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. Interacts with grk. Expressed in male and female somatic tissues. Detectable in the germline from germarium stages onwards and becomes enriched within the oocyte during early and middle stages of oogenesis. In early stages, it is present in the nurse cell oocyte cluster. It is highly expressed in stage 1-6 egg chambers, expression ceases during stage 7 and cannot be detected in stages 8 and 9. During stage 10, it is reexpressed in the nurse cells. Belongs to the cornichon family.