Appendage development LECTURE 9: Appendage development

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

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

Fly Wing M L1 L2 L3 L4 L5

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.

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

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

Dpp Determines Positions of L2 and L5 veins WT 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

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

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

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.

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

Initiation of Wing Development in Chickens

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