Conserved domains and lack of evidence for polyglutamine length polymorphism in the chicken homolog of the Machado-Joseph disease gene product ataxin-3

Ataxin-3 is a protein of unknown function which is mutated in Machado-Joseph disease by expansion of a genetically unstable CAG repeat encoding polyglutamine. By analysis of chicken ataxin-3 we were able to identify four conserved domains of the protein and detected widespread expression in chicken tissues. In the first such analysis in a non-primate species we found that in contrast to primates, the chicken CAG repeat is short and genetically stable.

Distribution of non-class-III beta-tubulin isoforms in neuronal and non-neuronal cells

beta-Tubulin isoforms in brain tissues and in cell lines were analyzed by high-resolution isoelectric focusing in combination with monoclonal antibodies. Post-translational modifications of brain non-class-III beta-tubulin isoforms were found in phylogenetically distant species ranging from pig to carp. Less extensive modifications were also observed in Neuro-2a, HeLa and 3T3 cells, where most acidic isoforms were glutamylated, while the basic, most abundant isoforms were not. The data suggest post-translational modification of non-class-III beta-tubulin isoforms in neuronal as well as in non-neuronal cells. Such modification might modulate interaction of tubulin with microtubule-associated proteins.

Immunological discrimination of beta-tubulin isoforms in developing mouse brain. Post-translational modification of non-class-III beta-tubulins

Individual beta-tubulin isoforms in developing mouse brain were characterized using immunoblotting, after preceding high-resolution isoelectric focusing, with monoclonal antibodies against different structural regions of beta-tubulin. Some of the antibodies reacted with a limited number of tubulin isoforms in all stages of brain development and in HeLa cells. The epitope for the TU-14 antibody was located in the isotype-defining domain and was present on the beta-tubulin isotypes of classes I, II and IV, but absent on the neuron-specific class-III isotype. The data suggest that non-class-III beta-tubulins in mouse brain are substrates for developmentally regulated post-translational modifications and that beta-tubulins of non-neuronal cells are also post-translationally modified.

Differences in the exposure of C- and N-terminal tubulin domains in cytoplasmic microtubules detected with domain-specific monoclonal antibodies

A panel of 11 monoclonal antibodies specific to alpha- or beta-tubulin subunits was used to study the location of tubulin molecules in cytoplasmic microtubules. Specificity of antibodies was confirmed by immunoblotting and immunofluorescence experiments on fixed cells. The limited proteolysis of tubulin with trypsin and chymotrypsin followed by immunoblotting demonstrated that the antibodies discriminated between structural domains of both subunits. Epitope mapping of isolated alpha-tubulin revealed that a set of antibodies against the N-terminal domain of the alpha-subunit (TU-01, TU-02, TU-03, TU-09, 6–11B-1) recognized at least four different antigenic determinants. Immunofluorescence staining of unfixed detergent-extracted cells showed that antibodies to determinants on C-terminal domains labelled microtubules, but these were not decorated with antibodies to N-terminal domains. The same results were obtained after microinjection of antibodies into living cells. The unchanged distribution of microtubules in injected cells was confirmed by double-label immunofluorescence with polyclonal antibodies. The data indicate that while parts of C-terminal domains of both subunits are exposed on the exterior of the microtubules, considerable regions of the N-terminal domains are either not exposed on the surface of cytoplasmic microtubules, or are masked by interacting proteins.