Cilia and models for studying structure and function.

Because of the highly conserved nature of the ciliary axoneme, researchers studying the structure and function of cilia have used many different model systems. Each system has advantages and disadvantages, but all provide important information relevant to the understanding and treatment of the ciliopathies. For example, Chlamydomonas is easy to grow and amenable to rapid genetic manipulation and therefore is excellent for motility studies and studies of the structural components of the axoneme. However, this organism cannot be used to study developmental defects or physiological abnormalities that occur in higher organisms (e.g., mucociliary clearance). Human cilia have the advantage of being obtained directly from the tissue of interest but are obtainable only in limited quantities and are difficult to manipulate. Mouse models of ciliopathies are more difficult to study than Chlamydomonas but can be useful to elucidate more aspects of the human diseases. In this review, the overlap between the structure of primary and motile cilia is discussed, and recent advancements in our understanding of cilia structure and function using these three different model systems are presented. Potential therapeutic approaches, based on fundamental knowledge gained from work in these model systems, are also presented.