Fig. 1
From: Big or fast: two strategies in the developmental control of body size
The insulin signaling network that links nutrition to growth and size. Nutrition in the form of amino acids stimulates insulin synthesis. Activation of the insulin receptor and receptor substrate (INR/INS) activates PKC and PKB/Akt via a multi-step pathway. PKC stimulates uptake of amino acids, which activate TOR. Insulin also activates TOR via PKB/Akt. TOR is inhibited by FOXO, which is inhibited by PKB/Akt. TOR stimulates protein synthesis via EIF4E transcriptional initiator, and causes cellular growth in tissues. In the prothoracic glands TOR stimulates ecdysone synthesis. Ecdysone is inhibited by FOXO when bound to Ultraspiracle (Usp) [16]. Inhibition of TOR by rapamycin inhibits growth and ecdysone synthesis. Ecdysone is also inhibited by juvenile hormone, which begins to decay at the critical weight, due to oxygen restriction. Thus, the ultimate control in this network resides in two environmental factors, nutrition and oxygen restriction