Fig. 3. bab expression depends on Dll in the antenna, leg and wing. Bab (purple in all panels) is not detected distally in Dll¹/Dll³ hypomorphic antennal discs (A). Note that some Dll (green) is still present in the hypomorphic discs. Bab is not detected in (arrow) or around (arrowheads) a Dll null clone in the antenna (B). Double labeling of similar antennal clones for Dll and a myc marker indicates that Dll is lost cell-autonomously, i.e. loss of Dll expression corresponds with loss of Myc expression. The non cell-autonomous loss of Bab surrounding these Dll null antennal clones is correlated with activation of Dac (Dong et al., 2001), which we demonstrate here is a bab repressor. Bab also is not detected within (arrows) or around Dll null clones in the leg (C,C'). These clones were identified by absence of expression of the myc marker. The arrowhead indicates a portion of a Dll⁺ myc⁺/Dll⁺ myc⁺ "twin spot" in which Bab expression has been lost non cell-autonomously. The twinspots carry twice as many copies of the myc gene than the surrounding Dll⁺ myc⁺/Dll^– heterozygous tissue and therefore stain more brightly. Although Bab expression is lost non cell-autonomously around Dll null clones in both antenna and leg discs, the mechanism by which this occurs in each may differ since Dll expression is also lost non cell-autonomously around the Dll null clones in the leg (J. C. and G. P., unpublished). Bab is lost cell-autonomously from a Dll null clone in the wing (arrow in D and D').

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