Figure 4.

Knock-out of Camk2b leads to an increase in the g-ratio (decrease in the thickness) of the myelin sheath, whereas myelination appears to be unaffected in Camk2^A303R mutant mice. A and inset in F, Representative electron micrographs of the ventral spinal cord of 21-d-old (P21) WT and Camk2b^−/− mice in A or Camk2^A303R mutant mice in F. Scale bars, 1 μm. B, D, F, Scatter plots depicting g-ratios versus axon diameters for P21 Camk2b^−/− (B), adult Camk2b^−/− (D), or P21 Camk2^A303R (F; black filled circles) and WT littermate (red open circles) ventral spinal cords. The lines represent linear fits to pooled data from all mice for each genotype. One hundred axons per animal were measured and three animals per genotype were analyzed. C, E, G, Bar graphs depicting average slopes (g-ratio versus axon diameter) and average g-ratios from individual animals (n = 3). Asterisks indicate statistically significant differences between WT and knock-out/mutant mice (*p < 0.05, Student's t test).