Activation of the kinase Pelle by Tube in the dorsoventral signal transduction pathway of Drosophila embryo

Abstract

THE concentration of Dorsal protein in the nucleus determines cell fate along the dorsoventral axis of the Drosophila embryo1-13. The dorsal-group genes and the cactus gene are required for production and transmission of a localized signal on the ventral side of the embryo4,5 which determines the position of the highest nuclear concentration of Dorsal protein1-3. The ventralizing signal produced in somatic cells6 is transmitted through the perivitelline space7 to the integral membrane protein Toll8. Inside the embryo it leads to dissociation of the cytoplasmic Dorsal-Cactus complex and subsequent nuclear localization of Dorsal protein9,10. Two components are known to mediate the signal transduction between Toll and Dorsal-Cactus11,12: Pelle, a serine/threonine protein kinase13, and Tube, a protein with an unknown biochemical activity14. Here we construct gain-of-function alleles of pelle and tube and show that pelle functions downstream of tube. In addition, Pelle and Tube interact directly with one another. We propose that Tube is a direct activator of the protein kinase Pelle.