The kidney is an essential organ that functions in filtering wastes, absorbing nutrients and water.The pronephros of Xenopus, which contains a single nephron, offers a simplified in vivo system to study the events of tubulogenesis, including the establishment of cell polarity and lumen formation.The Eph receptors are the largest sub-family of receptor tyrosine kinases (RTKs) and are widely involved in animal growth and development, including segmentation, axon guidance, cell migration, etc.