The immune molecule CD3zeta and its downstream effectors ZAP-70/Syk mediate ephrin signaling in neurons to regulate early neuritogenesis

Recent studies have highlighted the key role of the immune protein CD3 zeta in the maturation of neuronal circuits in the CNS. Yet, the upstream signals that might recruit and activate CD3 zeta in neurons are still unknown. In this study, we show that CD3 zeta functions early in neuronal development and we identify ephrinA1-dependent EphA4 receptor activation as an upstream regulator of CD3 zeta. When newly born neurons are still spherical, before neurite extension, we found a transient CD3 zeta aggregation at the cell periphery matching the initiation site of the future neurite. This accumulation of CD3 zeta correlated with a stimulatory effect on filopodia extension via a Rho-GEF Vav2 pathway and a repression of neurite outgrowth. Conversely, cultured neurons lacking CD3 zeta isolated from CD3 zeta(-/-) mice showed a decreased number of filopodia and an enhanced neurite number. Stimulation with ephrinA1 induces the translocation of both CD3 zeta and its activated effector molecules, ZAP-70/Syk tyrosine kinases, to EphA4 receptor clusters. EphrinA1-induced growth cone collapse was abrogated in CD3 zeta(-/-) neurons and was markedly reduced by ZAP-70/Syk inhibition. Moreover, ephrinA1-induced ZAP-70/Syk activation was inhibited in CD3 zeta(-/-) neurons. Altogether, our data suggest that CD3 zeta mediates the ZAP-70/Syk kinase activation triggered by ephrinA-activated pathway to regulate early neuronal morphogenesis.