A gradient of cactus protein degradation establishes dorsoventral polarity in the Drosophila embryo

• Published in: Developmental biology Vol. 180; no. 1; pp. 353 - 364
• Main Authors: Reach, M, Galindo, R L, Towb, P, Allen, J L, Karin, M, Wasserman, S A
• Format: Journal Article
• Language: English
• Published: United States 25-11-1996
• Subjects: Amino Acid Sequence; Animals; Cells, Cultured; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - metabolism; Drosophila melanogaster - embryology; Drosophila Proteins; Embryo, Nonmammalian - cytology; Embryo, Nonmammalian - physiology; Immunohistochemistry; Molecular Sequence Data; Phosphoproteins - chemistry; Phosphoproteins - metabolism; Phosphorylation; Protein-Serine-Threonine Kinases - metabolism; Recombinant Proteins - metabolism; Sequence Homology, Amino Acid; Signal Transduction
• ISSN: 0012-1606
• DOI: 10.1006/dbio.1996.0308

Dorsoventral polarity in the Drosophila embryo is established by a signaling pathway active on the ventral and ventrolateral surfaces of the embryo. Signal transduction via the protein kinase Pelle frees the Rel-related protein Dorsal from its cytoplasmic inhibitor Cactus, allowing Dorsal to translocate into ventral and ventrolateral nuclei and direct gene expression. Here, we show by immunochemical analyses that Pelle-mediated signaling induces the spatially graded degradation of Cactus. Using a tissue culture system which reconstitutes Pelle-dependent Cactus degradation, we show that a motif in Cactus resembling the sites of signal-dependent phosphorylation in the vertebrate homologs IkappaB-alpha and IkappaB-beta is essential for Pelle-induced Cactus degradation. Substitution of four serines within this motif with nonphosphorylatable alanine residues generated a mutant Cactus that still functions as a Dorsal inhibitor but is resistant to induced degradation. Injection of RNA encoding this altered form of Cactus has a dominant negative effect on establishment of dorsoventral polarity in the embryo. We conclude that dorsoventral signaling results in a Cactus concentration gradient and propose that signal-dependent phosphorylation directs the spatially regulated proteolysis of Cactus protein.