Practice question

Spatial regulation of Dorsal nuclear import depends on eggshell cues. Ventral follicle cells expressing Pipe modify vitelline membrane enabling Gastrulation defective cascade to cleave Spätzle ligand locally. Cleaved Spätzle binds Toll only on ventral side of embryo, recruiting MyD88, Tube, Pelle leading to phosphorylation and proteasomal degradation of Cactus ankyrin-repeat inhibitor which sequesters Dorsal cytoplasmically. Dorsal side retains intact Cactus, keeping Dorsal cytosolic. Consequently Dorsal translocates to nuclei exclusively in ventral cells, forming gradient peaked ventrally and absent dorsally. This ventral restriction provides positional information for dorsoventral patterning.