Histological analysis of myelination after CNS-specific Sox10 deletion and consequences of combined deletion of Sox8 and Sox10 on myelin gene expression.

(A–C) Light microscopy of 1 µm semi-thin sections of the spinal cord ventral horn in wildtype (wt) (A) and Sox10ΔCNS (ko) mice (B,C) at P14 following Richardson's stain. Myelinated axons are stained in the white matter (WM) of the wildtype, but not the mutant. Sections from Sox10ΔCNS mice contain myelin only in the anterior rootlet (AR) where it is formed by Schwann cells. C represents a higher magnification of the area boxed in B. GM, grey matter. Scale bars, 100 µm. (D–F) Transmission electron microscopy of the wildtype spinal cord ventral horn at P14 shows myelinated axons (D, black arrows) around an OL (OL) in the white matter. In contrast, OL in Sox10ΔCNS mice are surrounded by axons that lack myelin sheaths (E,F, black arrows). In mutant mice only Schwann cells in the anterior rootlet have formed myelin sheaths (F, white arrow). Scale bars, 2.5 µm. (G–R) Differentiating OL were visualized by in situ hybridization on transverse spinal cord sections from the forelimb region of wildtype (wt) (G,H,K,L,O,P) or Sox10ΔCNS Sox8lacZ/lacZ (dko) (I,J,M,N,Q,R) mice at P7 (G,I,K,M,O,Q), and P16 (H,J,L,N,P,R) using antisense probes against Mbp (G–J), Plp (K–N), and Myrf (O–R). Ventral horn region is shown. Scale bar, 200 µm.