Biology Reference
In-Depth Information
A
7
700
600
E
JH
6
5
500
400
4
3
300
200
2
100
1
1
2
3
4
5
6
7
8
9
10
11
12
days
1st
instar
2nd
instar
3rd
instar
Embryo
Larva
Prepupa
Pupa
Adult
B
Lateral clock
cells
Light
Clock
PTTH
neurons
PG
Rhythmic E titer
PTTH
E
Cyclic EcR
in target tissues
Gene expression cascade
Synchronization of internal and
external developmental cues
Figure 1.1 (A) Juvenile hormone (JH) and ecdysone (E) titers in Drosophila. JH titers
decline in third instar larvae, prior to the large ecdysone peak that triggers puparium
formation. (B) Daily ecdysone (E) titer rhythms in Rhodnius. Summary of the circadian
clocks that regulate developmental hormones in Rhodnius. Lateral ventral clock
neurons (LNv) signal to PTTH-producing neurons. Light and PTTH signals entrain the
PG cells for ecdysone secretion, resulting in rhythmic release of the hormone. The ecdy-
sone receptor, EcR, anticipates these daily rhythms by undergoing cyclic
nucleocytoplasmic oscillations in target cells. PG: prothoracic gland, PTTH: protho-
racicotropic hormone.
