Practice question

Gurken protein is secreted EGF family ligand transported to perinuclear region, where extracellular domain binds Torpedo receptor, Drosophila EGFR homolog expressed on follicle cells. Torpedo activation triggers Ras-MAPK and Pointed cascade repressing Pipe dorsally. Pipe, Toll, and Easter function downstream in vitelline modification and proteolysis and do not interact directly with Gurken. Specificity of Gurken-Torpedo interaction ensures spatial restriction of dorsal follicle fate, establishing symmetry break by nuclear migration that positions Gurken signal, linking oocyte cytoskeleton polarity to eggshell patterning and embryonic DV axis determination.