Practice question

Cactus negatively regulates Dorsal nuclear import by sequestration. Loss of Cactus permits constitutive nuclear Dorsal throughout axis, expanding twist and snail dorsally while repressing decapentaplegic and zerknüllt. Cuticle shows loss of dorsal hairs and amnioserosa, expanded ventral denticle belts producing ventralized embryos that fail to gastrulate properly. Dorsalized embryos result from Toll or Spatzle loss. Posteriorized phenotype involves torso pathway. Hence cactus mutations epitomize inhibitor removal causing hyperventralization, confirming I-kappa B-like antagonistic role maintaining graded Dorsal distribution necessary for DV pattern refinement and mesoderm specification.