Preparation of a monoclonal antibody specific for the class I isotype of β-tubulin: The β isotypes of tubulin differ in their cellular distributions within human tissues

Tubulin, the subunit protein of microtubules, is an α/β heterodimer. In many organisms, both α and β consist of various isotypes. Although the isotypes differ in their tissue distributions, the question of whether the isotypes perform different functions in vivo is unanswered. In mammals, the β(I) and β(IV) isotypes are quite widespread, and β(II) is less so, while β(III) and β(VI) have narrow distributions and β(V) distribution is unknown. As a tool for localizing the isotypes, we report the preparation of a monoclonal antibody specific for β(I), to add to our previously described monoclonal antibodies specific for β(II), β(III), and β(IV) [Banerjee et al., J. Biol. Chem. 263:3029-3034, 1988; 265:1794-1799, 1990;267:5625-5630, 1992]. In order to prepare this antibody, we have purified β(I)-rich rat thymus tubulin. We have used our battery of antibodies to localize the β isotypes in four human tissues: oviduct, skin, colon, and pancreas. We have found striking differences in their tissue distributions. There is little or no β(III) in these tissues, except for the columnar epithelial cells of the colon. β(II) is restricted to very few cells, except in the skin, where it is concentrated in the stratum granulosum. β(I) is widespread in all the epithelia. In the skin it is found in the entire stratum malpighii. In the oviduct, β(I) is found largely in the nonciliated epithelial cells. In the exocrine pancreas, β(I) occurs only in the centroacinar cells and not in the acinar cells; the latter do not stain with any of there antibodies. β(IV) is present at very low levels in skin and pancreas. By contrast, it is prominent in the colon and also in the oviduct, where it occurs in all the epithelial cells, especially in the ciliated cells, with the highest concentrations in the cilia themselves. These results suggest that the regulation of the expression and localization of isotypes in tissues is very complex.