Figure 7

Bimolecular fluorescence complementation (BiFC) can reveal a spatial control of protein interactions in the Drosophila embryo. (a) Spatial control of the BiFC signal resulting from the VCA/VNE complex assembly in the tracheal system. Despite the uniform expression of abdominalA (AbdA; anti-AbdA, red) and extradenticle (Exd; anti-HA, grey) fusion proteins in all tracheal branches with the breathless (btl)-Gal4 driver, BiFC is mostly apparent in the dorsal trunk (dt) and strikingly weaker in other tracheal branches. Enlargements (dotted-white boxes) focused on this discrepancy in the T2 segment between the dt and the dorsal branch (db). Note that endogenous AbdA protein is not present in this segment. (a') Statistical quantification of the VCA (red-filled boxplot) and VNE (grey-filled boxplot) expression levels in the dt and db of the T2 segment, as deduced from immunostainings. (a'') Despite comparable expression levels of VCA and VNE fusion proteins in the two tracheal branches, BiFC is statistically lower in the db than in the dt. A total of five nuclei in ten different embryos were quantified in the two corresponding branches. (b-b') Spatial dynamics of the BiFC signal in the dorsal epidermis of stage 15 embryos. Expression of fusion proteins (as revealed with anti-HA that specifically recognizes the HA-tagged VNE fusion protein, grey) in embryos heterozygous for the abdA-Gal4 driver is progressively lost in dorsal most parts of the epidermis, while endogenous AbdA (red, as revealed with an anti-AbdA antibody) continues to be homogeneously expressed. BiFC signal (green) follows the dynamic of the abda-Gal4 driver since it is no longer observed in dorsal most parts of the embryo, even when fusion proteins are not completely absent (as revealed with the anti-HA: white arrowhead in b', corresponding to the enlargement of white-dotted boxes in b).