Figure 6

Neurofascin B Regulates Myelin Sheath Elongation and Stability

(A and A′) Single time-point confocal images of a myelinating process in a Tg(sox10KalTA4, UAS mEGFP) control that makes contact with a target axon (A) and transitions into a recognizable myelin sheath (A′). Scale bar, 5 μm.

(B) Average length of myelin sheaths immediately upon formation in control and nfascb MO-injected animals. Control median = 4.02, 25^th percentile 3.45, 75^th percentile 4.93, n = 91 from 13 animals and nfascb MO median = 3.67, 25^th percentile 3.10, 75^th percentile 4.63, n = 195 sheaths from 21 animals, p = 0.0611, Mann–Whitney test.

(C and C′) Confocal images of a myelin sheath elongating over time during the period of sheath formation in a control animal. Arrowheads in all panels denote ends of myelin sheaths. Scale bar, 5 μm.

(D) Average speed of individual sheath elongation in controls over a 12-h period, starting from the hour of their formation during the critical period. Each point represents a single sheath, imaged across 13 animals. No significant difference in speed of growth based on time of sheath formation, p = 0.8933, Kruskal-Wallis test.

(E and E′) Single time-point confocal images of a myelin sheath elongating over time during the critical period of sheath formation in an nfascb MO-injected animal. Scale bar, 5 μm.

(F) Average speed of sheath elongation in nfascb MO-injected animal over a 12-h period, starting from the hour of their formation during the critical period. Each point represents a single sheath, imaged across 21 animals. No significant difference in speed of growth based on time of sheath formation, p = 0.6301, Kruskal–Wallis test.

(G and G′) Single time-point confocal images of a myelin sheath shrinking over time after the critical period in a nfascb MO-injected animal. Scale bar, 5 μm.

(H) Speed of elongation of individual myelin sheaths in control and nfascb MO-injected animals for the first 6 h after their formation and the following 6 h. (control n = 34 sheaths in 8 animals, nfascb MO n = 66 sheaths in 13 animals: 0–6 h: control mean speed 0.77 ± 0.40 SD, nfascb MO mean 0.56 ± 0.41 SD, p = 0.0133, Mann–Whitney-test. 6–12 h: control mean speed 0.89 ± 0.42 SD, nfascb MO mean 0.185 ± 0.60 SD, p < 0.0001, Mann–Whitney test. Note the large number of sheaths shrinking in nfascb MO-injected animals between 6–12 h after sheath formation.

(I and I′) Confocal images of a myelin sheath elongating in a wildtype animal. Scale bar, 10 μm.

(J and J′) Confocal images of a myelin sheath elongating in an nfascb^ue56 mutant. Scale bar, 10 μm.

(K) Speed of myelin sheath elongation in Tg(mbp:EGFP-CAAX) wildtype and nfascb^ue56 mutants (control mean speed 0.34 ± 0.40 SD, n = 118 from 6 animals, nfascb^ue56 mutant mean 0.06 ± 0.23 SD, n = 215 from 9 animals, p < 0.0001, Mann–Whitney test. 16.1% in controls and 36.4% in nfascb^ue56 represent shrinking myelin sheaths.

(L) Cell body myelination in nfascb^ue56 mutants. Scale bar, 10 μm.