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Comparative Study
, 15 (20), 1785-95

Ras Activity in the Drosophila Prothoracic Gland Regulates Body Size and Developmental Rate via Ecdysone Release

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Comparative Study

Ras Activity in the Drosophila Prothoracic Gland Regulates Body Size and Developmental Rate via Ecdysone Release

Philip E Caldwell et al. Curr Biol.

Erratum in

  • Curr Biol. 2005 Dec 6;15(23):2175

Abstract

Background: In Drosophila, each of the three larval instars ends with a molt, triggered by release of steroid molting hormone ecdysone from the prothoracic gland (PG). Because all growth occurs during the larval stages, final body size depends on both the larval growth rate and the duration of each larval stage, which in turn might be regulated by the timing of ecdysone release.

Results: Here, we show that the expression of activated Ras, PI3 kinase (PI3K), or Raf specifically in the PG reduces body size, whereas activated Ras or PI3K, but not Raf, increases PG cell size. In contrast, expression of either dominant-negative (dn) Ras, Raf, or PI3K increases body size and prolongs the larval stages, leading to delayed pupariation, whereas expression of dn-PI3K, but not of dn-Raf or dn-Ras, reduces PG cell size. To test the possibility that altered ecdysone release is responsible for these phenotypes, we measured larval ecdysone levels indirectly, via the transcriptional activation of two ecdysone targets, E74A and E74B. We found that the activation of Ras within the PG induces precocious ecdysone release, whereas expression of either dn-PI3K or dn-Raf in the PG greatly attenuates the [ecdysone] increase that causes growth cessation and pupariation onset.

Conclusions: We conclude that Ras activity in the PG regulates body size and the duration of each larval stage by regulating ecdysone release. We also suggest that ecdysone release is regulated in two ways: a PI3K-dependent growth-promoting effect on PG cells, and a Raf-dependent step that may involve the transcriptional regulation of ecdysone biosynthetic genes.

Comment in

  • Body-size Regulation: Combining Genetics and Physiology
    AW Shingleton. Curr Biol 15 (20), R825-7. PMID 16243018. - Review
    New research has revealed that the activity of the insulin-signaling pathway in the prothoracic gland of Drosophila modulates ecdysone release and thereby influences both …

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