Figure 3.

The IIS/TOR pathway regulates metamorphic hormone synthesis. Insulin-like peptide (ILP) secretion by the insulin producing cells in the central nervous system (CNS) depends on nutrition (Masumura et al., 2000; Brogiolo et al., 2001; Ikeya et al., 2002; Colombani et al., 2003). In well-fed final instar Drosophila melanogaster larvae, the prothoracic glands increase ecdysone synthesis in response to high concentrations of ILPs in the hemolymph (solid line in A) (Caldwell et al., 2005; Colombani et al., 2005; Mirth et al., 2005; Warren et al., 2006). In contrast, when larvae are starved early in the final instar, ecdysone synthesis is reduced/delayed (dashed line in A) (Caldwell et al., 2005; Colombani et al., 2005; Mirth et al., 2005). Juvenile hormone (JH) is produced in the corpora allata and the rate of JH synthesis and degradation changes in response to nutrition. Well-fed Manduca sexta larvae show a decrease in JH concentrations on day 1 (solid line in B) (Fain and Riddiford, 1975). In contrast, when Manduca larvae are starved at the onset of the final larval instar, JH concentrations remain high until they feed (dashed line in B) (Cymborowski et al., 1982).