Fig. 4. Polarized degradation of the Cactus-lacZ protein requires Dorsal. Maternally expressed full-length Cactus-lacZ visualized by lacZ activity exhibits a normal polarized distribution in the progeny of females heterozygous for dl¹ (A), while ventral degradation is not observed the progeny of females homozygous for dl¹ (B). Similarly, a deletion derivative Cactus(Nterm)lacZ in which the N-terminal 161 amino acids of Cactus are fused to lacZ, and which lacks the Dorsal-binding ankyrin repeat region, did not exhibit spatially regulated degradation (C).