Sensory neurons concentrate and organize molecules used to detect environmental stimuli into cilia, which are specialized microtubule-based structures on the cell surface that function as cellular antennas. The proteins that constitute the machinery of sensory transduction are synthesized elsewhere and must be separated from other cellular proteins and transported to the cilium. The importance of mechanisms that mediate trafficking of proteins to the sensory cilium is illustrated by disease-causing mutations that disrupt this process. Mutations that compromise ciliary trafficking of the photopigment rhodopsin or the enzyme guanylyl cyclase cause retinal dystrophies marked by photoreceptor degeneration and, ultimately, blindness. Despite the importance of protein trafficking to the cilium, its underlying molecular mechanisms remain poorly understood. We propose to use chemosensory BAG neurons of the nematode C. elegans as a model for discovery of mechanisms that select and transport cargo destined for the sensory cilium. Like vertebrate photoreceptor neurons, BAG neurons use cyclic GMP as a second messenger for sensory transduction, and the enzymes and effectors that control cyclic GMP signals and turn them into electrical signals are highly similar to those found in photoreceptor neurons. Trafficking of proteins to BAG cilia can be measured in situ using high-resolution fluorescence microscopy assays, and powerful genetic tools are available to acutely or chronically manipulate specific molecular pathways in BAG neurons and determine their function in trafficking to the cilium. Importantly, C. elegans permits discovery of novel factors that mediate ciliary trafficking through genetic screens and biochemical approaches. We propose to use this powerful experimental system to (1) delineate a molecular pathway that matches cargo destined for the sensory cilium with specific motors that will carry it through the dendrite to its destination, and (2) determine how trafficking mechanisms are regulated by physiological or developmental cues that trigger remodeling of the BAG cilium. These studies will advance understanding of a cellular process that is essential for sensory neuron function and viability and will integrate cellular trafficking mechanisms with physiological and developmental programs that impact sensory cilia in vivo.
The molecular mechanisms of sensation are organized into specialized cellular membranes - sensory cilia - that function as cellular antennas to detect stimuli such as light and odors. How sensory cilia are generated and maintained remains poorly understood, but it is clear that these processes are essential for sensory neuron function and viability because their dysfunction causes a number of disorders, e.g. retinal dystrophy leading to blindness. To advance understanding of how sensory neurons maintain and remodel sensory cilia, we have established a powerful experimental system that uses the invertebrate C. elegans for high-resolution and discovery-oriented studies of how cells transport material to the cilium under normal conditions and in response to physiological stress and developmental programs.
