Fig. 1. Identification and regulation of a wg midgut enhancer. (A) wg upstream regulatory elements that drive (red bars) or do not drive (black bars) expression in the midgut when fused to a lacZ reporter. (B-G) Comparison of wg transcription and XC enhancer activity. wg trancripts (B,D,F) and lacZ (C,E,G) transcripts were detected by in situ hybridization. Arrows indicate PS8, the site of wg midgut expression. At all stages examined, shown here as lateral views of stage 11 (B,C) and stage 13 (D,E) embryos, XC enhancer activity exclusively mimics wg expression in the embryonic midgut. (F,G) Magnified ventral views of stage 16 embryos. The arrowheads indicate the central midgut constriction. (H-K) XC enhancer regulation recapitulates wg regulation. The activity of the XC enhancer visualized by lacZ transcripts is lost in abdA^JX2 homozygous-mutant embryos (H) and diminished in dpp^s4 homozygous mutants (I). wg transcripts (J) and XC enhancer activity (K) are no longer detected in the central midgut following mesodermal expression of the Hth-En fusion protein in 24B-Gal4/UAS-hth-en embryos.