Fig. 6. Myosin Va is required for efficient retrograde transport in living MNs. (A) In rat MNs myosin Va shows an abundant punctate distribution and co-localises with TeNT H_C-Alexa 488 carriers (B, arrowheads). (C) Merged image of A and B. (D,E) Time-lapse imaging of TeNT H_C-Alexa 488 retrograde carriers (arrowheads, asterisks) in an axon of a wild-type (D) or a dilute lethal (E) mouse MN. Intervals between frames are 5 seconds. The cell body is located at the bottom in both D and E. Bars, 5 µm. See video 4. (F) Relative frequencies of speed values measured between two consecutive frames (interval = 5 seconds) for TeNT H_C carriers in wild-type MNs (193 carriers, filled circles; three embryos) and dilute lethal MNs (91 carriers, empty circles; two embryos). Wild-type and dilute lethal embryos are derived from the same litter. Retrograde movement is conventionally shown as positive. (G) In mouse MNs, the speed distribution profile of TeNT H_C is best described by the sum of three Gaussian curves centred at 0, 0.53 and 0.95 µm/second. A decrease of the fast component and an increase of pauses are observed in dilute lethal MNs (white bars), whereas the intermediate component remains unaltered relative to wild-type cells (black bars). Data are derived from the analysis of 357 carriers from five wild-type embryos and 141 carriers from three dilute lethal embryos. Error bars indicate mean ± s.e.m.

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