Figure 1.
Tau causes the disappearance of vesicles and organelles from neurites. (A) Peroxisomes: N2a cells were differentiated for 2 d by 1 μM retinoic acid, fixed in methanol, and immunostained for peroxisomes (left) and tubulin (right). In mock-transfected controls (top), peroxisomes and MTs are visible in the cell body and throughout the neurite. In cells stably expressing tau (bottom), peroxisomes are mostly absent from the neurites and clustered around the MTOC in the cell body. These cells also have shorter neurites than the controls, but microtubules are still present throughout the neurites. (B) WGA-labeled vesicles: similar experiment as in A but staining with rhodamine-labeled WGA (left). In mock-transfected cells (top), WGA-stained vesicles (presumably Golgi-derived [Gonatas and Avrameas, 1977]) are visible in the cell body and neurite (inset, proximal neurite). In tau stable cells (bottom), the vesicles are strongly reduced in the neurites, and the trans-Golgi network is more contracted in the cell body. (C) Quantitation of the number of peroxisomes (left) and Golgi-derived vesicles (right) in neurites of N2a cells derived from 20-μm stretches of proximal neurites. In tau-stable cells, the density of peroxisomes decreases to ∼6% of the control cells, and the density of vesicles decreases to ∼25% of the control. (D) Disappearance of neurofilaments and mitochondria from neurites of tau-expressing N2a cells. In control N2a cells (top), neurofilaments (left, stained by antibody SMI32) and mitochondria (center, stained by MitoTracker Red) both extend along the entire length of the neurite, whereas tau (right, stained by antibody K9JA) is not visible in the cells because its endogenous concentration is too low. In tau-stable cells (bottom), neurofilaments and mitochondria are strongly reduced in the neurite and clustered in the cell body, whereas tau is visible in both compartments.