Biology Reference
In-Depth Information
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
timeless
Ca
2+
period
period
Ca
2+
period;
timeless
period;
timeless
Ca
2+
period
Ca
2+
synaptic signal
timeless
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
Ca
2+
PTTH
neurons
PTTH
neurons
Ca
2+
Ca
2+
Ca
2+
midnight
LNs
midday
LNs
CYCLE
CLOCK
PERIOD
TIMELESS
B
Ecdysone
decrease
Circadian cues
ETH
EH
EHSN
Inka cell
CCAP
Bursicon
CCAP
neurons
CCAP
neurons
pre-ecdysis
ecdysis
(post-eclosion)
(pre-eclosion)
(eclosion)
Figure 1.3 (A) Diagram of the signaling events occurring in PG cells shortly before eclo-
sion. The peripheral clocks in PG cells are coordinated by synaptic input coming
from the circadian lateral neurons (LNs) that project onto the dendritic field of PTTH-
producing neurons, both of which are located in the CNS. The central clock present
in LNs is entrained by light. During the night, synaptic input from the LNs cause intra-
cellular [Ca
2
þ
] spikes in PG cells that trigger the nuclear translocation of PERIOD
-
TIMELESS heterodimers. This event may trigger the endocrine cascade underlying
eclosion. During daylight, intracellular [Ca
2
þ
] concentrations are lower than during
the night, and PERIOD
-
TIMELESS protein levels are very low, however, their transcripts
accumulate in the cytoplasm. (B) Signaling cascade controlling eclosion. Two days prior
to eclosion, ecdysone levels start to decline. This decrease stimulates the secretion of
eclosion hormone (EH) and ecdysis triggering hormone (ETH), which stimulate the
production of each other in a positive feedback loop. ETH stimulates pre-ecdysis (here
pre-eclosion, since this is the pupal-adult transition) behaviors, while EH increases the
secretion of two other peptide hormones, Crustacean cardioactive peptide (CCAP)
blocks pre-ecdysis and simultaneously triggers ecdysis, while bursicon regulates
