Table 1.

In these experiments it was not possible to stain for endogenous tau because the Abs available for this were mouse monoclonal, and the Abs against detyr-tubulin and Ac-tubulin were also from mouse. Thus we could not evaluate directly the effectiveness of tau sequestering in these experiments. However, in other experiments in which we stained Ab-injected cells for endogenous tau and the injected Ab, the large tau aggregates in the cell bodies also stained strongly for the injected Ab. Furthermore, the presence of a large tau aggregate in the cell body always correlated with the absence of tau staining in the distal axon. So, in the present experiments we evaluated the degree of tau sequestering indirectly by examining the Ab-injected cells for the presence of large aggregates of injected Ab in the cell body. The cells were extracted before fixation according to Procedure 3 as described in Materials and Methods and then were stained for the injected Abs as well as for the indicated tubulins. The extraction procedure removes most of the injected Ab not associated with the large tau aggregates in the cell body and proximal axon (data not shown), making the aggregates especially easy to visualize. All Ab-injected cells analyzed for these experiments had large aggregates of injected Ab in the cell body.

*Number of axons analyzed, injected/uninjected. Tyr-tubulin levels were compared in control and Ab-injected cells in two other experiments in which the cells were double-stained for tyrosinated tubulin and endogenous tau. In these experiments the amount of tyr-tubulin in MTs in injected axons was 135 and 97% of that in uninjected axons. The amount of tau in the injected axons was 7 and 11%, respectively, of that in the controls. The mean ± SD of tyr-tubulin in injected cells as a percentage of that in control cells for all experiments injecting tau Abs = 99 ± 18 (n = 7). The values obtained from anti-tau-injected cells were not significantly different from uninjected cells at p > 0.1 (except for the data for tyr-tub in Experiment 3, in which p = 0.0909).