Figure 1.
Pruning of early-stage myelin segments during oligodendrocyte myelination. (A1–A6) Time-lapse images of an oligodendrocyte (OL) in the spinal cord of a zebrafish larva. Lateral views with dorsal up and anterior left. Asterisk, OL soma; Green arrowhead, extending myelin segment; Red arrowhead, pruning myelin segments; hpf, hours post-fertilization. Scale: 20 μm. (B) Initiation time of myelination. Data were obtained from 27 OLs in 21 animals. (C) Time course showing change in the number of myelin segment after initiation. Same data set with B was used. hr, hour. (D) Time course showing changes in the mean length of pruning (red) and extending (green) segments after initiation. The numbers indicate the numbers of myelin segments examined in 27 OLs. (E) Pruning probability of early-stage myelin segments in individual OLs (n = 27). Same data set with B was used. The pruning probability was calculated by dividing the number of pruning segments after 96 h with the total segment number at the initiation time. (F–H) Axon diameter-dependency of myelin segment pruning. (F) Time-lapse images of an OL, one process of which wrapped Mauthner cell axon (arrow). Asterisk, OL soma; Green arrowhead, extending myelin segment; Red arrowhead, pruning myelin segments. Scale, 20 μm. (G) Pruning probability of different types of myelin segments. Number/number, pruning segment number/total segment number. (H) Lifespan of pruning myelin segments of M-axon- and non-M-axon-wrapping OLs. The numbers on bars represent the numbers of pruning segments examined. (I–L) NRG1-ErbB signaling is required for myelin segment pruning. The data obtained from OLs without contacting Mauthner cell axons were analyzed. (I) Mean number of total myelin segments per OLs at the myelination initiation timepoint. The numbers on bars represent the numbers of OLs examined. (J) Pruning probability of myelin segments. Number/number, pruning segment number/total segment number. (K) Life span of pruning myelin segments. (L) Mean number of total myelin segments per OLs 96 h after myelination initiation. n.s., no significance; *P < 0.05; **P < 0.01; ***P < 0.001 (unpaired Student's t-test and one-way ANOVA). Error bars represent mean ± SEM.