Structural maintenance and chemosensory function of human airway motile cilia.

Cilia are finger-like projections that extend from the surface of most cells. These microtubule-based structures serve important mechanical or sensory functions. Motile cilia have been implicated in fluid movement whereas the non-motile primary cilia have been shown to play a role in sensory signal transduction. There exists a dichotomy in the field that primary cilia have only sensory function and motile cilia only have mechanical function. The central question of this thesis project is "what are the structural and functional components of airway motile cilia and are these cilia sensory?" In Chapter 2, the role of Bardet-Biedl Syndrome (BBS) proteins in maintaining the structure and function of airway motile cilia is examined. We found that BBS proteins localize to the cilium and to ciliary-related structures in human airway epithelia. Using mutant mice we found that BBS proteins play an essential role in motile cilia structure and the loss of BBS proteins results in reduced ciliary beat. These proteins have previously been shown to play a role in primary cilia structure and function, and our studies indicate a novel function for BBS proteins. Chapter 3 examines the sensory role of motile cilia. Our data show that bitter taste receptors and components of the bitter taste signal transduction pathway localize to the motile cilia or to the ciliated cells. Ciliated cells also show an increase in intracellular calcium in response to bitter compounds, accompanied by a corresponding increase in cilia beat. The increase in intracellular calcium originates at the ciliated cells and is propagated to adjacent cells. Chapter 4 delves into the possibility that every motile ciliated cell also contains a single, primary cilium. Using immunostaining and Smoothened as a marker for primary cilia, we found that every group of motile cilia contains a single Smoothened-positive cilium. Furthermore, downstream components of the Sonic Hedgehog pathway are also present in ciliated cells. Chapter 6 is a summary chapter including possible explanations for observed outcomes and plans for future experiments. Our results indicate that the divide between primary and motile cilia may not be as great as has been previously thought.