Biology Reference
In-Depth Information
CHAPTER ONE
Developmental Checkpoints
and Feedback Circuits Time
Insect Maturation
Kim F. Rewitz
*
,1
, Naoki Yamanaka
†
, Michael B. O'Connor
†
,1
*
Department of Biology, Cell and Neurobiology, University of Copenhagen, Denmark
†
Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota,
USA
1
Corresponding authors: e-mail address: Kim.Rewitz@bio.ku.dk; moconnor@umn.edu
Contents
1.
Introduction
2
2. Checkpoint Controls for Progression of Development
4
2.1 Increasing complexity for control of ecdysone production and release
4
2.2 Linking nutrition to developmental timing
7
2.3 Signaling between the neuroendocrine timing system and a
tissue-autonomous size assessment program
10
2.4 The brain relays internal and external cues to the endocrine system
12
3. Signals Converging on the PG
14
3.1 PTTH and insulin/TOR coordinate PG cell growth and ecdysone production
14
3.2 TGF
b
/Activin and nitric oxide signaling are essential for steroidogenesis
19
4. Shaping Discrete Ecdysone Pulses
21
4.1 Feedback control of ecdysone production
21
4.2 Termination of ecdysone pulses by feedback regulated degradation
23
5. Summary and Perspectives
23
Acknowledgments
26
References
26
Abstract
The transition from juvenile to adult is a fundamental process that allows animals to
allocate resource toward reproduction after completing a certain amount of growth.
In insects, growth to a species-specific target size induces pulses of the steroid hormone
ecdysone that triggers metamorphosis and reproductive maturation. The past few years
have seen significant progress in understanding the interplay of mechanisms that
coordinate timing of ecdysone production and release. These studies show that the
neuroendocrine system monitors complex size-related and nutritional signals, as well
as external cues, to time production and release of ecdysone. Based on results discussed
here, we suggest that developmental progression to adulthood is controlled by check-
points that regulate the genetic timing program enabling it to adapt to different
