Fig 2: Higher polyQ-ATXN3 levels correlate with decreased mobility and a thinner molecular layer in SCA3 mice. (A) PolyQ-ATXN3 levels as measured by immunoassay in the plasma of Q28 and Q84 mice at 3 and 6 months of age. Error bars are the SEM. *p = 0.05, **p = 0.01, ***p = 0.001, ****p = 0.0001, ns = non-significant (1-way ANOVA with Tukey’s multiple comparisons test). (B) Correlation analysis between plasma polyQ-ATXN3 levels and the time spent mobile in the open field assay for 6-month-old Q84 mice. Pearson’s correlation coefficient (r) and p values are indicated. The line represents an estimated simple linear regression. (C) Correlation analysis between plasma polyQ-ATXN3 levels and the cerebellar molecular layer thickness at the posterolateral fissure (fpl) for 6-month-old Q84 mice. Pearson’s correlation coefficient (r) and p values are indicated. The line represents an estimated simple linear regression.

Fig 3: SCA3 mice show neuronal loss in the cerebellum and increased NFL levels in the CSF. (A–B) Representative images of the cerebellar Purkinje cell layer in Q28 (A) and Q84 (B) mice at 6 months of age. Slides were stained with H&E. MC: molecular cell layer; PC: Purkinje cell layer; GC: granular cell layer. Scale bars are 100 µm. (C) Average number of Purkinje cells (PCs) per mm of the Purkinje cell layer of the cerebellum in Q28 and Q84 animals at 3 and 6 months of age. (D) Average molecular layer thickness at the posterolateral fissure (fpl) in the cerebellum of Q28 and Q84 animals at 3 and 6 months of age. (E–F) Representative images of the cortex stained with NeuN in Q28 (E) and Q84 (F) mice at 6 months of age. Scale bars are 200 µm (G) Number of NeuN-positive cells per mm2 in the cortex of Q28 and Q84 animals at 3 and 6 months of age. (H) NFL levels in the CSF of Q28 and Q84 animals at 3 and 6 months of age. For all panels, error bars are the SEM. *p = 0.05, **p = 0.01, ***p = 0.001, ****p = 0.0001, ns = non-significant (1-way ANOVA with Tukey’s multiple comparisons test).

Fig 4: SCA3 mice show ataxia-like behavioral defects. (A) Schematic showing the experimental timeline used to analyze the Q28 and Q84 mice. AAV was injected at P0 and mice were analyzed for both behavior and pathology at 3 or 6 months. (B) Hindlimb clasping scores for Q28 and Q84 animals at 3 and 6 months of age. (C) Ledge test scores for Q28 and Q84 animals at 3 and 6 months of age. (D) Number of falls in 2 min on the wire hang assay for Q28 and Q84 animals at 3 and 6 months of age. (E) Latency to fall (seconds) on the rotarod over four consecutive days for Q28 and Q84 animals at 3 and 6 months of age. Asterisks at the top of the graph refer to analysis of Q28 versus Q84 in the 3-months cohort, while asterisks at the bottom of the graph refer to the 6-month-old animals. (F) Time (seconds) spent mobile during the open field assay for Q28 and Q84 animals at 3 and 6 months of age. For all panels, error bars are the standard error of the mean (SEM). *p = 0.05, **p = 0.01, ***p = 0.001, ****p = 0.0001, ns = non-significant (1-way ANOVA with Tukey’s multiple comparisons test for (B-D,F); 2-way ANOVA with Sidak’s multiple comparisons test for (E).

Fig 5: SCA3 mice develop pTDP-43 inclusions in the cortex. Representative images of IHC staining for pTDP-43 in the cortex (A–B) and cerebellum (C–D) of Q28 (A,C) and Q84 (B,D) mice at 6 months of age. Similar results seen at 3 months; see Supplementary Figure S8. Arrows mark inclusions. Insets in (B) are higher magnification images of inclusions. Scale bars are 100 µm.