Fig. 1. Signaling molecules expressed in the hindgut. The hindgut epithelium (pink) elongates during stages 11 to 16, changing from a short, wide tube to a long, narrow tube (A); the cell rearrangement that is a major contributor to this process is shown in B. The three domains of the hindgut (SI, small intestine; LI, large intestine; RE, rectum), and the genes encoding signaling molecules expressed therein, are indicated in (C); anterior is towards the left, dorsal is upwards and the gray region indicates boundary cells. The points of attachment of the renal tubules are indicated near the anterior of the SI by `V'. Hindgut morphology, outlined by apical staining with anti-Crb (red) and nuclear staining with anti-ß-Gal (green), is shown in stage 16 wild-type (D), drm (E), bowl (F) and (G) lin embryos, all carrying the byn^apro enhancer trap that drives expression of lacZ in the nuclei of the hindgut. (H-K) upd expression, detected by in situ hybridization in stage 13 embryos, is seen only in the anterior hindgut (small intestine) of wild-type (H, black arrowhead), is missing from drm (I) and bowl (J) embryos (white arrowheads), and is expanded throughout most of the hindgut in lin embryos (K, black arrowhead).