Trpc2-expressing sensory neurons in the mouse main olfactory epithelium of type B express the soluble guanylate cyclase Gucy1b2

Abstract

Chemoreception in the mouse olfactory system occurs primarily at two chemosensory epithelia in the nasal cavity: the main olfactory epithelium (MOE) and the vomeronasal epithelium. The canonical chemosensory neurons in the MOE, the olfactory sensory neurons (OSNs), express the odorant receptor (OR) gene repertoire, and depend on Adcy3 and Cnga2 for chemosensory signal transduction. The canonical chemosensory neurons in the vomeronasal epithelium, the vomeronasal sensory neurons (VSNs), express two unrelated vomeronasal receptor (VR) gene repertoires, and involve Trpc2 for chemosensory signal transduction. Recently we reported the discovery of two types of neurons in the mouse MOE that express Trcp2 in addition to Cnga2. These cell types can be distinguished at the single-cell level by expression of Adcy3: positive, type A and negative, type B. Some type A cells express OR genes. Thus far there is no specific gene or marker for type B cells, hampering further analyses such as physiological recordings. Here, we show that among MOE cells, type B cells are unique in their expression of the soluble guanylate cyclase Gucy1b2. We came across Gucy1b2 in an explorative approach based on Long Serial Analysis of Gene Expression (LongSAGE) that we applied to single red-fluorescent cells isolated from whole olfactory mucosa and vomeronasal organ of mice of a novel Trcp2-IRES-taumCherry gene-targeted strain. The generation of a novel Gucy1b2-IRES-tauGFP gene-targeted strain enabled us to visualize coalescence of axons of type B cells into glomeruli in the main olfactory bulb. Our molecular and anatomical analyses define Gucy1b2 as a marker for type B cells within the MOE. The Gucy1b2-IRES-tauGFP strain will be useful for physiological, molecular, cellular, and anatomical studies of this newly described chemosensory subsystem.

A Sensor for Low Environmental Oxygen in the Mouse Main Olfactory Epithelium

“…Type B cells can be visualized in the MOE of mice of the gene-targeted Gucy1b2-IRES-tauGFP strain, in which Gucy1b2 remains intact in its coding region and is coexpressed with a fusion protein of tau and GFP (Omura and Mombaerts, 2015) (Figure 1A). We hereafter abbreviate this mutant allele as Gucy1b2-GFP.…”

“…The mouse olfactory system comprises a variety of additional subsystems that detect a wide diversity of molecular cues in the external environment (Dey and Stowers, 2016, Munger et al., 2009). We have described a novel subpopulation of sensory neurons in the mouse MOE: type B cells (Omura and Mombaerts, 2014, Omura and Mombaerts, 2015, Saraiva et al., 2015). Type B cells express the transient receptor potential cation channel Trpc2, thought for many years to be expressed exclusively in vomeronasal sensory neurons (VSNs), where it is a critical component of signal transduction (Leypold et al., 2002, Lucas et al., 2003, Stowers et al., 2002).…”

“…Molecularly, type B cells are fundamentally different from canonical OSNs and VSNs (Omura and Mombaerts, 2014, Omura and Mombaerts, 2015, Saraiva et al., 2015), suggesting that their ligands are also fundamentally different. First, type B cells do not appear to express odorant receptor genes, vomeronasal receptor genes, or trace amine-associated receptor genes.…”

Neuropilin-1 and the Positions of Glomeruli in the Mouse Olfactory Bulb

“…An exception is a population of chemosensory neurons in the mouse main olfactory epithelium that express the cation channel Trpc2 (Liman et al, 1999), the cyclic-nucleotide gated channel subunit Cnga2, and the guanylate cyclase Gucy1b2: they do not express Adcy3 (Omura and Mombaerts, 2014, 2015). Glomeruli of Gucy1b2 + neurons can be examined easily and specifically in mice of the gene-targeted Gucy1b2-IRES-tauGFP strain: neurons that express Gucy1b2 coexpress GFP, and the expression level is high enough to visualize the signal in glomeruli by the intrinsic fluorescence of GFP (Omura and Mombaerts, 2015). Axons of Gucy1b2 + neurons coalesce typically into three glomeruli posteriorly in the olfactory bulb (Omura and Mombaerts, 2015).…”

“…Glomeruli of Gucy1b2 + neurons can be examined easily and specifically in mice of the gene-targeted Gucy1b2-IRES-tauGFP strain: neurons that express Gucy1b2 coexpress GFP, and the expression level is high enough to visualize the signal in glomeruli by the intrinsic fluorescence of GFP (Omura and Mombaerts, 2015). Axons of Gucy1b2 + neurons coalesce typically into three glomeruli posteriorly in the olfactory bulb (Omura and Mombaerts, 2015). The absence of Adcy3 expression in Gucy1b2 + neurons and the morphological similarity between Gucy1b2 + glomeruli and canonical glomeruli formed by the coalescence of axons of OR-expressing OSNs predict that Gucy1b2 glomeruli are Nrp1 – .…”