Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BMS242 Developmental Biology > L5 - Hh and Wnt > Flashcards

L5 - Hh and Wnt Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

What organism were Hh and Wnt disocvered in

A

Flies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Hh and Wnt are what type of genes

A

Segment polarity genes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe a Hh mutant, therefore what is the gene required for

A

Has no naked cuticle and is covered in a lawn of dendticles

Hh is therefore required for the formation of the naked cuticle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

During segment patterening what do Hh and Wnt do for each other

So what can be said about Hh and Wnt mutant phenotypes

A

Maintain each others expression

Since loss of either Hh or Wnt will also lead to loss of expression of the other one then phenotypes will be similar

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe the discovery of wnt in mice and flies

A

Discovered as wingless Wg in flies
Discovered as Int1 in mice

Wnt was an amalgamation of the names

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How many Wnts and Hhs do vertebrates have

A

Many orthologues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is significant regarding Hh in c.elegans

A

They do not have Hh present

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Describe the translation of the Hh signal

A

Translated as three regions

1) N terminal signal sequence - targets to sec pathway 2) C terminal autoproteolytic domain - that cleaves itself
3) Middle protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is found at the N term end of the Hh when first translated

A

Signal sequence which targets the protein to the secretory pathways

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is found at the C term end of Hh when first translated

A

Autoproteolytic domain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What occurs once the signal sequence has been cleaved and the C terminal autoproteolytic domain has been cleaved

(2 modifications)

A

Cholesterol mod at C’

Palmitoylation at N’

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the effect of palmitate and cholesterol

A

Both are strongly hydrophobic so make the Hh hydrophobic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What two proteins important for long range singalling of Hh

A

Dispatched and scube

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How many TMD in dispatched

A

12

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the proposed function of dispatched and scube

A

May help load Hh into lipoprotein particles or cytonemes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is required for the long range transmission of the hh

A

HSPGS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What does HSPG stand for

A

Heparan sulphate proteoglycans

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

When is the signal sequence of wnt cleaved

A

Once the protein has entered the secretory pathway

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the two modification of Wnt signal

A

Palmitoylation of cys77

Palmitioleic acid mod of ser209

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Where is palmitiylation of Wnt addeded

A

cycy77

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Where is palmitoleic acid added to Wnt

A

ser209

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the effect of the two modifications added to Wnt

A

Make wnt insoluble in water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

WHat is Wntless involved in

A

Getting wnt to the cell membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What may be involved in the transmission of the Wnt signal

A

Lipoprotein particles and cytonemes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is required for the long range transmission of the wnt signal

A

HSPGs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the structure of wntless

A

7 pass transmembrane protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is a cytoneme

A

Long cellular protrusion used to touch other cells causing them the change thier behaviour - signalling molecule accumulates at the top

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What does Hh bind to

A

Ptc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Ptc strucutre

A

12 TMD

Similar to the dispatched gene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

How does ptc act without hh bound

A

In a negative way by continuosuly inhibiting smoothened

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

WHat is the strucutre of Smo

A

7 TMD

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Is there a stoichiometric relationship between ptc and smo

What does this mean?

A

Doesnt work one to one
Single ptc molecule inhibits many smo by regulating the subcellular location and stability of smo (targets smo to a compartement where it is degraded)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What is the effect on smo and ptc when Hh binds to ptc

A

Both ptc and smo internalised and degraded
So now smo can be trafficked to the surface

THREE MAIN CHANGES OCCUR TO SMO
Relocation
Accumulation
Phosphorylation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

In mammals what is thought to serve as the focal point for Hh signalling

A

Cilia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Describe localisation of Ptc1 in absence of Hh

What is the effect of this on smo

A

Ptc1 localised to cilium so smo is excluded from this area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What occurs to the localisation of Ptc1 when Hh binding

