Figure 4. Myelination deficiency in Rac1-CKO mice is rescued by NF2/merlin mutation. A, Sciatic nerves from 3-month-old control, Rac1-CKO, NF2-del, and Rac1-CKO&NF2-del mice are shown. Rac1-CKO sciatic nerves are thinner than control nerves. Rac1-CKO&NF2-del nerves are similar to the size of control nerves. B, EM analysis of control, Rac1-CKO, NF2-del, and Rac1-CKO&NF2-del sciatic nerve cross-sections at P120. More myelinated axons are present in Rac1-CKO&NF2-del sciatic nerves than in Rac1-CKO nerves. Irregular SC protrusions in Rac1-CKO sciatic nerves in vivo remained in Rac1-CKO&NF2-del sciatic nerves (arrowheads). C, The number of myelinated axons is significantly increased in Rac1-CKO&NF2-del mice compared with Rac1-CKO mice. D, The number of axons in one-to-one SC–axon profile without myelination is decreased in Rac1-CKO&NF2-del mice versus Rac1-CKO mice. E, Western blot analysis of Pmp22, a peripheral myelin protein, in control, Rac1-CKO, NF2-del, and Rac1-CKO&NF2-del sciatic nerves. Quantification from three independent experiments shows Pmp22 expression was significantly decreased in Rac1-CKO sciatic nerves. Reduced Pmp22 expression in Rac1-CKO sciatic nerves was rescued in Rac1-CKO&NF2-del sciatic nerves. F, EM analysis of control (a), Rac1-CKO (b), NF2-del (c), and Rac1-CKO&NF2-del (d) nerves. Small axons are normally segregated by SCs and form Remak bundles in Rac1-CKO nerves and Rac1-CKO&NF2-del nerves, although no myelin sheath forms in Rac1-CKO nerves. For C and D, n ≥ 25 fields from at least 5 animals per genotype were analyzed. *p < 0.05, **p < 0.01, ***p < 0.001 by ANOVA statistical analysis, followed by Tukey's test. Error bars indicate ± SEM. Scale bars: B, top row, F, 5 μm; B, bottom row, 2 μm.