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.