Expression levels of α-syn-YFP do not correlate with PFF-mediated α-syn-YFP aggregate formation (associated with Figs. 1 and 2 ). α-syn-YFP expression levels do not predict PFF-mediated α-syn-YFP aggregation. F.I., fluorescence intensity. Bar graphs show relative α-syn-YFP expression per cell, calculated by summing total fluorescence across sequential z-planes (spaced 270 nm apart) after background subtraction, acquired under identical live-cell fluorescence spinning disc confocal microscopy conditions. Analysis includes iNs transiently expressing α-syn-YFP as well as iPSCs and SVG-A cells with stable α-syn-YFP expression; each dot represents a single cell. Horizontal bar denotes median value. Cells were preincubated with 4 µg/ml PFFs for 3 days before imaging. Aggregation was quantified as the percentage of cells containing PFF-mediated α-syn-YFP spots. The number of cells analyzed is indicated.