Figure 5.5
Phenotypes of wg^LOF and dpp^LOF legs that argue for a bipolar coordinate system instead of Meinhardt's 3-azimuth model. For gene abbreviations see App. 6.
a. Anterior face of a wild-type left 1st leg from mid-tibia to the distal tip. Ventral (V) and dorsal (D) sides face left and right. Landmarks include pre-apical bristle (PAB), sex comb, and claws. The apical bristle (not shown) is less prominent on 1st (vs. 2nd) legs. At right is a fate map (cf. Fig. 5.1c). Inner circle is the tarsus (1-8 are bristle rows). The sex comb begins as a ventral transverse row; claws and PAB are dorsal [1812]. Crooked white line delimits Dpp (~225° sector) and Wg (~135°) domains of influence (bounded by rows 2 and 7; cf. Fig. 5.2c) based on LOF defects (b-d). Because these sectors are so much larger than the slivers where dpp and wg are transcribed (cf. Fig. 5.4c) Dpp and Wg must act as secreted signals [834], but whether they are bona fide morphogens is debatable. These sectors may actually be more equal in size since D bristle rows are closer to one another than are V rows (cf. Fig. 5.1e).

b. In wg^LOF legs, V structures are missing and replaced (cf. key at bottom) by a set of D structures arranged in mirror symmetry [880, 1812]. This D/D ('Janus') symmetry extends through the sternopleura [177]. D/D legs also arise in arm^LOF [3317], dsh^LOF[2262], gam^LOF [599], pan^LOF [519], porc^LOF [2110], and sgl^LOF [1673] flies and are inducible by wg^null [1811], arm^null [3317] and probably arr^null [4570] V clones (cf. Fig. 5.6). D/D legs can also be created by heat-pulsing t.s. N^LOF larvae [886] -- a perplexing result since there is no known role for the Notch pathway in Wg signaling in legs. The few sex comb bristles that remain fail to rotate. A milder D/D duplication is seen in Egfr^LOF gro^LOF double mutants [3465]. Finally, various kinds of treatments that cause trauma (microcautery, irradiation, etc.) can produce D/D phenotypes [425, 2102, 3442, 3449, 3705], presumably because the dpp-ON D sector has more robust growth potency than the wg-ON V sector (cf. Dorsal Remnant Mystery, Fig. 5.2b) [1807].

c, d. In dpp^LOF legs, D structures tend to be missing from the tibia and tarsus [1812]. Often they are replaced with V structures (c), but sometimes not (d). c. V/V phenotype. When a second set of V structures arises, the first legs have U-shaped sex combs. Janus V/V legs are also seen in punt^LOF [3932, 4277] and tkv^LOF flies [753] and are inducible by dpp^null [1811] or punt^LOF D clones [3329]. d. 'V/-' phenotype. Missing structures in dpp^LOF legs are commonly not replaced. (No analogous 'D/-' phenotypes are seen with wg^LOF legs.) In such cases the V remnant tends to shorten and curl dorsally.

These figures are based on [177, 1811, 1812, 3317].