1. Appendage development
LECTURE 9:
Appendage development

2. Quiltwork Assembly of a Fly
Head
Tail T1 T2 T3 A1 A2 A4 A5 A6 A7 A3 A8
Metamorphosis

3. Outline of Vein Development1 2 3 4 5
3rd Larval Instar
Early Pupa M L 1 2 3 4 5 6 s C o
Mid-Pupa->Adult

4. Fly Wing M L1 L2 L3 L4 L5

5. The Players: A/P Axis
Engrailed (En) = Transcription factor expressed in posterior cells.
Hedgehog (Hh) = Signal whose expression is activated by En.
Dpp = Signal whose expression is activated by Hh signaling.
Sal = Transcription factor activated by Dpp signaling.

6. Determining the Positions of Veins
En -> Hh -> Diffuses ->
dpp in A/P Organizer
Dpp
Dpp -> Diffuses ->
sal -> L2 vein A P
sal
Organizer
A/P L2
dpp L3 L4 L3 L4 A P
dpp En hh L5
dpp L2 L3 L4 L5 L2 L3 L4 L5
sal

7. Hh Determines Positions of L3 and L4 Veins
dpp A P En L3 L4
En -> Hh -> Diffuses ->
dpp in A/P Organizer hh
dpp
Mutant with reduced
hh function A P En L3 L4 WT L2 L3 L4 L5
hh- mutant L2 L3 L4 L5

8. Dpp Determines Positions of L2 and L5 veinsWT L2 L3 L4 L5
Dpp A P
sal
Dpp -> Diffuses ->
sal -> L2 vein L2
Dpp A P L5
sal L3 L4
Mutant with reduced
dpp function
dpp- mutant L2 L3 L4 L5

9. Veins Form At Boundaries Along the A/P Axis+ E n h d p A P
Organizer
A/P
En -> Hh -> Diffuses ->
dpp in A/P Organizer L 2 3 4 s a l D p A P
Dpp -> Diffuses ->
sal -> L2 vein L5

10. The Developmental Path From Bcd to the L2 Vein
Maternal B i c oi d
gradient
defines posterior limit of hb
Ant.
Post.
Lowest level of Bcd needed to activate hb H b e v - 3 Hb
defines anterior
border of
eve
-3 stripe K n i W i n g D s c e - 5
Eve-3
defines anterior
border of en -5
stripe + E n h d p A P
En-5
defines position of
dpp
stripe in wing disc s a l D p A P
Dpp
defines anterior
border of
sal
domain
Sal
defines position of
L2 vein
stripe s a l D p + S L 2 X A P

11. The Players: D/V and P/D Axes
Apterous (Ap) = Transcription factor expressed in dorsal cells.
Notch (N) = Signaling system that induces margin at D/V border.
Distalless = Transcription factor activated at A/P & D/V intersection.

12. D/V Signaling Is Required for Wing Margin Formation and Wing Outgrowth
V -> D Signal ap
Expressing Cells
Non-expressing
Cells D V
Activation of
Notch Along
Future Margin
Ap -> Notch -> Wing Margin
= D/V Organizer
D/V Signaling Is Required for Wing Margin Formation and Wing Outgrowth
D/V Organizer -> Margin Formation
and Wing Growth
- cells
Wing imaginal disc in larva
Adult wing (viewed end on)
Adult wing with
- patch
Loss of
in Dorsal Cells
-> Margin Formation
Intersection of the D/V and A/P Organizers Induces Leg Outgrowth
D/V Organizer A P
A/P Organizer
Distalless
Expression
Distal
Proximal
Normal Leg
distalless
Mutant Leg D V
Fig. 4.4

13. Initiation of Wing Development in Chickens

15. Hh is the ZPA Factor ZPA Graft Hh Expression Hh Soaked Beads
Normal Wing
ZPA Transplant
ZPA Graft
Hh Expression
ZPA
0 mg/ml
4 mg/ml
8 mg/ml
16 mg/ml
Hh Soaked Beads