A chemical genetic approach reveals distinct EphB signaling mechanisms during brain development

The EphB family of receptor tyrosine kinases can signal bidirectionally and functions in a kinase-dependent and kinase-independent manner. To determine the importance of the kinase activity of EphBs for axonal guidance and synaptogenesis, the authors used a chemical genetic method and generated knock-in mice that allow the kinase activity of EphBs to be inhibited without altering kinase-independent functions of EphBs. They find that specific inhibition of EphB kinase activity had no effect on synaptogenesis, but impaired axonal guidance, thereby implicating the kinase function of EphB in one neuronal process, but not other processes that are nevertheless dependent on EphBs. EphB receptor tyrosine kinases control multiple steps in nervous system development. However, it remains unclear whether EphBs regulate these different developmental processes directly or indirectly. In addition, given that EphBs signal through multiple mechanisms, it has been challenging to define which signaling functions of EphBs regulate particular developmental events. To address these issues, we engineered triple knock-in mice in which the kinase activity of three neuronally expressed EphBs can be rapidly, reversibly and specifically blocked. We found that the tyrosine kinase activity of EphBs was required for axon guidance in vivo . In contrast, EphB-mediated synaptogenesis occurred normally when the kinase activity of EphBs was inhibited, suggesting that EphBs mediate synapse development by an EphB tyrosine kinase–independent mechanism. Taken together, our data indicate that EphBs control axon guidance and synaptogenesis by distinct mechanisms and provide a new mouse model for dissecting EphB function in development and disease.