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Fig. 4. Ubx prevents downregulation of tkv in the haltere pouch mediated by mtv expression and Dpp signaling. (A) In the wing pouch, P-Mad signal is strongly reduced in AB cells (arrow) (Tanimoto et al., 2000). (B-C'') In the haltere disc, P-Mad signal (in red in B) is narrower, but strong, in these cells (abutting the En expression domain, in green in B'). Merged image in B''. The boxed region is magnified in C,C'; the arrows point to the posterior P-Mad signal and the white line marks the A/P boundary. (D-E'') ptc-Gal4 UAS-GFP wing (D-D'') and haltere (E-E'') pouches, showing that high levels of Hh signaling (GFP signal, in green in D and E) and Dpp signaling (P-Mad, in red in D' and E') coincide in the haltere but not the wing disc (arrow in D'). Merged images in D'' and E''. (F,G) tkv-lacZ expression in the wing and haltere discs. The arrow in F marks the reduced expression in AB cells of the wing pouch. The expression detected with an anti-Tkv antibody is similar but does not show the downregulation in AB cells of the wing disc so neatly as the P-lacZ insertion. (H-H'') A big Ubx^- clone in the haltere disc, marked by the absence of GFP (H, in green), shows downregulation of Tkv protein expression (H', in red). Merged image in H''. (I-I''). Mutant Ubx clones (marked by the absence of GFP, in green in I) present reduced tkv-lacZ expression (I', in red) in medial (arrow) but not in lateral (arrowhead) regions of the haltere disc. Merged image in I''. (J,J') The ectopic expression of Ubx in Cbx^Twt mutants (J, in green) increases tkv-lacZ signal (J', in red). (K) The expression of mtv (mtv-lacZ, in green) in the wing disc is strong at the A/P boundary and in two lateral spots (arrowheads). In the haltere pouch (L), just these spots are observed. (M) In a mtv-lacZ/+; bx³/TM2 haltere disc there is mtv expression at the A/P boundary (arrow). (N,N') mtv (in red) is also derepressed (arrow) in haltere disc Ubx mutant clones (arrow), marked by the absence of GFP (in green in N). The arrowheads in K-N mark the lateral spots, and En expression, marking the posterior compartment, is shown in K-M in red. (O,O') Ectopic Ubx expression in Cbx^Twt wing discs (in red in O) strongly reduces mtv signal (in green) in medial regions (O,O'). (P) In MS1096-Gal4; tkv-lacZ/+; UAS-mtv/+ haltere discs the expression of tkv is downregulated in the dorsal (d) region, except in the periphery (arrows); compare with the expression in a tkv-lacZ haltere disc (G); v, ventral region. (Q) MS1096-Gal4; tkv-lacZ/+; UAS-tkv^QD/+ wing disc showing repression of tkv in the dorsal pouch (d). (R) No such repression is observed in haltere discs.

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