Eph/ephrin A- and B-family expression patterns in the leopard frog (Rana utricularia).

Eph/ephrin expression was studied in Rana utricularia larvae and adults with in situ receptor and ligand affinity probes. From stages TK-II (early limb bud) to VI (early foot paddle larva), tectal EphB expression is highest in a band extending transversely across the posterior optic tectum and grades off anteriorly and posteriorly. The ephrin-A expression gradient is parallel to the EphB gradient rather than being orthogonal to it. However, its high point occupies the posterior pole, and it runs from high-posteriorly to low-anteriorly. Tectal EphA expression is high anteriorly and low posteriorly, while ephrin-Bs are expressed only in a thin line at the dorsal midline. At later stages and in adults, tectal EphB expression becomes uniform.