Cell-autonomous role of EphB2 and EphB3 receptors in the thymic epithelial cell organization.

The role of EphB2 and EphB3 in the organization of thymic epithelial cells has been studied in EphB-deficient fetal thymus lobes grafted under the kidney capsule of WT mice. The deficient lobes, as compared with WT ones, showed altered distribution of medullary areas, shortening of medullary epithelial cell processes and presence of K5(-)K8(-) areas. EphB2 and EphB3 expressed on thymic epithelial cells play an autonomous role in their organization. The relevance of Eph/ephrinB forward and reverse signals for this process was evaluated in grafted fetal thymus lobes from mice expressing a truncated EphB2 receptor capable of activating reverse, but not forward, signaling. These deficient lobes showed important alterations of the thymic epithelial organization as compared with the grafted WT lobes, but a less severe phenotype than the grafted EphB2-deficient thymus lobes, which confirms the relevance of EphB2 forward signal for the thymic epithelial organization but, also, a role of the reverse signaling in determining the final epithelial phenotype.