Polycystic kidney disease, cilia, and planar polarity.

Cystic kidney diseases are characterized by dilated or cystic kidney tubular segments. Changes in planar cell polarity, flow sensing, and/or proliferation have been proposed to explain these disorders. Over the last few years, several groups have suggested that ciliary dysfunction is a central component of cyst formation. We review evidence for and against each of these models, stressing some of the inconsistencies that should be resolved if an accurate understanding of cyst formation is to be achieved. We also comment on data supporting a model in which ciliary function could play different roles at different developmental stages and on the relevance of dissecting potential differences between pathways required for tubule formation and/or maintenance.