What is the effect of this on smo

A

Ptc1 removed from cilium

Allows smo to accumulate in the cilum and initiate signalling

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

How was it seen that cilium is involved in Hh signalling

A

Mutations in mice which disrupt cilia formation Hh signalling is also inhibited

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

What is the effect on ci when Hh not present

A

There are two complexes which keep it out of the nuceleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What are the two complexes which keep ci out of the nucleus

A

One with supressor of fused gene (SUFU) binds ci

One contains costal2 and a fused serine threonine kinase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

How many kinases in the costal2 complex

Name them

What effect do they have on Ci

A

3

Casein kinase I, protein kinase A, glycogen synthase kinase 3B

Shorten Ci via slimb - involving ubquitination

41
Q

What is the effect of the shortened version of Ci

A

Acts as a transcriptional repressor molecule - CiR

Hh target genes are actively repressed

42
Q

When HH active

What occurs to the three kinases

What effect does this have on ci

A

Interaction with the three kinases and Ci is blocked so a full length Ci is released and will actively promote transcription of target genes

43
Q

When HH active

What occurs to SUFU

A

Phosphrylation of SUFU by fused proteins and promotes the formati`on of the active form of Ci

44
Q

How does Hh act negatively on its own pathway

A

Repression of patched - reduces and limits the level of activation

45
Q

How does Hh act positively on its own pathway

A

Gli1 is induced and this is unable to be proetolysed into a repressor

46
Q

How does Hh play a role in wing patterning

A

In th drosophila imaginal disc Hh expressed posteriorly

It then diffuses into the anterior causing the expression of Dpp

47
Q

How is Shh involved in the patterning of the neural tube

A

Shh from notochord induces Shh exp in FP
Shh from FP then diffuses throughout the neural tube and a morphogen gdt is formed
Neural fate dep on how much Shh seen and for how long

48
Q

How is Hh involved in the AP patterning of the limb

A

Shh expressed in the ZPA

Confers posterior identity to the developing limb

49
Q

What are the other examples of Hh signalling

A 
Brain dev
Branching in lung 
Prostate 
Teeth 
Tounge
50
Q

What is holoprosencephaly

A

Loss of the ventral brain structure

Results in fused eues and cyclopic embryoys

51
Q

What is cyclopamine

A

An inhibitor of Smo

52
Q

What is syn/polydactylyl caused by

A

Mis regulation of the hedgehog pathway

53
Q

What mutations can cause cancer by causing over activity of the Hh pathway

What are these genes

A

Loss of func in Ptc1 or SUFU

Tumour supressor genes

54
Q

What mutations can cause cancer by causing inhibition of the Hh pathway

A

Activating mutations in Smo

Smo is a protooncogene

55
Q

What is gorlin syndrome

A

Large numbers of basal cell carcinoma due to patient being heterozygous for Ptc
Mistakes can lead to the loss of the functional ptc gene so this cell would then form a BCC

56
Q

What may be used to treat cancer caused by overactive Hh

What was the issue with this

A

Smo inhibitors - GFC-0049

Starts well but then tumour comes back due to resistance acquired by a mutation in Smo

57
Q

What is the crucial transcription factor for Wnt signalling

A

B-catening

58
Q

Describe what happens to B-catenin when Wnt not activated

A

B-catenin is bound and destoryed by a desturction complex

59
Q

Where does wnt derive its name from

A

Amalgam of wingless Drosophila gene and Int vertebrate proto-oncogene

60
Q

Int-1 is a proto-oncogene, what causes its activation

A

Integration of the mouse mammary gland tumour virus

61
Q

Wingless (wg) mutants initially discovered produced wingless but viable flies, T or F

A

T

62
Q

Explain how wg and hh maintain each other’s expression in an auto-regulatory loop

A

Wg maintains hh by controlling the expression of engrailed (en), a transcription factor that regulates hh expression. Hh then in-turn maintains and directly upregulates wg

63
Q

What is significant about hh and wg knockout mutants

A

They exhibit the same phenotype – larvae with a lawn of denticles

64
Q

Unlike similar developmental signalling pathways, wnt expression is highly conserved throughout Kingdom Animalia, T or F

