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Fig. 4. Redundancy of the QA motif in the repression of limb selector expression. Dll expression in T1-A2 or A3 of stage 12 embryos. (A) Ubx⁺/Ubx⁺, (B) Ubx^QA/Ubx^QA, (C) Ubx^QA/Ubx^–, (D) Ubx^QA/Ubx^– adb-A^–, (E) Ubx^–/Ubx^–, (F) Ubx^– abd-A^–/Ubx^– adb-A^–. All genotypes tested had essentially non-overlapping phenotypes, except for those with no A1 Dll expression: Ubx⁺/Ubx⁺ (A), Ubx^QA/Ubx^QA (B), and Ubx^–/Ubx⁺ (not shown). At earlier stages, abdominal Dll expression in A1 was inconsistent; some Ubx⁺/Ubx⁺ occasionally expressed Dll in one or two cells in A1, while dose or activity reductions enhanced the number of cells affected (not shown). By stage 12, Ubx⁺/Ubx⁺ (A), Ubx^QA/Ubx^QA (B) and Ubx^–/Ubx⁺ (not shown) embryos did not express Dll in A1, suggesting Dll expression at this stage more accurately marks limb primordia. The Dll expression in A2 and A3 of Ubx^QA/Ubx^– adb-A^– embryos (D) was also present in Ubx^– adb-A^–/Ubx⁺ abd-A⁺ embryos (not shown) up to segment A7 and suggests a lag in repression when abd-A dose is reduced as later stages no longer express this ectopic Dll. Anterior is leftwards, dorsal is upwards. (G) Ubx^QA/Ubx^– sub-epidermal A1 leg tissue found in 1.7% of adults and pupae (5/296); an extreme specimen is shown. (H) Ubx^QA/Ubx^– adb-A^– sub-epidermal A1 leg tissue found in 6.7% of adults and pupae (13/194); an extreme specimen with a well-developed claw (Cl) and transverse bristle rows (TR) is shown. In addition to producing more well-developed ectopic A1 leg tissue, the frequency difference between Ubx^QA/Ubx^– and Ubx^QA/Ubx^– adb-A^– is significant (₁² =8.3, P<10^–2).

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