Schmidtea mediterranea: a model system for analysis of motile cilia

Cilia are cellular organelles that appeared early in the evolution of eukaryotes. These structures and the pool of about 600genes involved in their assembly and function are highly conserved in organisms as distant as single-cell protists, like Chlamydomonas reinhardtti, and humans (Silflow and Lefebvre, 2001). A significant body of work on the biology of cilia has been produced over the years, with the help of powerful model organisms including C. reinhardtti, Caenorhabditis elegans, sea urchins, and mice. However, specific limitations of these systems, especially regarding the ability to efficiently study gene loss-of-function, warrant the search for a new model organism to study cilia and cilia-based motility. Schmidtea mediterranea is a species of planarian (Class: Tubellaria) with a well-defined monostratified ciliated epithelium, which contributes to the motility of the organism, in addition to other more specialized ciliary structures. The use of S. mediterranea as an experimental system to study stem cell biology and regeneration has led to a recently sequenced genome and to the development of a wide array of powerful tools including the ability to inhibit gene expression via RNA interference. In addition, we have developed and describe here a number of methods for analyzing motile cilia in S. mediterranea. Overall, S. mediterranea is a highly versatile, easy to maintain, and genetically tractable organism that provides a powerful alternative model system for the study of motile cilia.