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Supersensitive detection and discrimination of enantiomers by dorsal olfactory receptors: evidence for hierarchical odour coding.

Sato T, Kobayakawa R, Kobayakawa K, Emura M, Itohara S, Kizumi M, Hamana H, Tsuboi A, Hirono J - Sci Rep (2015)

Bottom Line: The human olfactory system, however, discriminates (-)-wine lactone from its (+)-form rapidly within seconds.They were capable of supersensitive discrimination of enantiomers, consistent with their high detection sensitivity.This "enantiomer odour discrimination paradox" indicates that the most sensitive dorsal receptors play a critical role in hierarchical odour coding for enantiomer identification.

View Article: PubMed Central - PubMed

Affiliation: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, Hyogo 661-0974, Japan.

ABSTRACT
Enantiomeric pairs of mirror-image molecular structures are difficult to resolve by instrumental analyses. The human olfactory system, however, discriminates (-)-wine lactone from its (+)-form rapidly within seconds. To gain insight into receptor coding of enantiomers, we compared behavioural detection and discrimination thresholds of wild-type mice with those of ΔD mice in which all dorsal olfactory receptors are genetically ablated. Surprisingly, wild-type mice displayed an exquisite "supersensitivity" to enantiomeric pairs of wine lactones and carvones. They were capable of supersensitive discrimination of enantiomers, consistent with their high detection sensitivity. In contrast, ΔD mice showed selective major loss of sensitivity to the (+)-enantiomers. The resulting 10(8)-fold differential sensitivity of ΔD mice to (-)- vs. (+)-wine lactone matched that observed in humans. This suggests that humans lack highly sensitive orthologous dorsal receptors for the (+)-enantiomer, similarly to ΔD mice. Moreover, ΔD mice showed >10(10)-fold reductions in enantiomer discrimination sensitivity compared to wild-type mice. ΔD mice detected one or both of the (-)- and (+)-enantiomers over a wide concentration range, but were unable to discriminate them. This "enantiomer odour discrimination paradox" indicates that the most sensitive dorsal receptors play a critical role in hierarchical odour coding for enantiomer identification.

No MeSH data available.


Related in: MedlinePlus

Zonal distribution of carvone ORs.(A) Expression of the zonal marker O-MACS in carvone-responsive OSNs. Target-size cDNA products were obtained from 16/103 OSNs. The sequence of cDNA products from 3 OSNs (underlined numbers) were confirmed. Of the 4 OSNs that were specifically and most sensitive to (R)-(−)-carvone, one [5*, expressing murine OR car-c5 (mORcar-c5)] was O-MACS-positive. It is likely that the deletion of this most sensitive dorsal OR and cognate ORs increases the odour discrimination threshold of ΔD mice for carvone enantiomers. (B) Expression of olfactory marker protein in OSNs. Coronal section of the medial part of the mouse olfactory epithelium were in situ hybridised with a DIG-labeled antisense RNA probe (negative photography). D, dorsal; V, ventral; M, medial; L, lateral. A border line between dorsal and ventral zones is indicated by the broken red line. (C) Expression of mORcar-c5. Arrowheads indicate positive OSNs. Enlarged region is indicated by a broken lined box in the low-magnification photograph. (D) Expression of mORcar-b158. (E–G), Expression of mORcar-c5 in three different mice (negative photography). Enlarged region is indicated by a broken lined box in the low-magnification photograph. Positive OSNs are indicated by arrowheads in the enlarged regions and blue, green and red spots in (H) respectively. H, Expression region of mORcar-c5 (red line). (I) Expression regions of 15 carvone ORs. Different colours correspond to different ORs. (J) Temporally ordered signal inputs to the brain and relative number of the OSNs expressing the (R)-(−)-carvone-activated OR. The input orders are based on the OR sensitivities and relative response amplitudes. The numbers of OSNs shown by the hatched bars may be overestimated by potential cross-reactions with other ORs having >85% sequence homology. (K) Temporally ordered signal inputs to the brain and relative number of the OSNs expressing the (S)-(+)-carvone-activated OR. Numbers represent the ORs (Supplementary Information Table ST3).
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f3: Zonal distribution of carvone ORs.(A) Expression of the zonal marker O-MACS in carvone-responsive OSNs. Target-size cDNA products were obtained from 16/103 OSNs. The sequence of cDNA products from 3 OSNs (underlined numbers) were confirmed. Of the 4 OSNs that were specifically and most sensitive to (R)-(−)-carvone, one [5*, expressing murine OR car-c5 (mORcar-c5)] was O-MACS-positive. It is likely that the deletion of this most sensitive dorsal OR and cognate ORs increases the odour discrimination threshold of ΔD mice for carvone enantiomers. (B) Expression of olfactory marker protein in OSNs. Coronal section of the medial part of the mouse olfactory epithelium were in situ hybridised with a DIG-labeled antisense RNA probe (negative photography). D, dorsal; V, ventral; M, medial; L, lateral. A border line between dorsal and ventral zones is indicated by the broken red line. (C) Expression of mORcar-c5. Arrowheads indicate positive OSNs. Enlarged region is indicated by a broken lined box in the low-magnification photograph. (D) Expression of mORcar-b158. (E–G), Expression of mORcar-c5 in three different mice (negative photography). Enlarged region is indicated by a broken lined box in the low-magnification photograph. Positive OSNs are indicated by arrowheads in the enlarged regions and blue, green and red spots in (H) respectively. H, Expression region of mORcar-c5 (red line). (I) Expression regions of 15 carvone ORs. Different colours correspond to different ORs. (J) Temporally ordered signal inputs to the brain and relative number of the OSNs expressing the (R)-(−)-carvone-activated OR. The input orders are based on the OR sensitivities and relative response amplitudes. The numbers of OSNs shown by the hatched bars may be overestimated by potential cross-reactions with other ORs having >85% sequence homology. (K) Temporally ordered signal inputs to the brain and relative number of the OSNs expressing the (S)-(+)-carvone-activated OR. Numbers represent the ORs (Supplementary Information Table ST3).

