Fig. 4. Formation of the Wg gradient is severely affected in cells that are homozygous mutant for ttv, sotv and ttv, sotv. In this and subsequent figures, antibody staining is in red. The boundaries of informative clones are outlined in white. Staining for extracellular Wg reveals a shallow gradient in the wing pouch that is strongly reduced in clones of ttv (A,D), sotv (B,E) and ttv, sotv (C,F) that cross the Wg expression domain. Arrows draw attention to regions near the prospective wing margin, where a sharp decrease in extracellular wingless levels is visible across the clone boundary. Mutant clones of ttv (G), sotv (H) and ttv, sotv (I) that cross the Wg stripe cause a less dramatic reduction in cytoplasmic Wg levels.