article nature genetics • volume 33 • february 2003 129 Polycystins 1 and 2 mediate mechanosensation in the primary cilium of kidney cells Surya M. Nauli 1 *, Francis J. Alenghat 2 , Ying Luo 1 *, Eric Williams 1 , Peter Vassilev 3 , Xiaogang Li 1 , Andrew E.H. Elia 1 , Weining Lu 1 , Edward M. Brown 3 , Stephen J. Quinn 3 , Donald E. Ingber 2 & Jing Zhou 1 *These authors contributed equally to this work. Published online: 6 January 2003; doi:10.1038/ng1076 Several proteins implicated in the pathogenesis of polycystic kidney disease (PKD) localize to cilia. Furthermore, cilia are malformed in mice with PKD with mutations in TgN737Rpw (encoding polaris). It is not known, how- ever, whether ciliary dysfunction occurs or is relevant to cyst formation in PKD. Here, we show that polycystin- 1 (PC1) and polycystin-2 (PC2), proteins respectively encoded by Pkd1 and Pkd2, mouse orthologs of genes mutated in human autosomal dominant PKD, co-distribute in the primary cilia of kidney epithelium. Cells iso- lated from transgenic mice that lack functional PC1 formed cilia but did not increase Ca 2+ influx in response to physiological fluid flow. Blocking antibodies directed against PC2 similarly abolished the flow response in wild- type cells as did inhibitors of the ryanodine receptor, whereas inhibitors of G-proteins, phospholipase C and InsP 3 receptors had no effect. These data suggest that PC1 and PC2 contribute to fluid-flow sensation by the primary cilium in renal epithelium and that they both function in the same mechanotransduction pathway. Loss or dysfunction of PC1 or PC2 may therefore lead to PKD owing to the inability of cells to sense mechanical cues that normally regulate tissue morphogenesis. 1 Renal Division, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, 4 Blackfan Circle, Boston, Massachusetts 02115, USA. 2 Vascular Biology Program, Departments of Pathology and Surgery, Children’s Hospital and Harvard Medical School, Boston, Massachusetts, USA. 3 Endocrine-Hypertension Division, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, USA. Correspondence should be addressed to J.Z. (e-mail: zhou@rics.bwh.harvard.edu). Introduction Autosomal dominant PKD is a common lethal monogenic disorder, characterized by progressive development of fluid- filled cysts in the kidney. Mutations in PKD1 and PKD2, which respectively encode integral membrane proteins PC1 and PC2, account for all cases of autosomal dominant PKD 1–3 . PC1 activates a G-protein signaling pathway by bind- ing and activating heterotrimeric Gαi/o proteins 4,5 , which, in turn, modulate voltage-gated Ca 2+ and K + channels 5 . PC2 functions as a Ca 2+ -permeable cation channel 6–9 . PC1 and PC2 are known to heterodimerize 3,5,10 . The mechanism by which mutations in PKD1 and PKD2 lead to abnormal kidney develop- ment, however, is yet unclear. One clue to the pathogenesis of PKD is that, in addition to PC2, two other proteins, cystin and polaris, mutant forms of which are also associated with PKD 11,12 , localize to the primary cilium of renal epithelial cells 12–14 . A cilium is a tiny hair-like appendage about 0.25 μm in diameter that contains a micro- tubule bundle as a core. Cilia, which extend from the surfaces of many cell types and are found in many species, contribute to fluid movement 15 , chemoreception 16 and patterning of the left–right body axis 17 . The primary cilium is a non-motile cil- ium with a microtubule arrangement of 9+0; it is unique in that, in almost all cases, only one primary cilium is expressed on the apical surface of each epithelial cell. Kidney epithelial cells have well developed primary cilia that extend into the tubular lumen. The integrity of cilia in mice with mutations in Pkd2 is unknown, but shortened cilia have been found in renal tubules of mice with mutations in TgN737Rpw 18 . Mice with mutations in TgN737Rpw or Pkd2 develop defects in left–right symme- try 19,20 in addition to PKD. Although several proteins involved in PKD pathogenesis are expressed in cilia, it is not clear whether or how ciliary dysfunc- tion results in abnormal kidney development and cyst formation. The contribution of PC1 to cilium function is not known. Recent work has shown that the primary cilium of the kidney epithelium mediates sensation of mechanical signals produced by apical fluid shear stress and its transduction into an intracellular Ca 2+ © 2003 Nature Publishing Group http://www.nature.com/naturegenetics