Fig. 4: AstC acts on the APCs to promote AKH release and thereby maintain glycemic levels.

a AstC potentiates the starvation-induced activation of the APCs. Calcium-induced CaLexA-GFP in the APCs is increased by starvation in AKH>CaLexA control animals (gray); this increase is attenuated by AstC-R2 knockdown (p = 0.030; n = 17, n = 24, n = 20, and n = 26). b Illustrative images of calcium-induced GFP expression in the APCs. c AstC application to ex vivo cultured APCs from AKH>CaLexA females increased CaLexA-GFP and reduced AKH staining. These effects of AstC were abolished by APC-specific knockdown of AstC-R2 (AKH>CaLexA, AstC-R2-RNAi). Representative images of calcium-induced GFP expression and AKH release in the APCs are shown at right. (left panel, column 1 vs. 2, p = 0.031; column 2 vs. 3, p = 0.018; right panel, column 1 vs. 2, p = 0.019; column 2 vs. 3, p = 0.042; left to right, n = 17, n = 18, n = 18). d Immunostaining of the processed AKH peptide shows that starvation induces peptide release in AKH> control animals; this effect is blocked by AstC-R2 knockdown in the APCs (column 1 vs. 2, p = 0.0077; column 2 vs. 3, p = 0.0019; column 2 vs. 4, p = 0.0008; left to right, n = 11, n = 8, n = 12, n = 15). See also Supplementary Fig. 8b. e Likewise, AstC from the gut is required for starvation-induced AKH release (column 1 vs. 2, p = 0.0012; column 2 vs. 3, p = 0.0062; column 2 vs. 4, p < 0.0001; left to right, n = 10, n = 13, n = 16, n = 8). Illustrative anti-AKH images of the APCs are shown below each bar. f AstC signaling in the APCs is required for the maintenance of circulating sugar levels in the hemolymph during starvation (p = 0.024; left to right, n = 4, n = 8, n = 7, n = 4, n = 4). Error bars indicate SEM. ns, non-significant; *p < 0.05; **p < 0.01; and ***p < 0.001. Statistical significance was determined using one-way ANOVA with Kruskal–Wallis test (c–e) or two-tailed Mann–Whitney U test (a, f). Source data are provided as a Source data file.