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Published online by Cambridge University Press: 03 December 2009
The A-P axis is governed by Hh and Dpp but not by Wg
Like the leg disc, the wing disc uses Hedgehog to set up a border zone just ahead of the A/P compartment boundary (cf. Fig. 5.7), but its zone emits only one long-range morphogen – namely, Dpp. Wingless is irrelevant for the wing's A-P axis and instead functions along its D-V axis. Both morphogens are essential: wings fail to develop when the disc is deprived of either Dpp or Wg.
Topologically, the wing is like a squashed leg (Fig. 6.1). Its D and V faces are apposed, and its veins run along its length like the leg's bristle rows. However, while the prospective bristle rows converge centrally in the leg disc (cf. Fig. 5.1), the primordia of veins 2–5 are parallel to one another and intersect a perpendicular line (the future margin). Thus, it is unclear whether the wing has a true “tip” like the leg. Certainly, the expression of Dll in a band along the wing margin (Fig. 6.2) differs from the circle of Dll in the leg disc (cf. Fig. 5.4).
The stripe where dpp is expressed in a mature disc is ∼5 cells wide.
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