Omb regulates cell affinity in a concentration-dependent manner. Only Clones within a region corresponding to the boxed areas in A'' and B'' were selected for measurement. The position of the A/P boundary (broken line) was determined by Ci (A') or hh-lacZ (B') staining. Area (A) and perimeter (L) of clones were determined. For calculation of the shape factor, the formula 4ΠA/L2 was used. Clonal position relative to the A/P boundary was determined by measuring the distance between the center of the clone and the A/P boundary normalized to the distance from the edge of the wing imaginal disc to the A/P boundary. (A) wt control clones (generated in hs-flp hs-GFP FRT19/FRT19 larvae) were wiggly independent of their position. (B) l(1)ombD4clones (generated in hs-flp hs-GFP FRT19/l(1)ombD4FRT19 larvae) were round when close to the A/P boundary but wiggly in the periphery. (C-E) flip-out clones were generated by heat-shocking act5C>CD2>Gal4 (C), tubα1>CD2>Gal4, UAS-omb (D), and act5C>CD2>Gal4, UAS-omb (E) flies (all containing hs-flp22on the first chromosome). Clones were visualized by lack of CD2 staining. Larvae were reared at 18°C to reduce the dispersal of Omb-overexpressing cells. (F and G) Shape factor plotted as a function of clonal position. Clonal position value is "0" at the A/P boundary and "1" at the edge of the wing disc. A and P clones are represented by blue dots and red triangles, respectively. In (G), the decay of the Omb gradient, measured in a different wing disc, is shown as a green line. (H) Average shape factor of notum clones expressing no (blue), low (purple) or high (yellow column) Omb. The difference in shape factor was pairwise statistically significant (p < 0.001).