Practice question

During mid-oogenesis, oocyte nucleus migrates to dorsal-anterior corner secreting Gurken ligand. Nearby follicle cells expressing EGFR Torpedo bind Gurken, triggering Ras-Raf-MEK-ERK cascade and expression of dorsal follicle markers such as Fos, Broad-Complex and Keel. These cells produce dorsal eggshell appendages and dorsalize embryo indirectly by repressing Pipe sulfotransferase. Ventral follicle cells not receiving Gurken retain Pipe expression necessary for ventralizing Spätzle cleavage later. Therefore follicle population receiving Gurken signal adopts dorsalized fate, secreting dorsal patterning cues and shaping eggshell asymmetry essential for embryonic dorsoventral polarity.