|Select image to enlarge|
Phenotypes of wgLOF and dppLOF 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 . 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 , 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 wgLOF 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 . D/D legs also arise in armLOF , dshLOF, gamLOF , panLOF , porcLOF , and sglLOF  flies and are inducible by wgnull , armnull  and probably arrnull  V clones (cf. Fig. 5.6). D/D legs can also be created by heat-pulsing t.s. NLOF larvae  -- 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 EgfrLOF groLOF double mutants . 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) .
c, d. In dppLOF legs, D structures tend to be missing from the tibia and tarsus . 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 puntLOF [3932, 4277] and tkvLOF flies  and are inducible by dppnull  or puntLOF D clones . d. 'V/-' phenotype. Missing structures in dppLOF legs are commonly not replaced. (No analogous 'D/-' phenotypes are seen with wgLOF legs.) In such cases the V remnant tends to shorten and curl dorsally.
These figures are based on [177, 1811, 1812, 3317].