The distribution of tau and HMW microtubule-associated proteins in different cell types

To investigate the distribution of the tau and HMW microtubule-associated proteins (MAPS) and their relationship to microtubules in vivo, we have examined a wide variety of avian and mammalian cell types by immunofluorescence with antisera to these two proteins. Anti-HMW serum stains cytoplasmic microtubules in all mammalian cell types so far examined. However, anti-tau serum did not stain cytoplasmic microtubules in rat glial cells or in pig kidney cells. In mammalian neurons, fibroblasts and neuroblastoma cells, the staining of microtubules with both sera was similar. Anti-HMW serum did not stain primary cilia or cilia on isolated tracheal epithelial cells, whereas anti-tau serum did stain these ciliary microtubules. We believe these results indicate that some types of microtubules may be associated with only the tau or the HMW protein, whereas others may be associated with both tau and HMW protein. With respect to avian cells, anti-HMW serum did not stain microtubules in any of the three cell types examined, whereas the anti-tau serum stained them in two cell types. Furthermore, double diffusion tests indicated that anti-pig tau serum will precipitate both pig brain tau and tau protein isolated from chick brain, whereas anti-HMW serum will precipitate only pig brain and not chick brain HMW protein. We believe tau protein is antigenically similar in both avian and mammalian cells, whereas the HMW protein from these two sources is antigenically distinct.