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BMS 242 - Principles of Developmental Biology > Drosophila appendage development > Flashcards

Drosophila appendage development Flashcards

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1
Q

How are limbs patterned?

A

By signalling cascades

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2
Q

What do disruptions in the hh signalling pathway do in limbs?

A

Duplications of digits and wings

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3
Q

Where do the adult tissues of the fly develop from?

A

Imaginal discs

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4
Q

What are imaginal discs?

A

Small structures of epithelial cells that are set aside during embryogenesis (originate in the embryo)

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5
Q

When can the imaginal discs be seen?

A

At the segmentation stage of development

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6
Q

Where are the leg imaginal discs?

A

T1-T3

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7
Q

Where are the wing imaginal discs?

A

T2

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8
Q

Where are the haltare imaginal discs?

A

T3

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9
Q

What happens to the wing imaginal disc during larval development?

A

Increases in size from 30 cells to about 50,000 columnar cells by the end of the 3rd instar

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10
Q

What patterns the wing?

A

Signalling transduction pathways and morphogens (not pre detemined)

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11
Q

What is the wing split into?

A

4 quadrants:

  • Anterior
  • Posterior
  • Dorsal
  • Ventral
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12
Q

What does fate mapping of the 2D wing imaginal disc show?

A
  • Centre of the 2D structure becomes the wing blade
  • Surrounding part of the 2D that becomes the wing blade - becomes the HINGE
  • Surrounding the part that becomes the hinge - becomes the NOTUM
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13
Q

What does the hinge in the wing do?

A

Translates the muscular movement into the movement of the wing

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14
Q

What is the unfolding of the 2D imaginal disc to the 3D structure called?

What does the middle of the disc become?

A

Eversion

Middle of disc become edge of the wing

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15
Q

What does the patterning of the wing disc start with?

A

Axis formation

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16
Q

How do the cells in the wing disc know where they are?

A

Wing disc is divided into 4 compartments - producing ‘coordinates’ in the disc (map)

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17
Q

What are the 2 main molecules that define the quadrants in the disc and give the cells positional info?

A

Wingless and patched

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18
Q

Where is wingless expressed in the wing disc?

What does this become?

A

On the BOUNDARY between the dorsal and ventral disc

Becomes the EDGE of the wing

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19
Q

Where is patched expressed in the wing disc?

A

On the boundary between the anterior and posterior disc

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20
Q

What is patched?

A

A receptor for the hh signalling pathway

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21
Q

Where are sensory organ precursors present?

What are they?

A

Have stereotypical positions within the wing disc

Precursors for the sensory bristles that the fly uses on its wing

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22
Q

What are the 4 stages of establishing the XY axis of the wing disc?

A

1) Engrailed
2) Hedgehog
3) Decapentaplegic
4) Wingless

23
Q

What does engrailed define?

A

The posterior compartment of the wing disc

24
Q

What type of molecules is engralied?

A

Segment polarity gene

Transcription factor - sits inside the nucleus

25
Q

Why is engrailed expressed in the posterior half of the wing disc?

A

It is inherited from the segmentation machinery

Disc is made of a group of cells following segmentation - some of these cells already express engrailed

26
Q

How can engrailed be visualised using reporter genes?

Where does this show engrailed is expressed?

A
  • LacZ expressed in the place of the Engrailed DNA sequence
  • BUT under the control of the enhancers that control engrailed
  • When add colourless X-gal gas - lacZ converts the gas into blue precipitate

Shows engrailed to be expressed in the posterior of:

  • Segments
  • Wings
  • Legs
27
Q

How does engrailed affect hh signalling?

What does this cause?

A 
Represses Ci
(In Hh signalling, Ci is changed from a repressor to an activator)

Causes:

  • Ci to be active in the anterior of the disc
  • Ci to be repressed in the posterior of the disc
28
Q

What drives the expression of Hh?

What does this mean?

A

Engrailed

The cells where hh is expressed cannot respond to the hh as engrailed is expressed and represses ci

29
Q

Where is Hh high/low in the wing disc?

Why?

A

High in the posterior (made in the cells that express engrailed)

Low in the anterior (concentration gradient - hh is a morphogen, diffuses away from source)

30
Q

What is patched?

