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A
act b
act b
ILPs
ILPs
PDF neurons
PDF neurons
Brain lobes
B
Activins
ILPs
PTTH
Torso
Punt
Babo
InR
?
P
P
P
P
P
P
P
Ras
Pi3K
Smad2
Medea
NOS
?
P
Raf
P
E75
AKT
P
DHR3
Smad2 Medea
NO
P
P
E75
ERK
Smad2
?
DHR3
?
P
DHR4
BR
b ftz-f1
?
?
Cyp6t3
Halloween genes
5 b -Ketodiol
Cholesterol
Ecdysone
Figure 2.4 An overview of proposed mechanisms underlying regulation of ecdysone
biosynthesis in the Drosophila prothoracic gland. (A) A range of developmental factors
exert effects on the prothoracic gland to control the production of ecdysone pulses,
including PTTH, TGF b /Activins, ILPs, and circadian signals. (B) Multiple signaling cas-
cades that regulate ecdysone biosynthesis in the prothoracic gland. Inactivation of
these pathways could compromise ecdysone production and results in developmental
defects. Arrows represent positive regulations, and cross lines indicate inhibitory effects.
P, phosphorylation; NO, nitric oxide radical.
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