Compartmentation of alpha-tubulin in neurons: identification of a somatodendritic-specific variant of alpha-tubulin.
The composition of alpha-tubulin in axons was compared with that in cell bodies and dendrites in the rat. Pure axons and highly enriched preparations of cell bodies and dendrites were obtained from explant cultures of sympathetic neurons, dissolved directly into sodium dodecyl sulfate, and analysed by isoelectric focusing gel electrophoresis. Immunoblots using two different monoclonal antibodies against alpha-tubulin and fluorographs of [35S]methionine- and [3H]tyrosine-labeled alpha-tubulin all show several variants common to both compartments, and an additional variant, more basic than the others, prominent in the somatodendritic compartment but absent from the axonal compartment. This variant, termed alpha s, partitions with both cytoskeletal and soluble tubulin pools, indicating that microtubules in the somatodendritic compartment differ from microtubules in the axonal compartment with respect to alpha-tubulin composition. Pulse-chase and immunoprecipitation analyses suggest that extensive post-translational modification of alpha-tubulin occurs in the neuron. Newly synthesized alpha-tubulin (10-min pulse-label) is relatively simple in profile, consisting of a major band with the mobility of alpha s, and a minor band slightly lower in isoelectric point. The profile is somewhat more complex after 5 h chase time, but is much more complex after 20 h. The generation of additional bands appears to be at the expense of the band co-migrating with alpha s, suggesting that alpha s is the unmodified form of a primary translation product that undergoes extensive post-translational modification. The unmodified form of the primary translation product is restricted to the somatodendritic compartment, while many of its derivatives are present throughout the neuron.
Department of Anatomy, Temple University School of Medicine, Philadelphia, PA 19140.
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Baas
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Black
D000818:Animals; D000911:Antibodies, Monoclonal; D002478:Cells, Cultured; D003712:Dendrites / Q000378:metabolism*; D005728:Ganglia, Sympathetic / Q000378:metabolism*; D051381:Rats; D014404:Tubulin / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D014404:Tubulin