Slow transport of unpolymerized tubulin and polymerized neurofilament in the squid giant axon - PubMed (original) (raw)

Slow transport of unpolymerized tubulin and polymerized neurofilament in the squid giant axon

J A Galbraith et al. Proc Natl Acad Sci U S A. 1999.

Abstract

A major issue in the slow transport of cytoskeletal proteins is the form in which they are transported. We have investigated the possibility that unpolymerized as well as polymerized cytoskeletal proteins can be actively transported in axons. We report the active transport of highly diffusible tubulin oligomers, as well as transport of the less diffusible neurofilament polymers. After injection into the squid giant axon, tubulin was transported in an anterograde direction at an average rate of 2.3 mm/day, whereas neurofilament was moved at 1.1 mm/day. Addition of the metabolic poisons cyanide or dinitrophenol reduced the active transport of both proteins to less than 10% of control values, whereas disruption of microtubules by treatment of the axon with cold in the presence of nocodazole reduced transport of both proteins to approximately 20% of control levels. Passive diffusion of these proteins occurred in parallel with transport. The diffusion coefficient of the moving tubulin in axoplasm was 8.6 micrometer(2)/s compared with only 0.43 micrometer(2)/s for neurofilament. These results suggest that the tubulin was transported in the unpolymerized state and that the neurofilament was transported in the polymerized state by an energy-dependent nocodazole/cold-sensitive transport mechanism.

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Figures

Figure 1

Figure 1

Active transport and diffusion of fluorescently labeled neurofilament proteins in normal (A–D) and metabolically poisoned (E–H) squid giant axons. The metabolically poisoned axons show a small amount of spreading but no anterograde movement of the neurofilament. (A and E) Bright-field image showing the oil drop injected into the axon. (B and F) Fluorescent image of the neurofilament protein distribution soon after injection (_t_0). The oil drop is visible as a dark circle surrounded by bright neurofilament fluorescence. (C and G) Fluorescence distribution 3 hr later (_t_1), showing the anterograde (to the right) movement of the neurofilament protein in C. (D and H) Intensity trace of the neurofilament fluorescence. The axis is centered on the oil drop. (The scale bar in E is 250 μm for all images.)

Figure 2

Figure 2

Active transport and diffusion of fluorescently labeled tubulin proteins. Note that tubulin diffused much more extensively than the neurofilament shown in Fig. 1. The images are arranged as in Fig. 1: A and E, bright-field; B and F, fluorescent image soon after injection; C and G, 3 hr later; and D and H, trace of fluorescence intensity. (The scale bar in E is 250 μm for all images; length scales of the intensity traces are the same as Fig. 1.)

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References

    1. Sabry J, O’Connor T P, Kirschner M W. Neuron. 1995;14:1247–1256. - PubMed
    1. Grafstein B, Forman D S. Physiol Rev. 1980;60:1167–1283. - PubMed
    1. Nixon R A. Curr Opin Cell Biol. 1998;10:87–92. - PubMed
    1. Hoffman P N, Lasek R J. J Cell Biol. 1975;66:351–366. - PMC - PubMed
    1. Lasek R J. J Cell Sci Suppl. 1986;5:161–179. - PubMed

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