UNIVERSITY OF MASSACHUSETTS

The long-term goal of the proposed research is to reveal the physiological functions and in vivo mechanisms of G protein-coupled receptor (GPCR) endocytosis and postendocytic trafficking. GPCRs are the largest family of membrane receptors that receive sensory stimuli and mediate responses to neurotransmitters, neuropeptides, hormones, cytokines and growth factors. Numerous GPCRs undergo endocytosis upon stimulation, and get recycled back to the membrane after the stimulating ligand is removed. This cycle of endocytosis and recycling may enable the cell to adapt to the changing environment, and could be also required for the receptor to dissociate from the binding ligand and become resensitized. Failure of these processes has been implicated in drug tolerances such as that to morphine. Although a large body of works has elicited various mechanisms of receptor endocytosis in cultured cells, the studies on GPCR endocytosis in intact organisms are very limited. More importantly, it is unknown how the endocytosed receptors are recycled back to the cell surface. We have been using the Drosophila light receptor Rh1 rhodopsin as a model to study in vivo GPCR signaling and regulation. Recently we identified a null mutant of a gene encoding a CUB- and LDLa-domain protein (CULD), and found that the mutant photoreceptor neurons accumulated a huge amount of endocytic vesicles containing Rh1 protein, probably due to blocked recycling. We propose to take advantage of this culd mutant to study the mechanisms of Rh1 endocytosis and recycling, and to characterize their impacts on the visual sensory function. Using a combination of molecular genetic, biochemical and electrophysiological approaches, we will 1. Confirm that the CULD protein is required for the recycling of Rh1 in photoreceptors 2. Test the hypothesis that loss of CULD impairs the development of light sensitivity in photoreceptors

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