Fig. 1. Effect of rib mutations on tracheal branch outgrowth. (A) Three tracheal sacs in stage 11 wild-type (+) embryo stained with TL1 antiserum to show apical surface (lumen) of tracheal epithelium. (B) Similar view of stage 13 wild-type embryo. Primary branches have budded and dorsal trunk (DT) branches have fused. (C,D) Stage 13 rib^ex12 and rib^P7 homozygotes. Little branch budding or outgrowth has occurred. (E) Stage 13 bnl^P1 homozygote for comparison. (F) Five tracheal metameres of stage 14 wild-type embryo. (G,H) rib^ex12 and rib^P7 homozygotes at similar stage. Outgrowth of most branches is stalled, but there is rare aberrant branch outgrowth (arrowheads). All panels in this and other figures show lateral views (dorsal upwards, anterior leftwards) unless noted. Scale bars: in E, 10 µm in A-E; in H, 10 µm in F-H.

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