BETA(IV) IS THE MAJOR BETA-TUBULIN ISOTYPE IN BOVINE CILIA

Four different isotypes of beta-tubulin are known to be expressed in m ammalian brain. Monoclonal antibodies against beta(II), beta(III), and beta(IV) were used to characterize the beta-tubulin isotypes in two c iliated bovine tissues: non-motile sensory cilia of retinal rod cells and motile cilia of tracheal epithelium. Retinal rod outer segment (RO S) connecting cilia and cytoskeletons were purified by density gradien t centrifugation. This preparation contained more than 20 major protei n components, as shown by dodecyl sulfate polyacrylamide gel electroph oresis. Electroblots were used to quantitate the relative amounts of b eta(II), beta(III), and beta(IV). The connecting cilium and cytoskelet on of the rod outer segment has less type III beta-tubulin than brain and more type IV. The ratio of beta(IV) to beta(II) in the ROS is near ly a factor of 8 larger than in brain. Electron microscopic immunocyto chemistry showed extensive labeling of cilia by anti-type IV in thin s ections of retinas and trachea, and also in purified ROS cilia and cyt oskeletons. Labeling of cilia by anti-beta(II) was also observed, alth ough in the purified ROS cilia and cytoskeleton, the anti-beta(II) lab eling was primarily on amorphous non-ciliary material. The results sug gest that both motile and non-motile cilia are enriched in the type IV beta-tubulin subunit.