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BMS242 Developmental Biology > L14 - Drosophila Appendage Development > Flashcards

L14 - Drosophila Appendage Development Flashcards

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1
Q

Limbs are __________ patterned by ____________

A

Complex 3D structures patterend by conserved signalling cascades

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2
Q

Duplications of limbs is result of mutations due to a …

A

Defect in Hh signalling

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3
Q

What can be said about Hh signalling

A

Highlty conserved signalling pathway

Used in early patterning events and then again in limb development

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4
Q

How many instar stagges

A

3

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5
Q

Most of the adult tissue in drosophila is derived from

A

Imaginal discs

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6
Q

What are the imaginal discs made from

A

Diploid epithelial cells

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7
Q

What are the different immaginal discs

A 
Mouthparts
Antenna 
Eye
Leg 
Haltare 
Wing 
Genitalia
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8
Q

What does the number of discs depend on

A

The number of strcutures they go on to form

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9
Q

How many legs in drosophila

How many immaginal discs for the legs

A

6

6

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10
Q

When are the immaginal discs set aside

A

During embryogenesis

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11
Q

How can you see what the immaginal discs are

A

Using stains for specific marker genes

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12
Q

Describe what immaginal discs are seen in segments t1 - T3`

A

Leg - in all
Win - in T2
Haltare - in T3

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13
Q

Wing immaginal discs begins as a ____________

How many cells are they formed from?

A

2D epithelium

50000 cells

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14
Q

When do cells of the imaginal disc stop proliferating

A

At the third instar stage

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15
Q

What are the four segments of the wing disc

A

A P D V

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16
Q

The central region of the wing disc goes on to form the

A

Wing blade

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17
Q

The surrounding region of the wing blade goes on to form the

A

Hinge

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18
Q

What is the function of the wing hinge

A

Translate the force of the muscles which change the shape of the thorax into movements of the wing

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19
Q

What is responsible for forming the boundary between anteiror and posteiror

A

Patched gene expression (Hh)

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20
Q

What is reponsible for the formation of the boundary between dorsal and ventral

A

Wg gene expression

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21
Q

Nubbin gene expression is localised to the

A

Wing pouch

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22
Q

What type of gene is engraield

A

Segement polarity gene

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23
Q

Where is engrailed expressed

A

In the posterior of each segement

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24
Q

Describe the process used to visualse engrailed expression

A

LacZ expressed under the engrailed pormotoer
Use X gal
If there is LacZ present (forming B-galactosidease) Xgal gel goes from colourless to blue (insoluble)

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25
Q

Results of the En-LacZ show that

A

En expressed in the posterior of all sgements

Very sharp boundary

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26
Q

Describe Hh signalling when there is no Hh ligand

A 
Ptc represses Smo
Smo unable to signal 
Ci to SuFu 
Ci to Cos 2 and Fu - interacts with 3 kinases - cleaved to a shorter repressive form 
Enters nucelus - represses target genes
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27
Q

Describe the Hh signalling pathway when Hh is bound

A 
No repression of Smo 
Smo is phosphriylated 
Interaction with Ci and SuFU blocked 
Interaction with Ci and 3 kinases blocked 
Full length Ci enters the nucelus 
Acts as a transcritpional activator 
Causes transcription of target genes
28
Q

What are some examples of Hh target genes

A

DPp
Wg
Engrialed

29
Q

What is the function of en

On ci

On Hh

A

Causes promotion of Hh expresision

Blocks expression of Ci

30
Q

When is Ci expressed

A

In the absence of engrailed

31
Q

Pathched is a …. and a ….

