Contribution of the receptor guanylyl cyclase GC-D to chemosensory function in the olfactory epithelium

Abstract

The mammalian main olfactory epithelium (MOE) recognizes and transduces olfactory cues through a G protein-coupled, cAMPdependent signaling cascade. Additional chemosensory transduction mechanisms have been suggested but remain controversial. We show that a subset of MOE neurons expressing the orphan receptor guanylyl cyclase GC-D and the cyclic nucleotide-gated channel subunit CNGA3 employ an excitatory cGMP-dependent transduction mechanism for chemodetection. By combining gene targeting of Gucy2d, which encodes GC-D, with patch clamp recording and confocal Ca 2؉ imaging from single dendritic knobs in situ, we find that GC-D cells recognize the peptide hormones uroguanylin and guanylin as well as natural urine stimuli. These molecules stimulate an excitatory, cGMP-dependent signaling cascade that increases intracellular Ca 2؉ and action potential firing. Responses are eliminated in both Gucy2d-and Cnga3-null mice, demonstrating the essential role of GC-D and CNGA3 in the transduction of these molecules. The sensitive and selective detection of two important natriuretic peptides by the GC-D neurons suggests the possibility that these cells contribute to the maintenance of salt and water homeostasis or the detection of cues related to hunger, satiety, or thirst.O dor recognition by canonical olfactory sensory neurons (OSNs) of the main olfactory epithelium (MOE) begins when odor molecules bind to any one of many hundred G protein-coupled odorant receptors (1-4). Upon ligand binding, odorant receptors activate the G protein G␣ olf , which stimulates type III adenylyl cyclase to increase intracellular levels of cAMP (4-9). This second messenger then directly opens cAMPsensitive, cyclic nucleotide-gated (CNG) channels in the plasma membrane, resulting in the initial depolarization of the cell (3, 4). OSNs that use this cAMP-mediated transduction cascade respond to a wide variety of odors, including food odors, volatile pheromones, and peptides that bind major histocompatibility complex proteins (4, 10-12). A recently discovered second family of G protein-coupled receptors expressed in the MOE, the trace amine-associated receptors, may also function in the recognition of some odors or pheromones by coupling to the canonical cAMP pathway (13). However, there has been intense debate as to whether the cAMP cascade is the only excitatory sensory transduction mechanism in the MOE (11,14,15).A subpopulation of ciliated MOE neurons that express the orphan receptor guanylyl cyclase GC-D (16) are prime candidates to mediate cAMP-independent odor recognition. GC-D cells lack key components of the canonical OSN odor transduction cascade, including G␣ olf , type III adenylyl cyclase, the Ca 2ϩ /calmodulin-dependent phosphodiesterase PDE1C2, the cAMP-specific phosphodiesterase PDE4A, and the cAMPsensitive CNG channel subunits CNGA2 and CNGB1b (17,18). Instead, these neurons express a cGMP-specific CNG channel subunit, CNGA3, and a cGMP-stimulated phosphodiesterase, PDE2 (17,18). Although these cells were identified more than a de...

Grueneberg Ganglion Neurons Are Finely Tuned Cold Sensors

“…Experiments used three strains of mice: (1) OMP-GFP ϩ/Ϫ mice, heterozygous for both OMP and GFP (green fluorescent protein) (Potter et al, 2001); (2) Cnga3 Ϫ/Ϫ OMP-GFP ϩ/Ϫ mice in which genetically labeled GGNs were devoid of a functional CNGA3 channel [this strain was obtained by crossing Cnga3 Ϫ/Ϫ mice (Biel et al, 1999;Leinders-Zufall et al, 2007) Calcium imaging and data analysis. We used newborn mice [postnatal day 1 (P1)-P10] to prepare coronal tissue slices (60-to 100-m-thick) of the Grueneberg ganglion.…”

“…It consists of a cluster of neurons-henceforward referred to as Grueneberg ganglion neurons (GGNs)-that express olfactory marker protein (OMP) and project their axons to a small number of glomeruli in the caudal main olfactory bulb (Fuss et al, 2005;Koos and Fraser, 2005;Fleischer et al, 2006;Roppolo et al, 2006;Storan and Key, 2006). Interestingly, these glomeruli are near the necklace glomeruli innervated by olfactory sensory neurons expressing the receptor guanylyl cyclase GC-D (Fülle et al, 1995;Juilfs et al, 1997;Leinders-Zufall et al, 2007;Walz et al, 2007; for review, see Munger et al, 2009), and both GC-D-expressing neurons and GGNs express elements of a cGMP second messenger pathway, including the cGMP-specific cyclic nucleotide-gated channel CNGA3 and the cGMP-stimulated phosphodiesterase PDE2 (Juilfs et al, 1997;Meyer et al, 2000;Leinders-Zufall et al, 2007;Fleischer et al, 2009;Liu et al, 2009). They differ, however, in the membrane-bound guanylyl cyclases they express; GGNs express guanylyl cyclase type G but not GC-D (Fleischer et al, 2009;Liu et al, 2009).…”

Sniffing out social signals

“…Hu et al [21] provided evidence for CO 2 -mediated, carbonic anhydrase type II (CAII)-dependent Ca 2+ signals in GC-D-expressing neurons. By contrast, functional data from both wildtype and gene-targeted mice strongly support a role of GC-D-positive OSNs as sensitive and selective sensors for two natriuretic peptides -uroguanylin and guanylin [31]. Are these findings necessarily contradictory?…”

Uroguanylin induces electroencephalographic spikes in rats

“…Uroguanylin was previously shown to induce either GC-independent (in rat principal cells of the cortical collecting duct) or cGMP-dependent (in mammalian olfactory neurons) depolarization (Sindic et al, 2005;Leinders-Zufall et al, 2007). This later study has showed by both patch-clamp and confocal Ca 2+ -imaging studies that uroguanylin evokes an excitatory, cGMP-dependent signaling cascade that increases intracellular Ca 2+ and action potential firing.…”