Acts as cargo receptor necessary for the transportation of gurken (grk) to a transitional endoplasmic reticulum (tER) site and promotes its incorporation into coat protein complex II (COPII) vesicles. Associated with gurken, produces a signal received by torpedo resulting in a signaling pathway that first establishes posterior follicle cell fates and normal localization of the anterior and posterior determinants, later they act in a signaling event inducing dorsal follicle cell fates and regulating the dorsal-ventral pattern of egg and embryo (By similarity). Interacts with grk. Belongs to the cornichon family.