Fig. 5.

Actin tread-milling modulates neurite and growth cone mitochondrial dynamics. WT neurons were treated with latrunculin (B and G) or expressed actin mutant proteins favoring G-actin (R62D; C and H) or F-actin (G15S, D and I; S14C, E and J). Latrunculin shortened mitochondrial length (B and G) compared with controls (A and F). Actin R62D (C and H) decreased mitochondrial size and occupancy compared with controls (A and F). In contrast, actin G15S (D and I) but not S14C (E and J) increased mitochondrial size and occupancy. Growth cone stimulated with the attractive guidance cue BDNF (L and Q) harbored more mitochondria than a nontreated growth cone (K and P). (M and R) In contrast, ephrin-A5, a guidance cue disrupting F-actin, reduced growth cone mitochondrial number. Actin R62D (N and S) reduced mitochondrial number in growth cones compared with controls (K and P). (O and T) Actin G15S-enhanced mitochondrial number in growth cones. Individual growth cones labeled with a dashed line are indicated. Quantification of object size (U) and occupancy (V) was modulated by actin mutants and latrunculin. Quantification of mitochondria in growth cones, without (W) and with (X) normalization for growth cone area, is shown. (*P < 0.05; **P < 0.01; ***P < 0.001.) Numbers in bars represent numbers of independent experiments. (Scale bar: A–T, 10 μm.)