Distinct localization of a beta-tubulin epitope in the Tetrahymena thermophila and Paramecium caudatum cortex.

Many of the highly organized microtubular arrangements in ciliates are located in the cortical area containing membrane vesicles and vacuoles. In Tetrahymena thermophila and Paramecium caudatum, immunofluorescence microscopy with the monoclonal antibody TU-06, directed against beta-tubulin, revealed distinct staining of this cortical region alone, while the cilia and other microtubular structures were unstained. The specificity of the antibody was confirmed by immunoblotting and by preabsorption of the antibody with purified tubulin. Double-label immunofluorescence with antibodies against gamma-tubulin, detyrosinated alpha-tubulin, and centrin showed that the TU-06 epitope is localized outside the basal body region. This was also confirmed by immunogold electron microscopy of thin sections. Proteolytic digestion of porcine brain beta-tubulin combined with a peptide scan of immobilized, overlapping peptides disclosed that the epitope was in the beta-tubulin region beta81-95, a region which is phylogenetically highly conserved. As known posttranslational modifications of beta-tubulin are located outside this area, the observed staining pattern cannot be interpreted as evidence of subcellular sequestration of modified tubulin. The limited distribution of the epitope could rather reflect the dependence of TU-06 epitope exposition on conformations of tubulin molecules in microtubule arrangements or on differential masking by interacting proteins.

A fast and simple dot-immunobinding assay for quantification of mouse immunoglobulins in hybridoma culture supernatants.

Mouse monoclonal antibodies of IgG subclasses and IgM class in hybridoma culture supernatants were quantified using a dot-immunobinding assay. Immunoglobulins were bound to nitrocellulose (NC) membrane and, after blocking, the membrane was incubated with anti-mouse antibody conjugated to horseradish peroxidase (HRP). Binding was revealed by incubation with a sensitive chemiluminiscence reagent. Quantitation was achieved by densitometric comparison with standard curves produced by purified monoclonal antibodies of the same subclass or purified antibodies of the same clone as the antibody to be quantified. These quantitative results were compared with those obtained using purified IgG from mouse serum or purified mouse myeloma IgM as standards. The dot-immunobinding assay requires 1 microl of hybridoma culture sample and takes about 1 h in total. Good linearity between the staining intensity and the amount of immobilized immunoglobulins was observed over the range of 0.05-5 ng/spot. The assay is simple, reproducible and can process simultaneously a large number of samples.