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Fig. 7. Ligand and activity gradient of Dpp. Confocal microscopy images (left) and
schematic drawings (right) of the part of the wing imaginal disc that gives
rise to the adult wing. Hh (green), the synthesis of which is maintained by
Engrailed (En) in P-compartment cells, induces Dpp expression (red) along the
AP border. Dpp diffuses in both A and P directions and forms a gradient, which
can be visualized by the distribution of the chimeric Dpp-GFP protein (blue).
The level of Tkv, the Dpp receptor (purple), is very low along the AP border
because Hh downregulates its expression. In the middle of the wing disc,
abutting the AP border, the level of Tkv in the P compartment is higher than
it is in the A compartment, which causes a steeper Dpp gradient to be present
in the P compartment than in the A compartment. This dynamic Tkv pattern
accounts well for the shape of the activity gradient of Dpp signaling, as
shown by the levels of phosphorylated Mad (p-Mad).
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