Polarity of some motility-related microtubules.

Abstract

The structural polarity of microtubules from several systems in which these fibers are thought to contribute to cell motility was investigated. By using a method for displaying microtubule polarity in EM, it was found that the A and B subfibers of Tetrahymena ciliary outer doublets and the inner pair of single microtubules are oriented with their plus ends (i.e., their fast-growing ends) distal to the basal body. All of the microtubules in the axopodia of the heliozoan Actinosphaerium and all of the microtubules in the processes of melanophores from the angelfish Pterophyllum are likewise oriented with their plus ends distal to the cell centers. Apparently, cellular systems for motility, and even those capable of bidirectional motility, can be constructed from microtubules of a single polarity.