Primary cilia in normal and pathological tissues

The medical literature in pathology contains a surprising number of anecdotal reports of primary cilia, with authors often expressing some incredulity at finding such organelles. In this update of an earlier review, I will argue that primary cilia should by now be regarded as regular cell organelles, not some form of atypical response to unusual circumstances. In all situations in which their presence is essential, they unquestionably act as sensory transducers. Detection by electron microscopy has been the most reliable means until recently, but is time-consuming and slow for any systematic investigation or experimental approach. Immunostaining with an antibody direct against detyrosinated tubulin is rapidly changing the situation, and we can now detect their presence, frequency, disposition and overall characteristics relatively quickly, allowing better statistical analysis and correlations in abnormal physiological and pathological conditions. To be useful and meaningful, comparative studies need a reliable database of information about primary cilia under 'normal' circumstances. It is hoped that such work will in itself give much further insight into the general significance of these organelles, especially combined with the more experimental approaches that can now be adopted in the study of their development and function, which looks increasingly promising with the new technological improvements.