Head Tail

T1 T2 T3 A1 A2 A4 A5 A6 A7A3

A8

Metamorphosis

Quiltwork Assembly of a Fly

Outline of Vein DevelopmentM L1

L2

L3

L4

L5

3rd Larval Instar

Early Pupa

ML1 L2

L3

L4

L5

L6

sCo

Mid-Pupa->Adult

L1

L2

L3

L4

L5

M

Fly Wing

L2

L3

L4

L5

sal

Determining the Positions of Veins

hh

L2

dpp

dppAP En

En -> Hh -> Diffuses -> dpp in A/P Organizer

Dpp

Dpp -> Diffuses -> sal -> L2 vein

AP

L5

sal

sal

L3

L4

L3

L4

OrganizerA/P

dpp

L2

L3

L4

L5

hh- mutantL2

L3L4

L5

WTL2

L3

L4

L5

hh

dpp

Mutant with reduced hh function

AP En

L3L4

dpp

Hh Determines Positions of L3 and L4 Veins

hh dpp

dppAP En

L3

L4

En -> Hh -> Diffuses ->dpp in A/P Organizer

dpp- mutant

L2

L3

L4

L5

L2

DppAP

L5

salL3

L4sal

Mutant with reduced dpp function

WTL2

L3

L4

L5

L2

DppAP

L5

sal

sal

L3

L4

Dpp -> Diffuses -> sal -> L2 vein

Dpp Determines Positions of L2 and L5 veins

Veins Form At Boundaries Along the A/P Axis

L2L3 L4

salsal Dpp

A P

Dpp -> Diffuses -> sal -> L2 vein

L5

+

En

hh

dpp

+

dpp

A P

OrganizerA/P

En -> Hh -> Diffuses ->dpp in A/P Organizer

salsal Dpp

A P

Dpp defines anteriorborder of sal domain

+

En

hh

dpp

+

dpp

A P

En-5 defines position ofdpp stripe in wing disc

Hb

eve-3

Hb defines anteriorborder of eve-3 stripe

KniWingDisc

en-5

Eve-3 defines anteriorborder of en-5 stripe

Maternal Bicoid gradientdefines posterior limit of hb

Ant. Post.

Lowest level of Bcd needed to activate hb

Sal defines positionof L2 vein stripe

salDpp

++

Sal

L2

X

L2 A P

The Developmental Path From Bcd to the L2 Vein

Drosophila MelanogasterL1

L2

L3

L4

L5

M

CraneflyPsychodid

Mosquito Lacewing

Syrphid

D ->V Signal

V -> D Signal

ap Expressing Cells

ap Non-expressing Cells

DV

Activation ofNotch AlongFuture Margin

Ap -> Notch -> Wing Margin = D/V Organizer

D/V Signaling Is Required for Wing Margin Formation and Wing Outgrowth

D/V Organizer -> Margin Formationand Wing Growth

ap- cells

Wing imaginal disc in larva Adult wing (viewed end on) Adult wing with ap- patch

Loss of ap 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

DistallessExpression

Distalless

Distal

Proximal

Normal Leg distallessMutant Leg

DV

Fig. 4.4

Hox2

ZPA Morphogen = Hh

FGF

Hox Gene B

ZPA induced byHox gene B + FGF

FGF and a second Hox gene activate Hh expression in ZPA

wing bud leg bud

FGF

Hox Gene A Hox Gene CHox Gene B

GastrulatingChicken Embryo

FGF

Hox genes activate autoregulatory FGF expression in limb buds

Initiation of Wing Development in Chickens

A PGrafted ZPA

[Hh]

distanceAnt. Post.

4

32 2

3

4

43

2

43

2

ZPA -> HhBMP-4

A P

[Hh]

distanceAnt. Post.

4

32 43

2Anterior

Posterior

43

22

A PFraction ofZPA Grafted

4

[Hh]

distanceAnt. Post.

32 2

Hh diffuses from ZPA and specifies digits 2-4 at different concentrations

Wing bud with second grafted ZPA -> complete mirror duplicated digits

Wing bud grafted with a fraction of ZPA -> partial mirror duplication

Hh is the ZPA Factor

Normal Wing

ZPA Transplant

ZPA Graft

0 mg/ml

4 mg/ml

8 mg/ml

16 mg/ml

Hh Soaked BeadsHh Expression

ZPA

A P/

Hh

Dpp

Hh Hh

BMP-4

A P

Fly wing disc

A/PAxis

Vertebrate Limb Bud

D/VAxis

P/DAxis

D

V

A P

NotchSignaling A P

DV

NotchSignaling

D

V

A P

Distalless

A P

DV

Distalless

Fly Eye

A P

Specification of theeye disc in the embryo

>1,000-X growth

eyeless: A master eye gene?

Eye Primordium20-40 Cells

Furrow

A P

Growth and patterning ofeye imaginal disc in larvae

dpphh

Early Steps in Fly Eye Development

Sequential formation ofphotoreceptor clusters

R8R7

Furrow

R2R5

R3R4R8 R1

R6 R7

873 51

PhotoreceptorDevelopment

R8 R7

SevenlessReceptor

BossLigand

Boss-> SevenlessSignaling Specifies R7

Late Steps in Fly Eye Development