A

T – even found in sponges

65
Q

Why is it that vertebrates have more wnt genes

A

Due to genome duplication throughout evolution

66
Q

The wnt protein is produce by a cleavage event that separates its signalling sequence from the initially translated protein, T or F

A

T

67
Q

What is the role of porcupine in the early modification of wnt

A

Porcupine is an acyl transferase that adds palmitoleic acid modifications to a serine residue at point 209 in the wnt3a structure

68
Q

What is the hypothesised role of wntless in wnt signalling and what is its basic structure

A

Wntless is a 7 transmembrane domain protein potentially required for the transport of wnt to the plasma membrane and its subsequent release/presentation to target cells

69
Q

What is the effect of palmitoylation and palmitoleic acid modification of the wnt protein

A

Addition of these hydrophobic groups makes wnt insoluble in water

70
Q

What components of the extracellular matrix are involved in mediating the diffusion of wnts away from the sending cell

A

Heparan sulphate proteoglycans (HSPGs)

71
Q

What is significant about the fact that most of the effects of Wnt signalling can be elicited by a membrane bound form of the protein in Drosophila

A

It suggests that wnts act as juxtacrine signalling molecules or that they don’t diffuse far and act on adjacent cells in Drosophila

72
Q

Recall the two main receptors involved in reception and transmission of wnt signalling in Drosophila

A

Frizzled and Arrow

73
Q

What is the name of the nuclear factor in Drosophila that is induced as a result of wnt signalling and its corresponding vertebrate homologue

A

Armadillo (vertebrate homolog – ?-catenin)

74
Q

What are the names of the arrow receptor homologues found in humans

A

LRP5 and 6

75
Q

Both the frizzled genes and arrow/LRP5&6 act in combination as receptors for wnt signalling molecules, T or F

A

T

76
Q

Describe the structure of the frizzled receptor and how it interacts with wnts

A

7 transmembrane domain protein. Wnt binds to the cysteine-rich domain (CRD) in the N-terminus of the Fz protein

77
Q

Describe the structure of the LRP5&6/Arrow receptor for wnt

A

Single pass transmembrane protein

78
Q

What happens when wnt binds to LRP5/6/Arrow and the Fz receptors

A

These two receptors come together to form an active wnt signalling complex

79
Q

Which important extracellular wnt inhibitor is overexpressed in order to downregulate wnt signalling in experiments

A

Dickkopf1 (Dkk)

80
Q

How does Dkk act to downregulate wnt signalling

A

Dkk is coupled to Kremen. Activation of Dkk by wnt binding promotes the internalisation of the LRP receptors

81
Q

Describe the composition of the degradation complex involved in wnt signalling

A

Consists of the scaffold protein axin bound to APC, GSK3?, CK1? and slimb

82
Q

Describe what happens in the absence of wnt signalling

A

Also bound to the degradation complex via an interaction with APC is ?-catenin. In the absence of wnt signalling ?-catenin is phosphorylated by CK1? and then by GSK3?. This poly-phosphorylated ?-catenin is then recognised by the slimb protein which ubiquitinates the ?-catenin marking it for degradation by the proteasome system. With low levels/absence of ?-catenin T cell factor (TCF) transcription factors are bound to the promoter regions of wnt target genes. Also bound to these TCFs is a transcriptional repressor known as groucho. Groucho inhibits the transcription of wnt target genes

83
Q

Describe what happens in the presence of wnt signalling

A

Wnt binds to its Fz and arrow/LRP 5&6 receptors in the membrane. These receptors come together and form an active complex which recruits the dishevelled protein to the complex. Dishevelled is then phosphorylated and as a result may bind to axin in the intracellular destruction complex. Arrow/LRP is then also phosphorylated this time by GSK3? and the receptor recruits axin also. Binding of the destruction complex to the receptor complex displaces the slimb protein. With slimb lost the destruction complex is inactivated. ?-catenin then accumulates inside the cell due to it not being ubiquitinated and marked for degradation by slimb. It then translocates to the nucleus of the receiving cell and displaces groucho from the TCF DNA binding proteins. In combination with additional downstream transcriptional activators this leads to the transcription and expression of wnt target genes.

