For the quantification of filopodia, we took from each coverslip five high-magnification images (40x) where individual neurites could be visualized. To ensure comparable abundance of human tau for each condition, we assessed the morphology of neurites with similar intensity of the human tau immunostaining. A total of 15 images were analyzed for each condition in a blind manner. The number of filopodia present per 100 µm of neurite length was measured using ImageJ.