Fig. 4. Expression of drm during embryogenesis. Whole-mount in situ hybridization with drm-specific probe shows the dynamic expression pattern of drm between embryonic stages 5 and 13 (A-H). drm expression is first observed at stage 5 in a ventral crescent in the posterior midgut-hindgut primordium (at 10% EL), a weakly stained anterior spot in the foregut-proventriculus primordium (at 95-100% EL) (black and white arrows in A-H indicate expression in posterior and anterior gut, respectively), and in seven transverse stripes (arrowheads; A). By stage 6, the posterior crescent has expanded to encircle the amnioproctodeal plate (B, dorsolateral view), and secondary transverse stripes arise between the initial seven to give a total of 14. Between stages 7 and 9, drm-expressing cells internalized with the proctodeal invagination are located at the midgut-hindgut junction (C-E). At stage 10, drm is expressed in the invaginating stomodeum and transiently in the Malpighian tubule buds (F). Between stages 11 and 13, drm expression is refined to the posterior midgut, the ureters of the Malpighian tubules, the anterior small intestine, the proventriculus anlage, and at the anterior boundary of each segment. Expression is also observed in the pharynx and stigmatophore. Whole-mount drm-GAL4:UAS-lacZ embryos stained with anti-ß-gal (I-K) reveal, by stage 13, lacZ expression in more extensive domains (both anteriorly and posteriorly) than those seen for drm mRNA expression at the same stage (I, dorsal view; compare Fig. 4H). At stage 16 (J and K, higher magnification), ß-gal is present throughout the entire proventriculus, anterior midgut, posterior midgut, Malpighian tubules, and small intestine. Dotted lines outline the proventriculus (J), posterior midgut, small intestine, and large intestine (K). MTB, Malpighian tubule buds; MT, Malpighian tubules; PV, proventriculus; AMG, anterior midgut; PMG, posterior midgut; HG, hindgut; SI, small intestine; LI, large intestine.

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