Microtubules

Abstract

The presence of elongated tubular structures in cilia and flagella was recognised during the early days of electron microscopy (Fawcett and Porter, 1954). But although the term ‘microtubule’ was introduced by Slautterback (1963) as a result of the examination of cells fixed in osmium tetroxide, it was the introduction of glutaraldehyde as a fixative, together with improvements in embedding and staining techniques, which led to a proper appreciation of the widespread occurrence of microtubules, apart from those in cilia, flagella, basal bodies and centrioles, as a feature of the cytoplasm of virtually all types of eukaryotic cell. It has also become clear that microtubules are more stable in some situations than in others; those in cilia and flagella are the most stable, while those found in the mitotic spindle and more generally throughout the cytoplasm are much more easily disrupted by, for example, low temperatures, high hydrostatic pressures, high Ca²⁺ concentrations, and by the so-called ‘spindle poisons’. It is the general cytoplasmic variety of microtubule with which we are chiefly concerned, but we shall also take account of information derived from work on microtubules found elsewhere in the cell.