Biology Reference
In-Depth Information
flexibility, nutrient-dependent growth regulators must feed into the endocrine system
that controls the timing of maturation. Work on the fruit fly
has revealed a
central role of secreted signal molecules with similarity to the conserved insulin-like
growth factors (IGFs) in the decision making process. These molecules are involved
in checkpoints that allow the endocrine system to decide whether to release the steroid
hormone, ecdysone, that triggers maturation or extent development, depending on
nutrient levels and growth status. Importantly, different dietary components influence
timing of maturation in Drosophila, with proteins having the greatest impact; fat and
sugar play a minor role, at least within the limits of what can be considered a balanced
diet. Remarkably, excess dietary sugar concentrations that mimic physiological condi-
tions associated with diabetes, negatively affect growth and delays maturation. Alto-
gether, this shows that the source of energy in the diet is important for timing and
may provide a paradigm for understanding the emerging links between diet, obesity
and diabetes, and the onset of puberty. Here, we provide an overview of the system
underlying developmental timing of maturation in Drosophila and review recent suc-
cess in understanding its coupling to nutrition and growth.
Drosophila
1. INTRODUCTION
Animals grow towards a genetically determined adult size primarily
defined by the amount of growth during the juvenile stages. Since the
growth rate depends on the nutritional conditions, animals must be able
to adjust the duration of the growth period to reach a similar final size under
different environmental conditions. This ensures that the transition to adult-
hood only occurs after a certain amount of growth has been completed
during development (
Mirth & Riddiford, 2007; Rewitz & O'Connor,
2011; Tennessen & Thummel, 2013, 2011; Yamanaka, Rewitz, &
O'Connor, 2013
). Based on recent insight, it has become clear that the sys-
tem coordinating growth and developmental timing of maturation is
remarkably conserved from flies and humans. Work on
Drosophila
has
unveiled a central role for conserved insulin-like peptides in determining
this transition. These signaling molecules are regulators of nutrient-
dependent growth and are involved in crosstalk between different organs
that eventually converge on the endocrine system to time the release of
ecdysone, the temporal cue that triggers maturation (
Colombani,
Andersen, & Leopold, 2012; Colombani et al., 2005, 2003; Garelli,
Gontijo, Miguela, Caparros, & Dominguez, 2012
). Consequently, the
Drosophila
larva is able to slow its developmental progression to adulthood
under poor nutrient conditions and accelerate development in nutrient
