The vesicle-tethering exocyst complex is a key regulator of cell polarity. The subunit Exo70 is required for the targeting of the exocyst complex to the plasma membrane. While the N-terminus of Exo70 is important for its regulation by GTPases, the C-terminus binds to PI(4,5)P2 and Arp2/3. Here, we compare N- and C-terminal tagged Exo70 with respect to subcellular localization, dynamics and function in cell membrane expansion. Using high-resolution imaging, we determined the spatial distribution and dynamics in different sub-compartments of un-polarized and polarized cells. With lattice light-sheet microscopy, we show that HaloTag-Exo70, but not Exo70-HaloTag, promotes the outgrowth of filopodia-like structures from the axon of hippocampal neurons. Fluorescence lifetime imaging of sfGFP-Exo70 and molecular modeling results suggest that the assembly of sfGFP-Exo70 with the exocyst complex is reduced. This is supported by single particle tracking data showing higher mobility of N- than C-terminal tagged Exo70 at the plasma membrane. The distinct spatiotemporal properties of N-terminal tagged Exo70 were correlated with pronounced filopodia formation in unpolarized cells and neurons, a process that is less reliant on exocyst complex formation. We therefore propose that N-terminal tagging of Exo70 shifts its activity to processes that are less

Tagging of Exo70 at the N-terminus compromises its assembly with the exocyst complex and changes its spatiotemporal behavior at the plasma membrane