Follistatin - what is it?

Answer 10

activin binding protein
inhibits mesoderm producing activity of activin
promotes neural differentiation

Question 11

where is follistatin found?

Answer 11

gastrula stage: mRNA in spemann organiser and neural inducing tissues

Question 12

Follistatin experiment

Answer 12

overexpress follistatin
bin activin and prevent receptor signal
neural tissue

Question 13

conclusions from follistatin experiment

Answer 13

trunacted activin receptor and this experiment - negative role for activin signalling in neural induction

Question 14

Noggin

Answer 14

protein - mRNA in neural inducing tissues

Question 15

what does noggin bind to and prevent signalling?

Answer 15

BMP

Question 16

Noggin experiment

Answer 16

Inject mRNA into ventral blastomere - partial 2nd neural axis induces neural tissue directly from ectoderm

Question 17

noggin - direct and indirect neural induction

Answer 17

ectoderm + purified noggin = direct neural tissue

overexpress noggin = mesoderm intermediate

Question 18

noggin conclusion

Answer 18

noggin present right time and place to be neural inducer

induce neural fate directly or indirectly

Question 19

chordin - what is it, what does it do and where is it found?

Answer 19

protein, binds BMP

mRNA spemann organiser

Question 20

chordin - direct or indirect?

Answer 20

directly induces neural tissue

Question 21

evidence for chordin, follistatin and noggin working together

Answer 21

inhibit 1 = minor neural plae defect
all = substantial defect
stain for sox2

Question 22

similarities of 3 neural inducers

Answer 22

present right time and place
soluble proteins
induce neural tissue by blocking BMP binding

Question 23

what does BMP-4 induce?

Answer 23

epidermis

Question 24

What is BMP-4?

Answer 24

protein - TGFb family
binds to activin receptor
mRNA in ectoderm/epidermis not in spemann organiser

Question 25

BMP-4 experiment

Answer 25

inject mRNA - ventralises, mRNA to inhibit BMP-4 dorsalises | inject with mRNA against BMP-4 receptor (ventral injection) - partial second axis

Question 26

what does BMP-4 regulate?

Answer 26

dorsal/ventral patterning in xenopus

Question 27

what does BMP-4 inhibit?

Answer 27

neural tissue

Question 28

animal cap + BMP-4/mutant BMP-4 findings

Answer 28

animal cap + mutant BMP-4 or receptor or BMP-4 inhibitor = neural tissue dissociate cells - no BMP-4 = neural +BMP-4 = epidermis

Question 29

challenges to default model

Answer 29

neither chordin nor noggin can induce neural tissue if FGF signalling blocked BMP signalling necessary but not sufficient

Question 30

Evidence - challenge to neural default model

Answer 30

inject mRNA BMP antagonist into blastomere contribute to epidermis but not neural plate - no neural tissue co-inject with FGF = neural tissue

Question 31

What regions of embryo is BMP-4 not produced?

Answer 31

those with high nuclear b-catenin (controlled by wnt)

Question 32

Anterior patterning of neural plate

Answer 32

activin, follistatin, chordin, noggin, BMP

Question 33

What signals posteriorise neural plate?

Answer 33

wnt and FGF

Question 34

ectoderm - what happens if block BMP-4?

Answer 34

anterior CNS

Question 35

ectoderm - block BMP-4 and add FGF?

Answer 35

posterior CNS

Question 36

wnt

Answer 36

class of secreted glycoproteins that regulate b-catenin activity and gene transcription

Question 37

what happens if wnt overexpressed?

Answer 37

over-dorsalised embryo | explants undergo neural differentiation

Question 38

evidence wnt posteriorises

Answer 38

gradient of nuclear b-catenin high posteriorly | wnt induces hindbrain markers in neurulised animal caps

Question 39

3 models of A/P patterning of neuroectoderm

Answer 39

ectoderm pre-patterned - signals from mesoderm ectoderm homogeneous and mesoderm prepatterned 2 signal model - ectoderm induced to become anterior neural tissue, then posteriorised from posterior mesoderm

Question 40

diffusible factor from roof plate inducing commissural neurons

Answer 40

BMPs, dorsalin 1

Question 41

Induction of motor neurons and floorplate by notochord

Answer 41

motor neurons always form at set distance from floor plate inducing signal

Question 42

induction by floor plate

Answer 42

notochord between edges of neural folds at time of fusion = floor plate where roof plate should be extra lateral floor plate = ectopic lateral floorplate

Question 43

what does floorplate secrete?

Answer 43

shh

Question 44

what does roofplate secrete?

Answer 44

BMP/wnt

Question 45

netrin affect on commissural axons

Answer 45

protein in spinal cord stimulate outgrowth of commissural axons attract axons toward floor plate

Question 46

where is netrin 1 expressed?

Answer 46

floor plate

Question 47

where is netrin 2 expressed?

Answer 47

ventral 2/3 of spinal cord but not floor plate

Question 48

shh

Answer 48

produces protein | ventralising factor in vertebrae spinal cord

Question 49

commisural axons - wnt and shh

Answer 49

attracted to floorplate by shh ventral midline, switch to repulsion, steer growth cones anteriorly attract anteriorly to wnt

Question 50

Evidence that shh indices floor plate and motor neurons

Answer 50

embryos - shh in notochord shh ectopic = ectopic floor plate neural tube cells made to express shh - motor neurons

Question 51

how can shh form floor plate and motor neurons?

Answer 51

floor plate induction by amino-terminal cleavage product - contact dependent motor neurons - diffusible factor