Figure 5.

Human βIV Spectrin Variants Disrupt Nodal Ion Channel Clustering

(A–F) Immunostaining of human sural nerve biopsies from individuals with the p.Arg504Gln; p.Arg2435Cys and p.Trp903^∗ variants was performed with antibodies against neurofascin (Nfasc, red) and βIV spectrin (green) (A and B). Immunostaining of human sural nerve biopsies from individuals with p.Arg504Gln; p.Arg2435Cys and p.Trp903^∗ variants was performed with antibodies against neurofascin (Nfasc, red) and Na⁺ channels (Nav, green) (C and D). Immunostaining of human sural nerve biopsies from individuals with p.Arg504Gln; p.Arg2435Cys and p.Trp903^∗ variants was performed with antibodies against neurofascin (Nfasc, red) and KCNQ2 K⁺ channels (green) (E and F). Nodes are indicated by arrowheads. NB: the exposure times for immunostaining of βIV spectrin, Na⁺ channels, and KCNQ2 in the p.Trp903^∗ variant are much longer than the exposure times in the p.Arg504Gln; p.Arg2435Cys variant to allow detection of these proteins. This is evident from the high background seen along the axons. The scalebar represents 10 μm and applies to all panels (A–F).

(G) Immunostaining of the optic nerve from the indicated genotypes with antibodies against Caspr (green), KCNQ2 (red), or KCNQ3 (red). Arrowheads indicate nodes with KCNQ2 or KCNQ3 immunostaining, whereas arrows indicate nodes without any nodal labeling for these channels. The scale bar represents 10 μm.

(H) Quantification of the percent of nodes labeled for KNCQ2 or KCNQ3 in the indicated mice. n = 3 mice for each genotype. The mean ± SEM is shown. ^∗∗p < 0.001; ^∗∗∗p < 0.0001.