Fig. 2.

Model of the regulatory network that controls lipogenesis and lipolysis in the fat body of Drosophila. Only signals that control adiposity by directly acting on the fat body, or by being released from the tissue, are shown. The color RED indicates down-regulation upon starvation and GREEN up-regulation upon starvation. Question marks indicate connections that have been shown to exist in mammalian systems, but not yet in Drosophila, or that need clarification of mechanistic details. The model combines data derived from studies in larvae and adults and it is important to emphasize that regulatory mechanisms are not necessary the same in larval and adult fat body. For instance, a role for AKH and iCa²⁺ has so far only been described for adult fat body; the effects of mir-8 and of 20E on adp and of mir-8 have only been demonstrated for larvae, although Adp controls adiposity in both larvae and adults; Sir2 has been shown to control fat depots in both larvae and adults, but interaction with HNF4 has only been described for adults; Hh controls adiposity in both larvae and adults, but secretion by the midgut has only been demonstrated for larvae; the LKB1-SIK3-HDAC4 signaling axis has been studied in larval, but not in adult, fat body; Dilp 6 plays a role in both larval and adult fat body, but signaling to oenocytes has only been demonstrated for adults; finally, the effects of PI3K and TOR down-regulation in the PG suggest that ecdysone is down-related in larvae in response to starvation, but this is not the case in female adult flies that show an up-regulation of ecdysteroids.