Mentions: Similar to wine lactones, the capability of ΔD mice to discriminate carvone enantiomers was also paradoxical, with a 1010-fold reduction in discrimination sensitivity (10−9 w/w, larger asterisk in Fig. 1F, Table 1). They could detect one or both of the (R)-(−)- and (S)-(+)-carvones, but were unable to discriminate them over a wide concentration range (10−11–10−17 w/w, blue arrows in Fig. 2A). Again, this contrasted with relatively consistent detection and discrimination thresholds in WT mice. Our findings indicated that the most sensitive dorsal ORs play critical roles in olfactory signal processing and odour discrimination. Using single-cell PCR, we detected the dorsal zone marker in at least 1 of the 4 most sensitive OSNs for (R)-(−)-carvone (mORcar-c5, Fig. 3, Supplementary Information Table ST3). The dorsal OR of this OSN is likely to be one of the receptors responsible for supersensitive discrimination of enantiomers by WT mice at threshold. Our results are consistent with a previous report on the capability of ΔD mice to discriminate carvone enantiomers at a high concentration of 6.5 × 10−2 w/w, after correcting for total volume of the odourant solution5.


Supersensitive detection and discrimination of enantiomers by dorsal olfactory receptors: evidence for hierarchical odour coding.

Sato T, Kobayakawa R, Kobayakawa K, Emura M, Itohara S, Kizumi M, Hamana H, Tsuboi A, Hirono J - Sci Rep (2015)

