Figure 7.

The ratio between plus- and minus-end–directed transport of mitochondria is altered by tau overexpression. Tau-stable and control cells were treated with nocodazole to disrupt the microtubule cytoskeleton and to achieve an even distribution of mitochondria in both cell lines. The drug was washed out after 2 h of incubation and mitochondria were stained with MitoTracker™ Red. Translocations of the organelles were then recorded for 2 min with a time interval of 1 s. The direction of movement was regarded as plus-end directed when the organelles were transported to the periphery (+), minus-end directed when transport was towards the nucleus (−), and neutral (−/+) when movement was vertical to the axis between nucleus and periphery of the cells. Note that the relative number of transported mitochondria is significantly lower for all three groups in the tau-stable cell line (P < 0.0001, two tailed Student's t test). However, in tau-stable cells, the plus-end– directed movement is significantly more affected (∼10-fold) than the reverse direction (2-fold). This leads to the phenotype of mitochondrial clustering. At least 40 cells were analyzed for quantitation, the total number of mitochondria ranged between 100 and 700 in both cell lines.