(A-D) Primary rat hippocampal neurons were transduced with GFP-TDP-25 variants, GFP-NPM1 or Htt97Q-GFP and analyzed by fluorescence recovery after photobleaching (FRAP) at DIV5+8, except Htt97Q-GFP which was analyzed at DIV5+6 to avoid excessive toxicity. Example images with indicated bleach regions (dashed circles) are shown (A, C). Scale bar = 1.5 µm. Resulting normalized FRAP curves (relative fluorescence intensity over time) with values representing means ± SD are shown in (B, D). (B) Comparison of the averaged recovery fraction of the last six timepoints obtained from three independent experiments. GFP-NPM1 (0.982 ± 0.019, mean ± CI, n=37 cells) vs GFP-TDP-25 wt (0.097 ± 0.013, n=35 cells) vs GFP-TDP-25 mut (0.085 ± 0.006, n=38 cells): H(1)=74.134, df=2, ***p<2.2*10-16, η²[H]=0.674, Kruskal-Wallis Test. GFP-NPM1 vs GFP-TDP-25 wt: ***p<2*10-16, GFP-NPM1 vs GFP-TDP-25 mut: p<2*10-16, GFP-TDP-25 wt vs GFP-TDP-25 mut: p=0.11, Pairwise Wilcoxon Rank Sum Tests with Benjamini-Hochberg correction. In (D), the recovery fraction averaged at >20 min timepoints was compared from four independent experiments. Htt97Q-GFP (0.094 ± 0.017, n=25 cells) vs GFP-TDP-25 wt (0.312 ± 0.041, n=23 cells) vs GFP-TDP-25 mut (0.271 ± 0.029, n=24 cells): H(1)=46.376, df=2, ***p=8.501*10-11, η²[H]=0.643, Kruskal-Wallis Test. Htt97Q-GFP vs GFP-TDP-25 wt ***p=1.9*10-11, Htt97Q-GFP vs GFP-TDP-25 mut ***p=4.3*10-12, GFP-TDP-25 wt vs GFP-TDP-25 mut: p=0.12, Pairwise Wilcoxon Rank Sum Tests with Benjamini-Hochberg correction. 