Figure 6. Pathogenic SPTAN1 mutations produce phenotypes similar to Sptan1 deletion.

(A) All reported αII spectrin mutations reside at the C-terminal, a critical region required for spectrin heterodimer formation. (B) Neurons cotransfected with WT SPTAN1 and GFP show normal morphology compared with GFP alone except for decreased soma size. Neurons transfected with p.R2308_M2309dup or p.E2207del are smaller and have shortened or absent apical dendrites and abnormal basal dendrites. Arrowheads indicate well-formed apical dendrites in GFP and WT SPTAN1 groups, and arrows indicate the apical tufts in layer I cortex (seen best in the GFP group). Apical dendrites and tufts in the mutant groups are minimal. (C) Higher-magnification images reveal the severely altered neuronal morphology in the mutant overexpression groups. Arrows indicate the lack of apical dendrites, and arrowheads denote impaired basal dendritic trees. Scale bars: 100 μm in B, 50 μm in C. (D) Most neurons transfected with GFP (76.2%) or WT SPTAN1 (63.9%) display intact apical dendrites. Neurons transfected with mutant SPTAN1 constructs typically lack apical dendrites (20.3% in p.R2308_M2309dup; 19.0% in p.E2207del overexpression group). Percentage data are transformed to arcsine values for statistical comparisons. (E) The soma size of neurons transfected with WT or mutant SPTAN1 is significantly smaller than that of GFP controls, and both mutants show significantly reduced soma size compared with WT SPTAN1. For apical dendrite analysis, n = 32 neurons from 3 brains for GFP control; n = 20 neurons from 3 brains with WT SPTAN1; n = 43 neurons from 4 brains with SPTAN1 p.R2308_M2309dup; n = 37 neurons from 3 brains with SPTAN1 deletion were used. For soma size analysis, 25 neurons from 3 GFP brains, 53 neurons from 3 brains with WT SPTAN1, 47 neurons from 3 brains with SPTAN1 p.R2308_M2309dup, and 50 neurons from 4 brains with SPTAN1 p.E2207del were used. ANOVA test: *P < 0.05; **P < 0.01; ***P < 0.001.