PSD-95 increases microtubule crossing at dendrite branch points. A–C, EM images of microtubules of hippocampal neurons transfected at DIV 10 and fixed on DIV 12. Asterisks indicate a branch point from a dendrite. A, Control neurons that express GFP have organized microtubules at dendrite branch points. B, Neurons that overexpress PSD-95-GFP show disorganized microtubules at that cross at dendrite branch points when compared to control GFP expressing neurons. C, Neurons that express PSD-95ΔSH3-GFP show organized microtubules at dendrite branch points, similar to control neurons expressing GFP. D, Quantitation of the number of microtubules that cross at dendrite branch points in transfected hippocampal neurons represented in A–C. Microtubules cross dendrite branch points more often in neurons that overexpress PSD-95-GFP when compared to microtubules of neurons that overexpress GFP or PSD-95ΔSH3 GFP. **p < 0.01 by Kruskal–Wallis test followed by Dunn's multiple comparison test. n = 5 neurons for each condition. E, Example of how microtubule crossings were counted. A 0.5 μm line (black box) was drawn and any microtubules crossing that line were counted (arrows). Scale bars: A–C, E, 0.5 μm. Error bars indicate SEM.