RPTP is required for rigidity-dependent inhibition of extension and differentiation of hippocampal neurons

Receptor-like protein tyrosine phosphatase (RPTP)-knockout mice have severe hippocampal abnormalities similar to knockouts of the Src family kinase Fyn. These enzymes are linked to the matrix-rigidity response in fibroblasts, but their function in neurons is unknown. The matrix-rigidity response of fibroblasts appears to differ from that of neuronal growth cones but it is unknown whether the rigidity detection mechanism or response pathway is altered. Here, we report that RPTP is required for rigidity-dependent reinforcement of fibronectin (FN)-cytoskeleton bonds and the rigidity response in hippocampal neuron growth cones, like in fibroblasts. In control neurons, rigid FN surfaces inhibit neurite extension and neuron differentiation relative to soft surfaces. In RPTP^-/- neurons, no inhibition of extension and differentiation is found on both rigid and soft surfaces. The RPTP-dependent rigidity response in neurons is FN-specific, and requires clustering of _v6 integrin at the leading edge of the growth cones. Further, RPTP is necessary for the rigidity-dependent concentration of Fyn and p130Cas phosphorylation at the leading edge of the growth cone, like it is in fibroblasts. Although neurons respond to rigid FN surfaces in the opposite way to fibroblasts, we suggest that the mechanism of detecting FN rigidity is similar and involves rigidity-dependent RPTP recruitment of Fyn.