Figure 3

Myelination promotes vesicular fusion along reticulospinal axons

(A and B) SypHy activity and myelination profile of reticulospinal axons in wild-type (WT) (A) and hypomyelinated myrf^UE70 mutants (B). Magenta arrowheads indicate collateral SypHy activity. Kymographs represent SypHy activity of the axonal region above.

(C) Myelin coverage in WT and myrf (p = 0.002, Mann-Whitney test, 25 axons from 19 WT animals and 12 axons from 11 myrf animals).

(D and E) Axonal (D), but not collateral (E), SypHy frequency is decreased in myrf mutants (D, p = 0.022; E, p = 0.476; Mann-Whitney test, N as in C).

(F and G) Amplitude (F) and duration (G) of SypHy events is similar in WT and myrf mutants. Violin plots represent all analyzed events and circles denote average per axon (WT versus myrf; F, p = 0.112 ax, p = 0.396 col; G, p = 0.317 ax, p = 0.144 col; Mann-Whitney tests, n = 39–216 axonal and 77–181 collateral events from N = 23 axons from 17 WT animals and 11 axons from 10 myrf animals). Note that axonal versus collateral comparisons are significant: (F) p < 0.001 WT, p = 0.008 myrf, ANOVA with Bonferroni correction for multiple comparisons; (G) p = p < 0.001 WT, p = 0.088 myrf, Kruskal-Wallis with Dunn’s multiple comparisons test (for all, N = 23 WT axons and 11 myrf axons).

(H) Myelination profile and SypHy activity of a Rohon-Beard axon. Kymograph of bracketed region.

(I) Axonal SypHy frequency in rarely myelinated Rohon-Beard axons is significantly reduced compared to reticulospinal axons (p = 0.006 all RS versus Rohon-Beard, p > 0.05 unmyelinated. RS versus Rohon Beard, p = 0.001 myelinated. RS versus Rohon Beard; Kruskal-Wallis with Dunn’s multiple comparison test, 94 RS axons in 87 animals and 12 Rohon-Beard axons from 11 animals).

Scale bars, 5 μm, 60 s (A, B, and H). Graphs display median and interquartile range.

See also Videos S5 and S6.