FIGURE 4:

Plectin-isoform dependent rescue of compromised AChR clustering and IF anchorage in plectin-deficient myotubes. (A) Confocal fluorescence images of Plec^−/− (top five rows) and Plec^+/+ (bottom row) myotubes after transfection with plasmids encoding various intact or mutant versions of plectin-GFP fusion proteins. Schematic drawings of plectin variants precede each row. Single- and two-channel images (merged) of triple-labeled specimens are presented as indicated on top. Note that among three different isoforms of plectin tested, only P1f showed targeting to AChR complexes (white arrowheads in the top and two lower rows), whereas recruitment of desmin IFs toward receptor complex was dependent on P1f comprising an intact IFBD (yellow arrowheads). Bar, 10 μm. (B, C) Quantification of numbers (B) and densities (C) of large AChR clusters measured in three independent experiments for each series of transfections. Note that only full-length or rodless P1f could restore compact receptor clusters. Myotubes analyzed in B: Plec^+/+, 359; Plec^−/−, untransfected, 727, and transfected 536. Clusters examined in C: Plec^+/+, 273; Plec^−/−, untransfected, 530, and transfected, 758. Mean ± SEM. *p < 0.05 and ***p < 0.001 compared with Plec^+/+; unpaired Student's t test.