Where is it expressed?

A

Hh receptor
AND
Hh TARGET gene

Patched receptor expressed on the boundary between anterior and posterior cells

31
Q

Where can cells respond to hh signalling?

A

Only on the boundary between anterior and posterior and onwards (anteriorly)

32
Q

What is dpp a transcriptional target of?

A

hh

33
Q

Where is dpp expressed?

Why?

A

In a STRIPE along the anterior posterior boundary of the wing disc

These cells can respond to hh signalling as there is no engrailed expressed that represses ci - target genes can be expressed

34
Q

Why is dpp only expressed in a small stripe at the anterior posterior boundary?

A

Hh morphogen doesn’t travel that far as the hh protein is is heavily modified by lipids

35
Q

What is the homologue of dpp in drosophila?

A

TGF-beta

36
Q

What type of molecule dpp?

A

Morphogen

37
Q

What happens after dpp is made at the AP boundary of the wing disc?

What does this form?

A

Dpp diffuses from the boundary into both the anterior and posterior

Forms a gradient in both directions

38
Q

What does the gradient of dpp tell the cells?

A

Telling the cells how far they are away from the midline (fixed reference point)

39
Q

What signal transduction cascade is dpp the extracellular ligand of?

A

The TGF-beta signalling cascade

40
Q

What 2 receptors does dpp interact with?

A

Type I and II receptors (Tkv an Pnt)

41
Q

What happens when dpp binds to type II receptor?

A
  • Forms a heterodimer with type I receptor

- Phosphorylates and activates Mad (transcription factor)

42
Q

What does Mad do when it is activated?

A

It switched genes on/off:

  • Omb, sal = on
  • Brinker = off
43
Q

When is sal induced?

What is the boundary of sal?

What does this show about the threshold of sal?

A

At very high levels of p-Mad (at AP the boundary)

Very sharp boundary

High threshold

44
Q

What is the threshold for omb?

How is this seen?

A

Broad threshold

Broad pattern of expression

45
Q

What do the cells in the middle of disc (in the AP direction) express?

Why is this unusual?

A

BOTH sal and omb

Normally, target genes of morphogens switch off other genes to ensure that only ONE target gene is on

46
Q

What do LOW levels of dpp induce?

What do HIGH levels of dpp induce?

How does this give cells positional information?

A

Omb expression only

Sal AND OMB

Different types of cells define different areas of the map

47
Q

What is a morpho trap?

A

Membrane tethered anti-GFP

48
Q

What happens when express a morphotrap in the middle of the wing disc after adding dpp-GFP?

A
  • Traps dpp-GFP
  • Preventing it from diffusing
  • Lack of dpp gradient
  • p-Mad is trapped in the same cells
  • Brinker is active in more cells and is closer to the midline (no dpp signalling)
49
Q

What happens if make a clone of cells in the posterior compartment that are LACKING in ENGRAILED?

A
  • No hh made
  • But can make Ci (not blocked by engrailed)
  • SO, can respond to hh made by surrounding cells that diffuse in)
  • These cells then express patched and dpp
  • Forms an ectopic midline
  • Another reference point in the map, defining the middle of the wing
50
Q

What is the midline of the wing disc defined as?

A

The boundary between dpp-expressing and dpp-non-expressing cells

51
Q

What happens if make a clone of engrailed expressing cells into the anterior?

A
  • Express hh

- Induces dpp in the SURROUNDING CELLS (can respond to hh as Ci is not repressed)

52
Q

What happens is make a clone of patch LACKING cells in the ANTERIOR (away from the midline)?

A
  • No inhibition of smoothened
  • Downstream target genes are activated
  • Dpp activated inside of the clone
  • Artificial midline
  • Production of dpp in the clone
  • Diffuses out and patterns the cells around the clone
  • Mirror image of symmetry of ectopic wing
  • Formation of triple anterior wing
53
Q

What happens is prevent patched receptor expression IN the midline?

A

Hh moves PAST this region (not bound by the receptor) until find a receptor past the patched mutant

BMS 242 - Principles of Developmental Biology (15 decks)

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