Imaging and Functionality of Primary Cilia Kidney cells contain solitary immotile hair-like structures, called primary cilia, that protrude from the cell membrane into the cavity of the nephron, the basic structural unit of the kidney which filters blood. The function of primary cilia was originally unknown; however new work has identified a link between the malfunction of primary cilia and autosomal dominant polycystic kidney disease (ADPKD), the most common single gene disorder to affect the kidney. ADPKD causes the growth of fluid-filled epithelial cysts which progressively destroys kidney function leading to renal failure. The malfunction of primary cilia in ADPKD suggests that these organelles might act as flow sensors, signalling changes in luminal fluid flow to control cross-membrane ion transport along the nephron.
SEM image of a primary cilium on fixed MDCK cells. |
AFM image of a primary cilium on fixed MDCK cells. |
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An interdisciplinary approach has been adopted to investigate the biophysical properties of
the primary cilium. Madin-Darby Canine Kidney (MDCK) cells have been imaged using Scanning
Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), observing both fixed cells and
cells in vivo. Primary cilia have also been removed from the MDCK cell surface and their
physical properties investigated. In particular, a combined AFM/confocal microscope has been
used to compare the physical structure of the primary cilium with some of its chemical signature
using immunofluorescence. The staining observed confirms that the structures protruding from
the cells in the AFM images are the primary cilia, and through antibody-recognition imaging, it
has been possible to locate specific proteins on the surface of the primary cilium.
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Combined confocal (immunofluorescence for tubulin and actin) and AFM images, the latter presented as an overlay in the centre of the confocal image. |