84
Q

Explain how ?-catenin degradation is achieved by the destruction complex

A

?-catenin is phosphorylated by CK1? first, which primes it phosphorylation by GSK3?. Phosphorylation by both kinases is required for ?-catenin recognition by an E3 Ubiquitin ligase complex (which contains b-TrCP/Slimb) and subsequent degradation by the proteasome. The serine/threonine phosphates and surrounding amino acid sequence in ?-catenin as a result of phosphorylation forms an optimal binding site for b-TrCP/Slimb. ?-TrCP/Slimb binds only after GSK3 phosphorylates the 3rd and 4th phosphorylation sites

85
Q

Where does CK1? phosphorylation occur within the ?-catenin/armadillo structure

A

Sites within the N-terminal tail

86
Q

The S/TXXXS/T(P) is the ideal site for GSK?, what does this mean

A

A serine or threonine residue followed by 3 residues of any identity and then another serine or threonine that has been phosphorylated by CK1?

87
Q

What is the name of the vertebrate homologue of slimb

A

?-TrCP

88
Q

Describe the structure of the SCF E3 ubiquitin ligase complex involved in ?-catenin/armadillo degradation

A

The Skp1-Cullin-F-box E3 ubiquitin ligase complex consists of the ring finger protein Roc1 which binds to an E2 ligase, the scaffold protein cul1 and skp1

89
Q

Explain the role of SCF in ?-catenin/armadillo degradation

A

The F-box protein interacts with Skp1 via its F-box. The F-box of also interacts with the substrate via the WD40 domain that interacts specifically with phosphorylated targets

90
Q

How does the absence of Wnt signalling lead to no expression of wnt target genes

A

Without ?-catenin binding to TCF, groucho remains bound. The transcriptional repression by groucho is mediate by its recruitment of histone deacetylases thought to make DNA refractive to transcriptional activation

91
Q

How therefore does wnt signalling lead to expression of downstream target genes

A

In the nucleus increases levels of ?-catenin displace groucho from the TCF complex. Displacement of groucho leads to the recruitment of histone acetylase CBP/p300 and another transcriptional activator called BRG-1. These lead to transcription of wnt target genes

92
Q

Explain how interactions between TCF/?-catenin and chromatin could also be mediated by legless (Bcl9) and pygopus genes

A

Mutations in these genes result in wingless-like phenotypes in Drosophila. Both genes also promote wnt signalling in mammalian cell cultures.

93
Q

Wnt signalling components are also involved in directing planar cell polarity and convergent extension, T or F

A

T

94
Q

Explain the negative feedback mechanism of wnt signalling

A

Dickkopf1 (Dkk) activation by wnt binding promotes the internalisation of the LRP receptors. This decreases further wnt signalling activation and has important homeostatic roles.

95
Q

Give examples of planar cell polarity events caused by wnt signalling

A

Wnt signalling aligns all the hairs in the skin in a certain direction

96
Q

Explain how defective wnt signalling can cause cancer, particularly in the gut

A

Patients who are heterozygotes for APC loss of function mutations suffer from familial adenomatous polyposis. This is where sporadic loss of the other functional wild type APC allele in the gut results in activation of the wnt signalling in such cells. This causes hyperproliferation and culminates in the formation of polyps which may accumulate further mutations and cause colon cancer.

97
Q

The APC gene is a proto-oncogene, T or F

A

F – it’s a tumour suppressor gene (loss of function results in tumorigenesis)

98
Q

Give an example of another disease phenotype caused by mutation(s) in wnt signalling

A

Tetra-amelia is a disease where the infant is born without limbs. This is caused by a mutation in wnt3

BMS242 Developmental Biology (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions