Fig. 1.
The dS6K activity in DILP neurons mediates hunger regulation of both food preference and ingestion rate. Transgenic analysis of dS6K activity was performed by using the Drosophila GAL4/UAS binary expression system (40). UAS-dS6KDN and UAS-dS6KACT encode a dominant-negative and constitutively active form of dS6K, respectively. All of the fly lines used are in a w background. All of the controls in this and other figures are isogenic to the relevant experimental larvae except for the transgene tested. (A) Quantification of liquid and solid food intake by synchronized w1118 larvae (74 h after egg laying, AEL) in response to increasing food deprivation. The number of larval mouth-hook contractions within a 30-s interval was measured. We found that larvae display virtually identical feeding responses to various liquid and solid foods containing 10% glucose, apple juice, or 10% glucose/yeast under deprived and nondeprived conditions (see Fig. 6). (B) DILP neurons expressing GFP in dilp2-gal4 × UAS-GFP larvae. The dilp2-gal4 driver selectively directs a GFP reporter expression in the two clusters of medial neurosecretory cells, as indicated by arrowheads. No GFP expression was detected in cells of other tissues including the gut, imaginal discs, or salivary glands. (Magnification: ×200.) (C and D) Synchronized third-instar larvae were withheld from food for 0 or 120 min before the assay. Control larvae: w × UAS-dS6KDN; w × UAS-dS6KACT. Experimental larvae: dilp2-gal4 × UAS-dS6KDN; dilp2-gal4 × UAS-dS6KACT. At least 30 larvae per group were assayed in three separate trials. Fed larvae expressing dS6KDN in DILP neurons showed significant increases in the feeding of liquid and solid food relative to controls (P < 0.0001), whereas those overexpressing dS6KACT showed no changes in the feeding responses (P > 0.34). Fasted larvae expressing dS6KACT in DILP neurons showed attenuated feeding of the liquid and solid food relative to controls (P < 0.0001), but those overexpressing dS6KDN showed no altered feeding responses (P > 0.16). At least 20 larvae per group were assayed in three separate trials. All statistical analyses were performed by using ANOVA. Error bars are the SEM.