Fig. 1.

Tau distribution in saponin-extracted cultured hippocampal neurons. A, Double staining for tau (left) and MAP2 (right) of saponin-extracted neurons. Whereas MAP2 is present in all neurites, including the growth cones and the cellular soma, anti-tau staining is concentrated in the distal portion of the axonal shaft (arrowheads). B, Double staining for tau (left) and actin filaments (right) in saponin-extracted neurons. Note that anti-tau staining is restricted to the distal axonal shaft and the proximal growth cone (arrowheads), whereas actin filaments are prominent in the distal growth cones, including filopodia. For all experiments, cells were grown for 3 d in serum-free medium. Cells were extracted and fixed as described under Materials and Methods. Tau-specific staining was obtained by affinity-purified tau polyclonal and MAP2 staining by monoclonal anti-MAP2 antibody (AP20). Double staining in A used FITC-coupled donkey anti-rabbit and Texas Red-coupled goat anti-mouse antibody. Actin filaments were visualized with rhodamine-coupled phalloidin in the secondary antibody reaction. Scale bar, 20 μm.