Figure 6. rotund is required for bab2 activation only in proximal-most rings, in both leg and antenna.

GFP expression (green), Bab2 immunostaining (blue) and LAE-RFP expression (red) alone, as well as the merged images of leg (A–A″′ and C–C″′) and antennal (ant) (B–B″′ and D–D″′) discs from late third-instar larvae, either wild-type (A–B) or carrying rn null mutant clones (C–D), are shown. rn expression was monitored by combining rn-Gal4 and UAS-GFP constructs (rn>GFP). LAE regulatory activity was monitored with a LAE-RFP construct (Materials and methods). rn-Gal4 reporter expression is not detected in the distal-most bab2-expressing cells (yellow brackets), and extends more proximally than bab2 expression (white brackets). In mosaic tissues, rn¹⁶ mutant clones (examples are circled by dashed lines) are detected by the absence of GFP (black areas). Note that only proximally-located mutant cells (white arrows), and not those located in the distal-most ring (yellow arrows), display strongly diminished bab2 and LAE-RFP expression, in either leg or antennal tissues.