Agonist-independent GPCR activity regulates anterior-posterior targeting of olfactory sensory neurons.

G-protein-coupled receptors (GPCRs) are known to possess two different conformations, active and inactive, and they spontaneously alternate between the two in the absence of ligands. Here, we analyzed the agonist-independent GPCR activity for its possible role in receptor-instructed axonal projection. We generated transgenic mice expressing activity mutants of the β2-adrenergic receptor, a well-characterized GPCR with the highest homology to odorant receptors (ORs). We found that mutants with altered agonist-independent activity changed the transcription levels of axon-targeting molecules--e.g., Neuropilin-1 and Plexin-A1--but not of glomerular segregation molecules--e.g., Kirrel2 and Kirrel3--thus causing shifts in glomerular locations along the anterior-posterior (A-P) axis. Knockout and in vitro experiments demonstrated that Gs, but not Golf, is responsible for mediating the agonist-independent GPCR activity. We conclude that the equilibrium of conformational transitions set by each OR is the major determinant of expression levels of A-P-targeting molecules.