Fig. 2 Apparent free MTs are not growing ends of long stable MTs. Correlative fluorescence and electron microscopy of the same MT. (A) Cy-3 MTs in living PtK1 cell just before fixation; (B) tubulin immunofluorescence staining; (C) merged image of Cy-3 tubulin in red and tubulin antibody staining in green, showing essential identity. (D) electron microscopy of a free MT in rat embryo fibroblast visualized as platinum replica after actin removal by gelsolin treatment. Inset: Cy-3 MTs in same cell just before extraction and fixation. Boxed region of inset shown in (D). Red overlay of MTs in the EM image shows exact correspondence with the fluorescence image. Scale bars, A-C, 3 µm; D, 1 µm.