Fig. 2. Absence of endogenous (Endo-) and exogenous (Exo-) Ubx when expressing Ubx with certain Gal4 lines. (A-A''') Absence of Ubx protein (in red in A') in UAS-GFP MS372-Gal4/UAS-Ubx Ubx^lac1 haltere discs (GFP in green in A) correlates with the absence of Endo-Ubx, detected by the expression of Ubx^lac1 (A'', greyscale). Merged image in A'''. The inset indicates a region without GFP, Ubx or Endo-Ubx expression. (B-B'') Exo-Ubx and Endo-Ubx expression in UAS-Ubx-HA/+; MS372-Gal4 UAS-GFP/Ubx^lac1 haltere discs. GFP is shown in B (in green), the Exo-Ubx protein is detected with an antibody against the haemagglutinin (HA) epitope (B, in red) and the Endo-Ubx with an antibody against the β-galactosidase protein (greyscale in B'). Merged image in B''. Note the coincidence of Exo-Ubx and GFP expression but not of Endo-Ubx and the absence of Endo-Ubx in many cells, probably owing to the long stability of the β-galactosidase protein. The inset indicates a region without GFP, Exo-Ubx or Endo-Ubx expression. (C) Ubx expression in a tub-Gal80^ts/+; dpp-Gal4 UASGFP/UAS-Ubx haltere disc transferred from 17 to 29°C and then back to 17°C during the larval period. Ubx is absent in most of the anterior compartment. Discs are oriented with the anterior compartment towards the left and the ventral compartment upwards.