Microtubules: Transmission electron microscopic images

Microtubules assembled in vitro from tubulin in  the presence of microtubule-associated proteins (MAP1, MAP2, tau).
Whole-mount preparation, uranyl acetate staining.

Cross-sections of microtubules assembled in vitro from microtubule protein (tubulin plus microtubule-associated proteins) in the presence of taxol.
Tannin-glutaraldehyde fixation, ultrathin sectioning, and poststaining with lead citrate.
The microtubules have typically 13 or 14 protofilaments.
Taxol, known to promote tubulin assembly and to stabilize microtubules, causes the appearance of some C-shaped protofilament ribbons.
 

Cross sections, demonstrating the variability of the protofilament number of microtubules re-assembled under different in vitro conditions
Böhm K.J., Vater W., Fenske H., Unger E.: Effect of microtubule-associated proteins on the protofilament number of microtubules assembled in vitro.
Biochim. Biophys. Acta 800, 119-126 (1984)

A-D -  Microtubules with MAPs (see arrow heads) attached to their surface
E-F -  MAP-free microtubules

Microtubules labelled with monoclonal anti-MAP2 antibody and 10-nm gold conjugated anti-mouse anti-IgG

Cross-sectioned microtubules incubated with DAPI. The DNA-fluorochrome DAPI binds to the surface of microtubules and enables the binding of additional protofilaments
Vater W., Böhm K.J., Unger E.: Effects of the fluorescence dye DAPI on microtubule structure in vitro: Formation of novel types of tubulin assembly products.
Acta histochem. 94, 54-66 (1993)

Ca²⁺-induced tubulin rings.  Whole-mount preparation, uranyl acetate staining.

a,b - Ultrathin cross sections of glutaraldehyde-fixed, vestopal-embedded sheets
c,    - Zn²⁺-induced tubulin sheets, whole-mount preparation, negative staining with uranyl acetate

Yeast spindle microtubules