Figure 1.

Topographic map from retina to SC is dependent on two systems of reciprocal gradients. (A) Temporal-nasal (TN) axis of the retina is mapped onto the anterior-posterior (AP) [also called rostral-caudal (RC)] axis of SC. This mapping is established through the graded expression of EphA receptors in retina and reciprocal expression of ligands from ephrin-A family in SC. (B) Similar principle applies to the mapping of dorsal-ventral (DV) axis of the retina onto medial-lateral (ML) axis of the target, where topography is formed based on gradients of EphB/ephrin-B pair1.