Microtubule-Membrane Interactions in Cilia and Flagella

Abstract

This chapter discusses the microtubule-membrane interactions in cilia and flagella. Cilia and eukaryotic flagella are specialized organelles that project from the cell surface. They are responsible for the movements of whole cells and for the movements of materials across cell surfaces. All eukaryotic cilia and flagella possess the same uniform substructure of nine doublet microtubules (the outer doublets) surrounding two single central microtubules. The microtubule-membrane bridges, along the long axis of the doublet microtubule, are the second major sites to which membranes are attached. These bridges are responsible for the attachment of the doublet microtubules to the ciliary necklace and ciliary granule plaques at the ciliary base, to accessory fibers in sperm, protozoans, and ctenophores, to extraciliary structures such as mastigonemes, and to adjacent ciliary or plasma membranes as in ctenophores, mussel gill laterofrontal cilia, and in trypanosomes. The morphological studies of cilia in a wide variety of organisms revealed that the microtubules comprising the axonemes are attached to the membrane where they are enveloped.