PROJECT SUMMARY / ABSTRACT Ciliopathies are a collection of diseases that feature genetic mutations that impair primary cilia morphology or function and are characterized by symptoms that include developmental disorders, obesity, cognitive and behavioral deficits in humans. Primary cilia are immotile organelles that protrude off neuronal soma often adjacent to the nuclear compartment. A growing body of evidence indicates that extracellular stimuli (i.e., neuromodulators) transmits specialized signaling through G protein-coupled receptors (GPCRs) located on neuronal primary cilia to influence transcriptional changes and neuronal activity. Thus, determining how to specifically target neuronal ciliary GPCRs, will lead to novel therapeutic approaches for neurological and neuropsychiatric diseases. This proposal will focus on identifying selective ciliary targeting mechanics employed by neural Gαi-coupled GPCRs and the impact of ciliary GPCR signaling on gene transcription. We found that in brain sections, neural Gαi-coupled GPCRs, such as the mu opioid receptor, are expressed in neuronal primary cilia of some neuronal populations but not others suggesting cell and/or receptor-selective ciliary targeting machinery. In Specific Aim 1, we dissect whether ciliary targeting mechanics are cell-specific and/or receptor-selective in three distinct cell types. In Specific Aim 2, we employ Proteomics-based approaches to identify novel GPCR-associated proteins involved in ciliary targeting of Gαi-coupled GPCRs in cells and brain tissue. In Specific Aim 3, we will evaluate the contribution of ciliary Gαi-coupled GPCR cyclic-AMP signaling to neuronal transcription. Collectively, this proposal will attempt to discern the mechanisms underlying ciliary targeting of neuronal GPCRs and the neuromodulatory function of ciliary GPCRs.