Figure 4.

Oligodendrocytes myelinate motor axons in mutants lacking Schwann cells. A, A′, Transverse sections of a 5 dpf wild-type larva labeled with MBP (red) and acetylated Tubulin (blue) antibodies. MBP was present in the white matter of the spinal cord (asterisks) and along ventral motor roots (white arrow). B, B′, Transverse section of a 5 dpf mob ^−/−;mos ^−/− larvae. Spinal cord expression of MBP was normal (white asterisks). MBP was also present along motor axons (arrow), although at reduced levels compared to wild type. A′ and B′ are enlarged views of the boxed regions in A and B. C, D, Electron micrographs of motor nerves in wild-type (C) and mob ^−/−;mos ^−/− (D) larvae at 5 dpf. Loosely compacted myelin surrounded motor axons in both wild type and mutant (red arrowheads). Scale bars: 24 μm (A–B′), 500 nm (C, D).