Fig. 8. Defective axon sorting, dysmyelination and axonal degeneration in the mutant sciatic nerve. (A) Normal control nerve at postnatal day 30 (P30); note orderly arrangement of uniformly sized axons sorted within the cytoplasm of a non-myelin forming Schwann cell (nmsc), and, in parallel, a myelin forming Schwann cell (msc) surrounding a single large diameter axon (ax) with a myelin cuff (m). (B-F) sciatic nerve sections from Ebf2^-/- mice. (B) At P30, two 4 µm axons (arrows) are abnormally fasciculated within the cytoplasm of a nmsc. Likewise, in C (P60), a single Schwann cell ensheathes an unmyelinated axon and a myelinated one; arrow indicates SC basal lamina joining myelinated and unmyelinated axons; note adjacent unmyelinated 3 µm axon (arrowhead). (D) A longitudinal section from a P45 nerve reveals segmental dysmyelination: an internode is myelinated (arrowheads) proximal to a node (n), while the subsequent internode remains unmyelinated (arrows). (E) A hypomyelinated axon at P60, a stage at which myelination is complete in controls; arrow indicates an abnormally thin myelin sheath. (F) A P30 axon shows cytoplasmic vacuoles (arrow), indicative of axonal degeneration. ax, axon; m, myelin; msc, myelin-forming Schwann cell; n, node of Ranvier; nmsc, nonmyelin-forming Schwann cell. Scale bars: 1 µm in A-E; 0.5 µm in F.