Given that actin polymerization is required during the early stages of phagocytosis and that ALS-linked PFN1 variants can modify actin polymerization27,38, we also measured F-actin levels with phalloidin in fixed-cells at baseline (i.e., in the absence of synaptosomes) and at 0 h post-washout. Here, PFN1 is linked to amyotrophic lateral sclerosis.