Figure 7

Caspr Regulates Myelin Sheath Elongation and Stability, but Not Targeting

(A and B) Confocal images of single oligodendrocytes labeled mosaically using mbp:mCherry-CAAX in wildtype (A) and caspr^sa12772 mutants at 5 dpf. Scale bar, 10 μm.

(C–E) Number of myelinated cell bodies (C), number of myelin sheaths (D), and the length of myelin sheaths (D), made by individual oligodendrocytes in wildtype, het, and caspr^sa12772 mutants.

(C) Myelination of cell bodies is increased slightly in caspr^sa12772 mutant oligodendrocytes (wildtype median 0.0, 25^th percentile 0.0, 75^th percentile 0.0, n = 15 animals; caspr^sa12772/+ median 0.0, 25^th percentile 0.0, 75^th percentile 0.0, n = 35, caspr^sa12772 median 0.25, 25^th percentile 0.0, 75^th percentile 1.5 , n = 25 animals; wildtype versus caspr^sa12772/+ p = 0.8056, wildtype versus caspr^sa12772 p = 0.0305, caspr^sa12772/+ versus caspr^sa12772 p = 0.0156, all Mann–Whitney test.

(D) Number of myelin sheaths per oligodendrocytes is similar in wildtype, caspr^sa12772/+ and caspr^sa12772 (wildtype mean 11.78 ± 5.14 SD, n = 15 animals, caspr^sa12772/+ mean 11.19 ± 3.26 SD, n = 33 animals, caspr^sa12772 mean 12.00 ± 3.54 SD, n = 24; ANOVA = 0.712).

(E) Myelin sheath length is reduced in caspr^sa12772 mutants (wildtype mean 29.14 ± 1.71 SEM, n = 15, caspr^sa12772/+ mean 27.58 ± 1.31 SEM, n = 33 animals, caspr^sa12772 mean 23.55 ± 1.30 SEM, n = 24 animals; wildtype versus caspr^sa12772/+ p = 0.4954, wildtype versus caspr^sa12772 p = 0.0124, caspr^sa12772/+ versus caspr^sa12772 p = 0.0374, all t test).

(F and G) Confocal images of the dorsal horn of the spinal cord in wildtype (F) and Caspr mutant (G) mice, indicating the region indicated by dashed lines wherein myelinated cell bodies were searched for. Scale bar, 50 μm.

(F′ and G′) Higher magnification views of regions within the dorsal horn of wild type (F′) and Caspr mutant (G′) animals stained with antibodies that recognize myelin basic protein (green), NeuN (red), and DAPI (blue). Scale bar, 5 μm.

(H) Graph showing that essentially no myelinated cell bodies were observed in wild type or Caspr mutant animals. Wild type mean 0.2800 ± 0.049 SEM, n = 5 (10 sections per mouse), Caspr^−⁄− 0.257 ± 0.083 SEM, n = 5 (10 sections per mouse), p = 0.8147, t test.

(I and J) Confocal images of teased fiber preparations taken from wild type (I) and Caspr mutant (J) mice, stained with antibodies that detect Kv1.1 (red), Neurofascin 186 (green), and neurofilament 200 (red). Scale bars, 25 μm.

(K) Quantitation of myelin sheath length in Caspr mutant mice. Caspr internode lengths are reduced compared to wild type; wild type mean 310.7 ± 5.32 SEM, n = 5, Caspr 226.5 ± 8.96 SEM, n = 5 animals, 50 internodes per mouse, p < 0.0001, t test.

(L and L″) Confocal images of a myelin sheath elongating in a wildtype Tg(mbp:EGFP-CAAX) animal. Scale bar, 10 μm.

(M and M′) Confocal images of a myelin sheath elongating in a caspr^sa12772 mutant. Scale bar, 10 μm.

(N) Speed of myelin sheath elongation in wildtype and caspr^sa12772 mutants: wildtype mean 0.36 ± 0.35 SD, n = 122 sheaths from 6 animals, caspr^sa12772 mean 0.16 ± 0.31 SD, n = 151 sheaths from 7 animals, p < 0.0001, Mann–Whitney test. 14.8% in controls and 28.5% in nfascb^ue56 represent shrinking myelin sheaths.