Identification of novel osmosensing receptors in C. elegans

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Project Summary The ability to sense osmolarity changes and maintain fluid osmolarity is required for normal physiological functions of every single cell and thus vital for human health. Fluid imbalance, caused by high osmolarity (hyperosmolarity) or low osmolarity (hypoosmolarity), can lead to irreversible damage to organs and cause lethal neurological trauma. In humans, the osmolarity of body fluids is continuously monitored in the brain and kept within a very narrow range (275-299 mOsm/kg). As little as a one percent increase in blood osmolarity is enough to trigger thirst. A key element for such robust osmoregulation is the molecular osmosensors that detect osmolarity changes. However, the molecular identities of osmosensors in the animal kingdom have remained elusive. The difficulty in identifying osmosensors in animals is partly due to the lack of an unbiased screening system. Previous efforts to identify osmosensors in animals were restricted to TRP channels. However, osmosensors do not necessarily fall into the TRP channel family and thus may have eluded detection. The nematode C. elegans is an ideal model to study osmosensing. Like mammals, C. elegans has osmosensing systems, and conserved signaling molecules have been identified. This, together with its short generation time (~3 days) and facile and rich genetic tools, makes C. elegans an ideal system for identifying novel osmosensors. To identify osmosensors in C. elegans, we designed and conducted a neural activity- based genetic screen. We have identified OSMS-1 and OSMS-2 as candidate osmosensors in C. elegans. Despite this exciting finding, many questions remain unanswered. In the current proposal, we propose to test the hypothesis that OSMS-1 and OSMS-2 are bona fide osmosensors and characterize the molecular mechanisms by which OSMS-1 and OSMS-2 sense osmolarity. We will take a multidisciplinary approach by integrating molecular genetics, behavioral analysis, calcium imaging, electrophysiology, and cryo-EM. To do so, I will receive extensive training on calcium imaging, cell culture, electrophysiological recording, and cryo- EM. The K99/R00 award will allow me to acquire these skills with guidance from my mentors Drs. Shawn Xu and Melanie Ohi, which will help me to launch an independent research career. The proposed work will lead to the identification of the first osmosensors in the animal kingdom, gain a molecular understanding of how osmosensors sense osmotic stimuli, and provide novel insights into osmosensation, osmoregulation and related human diseases.