The role of the prothoracic gland in determining critical weight for metamorphosis in Drosophila melanogaster

Curr Biol. 2005 Oct 25;15(20):1796-807. doi: 10.1016/j.cub.2005.09.017. Epub 2005 Sep 22.


Background: The timely onset of metamorphosis in holometabolous insects depends on their reaching the appropriate size known as critical weight. Once critical weight is reached, juvenile hormone (JH) titers decline, resulting in the release of prothoracicotropic hormone (PTTH) at the next photoperiod gate and thereby inducing metamorphosis. How individuals determine when they have reached critical weight is unknown. We present evidence that in Drosophila, a component of the ring gland, the prothoracic gland (PG), assesses growth to determine when critical weight has been achieved.

Results: We used the GAL4/UAS system to suppress or enhance growth by overexpressing PTEN or Dp110, respectively, in various components of the ring gland. Suppression of the growth of the PG and CA, but not of the CA alone, produced larger-than-normal larvae and adults. Suppression of only PG growth resulted in nonviable larvae, but larvae with enlarged PGs produced significantly smaller larvae and adults. Rearing larvae with enlarged PGs under constant light enhanced these effects, suggesting a role for photoperiod-gated PTTH secretion. These larvae are smaller, in part as a result of their repressed growth rates, a phenotype that could be rescued through nutritional supplementation (yeast paste). Most importantly, larvae with enlarged PGs overestimated size so that they initiated metamorphosis before surpassing the minimal viable weight necessary to survive pupation.

Conclusions: The PG acts as a size-assessing tissue by using insulin-dependent PG cell growth to determine when critical weight has been reached.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Body Weight / physiology*
  • Drosophila / growth & development*
  • Drosophila Proteins / metabolism
  • Ecdysteroids / metabolism
  • Endocrine Glands / anatomy & histology
  • Endocrine Glands / metabolism
  • Endocrine Glands / physiology*
  • Gene Expression Regulation, Developmental / physiology
  • Immunoenzyme Techniques
  • Insect Hormones / metabolism*
  • Insulin / metabolism
  • Larva / growth & development
  • Metamorphosis, Biological / physiology*
  • PTEN Phosphohydrolase / metabolism


  • Drosophila Proteins
  • Ecdysteroids
  • Insect Hormones
  • Insulin
  • prothoracicotropic hormone
  • PTEN Phosphohydrolase
  • PTEN protein, Drosophila