Fig. 2.

Amino acid sensing by the larval fat body. a In low-protein diets, the fat body secretes Eiger cytokine, which is cleaved by the enzyme TACE. Then, Eiger binds to its receptor Grindelwald (Gnrd) located on Insulin Producing Cells (IPCs) to repress expression of dilp2 and dilp5 genes through the Jun N-terminal kinase (JNK) activation. In addition, IPC-connecting neurons (ICNs) inhibit IPC neuronal activities and thus inhibit the release of DILPs. In consequence, metabolism and larval growth are reduced. b In high-amino acids diets, TORC1 (Target of Rapamycin) inhibits TACE and induces the release of two growth blocking peptides (GBP1 and GBP2). These peptides repress the inhibitory activity of ICNs allowing the release of DILPs and larval growth. TORC1 also promotes the secretion of Stunted (Sun) cytokine. Sun binding to its receptor Methuselah (Mth) promotes the release of DILPs, which influences metabolism and larval growth. AA amino acids, DILP Drosophila insulin-like peptide, EGFR EGF receptor, GBP growth-blocking peptide, Gnrd Grindelwald, ICNs IPC-connecting neurons, IPCs insulin-producing cells, JNK jun N-terminal kinase, Mnd minidiscs, Mth Methuselah, Slif Slimfast, Sun stunted, TACE TNFα-converting enzyme, TORC1 target of rapamycin