Ecdysone control of developmental transitions: lessons from Drosophila research

Abstract

The steroid hormone ecdysone is the central regulator of insect developmental transitions. Recent new advances in our understanding of ecdysone action have relied heavily on the application of Drosophila melanogaster molecular genetic tools to study insect metamorphosis. In this review, we focus on three major aspects of Drosophila ecdysone biology: (a) factors that regulate the timing of ecdysone release, (b) molecular basis of stage- and tissue-specific responses to ecdysone, and (c) feedback regulation and coordination of ecdysone signaling.

Figure 1

Schematic illustration of (a) the classical scheme and (b) the revised scheme of insect endocrinology. In the classical scheme, all the environmental as well as internal regulatory cues (circles) affect the function of the PTTH-producing neurons. In the revised scheme, such signals converge on the PG, which in turn decides the timing of developmental transition. Abbreviations: E, ecdysone; PTTH, prothoracicotropic hormone; PG, prothoracic gland; IPC, insulin-producing cell; X, unknown prothoracicostatic factor(s).

Figure 2

Signaling pathways that positively regulate ecdysteroidogenesis in the PG in Drosophila melanogaster. Only the key components of each signaling pathway are depicted. Abbreviations: PG, prothoracic gland; PTTH, prothoracicotropic hormone; MAPK, mitogen-activated protein kinase; NO, nitric oxide; InR, insulin receptor; TOR, target of rapamycin.

Figure 3

An integrative model of how βFTZ-F1 regulates ecdysone signaling in conjunction with other factors. Nuclear receptors are colored blue, the EcR coactivator/corepressor is colored red, the JH receptor Met is colored orange, and the ligands for the receptors are colored white. Abbreviations: 20E, 20-hydroxyecdysone; EcR, ecdysone receptor; Met, Methoprene-tolerant; JH, juvenile hormone; NO, nitric oxide; USP, Ultraspiracle.

Figure 4

Feedback regulation of ecdysone signaling in peripheral tissues. See text for details. Abbreviations: 20E, 20-hydroxyecdysone; EcR, ecdysone receptor; IIS, insulin/IGF signaling; USP, Ultraspiracle.

Figure 5

Interorgan communication upon ecdysone response. (a) Fly larval organs involved in the interplays described in the text. (b) Coordinated ETH/ETHR signaling that triggers ecdysis behavior. (c) Communication between the fat body and imaginal discs promotes the development of adult structures during metamorphosis. Abbreviations: 20E, 20-hydroxyecdysone; PG, prothoracic gland; CNS, central nervous system; ETH, ecdysis-triggering hormone; ETHR, ETH receptor; IIS, insulin/IGF signaling; Crol, crooked legs.