Biology Reference
In-Depth Information
CHAPTER ONE
How Clocks and Hormones Act
in Concert to Control the Timing
of Insect Development
Francesca Di Cara, Kirst King-Jones
1
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
1
Corresponding author: e-mail address: kirst.king-jones@ualberta.ca
Contents
1. General Considerations: The Problem of Time in Development
2
2. Evidence for Mechanisms Controlling the Timing of Developmental Events
3
3. Developmental Timing in Insects is Under Hormonal Control
4
4. Circadian Control and Developmental Transitions
7
5. Circadian Core Clock in Flies
9
6. Evidence of a Clock in the Insect Prothoracic Glands
12
7. Circadian Oscillations of EcR
13
8. Oscillations in the Prothoracic Gland: Input from the Brain
14
9. The Timing of CCAP Neuronal Differentiation is Ecdysone-Controlled
19
10.
JHs and Developmental Timing
23
11. Outlook
26
References
28
Abstract
During the last century, insect model systems have provided fascinating insights into
the endocrinology and developmental biology of all animals. During the insect life
cycle, molts and metamorphosis delineate transitions from one developmental stage
to the next. In most insects, pulses of the steroid hormone ecdysone drive these devel-
opmental transitions by activating signaling cascades in target tissues. In holometabo-
lous insects, ecdysone triggers metamorphosis, the remarkable remodeling of an
immature larva into a sexually mature adult. The input from another developmental hor-
mone, juvenile hormone (JH), is required to repress metamorphosis by promoting juve-
nile fates until the larva has acquired sufficient nutrients to survive metamorphosis.
Ecdysone and JH act together as key endocrine timers to precisely control the onset
of developmental transitions such as the molts, pupation, or eclosion. In this review, we
will focus on the role of the endocrine system and the circadian clock, both individually
and together, in temporally regulating insect development. Since this is not a coherent
field, we will review recent developments that serve as examples to illuminate this com-
plex topic. First, we will consider studies conducted in Rhodnius that revealed how
