Figure 6

Ultrastructural examination of Whirlin knockout sciatic nerves reveals organelle accumulation and cytoskeletal disruption. Low magnification electron micrographs through the internodal regions of sciatic nerves in wild-type (7 week-old) and Whrn knockout mice (7 week-old, 3 month-old) in cross section (A vs. B, C) and longitudinal orientations (D vs. E, F). Overall cellular organization between Whrn knockout and wild-type sciatic nerve fibers is conserved with tightly compacted myelin around each axon. Low magnification, longitudinal electron micrographs through the nodal and paranodal regions of sciatic nerves are presented for wild-type (7 week-old, G) and Whrn knockout mice (7 week-old, H; 3 month-old, I). At a higher magnification, the wild-type (J) paranodal loops have clearly defined characteristic transverse, electron-dense septa (concave arrowheads) and parallel arrays of cytoskeletal elements. In contrast, Whrn mutant paranodal septa (K, L, concave arrowheads) are less definitive and fuzzy with associated accumulation of organelles (flat arrowheads), particularly mitochondria and transport vesicles. Scale bars: A–I, 2 μm, J–L, 400 nm.