title: Primary cilia are not calcium-responsive mechanosensors.
abstract: Primary cilia are solitary, generally non-motile, hair-like protrusions that extend from the surface of cells between cell divisions. Their antenna-like structure leads naturally to the assumption that they sense the surrounding environment, the most common hypothesis being sensation of mechanical force through calcium-permeable ion channels within the cilium. This Ca(2+)-responsive mechanosensor hypothesis for primary cilia has been invoked to explain a large range of biological responses, from control of left-right axis determination in embryonic development to adult progression of polycystic kidney disease and some cancers. Here we report the complete lack of mechanically induced calcium increases in primary cilia, in tissues upon which this hypothesis has been based. We developed a transgenic mouse, Arl13b-mCherry-GECO1.2, expressing a ratiometric genetically encoded calcium indicator in all primary cilia. We then measured responses to flow in primary cilia of cultured kidney epithelial cells, kidney thick ascending tubules, crown cells of the embryonic node, kinocilia of inner ear hair cells, and several cell lines. Cilia-specific Ca(2+) influxes were not observed in physiological or even highly supraphysiological levels of fluid flow. We conclude that mechanosensation, if it originates in primary cilia, is not via calcium signalling.
authors.affiliation: Department of Cardiology, Howard Hughes Medical Institute, Boston Children's Hospital, Boston, Massachusetts 02115, USA.
authors.forename: M
authors.initials: M
authors.lastname: Delling
authors.affiliation: Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: A A
authors.initials: AA
authors.lastname: Indzhykulian
authors.affiliation: Department of Cardiology, Howard Hughes Medical Institute, Boston Children's Hospital, Boston, Massachusetts 02115, USA.
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.affiliation: Image and Data Analysis Core (IDAC), Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: T
authors.initials: T
authors.lastname: Xie
authors.affiliation: Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: D P
authors.initials: DP
authors.lastname: Corey
authors.affiliation: Department of Cardiology, Howard Hughes Medical Institute, Boston Children's Hospital, Boston, Massachusetts 02115, USA.|Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: D E
authors.initials: DE
authors.lastname: Clapham
mesh_terms: D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D020013:Calcium Signaling; D002923:Cilia / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000166:cytology; D004847:Epithelial Cells / Q000166:cytology; D005260:Female; D006199:Hair Cells, Auditory, Inner / Q000166:cytology; D007668:Kidney / Q000166:cytology; D008297:Male; D040542:Mechanotransduction, Cellular; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological
chemical_list: D002118:Calcium