Establishment of dorsal-ventral polarity of the Drosophila egg requires capicua action in ovarian follicle cells

The dorsal-ventral pattern of the Drosophila egg is established during ooge nesis. Epidermal growth factor receptor (Egfr) signaling within the follicu lar epithelium is spatially regulated by the dorsally restricted distributi on of its presumptive ligand, Gurken. As a consequence, pipe is transcribed in a broad ventral domain to initiate the Toll signaling pathway in the em bryo, resulting in a gradient of Dorsal nuclear translocation. We show that expression of pipe RNA requires the action of fettucine (fet) in ovarian f ollicle cells. Loss of maternal Jet activity produces a dorsalized eggshell and embryo. Although similar mutant phenotypes are observed with regulator s of Egfr signaling, genetic analysis suggests that fet acts downstream of this event. The fet mutant phenotype is rescued by a transgene of capicua ( cic), which encodes an HMG-box transcription factor. We show that Cic prote in is initially expressed uniformly in ovarian follicle cell nuclei, and is subsequently downregulated on the dorsal side. Earlier studies described a requirement for cic in repressing zygotic target genes of both the torso a nd Toll pathways in the embryo. Our experiments reveal that cic controls do rsal-ventral patterning by regulating pipe expression in ovarian follicle c ells, before its previously described role in interpreting the Dorsal gradi ent.