Rescue of ARF4^+/−/ARF5^−/− phenotypes by exogenous ARF5 expression in the cerebellar PCs. A, B, Sagittal section of a postnatal week 8 (P8w) mouse cerebellum injected with AAV9 vectors expressing ARF5-HA at P14 and immunolabeled with an anti-HA antibody. Scale bars: A, 300 μm; B, 20 μm. C, Head-tremor frequency of P8w mouse during 3 min of movement was counted from video recordings. ARF4^+/−/ARF5^−/− mice were injected PBS (n = 12) or AAV9 vectors expressing ARF5-HA (n = 12) at P14. **p < 0.001, Student's t test. D, The proportion of Nav1.6-positive AISs to ankyrin-G-positive AISs in ARF4^+/−/ARF5^−/− mice injected with PBS (n = 24) and AAV9 vectors expressing ARF5-HA (n = 33) at P8w. **p < 0.001, Student's t test. E, F, Sagittal sections of P8w ARF4^+/−/ARF5^−/− mouse cerebella injected with PBS (E) or AAV9 vectors expressing ARF5-HA (F) immunolabeled with anti-Nav1.6 (green) and anti-calbindin (magenta) antibodies. White arrows indicate Nav1.6 immunoreactivities in the AIS of PCs. Scale bars, 20 μm.