Specific changes in axonally transported proteins during regeneration of the frog (Xenopus laevis) optic nerve

Abstract

Labeled proteins in intact and regenerating optic nerves of juvenile Xenopus clawed frogs were examined at three different time points (2 to 4 hr, 18 hr, and 5 to 9 days) following [35S]methionine injection into the eye. The distal axon tips of optic nerves were transected at the margin of the tectal lobe and regeneration of the nerve was followed by three methods: autoradiography, tissue section counting following [3H]proline injection into the eye, and electrophysiological mapping of the visual field projection. By these methods, regrowth was found to occur 2 weeks after transection, but the fibers had not yet sorted their retinotopic pattern. Two-dimensional gel separation of labeled nerve proteins revealed 250 to 300 identifiable proteins, 89 of which (including all spots which differed consistently upon direct comparison of regenerating versus normal nerves) were selected for quantitative treatment. Nine of these spots (240, 135, 65, 64, 58, 54, 56, 31, and 26 kilodaltons) were shown to increase and six (56, 49, 42, 29, 17, and 15 kilodaltons) were shown to decrease significantly in regenerating nerves. By using a crush control and tracking the labeled proteins into the tectum over time, these proteins were shown to be axonally transported proteins. In addition, four other nonaxonally transported proteins also changed during regeneration.