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Is TrpM5 a reliable marker for chemosensory cells? Multiple types of microvillous cells in the main olfactory epithelium of mice.

Hansen A, Finger TE - BMC Neurosci (2008)

Bottom Line: Tests with a large panel of cell markers indicate that the TrpM5-positive cells are not sensory since they express neither neuronal markers nor are contacted by trigeminal nerve fibers.We conclude that TrpM5 is not a reliable marker for chemosensory cells.Activity of these microvillous cells may however influence functionality of local elements of the olfactory system.

View Article: PubMed Central - HTML - PubMed

Affiliation: Rocky Mountain Taste and Smell Center, Dept. of Cell and Developmental Biology, School of Medicine, University of Colorado Denver, Aurora, 80045, USA. Anne.Hansen@uchsc.edu

ABSTRACT

Background: In the past, ciliated receptor neurons, basal cells, and supporting cells were considered the principal components of the main olfactory epithelium. Several studies reported the presence of microvillous cells but their function is unknown. A recent report showed cells in the main olfactory epithelium that express the transient receptor potential channel TrpM5 claiming that these cells are chemosensory and that TrpM5 is an intrinsic signaling component of mammalian chemosensory organs. We asked whether the TrpM5-positive cells in the olfactory epithelium are microvillous and whether they belong to a chemosensory system, i.e. are olfactory neurons or trigeminally-innervated solitary chemosensory cells.

Results: We investigated the main olfactory epithelium of mice at the light and electron microscopic level and describe several subpopulations of microvillous cells. The ultrastructure of the microvillous cells reveals at least three morphologically different types two of which express the TrpM5 channel. None of these cells have an axon that projects to the olfactory bulb. Tests with a large panel of cell markers indicate that the TrpM5-positive cells are not sensory since they express neither neuronal markers nor are contacted by trigeminal nerve fibers.

Conclusion: We conclude that TrpM5 is not a reliable marker for chemosensory cells. The TrpM5-positive cells of the olfactory epithelium are microvillous and may be chemoresponsive albeit not part of the sensory apparatus. Activity of these microvillous cells may however influence functionality of local elements of the olfactory system.

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Cell types in the MOE of mice. A Different types of microvillous cells (MV) (arrows) in the MOE labeled by GFP. Note that the olfactory epithelium varies in thickness. B Higher magnification of TrpM5a MV cells. C ORNs retrogradely labeled from the olfactory bulb by DiI. D Typical long slender ciliated ORNs retrogradely labeled by DiI.
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Figure 1: Cell types in the MOE of mice. A Different types of microvillous cells (MV) (arrows) in the MOE labeled by GFP. Note that the olfactory epithelium varies in thickness. B Higher magnification of TrpM5a MV cells. C ORNs retrogradely labeled from the olfactory bulb by DiI. D Typical long slender ciliated ORNs retrogradely labeled by DiI.

Mentions: In transgenic mice where the TrpM5 promoter drives the expression of green fluorescent protein (GFP), GFP-positive cells are scattered throughout the main olfactory epithelium (Fig. 1). Lin et al. [14] focused on the TrpM5-positive ORN population whereas the current paper and a companion paper (Lin et al., this issue) examine non-ORN cell types.


Is TrpM5 a reliable marker for chemosensory cells? Multiple types of microvillous cells in the main olfactory epithelium of mice.

Hansen A, Finger TE - BMC Neurosci (2008)

Cell types in the MOE of mice. A Different types of microvillous cells (MV) (arrows) in the MOE labeled by GFP. Note that the olfactory epithelium varies in thickness. B Higher magnification of TrpM5a MV cells. C ORNs retrogradely labeled from the olfactory bulb by DiI. D Typical long slender ciliated ORNs retrogradely labeled by DiI.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2629774&req=5

Figure 1: Cell types in the MOE of mice. A Different types of microvillous cells (MV) (arrows) in the MOE labeled by GFP. Note that the olfactory epithelium varies in thickness. B Higher magnification of TrpM5a MV cells. C ORNs retrogradely labeled from the olfactory bulb by DiI. D Typical long slender ciliated ORNs retrogradely labeled by DiI.
Mentions: In transgenic mice where the TrpM5 promoter drives the expression of green fluorescent protein (GFP), GFP-positive cells are scattered throughout the main olfactory epithelium (Fig. 1). Lin et al. [14] focused on the TrpM5-positive ORN population whereas the current paper and a companion paper (Lin et al., this issue) examine non-ORN cell types.

Bottom Line: Tests with a large panel of cell markers indicate that the TrpM5-positive cells are not sensory since they express neither neuronal markers nor are contacted by trigeminal nerve fibers.We conclude that TrpM5 is not a reliable marker for chemosensory cells.Activity of these microvillous cells may however influence functionality of local elements of the olfactory system.

View Article: PubMed Central - HTML - PubMed

Affiliation: Rocky Mountain Taste and Smell Center, Dept. of Cell and Developmental Biology, School of Medicine, University of Colorado Denver, Aurora, 80045, USA. Anne.Hansen@uchsc.edu

ABSTRACT

Background: In the past, ciliated receptor neurons, basal cells, and supporting cells were considered the principal components of the main olfactory epithelium. Several studies reported the presence of microvillous cells but their function is unknown. A recent report showed cells in the main olfactory epithelium that express the transient receptor potential channel TrpM5 claiming that these cells are chemosensory and that TrpM5 is an intrinsic signaling component of mammalian chemosensory organs. We asked whether the TrpM5-positive cells in the olfactory epithelium are microvillous and whether they belong to a chemosensory system, i.e. are olfactory neurons or trigeminally-innervated solitary chemosensory cells.

Results: We investigated the main olfactory epithelium of mice at the light and electron microscopic level and describe several subpopulations of microvillous cells. The ultrastructure of the microvillous cells reveals at least three morphologically different types two of which express the TrpM5 channel. None of these cells have an axon that projects to the olfactory bulb. Tests with a large panel of cell markers indicate that the TrpM5-positive cells are not sensory since they express neither neuronal markers nor are contacted by trigeminal nerve fibers.

Conclusion: We conclude that TrpM5 is not a reliable marker for chemosensory cells. The TrpM5-positive cells of the olfactory epithelium are microvillous and may be chemoresponsive albeit not part of the sensory apparatus. Activity of these microvillous cells may however influence functionality of local elements of the olfactory system.

Show MeSH