A

Receptor for Hh

Also a TARGET gene for Hh

32
Q

What is the effect of Hh on Ptc expresison

What is this known as

A

Increases expression of Ptc

Positive feedback

33
Q

Where is engrailed expression hi

A

P

34
Q

Where is Ci expression hi

A

A

Where there is no En

35
Q

Descirbe the expression of Hh about the AP axis

A

High posterior

Diffusible molecule so diffuses into the anterior and a concnetration gradient is fomred

36
Q

Where is engrailed not expressed

A

Anteriorly

37
Q

To be competent to respond to hedgehog what must cells also be expressing

A

Ci

38
Q

What is the effect of Hh on Ptc

A

Upregualtion

39
Q

Dpp is a target …

A

Of Hh signalling

40
Q

What is the effect of Hh signalling of Dpp

A

Increased expression of dpp

41
Q

What is the homologue of Dpp

A

TGF-B

42
Q

Where is response to Hh seen

A

anterior compartment as these cells express Ci - only the ones that are in reach of Hh diffusion from the posterior

43
Q

When Dpp is transcribed what is the effect of this

A

Dpp is also diffusible so another concentration gradient is establsihed going both anterior and posterior

44
Q

Desribe the pathway of Dpp

A

Dpp –> Tkv/pnt –> Mad

Mad –/ brn
Mad –> Omb,sal

45
Q

What is the active version of mad known as

A

p-mad

46
Q

What genes do mad activate

A

Omb, Sal

47
Q

What genes does mad repress

A

Brinked

48
Q

What is Tkv/Pnt

A

Type1/type 2 receptor heterodimer

49
Q

Describe the distribution of hh mRNA

A

Hh is localised to cells in the posterior that are seeing engrailed

50
Q

What is the expression of Dpp mRNA

A

Expressed in a gradient based on Hh concentration gradient eastblished

51
Q

What is the expression of p-MAd

A

Expressed in a concentration gradient since Dpp diffuses both anteriorly and posteriorly

52
Q

How can you detect Dpp expression

A

Using a GFP fusion protein

53
Q

Dpp acts as a ___________

A

Morphogen

54
Q

What is the effect of high levels of Dpp

A

Sal and Omb expression

55
Q

What genes are expressed by low Dpp levels

A

Only induce expression of Omb expression

56
Q

What is a morphotrap

A

Expressing nanobodies which bind to a part of the morphogen preventing diffusion of the morphogen

57
Q

Describe what morphotrap is used in the investigation of Dpp

A

Express GFP-Dpp
Anti-GFP nanobodies (single chain AB) which are tethered to the membrane
This traps dpp at the membrane where it is produced preventing the formation of a gradient

58
Q

Describe the effects of GFP-dpp and anti-GFP which is membrane bound

A

Shows dpp expressed in the centre of the disc

No gradient formed

59
Q

What was seen on the morphotrap when probing for p-mad

A

Dpp is held in the centre - cant diffuse away

Lack of a gradient of p-mad trapped in cells

60
Q

What is the effect of p-mad on brinker

A

Repression of brinker

61
Q

What is seen from the morphotrap when probing for anti-brk

A

Dpp expression represses the expression of Brk

Brk expression domains is expanded horizontally

62
Q

Pathway from En to patterning

A

En –> Hh –> Dpp –> Patterning events

63
Q

Describe what happens when a group of cells are transplanted into the anterior of the wing which are engrail (-/-)

A 
Ci produced in group of cells (due to effect on engrailed from nearby cells)
Hh from surrounding cells diffuses over 
Expression of Ptc and Dpp 
Dpp defines the midline 
Formation of an ectopic midline
64
Q

What is the effect of transplanting a group of cells that express engrailed into the anterior

A

Engrailed - makes Hh
No Ci
Cells transplanted dont respond to Hh
Hh diffuses to neighbouring cells (which express Ci and no Engrailed) dpp expresion and ectopic midline

65
Q

What is the effect of putting a group of Ptc (-/-) into the anteiror

A

No supresison of smo by Ptc
Hh signalling consitiutively active
Even without the ligand still active signalling
Act Ci enters nucleus in this group of cells - dpp induced - ectopic axis

66
Q

Where there is an actopic activation and formation of a midline we see

A

Duplication of sturcutures

67
Q

Describe the effect of putting Ptc KO cells at the boundary where Dpp is usuaully expressed

A

Ptc normally binds Hh
Without ptc Hh can diffuse further
Dpp expression shifted anteriorly

BMS242 Developmental Biology (17 decks)

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