(A) Schematic drawing of larval midgut/hindgut indicating gastric caeca (GC), anterior midgut (AM), middle midgut (MM), posterior midgut (PM), and hindgut (HG). (B and C) Bright field images of the proximal midgut region of larvae 96 hours after egg deposition. Red asterisks in C mark the shortened gastric caeca upon loss of Pngl. Scale bar, 100 µm. (D and E) Bright field images of midgut from third instar larvae fed with food containing bromophenol blue. Acid zone is delimitated by the red dotted boxes. Scale bar, 100 µm. (F) Schematic drawing of Dpp signaling in the embryonic midgut. (G–H’) pMad staining of stage 14 embryos of the indicated genotypes. In G and H, limited projection views are shown to highlight pMad expression in PS3 (arrow) and PS7 (arrowhead). G’ and H’ are full projection view of the datasets shown in G and H. Note that expression of pMad in ectodermal bands and other regions are not affected by the loss of Pngl (double-arrowheads). (I–L’) Fas3 (VM marker) and Labial staining of stage 15 and 16 embryos of indicated genotypes. Midgut constrictions are marked by numbers along the anterior-posterior axis.