Zonal distribution of carvone ORs.(A) Expression of the zonal marker O-MACS in carvone-responsive OSNs. Target-size cDNA products were obtained from 16/103 OSNs. The sequence of cDNA products from 3 OSNs (underlined numbers) were confirmed. Of the 4 OSNs that were specifically and most sensitive to (R)-(−)-carvone, one [5*, expressing murine OR car-c5 (mORcar-c5)] was O-MACS-positive. It is likely that the deletion of this most sensitive dorsal OR and cognate ORs increases the odour discrimination threshold of ΔD mice for carvone enantiomers. (B) Expression of olfactory marker protein in OSNs. Coronal section of the medial part of the mouse olfactory epithelium were in situ hybridised with a DIG-labeled antisense RNA probe (negative photography). D, dorsal; V, ventral; M, medial; L, lateral. A border line between dorsal and ventral zones is indicated by the broken red line. (C) Expression of mORcar-c5. Arrowheads indicate positive OSNs. Enlarged region is indicated by a broken lined box in the low-magnification photograph. (D) Expression of mORcar-b158. (E–G), Expression of mORcar-c5 in three different mice (negative photography). Enlarged region is indicated by a broken lined box in the low-magnification photograph. Positive OSNs are indicated by arrowheads in the enlarged regions and blue, green and red spots in (H) respectively. H, Expression region of mORcar-c5 (red line). (I) Expression regions of 15 carvone ORs. Different colours correspond to different ORs. (J) Temporally ordered signal inputs to the brain and relative number of the OSNs expressing the (R)-(−)-carvone-activated OR. The input orders are based on the OR sensitivities and relative response amplitudes. The numbers of OSNs shown by the hatched bars may be overestimated by potential cross-reactions with other ORs having >85% sequence homology. (K) Temporally ordered signal inputs to the brain and relative number of the OSNs expressing the (S)-(+)-carvone-activated OR. Numbers represent the ORs (Supplementary Information Table ST3).
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f3: Zonal distribution of carvone ORs.(A) Expression of the zonal marker O-MACS in carvone-responsive OSNs. Target-size cDNA products were obtained from 16/103 OSNs. The sequence of cDNA products from 3 OSNs (underlined numbers) were confirmed. Of the 4 OSNs that were specifically and most sensitive to (R)-(−)-carvone, one [5*, expressing murine OR car-c5 (mORcar-c5)] was O-MACS-positive. It is likely that the deletion of this most sensitive dorsal OR and cognate ORs increases the odour discrimination threshold of ΔD mice for carvone enantiomers. (B) Expression of olfactory marker protein in OSNs. Coronal section of the medial part of the mouse olfactory epithelium were in situ hybridised with a DIG-labeled antisense RNA probe (negative photography). D, dorsal; V, ventral; M, medial; L, lateral. A border line between dorsal and ventral zones is indicated by the broken red line. (C) Expression of mORcar-c5. Arrowheads indicate positive OSNs. Enlarged region is indicated by a broken lined box in the low-magnification photograph. (D) Expression of mORcar-b158. (E–G), Expression of mORcar-c5 in three different mice (negative photography). Enlarged region is indicated by a broken lined box in the low-magnification photograph. Positive OSNs are indicated by arrowheads in the enlarged regions and blue, green and red spots in (H) respectively. H, Expression region of mORcar-c5 (red line). (I) Expression regions of 15 carvone ORs. Different colours correspond to different ORs. (J) Temporally ordered signal inputs to the brain and relative number of the OSNs expressing the (R)-(−)-carvone-activated OR. The input orders are based on the OR sensitivities and relative response amplitudes. The numbers of OSNs shown by the hatched bars may be overestimated by potential cross-reactions with other ORs having >85% sequence homology. (K) Temporally ordered signal inputs to the brain and relative number of the OSNs expressing the (S)-(+)-carvone-activated OR. Numbers represent the ORs (Supplementary Information Table ST3).
Mentions: Similar to wine lactones, the capability of ΔD mice to discriminate carvone enantiomers was also paradoxical, with a 1010-fold reduction in discrimination sensitivity (10−9 w/w, larger asterisk in Fig. 1F, Table 1). They could detect one or both of the (R)-(−)- and (S)-(+)-carvones, but were unable to discriminate them over a wide concentration range (10−11–10−17 w/w, blue arrows in Fig. 2A). Again, this contrasted with relatively consistent detection and discrimination thresholds in WT mice. Our findings indicated that the most sensitive dorsal ORs play critical roles in olfactory signal processing and odour discrimination. Using single-cell PCR, we detected the dorsal zone marker in at least 1 of the 4 most sensitive OSNs for (R)-(−)-carvone (mORcar-c5, Fig. 3, Supplementary Information Table ST3). The dorsal OR of this OSN is likely to be one of the receptors responsible for supersensitive discrimination of enantiomers by WT mice at threshold. Our results are consistent with a previous report on the capability of ΔD mice to discriminate carvone enantiomers at a high concentration of 6.5 × 10−2 w/w, after correcting for total volume of the odourant solution5.

Bottom Line: The human olfactory system, however, discriminates (-)-wine lactone from its (+)-form rapidly within seconds.They were capable of supersensitive discrimination of enantiomers, consistent with their high detection sensitivity.This "enantiomer odour discrimination paradox" indicates that the most sensitive dorsal receptors play a critical role in hierarchical odour coding for enantiomer identification.

View Article: PubMed Central - PubMed

Affiliation: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, Hyogo 661-0974, Japan.

ABSTRACT
Enantiomeric pairs of mirror-image molecular structures are difficult to resolve by instrumental analyses. The human olfactory system, however, discriminates (-)-wine lactone from its (+)-form rapidly within seconds. To gain insight into receptor coding of enantiomers, we compared behavioural detection and discrimination thresholds of wild-type mice with those of ΔD mice in which all dorsal olfactory receptors are genetically ablated. Surprisingly, wild-type mice displayed an exquisite "supersensitivity" to enantiomeric pairs of wine lactones and carvones. They were capable of supersensitive discrimination of enantiomers, consistent with their high detection sensitivity. In contrast, ΔD mice showed selective major loss of sensitivity to the (+)-enantiomers. The resulting 10(8)-fold differential sensitivity of ΔD mice to (-)- vs. (+)-wine lactone matched that observed in humans. This suggests that humans lack highly sensitive orthologous dorsal receptors for the (+)-enantiomer, similarly to ΔD mice. Moreover, ΔD mice showed >10(10)-fold reductions in enantiomer discrimination sensitivity compared to wild-type mice. ΔD mice detected one or both of the (-)- and (+)-enantiomers over a wide concentration range, but were unable to discriminate them. This "enantiomer odour discrimination paradox" indicates that the most sensitive dorsal receptors play a critical role in hierarchical odour coding for enantiomer identification.

No MeSH data available.


Related in: MedlinePlus