Microtubules can be seen in a bundle in this negatively stained preparation to the left. Recall that negative staining starts by immobilizing the preparation on plastic on an electron microscopic grid. Then heavy metal stain is deposited around the structures, delineating their structure. This preparation may allow you to see the tubulin molecules in the protofilaments.
This transmission electron micrograph to the right shows the microtubules in longitudinal ultrathin section. Note, the tubulin molecules cannot be visualized in this preparation.
Early electron microscopists found that in order to preserve microtubules, they had to fix the cells in glutaraldehyde at room temperature. Why do you think the temperature conditions were important? What might happen if they fixed the cells for 30 min in the cold?
Sometimes, you can see collections of microtubules at the periphery of cells. They may be involved in both motility and cytoskeletal functions in this region. It is difficult to see the structure of separate microtubules. Also, microfilaments may also be accumulating in this region.
The extensive distribution of microtubules can really be appreciated in the light microscope after immunolabeling for tubulin with fluorescein-labeled antibodies. This micrograph shows cells in culture labeled for tubulin. The labeling is so fine, the small microtubules can be delineated.
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