Abstract
In both mammals and insects, steroid hormones play a major role in directing the animal's progression through developmental stages. To maximize fitness outcomes, steroid hormone production is regulated by the environmental conditions experienced by the animal. In insects, the steroid hormone ecdysone mediates transitions between developmental stages and is regulated in response to environmental factors such as nutrition. These environmental signals are communicated to the ecdysone-producing gland via the action of neuropeptide and peptide hormone signalling pathways. While some of these pathways have been well characterized, there is evidence to suggest more signalling pathways than has previously been thought function to control ecdysone production, potentially in response to a greater range of environmental conditions. Here, we review the neuropeptide and peptide hormone signalling pathways known to regulate the production of ecdysone in the model genetic insect Drosophila melanogaster, as well as what is known regarding the environmental signals that trigger these pathways. Areas for future research are highlighted that can further contribute to our overall understanding of the complex orchestration of environmental, physiological and developmental cues that together produce a functioning adult organism.
Highlights
Most animals go through several developmental stages during their life cycle
To maximize animal fitness and survival, the rate and duration of each of these developmental stages must be precisely regulated in response to environmental conditions
If a pulse of ecdysone is absent or incorrectly produced, the animal suffers developmental defects such as delays in development, which can be accompanied by changes in final body size, or even lethality [3,5,6,7,15]
Summary
Most animals go through several developmental stages during their life cycle. For example, after hatching most insects go through multiple nymphal or larval stages before initiating metamorphosis into adults. The duration and rate of growth of the larval stages, as well as the initiation of pupariation, are under the control of carefully timed pulses of ecdysone (figure 1). If a pulse of ecdysone is absent or incorrectly produced, the animal suffers developmental defects such as delays in development, which can be accompanied by changes in final body size, or even lethality [3,5,6,7,15]. This demonstrates the importance of this hormone in regulating these developmental transitions and for overall growth. While all the roles ecdysone plays throughout the life cycle are important, this review focuses on the role ecdysone plays in regulating development during the larval stages and the environmental control of ecdysone in this context
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