Fig. 8. KBP is required for axonal growth, cytoskeletal organization and myelination in the CNS. (A,B) TEM images of transverse sections through the ventral spinal cord of a wild type (A) and kbp^st23 mutant (B) at 50 hpf. Axons with a diameter greater than 0.75 µm are indicated by a white asterisk. There are fewer large-diameter axons in the kbp^st23 mutant. Cytoskeletal disorganization is apparent in the large Mauthner axon (M) in the kbp^st23 mutant compared with wild type. Scale bars: 0.75 µm. (C,D) TEM images of transverse sections through the ventral spinal cord show high magnification views of the Mauthner axon (M) in a wild type (C) and kbp^st23 mutant (D) at 50 hpf. There are more properly oriented microtubules (e.g. arrowheads) and neurofilaments (e.g. arrows) in the wild type than in the kbp^st23 mutant (D) Mauthner axon. Scale bars: 200 nm. (E,F) TEM images of transverse sections through the ventral spinal cord show that there are more myelinated axons (white asterisks) in wild type (E) than in the kbp^st23 mutant (F) at 72 hpf. Examples of large diameter kbp^st23 mutant axons with a disorganized cytoskeleton are indicated by black asterisks. Scale bars: 0.75 µm. (G-I) TEM images of transverse sections through the ventral spinal cord show that there are more large-diameter myelinated axons in the wild type (G) compared with kbp^st23 mutants (H,I) at 7 dpf. Scale bars: 2 µm.