primary cilium
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||image_reduire{0,60}|inserer_attribut{alt,Primary cilia (non-motile cilia) and cystogenesis}) ] [ (
||image_reduire{0,60}|inserer_attribut{alt,Link between primary cilium and planar cell polarity pathway}) ]
Primary cilia are single, hair-like structures appearing on the apical surface of cells.
Primary cilia link mechanosensory, visual, osmotic, gustatory and other stimuli to mechanisms of cell-cycle control and epithelial cell polarity.
The architecture of the microtubule backbone distinguishes motile cilia, in which nine doublets of microtubules surround a central pair (9+2), from primary cilia, in which the central pair of microtubules is absent (9+0).
Functions
Primary cilia link mechanosensory, visual, osmotic, gustatory and other stimuli to mechanisms of cell-cycle control and epithelial cell polarity.
Primary cilia are essential for left-right axis determination in the embryo as demonstrated by mouse models of insertional mutagenesis.
Pathology
Recent data have shown molecular anomalies of the primary cilium as the key mechanism of renal cystogenesis in human genetic cystic kidney diseases.
Interestingly, primary cilia are also present in the embryonic node and are essential for left-right axis determination.
Several mouse models with defects in nodal ciliary synthesis and/or function have been shown to develop laterality disturbances.
One of these, the inv mouse, is a model of insertional mutagenesis of the inv mouse gene. The inv gene is the murine homolog of the NPHP2/INVS gene, a gene mutated in human nephronophtisis type 2. Homozygote mice exhibit a complex phenotype: consistent situs inversus in all cases, and severe cystic changes of the kidneys and pancreas.
Interestingly, the protein product of the human NPHP2/INVS gene, inversin, has recently been shown to be present in the cilia of both the embryonic node and renal tubules. This thus links renal cysts formation to mutations of a primary cilia gene and left-right axis determination.
See also
motile cilia and flagella
References
Davenport JR, Yoder BK. An incredible decade for the primary cilium: a look at a once-forgotten organelle. Am J Physiol Renal Physiol. 2005 Dec;289(6):F1159-69. PMID: #16275743#
Pan J, Wang Q, Snell WJ. Cilium-generated signaling and cilia-related disorders. Lab Invest. 2005 Apr;85(4):452-63. PMID: #15723088#