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#dorsal protein

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Drosophila -ll

Protein complex restricting dorsal protein:

Dorsal protein activity gradient depends on physical sequestration by Cactus inhibitor forming stable cytoplasmic heterodimer covering Dorsal nuclear localization signal and DNA-binding domain. Complex concentration high dorsally where Cactus unphosphorylated, low ventrally where Toll signaling triggers Pelle kinase phosphorylation and Slimb-mediated degradation. Gurken-Torpedo regulates follicle Pipe transcription upstream, Pipe-Spatzle regulates Toll ligand processing extracellularly, Wingless-Frizzled regulates segment polarity maintenance. Dorsal-Cactus interaction therefore represents final intracellular checkpoint directly restricting transcription factor availability. Stoichiometric excess of Cactus can ventralize embryo, while Cactus degradation dynamics sharpen Dorsal nuclear gradient establishing thresholds for twist, snail, and short gastrulation activation along DV axis.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Dorsal-Cactus complex restricting nuclear translocation - ventral degradation.

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Drosophila -ll

Mutations in cactus gene lead to:

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.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: cactus loss-of-function ventralized embryos - ubiquitous Dorsal nuclear entry.

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