Brain homogenate (0.5%) from an age-matched, uninoculated TgM83+/+ mouse did not induce α-synuclein aggregation or phosphorylation in astrocyte cultures from either line (light blue circles, Fig. 2a, b). This finding further argues that the level of accumulation of phosphorylated α-synuclein inclusions in astrocytes is dependent on the level of transgene-encoded α-synuclein protein in cells exposed to MSA brain homogenate. Here, SNCA is linked to multiple system atrophy.