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. 2007 Mar 14;27(11):2896–2907. doi: 10.1523/JNEUROSCI.4674-06.2007

Figure 6.

Figure 6.

Expression of tau, but not of tau plus MARK2 reduces mitochondrial density and movement in neuronal dendrites and cell bodies. Confocal stacks with optical slices of 1 μm were taken and evaluated. A, Cell body of an untransfected neuron stained with MitoTracker 589 (top center: x–y plane; above, x–z plane; left, y–z plane). B, D, and E show only one optical slice of 1 μm. B, Mitochondria occur throughout the cell body and dendrites. C, After 3d days of tau transfection, the cell body is devoid of mitochondria. D, Dendrites of tau transfected cells display a loss of mitochondria 3 d after transfection. E, A neuron transfected with tau plus MARK2. MitoTracker 589 (all mitochondria) and MitoFluor Far Red 680 (active mitochondria) were added to the culture to visualize active and inactive mitochondria. Doubly transfected cells do not show a loss of mitochondria or membrane potential after 3 d of transfection. F, Kymographs showing that in untransfected cultures (top), mitochondria can perform saltatory movements in both directions (prox, proximal; dist, distal) (horizontal arrow, 10 μm; vertical arrow, 1 min). In neurons transfected with tau (middle), mitochondria show almost no movement (time point was chosen at 2 d after transfection to visualize mitochondria before they disappear). Doubly transfected neurons (bottom) display saltatory movements in both directions, comparable with control. G, Quantification of stationary mitochondria (immobile >10 min), and anterograde and retrograde movements of mitochondria in dendrites. Transfection of tau for 2 d increases the fraction of immobile mitochondria to ∼100%, but movement is partially rescued in doubly transfected cells. Conversely, the mobile fraction decreases strongly after tau-transfection in both directions (middle and left), but is rescued by tau plus MARK2 transfection. (Number of mitochondria in three different neurons each: control, nstatic = 18, nantero = 12, nretro = 9; Tau, nstatic = 25, nantero = 2, nretro = 2; MARK2 plus tau, nstatic = 22, nantero = 7, nretro = 9.) Scale bars: (in C, E) A–E, 10 μm. Error bars indicate SE.