FYN and frontotemporal dementia: Importantly, Tau was found to modulate Fyn mobility in dendritic shafts. Although the mutant Tau lacking its microtubule binding domains (ΔTau) did not affect Fyn mobility, the FTD-linked P301L mutant Tau largely increased Fyn trapping in nanodomains in the spines by increasing Fyn occupancy in the confined state and decreasing its occupancy in the free diffusive state.