Ultrastructural, tomographic and confocal imaging of the chondrocyte primary cilium in situ

Authors

  • C.G. Jensen,

    Corresponding author
    1. Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
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  • C.A. Poole,

    1. Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
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  • S.R. McGlashan,

    1. Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
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  • M. Marko,

    1. Wadsworth Center for Laboratories and Research, New York State Department of Health, Empire State Plaza, PO Box 509, Albany, NY, USA
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  • Z.I. Issa,

    1. Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
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  • K.V. Vujcich,

    1. Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
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  • S.S. Bowser

    1. Wadsworth Center for Laboratories and Research, New York State Department of Health, Empire State Plaza, PO Box 509, Albany, NY, USA
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Corresponding author. Tel.: +64-(0)9-3737599x86060; fax: +64-(0)9-3737484 c.jensen@auckland.ac.nz

Abstract

Hyaline cartilage chondrocytes express one primary cilium per cell, but its function remains unknown. We examined the ultrastructure of chick embryo sternal chondrocyte cilia and their interaction with extracellular matrix molecules by transmission electron microscopy (TEM) and, for the first time, double-tilt electron tomography. Ciliary bending was also examined by confocal immunohistochemistry. Tomography and TEM showed the ciliary axoneme to interdigitate amongst collagen fibres and condensed proteoglycans. TEM also revealed the presence of electron-opaque particles in the proximal axoneme which may represent intraciliary-transport (ICT) particles. We observed a wide range of ciliary bending patterns. Some conformed to a heavy elastica model associated with shear stress. Others were acutely deformed, suggesting ciliary deflection by collagen fibres and proteoglycans with which the cilia make contact. We conclude that mechanical forces transmitted through these matrix macromolecules bend the primary cilium, identifying it as a potential mechanosensor involved in skeletal patterning and growth.

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