Table I

Quantitation of the Phenotypic Effects of Tau Overexpression in N2a-Neuroblastoma Cells

N2a tau40N2a mock
Neurites   5.4%15%
(length >30 μm)
Mitochondria in neurites17%94%
(>6 per neurite)
ER distribution82%23%
  • A minimum of 150 cells were analyzed in four (neurite length and mitochondria) or three (ER distribution) independent experiments. In differentiated, mock-transfected cells, 15% of the cells developed neurites longer than 30 μm, whereas, in tau-stable cells, this value drops to only 5.4%. The effect of tau-overexpression becomes even more impressive when analyzing the mitochondria present in the neuritic structures: only 17% of tau-stable cells transported more than six mitochondria into their neurites, compared with 94% of control cells. The average number of mitochondria in the control cells was ∼10–20 per neurite (data not shown). The ER was regarded as clustered when it did not surround the nucleus of the cells. In tau-stable cells, up to 82% displayed this phenotype. In contrast, in mock-transfected cells, only 23% of cells had a similar appearance.