Figure 3.

N-WASP is required for membrane wrapping and longitudinal extension of the myelin unit. (A) Fluorescence immunostaining of P30 teased sciatic nerve fibers of control mice using antibodies to MBP and Caspr (to label the paranodal junction; arrowheads). The internodal length is 563 µm. (B) Immunolabeling of teased sciatic nerve fibers of mutant mice using antibodies to MBP and gliomedin (Gldn). Axon a is almost completely (92%; 516–560 µm) covered by nine internodes with a mean length of 57.3 µm each (ranging from 33 to 74 µm), whereas only two internodes are present in axon b. The unmyelinated regions along the axon are associated with multiple Schwann cell nuclei (DAPI). (A and B) Bars, 50 µm. (C and D) Labeling of mutant sciatic nerves using antibodies to MBP and Caspr. The arrowhead in C marks the presence of an immature short (29 µm) internode. Three segments containing split MBP staining are marked with arrowheads in D. Internodal axonal Caspr staining is detected in the middle of the top right and bottom internodes. (E and F) Labeling of teased sciatic nerve fibers of mutant mice using antibodies to P0 and neurofilament (NFH). Note the presence of myelin sheaths that did not entirely enclose the axon (arrowheads). (G) Quantitation of the divergence of internodal length in wild-type (WT) and mutant mice, which is presented as a percentage of the total number of segments measured for each genotype. n = 100 and 17 segments for mutant and wild-type nerves, respectively. KO, knockout. (H) Caspr immunoreactivity (arrowhead) reflects the formation of a thin myelin sheath in the mutant. Bar, 5 µm. (I–L) Phalloidin labeling (actin) of control (I and K) and mutant sciatic nerves (J and L) together with antibodies to P0 (I and J) or DRP2 (K and L). Arrowheads mark the membrane appositions labeled by DRP2. The asterisks mark areas of Schwann cell nuclei. (C–F and I–L) Bars, 20 µm.