Trans-Activation between EphA and FGFR Regulates Self-Renewal and Differentiation of Mouse Embryonic Neural Stem/Progenitor Cells via Differential Activation of FRS2α.

Ephs and FGFRs belong to a superfamily of receptor tyrosine kinases, playing important roles in stem cell biology. We previously reported that EphA4 and FGFR form a heterodimer following stimulation with ligands, trans-activating each other and signaling through a docking protein, FRS2α, that binds to both receptors. Here, we investigated whether the interaction between EphA4 and FGFRs can be generalized to other Ephs and FGFRs, and, in addition, examined the downstream signal mediating their function in embryonic neural stem/progenitor cells. We revealed that various Ephs and FGFRs interact with each other through similar molecular domains. When neural stem/progenitor cells were stimulated with FGF2 and ephrin-A1, the signal transduced from the EphA4/FGFR/FRS2α complex enhanced self-renewal, while stimulation with ephrin-A1 alone induced neuronal differentiation. The downstream signal required for neuronal differentiation appears to be MAP kinase mainly linked to the Ras family of G proteins. MAP kinase activation was delayed and sustained, distinct from the transient activation induced by FGF2. Interestingly, this effect on neuronal differentiation required the presence of FGFRs. Specific FGFR inhibitor almost completely abolished the function of ephrin-A1 stimulation. These findings suggest that the ternary complex of EphA, FGFR and FRS2α formed by ligand stimulation regulates self-renewal and differentiation of mouse embryonic neural stem/progenitor cells by ligand-specific fine tuning of the downstream signal via FRS2α.