DESCRIPTION (provided by applicant): Serotonin (5-hydroxytryptamine; 5-HT) is a monoaminergic neurotransmitter that modulates numerous sensory and motor processes as well as a wide variety of behaviors including sleep, appetite, pain perception, locomotion, thermoregulation, hallucinations, and sexual behavior. Recent studies from our laboratory have indicated that the function of the 2C-subtype of serotonin receptor (5-HT2 c R) is modulated by a novel RNA modification process referred to as RNA editing. Editing of 5-HL2cR transcripts is responsible for the tissue-specific expression of as many as twenty-four 5-HT2cR isoforms and is proposed to represent a regulatory mechanism by which cells modulate their response to extracellular signals by altering the efficacy and specificity of receptor/G-protein interactions; the long term objectives of the proposed research are to define the cellular mechanisms involved in the regulation of serotonergic signal transduction in the central nervous system. We propose to examine the signaling properties of distinct 5-HT2cR isoforms using a high-throughput, cell-based assay to identify functional interactions between 5-HT, cR isoforms and the a-subunits of several heterotrimeric G-proteins. These studies will be extended to examine the functional responses of other edited 5-HT2cR isoforms that are highly expressed in the rat and human brain and to dissect the 5-HT2cR-activated signaling pathways leading to activation of phospholipase D, mitogenactivated (MAP) kinase and rearrangements of the actin cytoskeleton. To examine the physiological relevance of multiple, edited 5-HT2cR isoforms, mice capable of expressing only, a single 5-HT2CR isoform will be generated by targeted gene modification in embryonic stem cells; the non-edited (INI) and fully-edited (VGV) 5-HT2c R isoforms have been selected for these studies, as they demonstrate the greatest differences in receptor: G-protein coupling efficacy In additional to gross alterations in animal phenotype and brain morphology, mutant mice will be examined for alterations in physiological systems in which the 5-HT2cR has already been implicated, including tumorigenesis, seizure activity, feeding behavior, locomotor activity and hippocampal function. To further examine the role of 5-HT2cR editing in cellular transformation, NIH-3T3 cells expressing specific 5-HT2cR isoforms will be assessed for a number of transformed cellular characteristics including increased mitogenesis, loss of contact inhibition, loss of anchorage dependence and the ability to generate tumors in nude mice. It is anticipated that these studies will provide new insights concerning the regulation of cellular processes involved in the transduction of serotonergic signals and the role(s) of multiple serotonin receptors in the nervous system.