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Advanced Developmental Biology > Wnt and Shh signalling in invertebrates > Flashcards

Wnt and Shh signalling in invertebrates Flashcards

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1
Q

Where were Shh and WNT signalling discovered and what was SHH labelled as?

A

-Drosophila
- SHH labelled a segment polarity gene

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2
Q

How are SHH and WNT connected in terms of feedback?

A

Shh induces WNT expression and WNT signals back and reinduces Shh
- Shh expressed in posterior embryo and WNT expressed in anterior

***SO, if you lose one signalling you use the other and when they aren’t expressed there is no segmentation/polarity

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3
Q

How did the name WNT come about?

A

Int1 in mice was discovered at the same time as WNT and SHH,
The name comes from the morphing of Wg (wingless) in drosophila with Int1 in mice - making WNT

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4
Q

What are the three orthologues of the SHH genes that vertebrates have?

A

Shh
Desert hedgehog
Indian hedgehog

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5
Q

How is the signal generated in the producing cell regarding SHH?

A
  • SHH protein is produced with signalling peptide which enters secretory pathway and is then cleaved off
  • C terminus is a proteolytic enzyme which then cleaves itself
  • This causes cholesterol modification (cholesterol added on)
  • Fatty acid is then attached to N terminus making it hydrophobic
  • Hydrophobic means it cant move from the membrane so proteins such as ‘Dispatched’ and Scube help it to travel its signl
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6
Q

How is the signal generated in the producing cell regarding WNT?

A
  • Two fatty acids added, one to the cysteine and one to the serine (fatty acid modification)
  • Wnt = hydrophobic , cant move
  • Wntless is a gene which then lets Wnt get on to the outer membrane
  • Cytonemes + HSPGs known to be important to let Wnt detach from the membrane
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7
Q

What are cytonemes and what do they do?

A
  • Long cellular protrusions which grow out from the cell and at the tip the Wnt ligand is positioned
  • Reaches out and sends a signal so the Wnt signalling can get far away from the producing cell
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8
Q

What is the use of HSPGs?

A
  • WNT can bind to HSPGs at the polysaccharides but also has a binding pocket for palmitate
  • Palmitate allows WNT to be handed over from molecule to molecule and also to other cells
  • Facilitated diffusion vibes
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9
Q

What are the downstream signalling evens involved with SHH, patched and smoothened?

A

Patched= SHH receptor
- When SHH is not there, patched is inhibiting Smoothened which is involved in the downstream cascade
- When SHH binds, patched is inactivated and smoothened becomes activated + relocates to membrane and accumulates

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10
Q

How many patched genes are there in vertebrates?

A

2:
Patched 1 and Patched 2

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11
Q

What are cilia important for in vertebrates regarding SHH signalling?

A
  • They are a ‘focal point’ for signalling
  • Smo and Patched are only present at the cilia, this was discovered in mouse mutants where they had no cilia
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12
Q

How does Patched work?

A
  • In the absence of Hh ligands, PTCH restricts SMO by depleting cholesterol from the membrane where SMO is.
  • Inhibition prevents SMO from propagating the Hedgehog signal.
  • When Hh ligands bind to PTCH, restriction is lifted
  • PTCH no longer depletes cholesterol, allowing itl to accumulate in the membrane , activating SMO.
  • So one molecule of patched can activate multiple Smo because if one Patched is keeping cholesterol out of the membrane then no Smo will be turned on
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13
Q

What is happening downstream when SHH is not bound?

A
  • Ci is the transcriptional activator which in its full length leads to hh signalling effects
  • Two complexes stop it from being able to perform:
    1. Complex containing Cos2 (kinesin) and Fuse (kinase) This is the first complex bound to smoothened
    2. Contains the Ci and supressor of fused gene
  • Under the influence of the first complex, a complex containing CKI, GSK3 and PKA can act on Ci
  • This then means Ci is processed to its shorter form via Slimb via ubiquitination
  • The shorter form acts as a transcriptional repressor and is called CiR, repressing hedgehog genes
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14
Q

What is Ci called in vertebrates?

A

Gli 1,2 and 3

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15
Q

What is the downstream signalling of hh when there is a ligand present?

A
  • The interaction of Ci with the three kinases (CKI,PKA, GSK3) is blocked
  • Full Ci length is released that will actively promote transcription of target genes
  • This active formation is thought that the supressor of fusion
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16
Q

What is the Wnt signalling pathway when Wnt is not bound?

A
  • Two receptors called Frizzles and Arrow
  • Important TF is bcatenin
  • When it is produced, it binds a destruction complex (consisting of APC, Axin, CK1, GSK3)
  • Bcatenin is bound by this complex, is phosphorylated by GSK3 meaning it is then recognised by Slimb which is a ubiquitination complex leading to ubiquitination of Bcatenin
  • This means it cannot enter the nucleus
17
Q

What is the Wnt signalling pathway when Wnt is bound?

A
  • It brings together arrow and frizzled creating a complex
  • This leads to Dsh being phosphorylated on arrow receptor
  • This leads to the lost of Slimb
  • Bcatenin is produced and binds to destructive but it gets stuck due to no slimb, no destruction
  • This means more B catenin is produced meaning it enters the nucleus and binds to TCF which is promoter of Wnt
  • B catenin acts as an activating complex for Wnt
18
Q

What is the role of WNT signalling in drosophila?

A

Drosophila-segmentation and expressed at D/V boundary of the wing required for patterning and outgrowth

19
Q

How is Wnt signalling important in C-elegans?

A
  • Required for neuron expression - doesnt have Shh
20
Q

How is Wnt signalling important in vertebrate intestines?

A

maintains the stem cells of the gut -> lost of signalling leads to loss of stem cells

21
Q

How is Wnt signalling relevant in cancer causing?

A
  • Ectopic Wnt signalling can occur by loss of APC (part of destruction complex) which leads to a cancer called familial adenomatous polyposis (colon and rectum cancer)
  • Sporadic colon cancer due to gain of function of Wnt signalling
  • Also important in breast cancer, prostate cancer and melanomas
22
Q

Give two examples of diseases caused by Wnt?

A
  • Tetra-amelia, Wnt3 mutated leading to absence of limbs
  • More Wnt signalling can lead to increased bone density
23
Q

Give examples of the non-canonical pathways of Hh

A
  • Smo-Ca2+ - AMPK pathway
  • Metabolic reprogramming towards aerobic glycolysis - shh induces lactate at higher level
  • Certain inhibitors of canonical Hh singalling pathway activated non-canonical AMPK signalling
24
Q

Give examples of the non-canonical Wnt pathway

A
  • Planar cell polarity/conversion extension pathway
  • Polarises cells in a particular sheet, seen in hairs on drosophila wings

Advanced Developmental Biology (13 decks)

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