An anteroposterior Dorsal gradient in the Drosophila embryo

Recruitment of Tube and Pelle to signaling sites at the surface of the Drosophila embryo

A signaling pathway initiated by activation of the transmembrane receptor Toll defines dorsoventral polarity in the Drosophila embryo. Toll, which is present over the entire surface of the embryo, is activated ventrally by interaction with a spatially restricted, extracellular ligand. Tube and Pelle then transduce the signal from activated Toll to a complex of Dorsal and Cactus. Here we demonstrate by an mRNA microinjection assay that targeting of either Tube or Pelle to the plasma membrane by myristylation is sufficient to activate the signal transduction pathway that leads to Dorsal nuclear translocation. Using confocal immunofluorescence microscopy we also show that activated Toll induces a localized recruitment of Tube and Pelle to the plasma membrane. Together, these results strongly support the hypothesis that intracellular signaling requires the Toll-mediated formation of a membrane-associated complex containing both Tube and Pelle.

Localized requirements for windbeutel and pipe reveal a dorsoventral prepattern within the follicular epithelium of the Drosophila ovary

Establishment of dorsoventral polarity within the Drosophila embryo requires extraembryonic positional information generated during oogenesis. The genes windbeutel, pipe, and nudel are required within the somatic follicle cells of the ovary for production of this spatial cue. Using a novel follicle cell marker system, we have directly evaluated the effect of mutant follicle cell clones on the embryonic dorsoventral pattern. We find no spatially localized requirement for nudel activity. In contrast, windbeutel and pipe are required only within a restricted ventral region of the follicular epithelium. This ventral region can determine lateral embryonic cell fates nonautonomously, indicating that spatial information originating ventrally is subsequently refined, perhaps via diffusion, to yield the gradient of positional information that determines the embryonic dorsoventral pattern.