Recombinant Mouse Olfactory receptor 151 (Olfr151)

What is Olfr151 and what are its synonyms in scientific literature?

Olfr151 is a G protein-coupled receptor belonging to the olfactory receptor family expressed in mouse olfactory sensory neurons (OSNs). It is also known by several synonyms in scientific literature including Mor171-2, Olfr7, Odorant receptor M71, Olfactory receptor 171-2, and Olfactory receptor 7H. The protein is registered in UniProt with the identifier Q60893 . This receptor plays a crucial role in both odor detection and the developmental organization of the olfactory system, particularly in axon guidance and glomerular formation in the olfactory bulb .

How does recombinant Olfr151 compare to native Olfr151 in functional studies?

Recombinant Olfr151 serves as a valuable research tool but has important differences from native Olfr151 that researchers should consider:

The functional differences highlight why complementary approaches using both recombinant proteins and in vivo models are necessary for comprehensive research on Olfr151 .

What are the optimal storage conditions for recombinant Olfr151 protein?

For optimal stability and activity maintenance of recombinant Olfr151 protein, the following storage conditions are recommended:

• Long-term storage: Store at -20°C to -80°C, with -80°C preferred for extended periods

• Working aliquots: Store at 4°C for up to one week

• Physical form: Maintain as lyophilized powder until ready for use

• Aliquoting: Division into single-use aliquots is essential to avoid repeated freeze-thaw cycles

The protein should be stored in a Tris/PBS-based buffer containing 6% Trehalose at pH 8.0, which helps maintain stability during freeze-thaw transitions. It is strongly advised to avoid repeated freeze-thaw cycles as they significantly reduce protein activity and integrity .

What reconstitution protocol is recommended for lyophilized Olfr151?

The optimal reconstitution protocol for lyophilized Olfr151 involves the following steps:

• Briefly centrifuge the vial containing lyophilized protein to ensure all material is at the bottom

• Reconstitute in deionized sterile water to a final concentration of 0.1-1.0 mg/mL

• Add glycerol to a final concentration of 5-50% (with 50% being the standard recommendation)

• Aliquot into single-use volumes

• Store reconstituted aliquots at -20°C/-80°C for long-term storage

This protocol helps maintain protein stability while preventing protein aggregation and degradation. The addition of glycerol serves as a cryoprotectant, which is particularly important for membrane proteins like olfactory receptors .

What expression systems are most effective for producing functional recombinant Olfr151?

The choice of expression system significantly impacts the functionality of recombinant Olfr151:

How can the interaction between Olfr151 and Receptor Transporting Proteins (RTPs) be studied experimentally?

The crucial interaction between Olfr151 and RTPs can be investigated through several complementary approaches:

• Co-immunoprecipitation (Co-IP): Using tagged versions of Olfr151 and RTPs to pull down protein complexes and analyze interactions

• Fluorescence Resonance Energy Transfer (FRET): Tagging Olfr151 and RTPs with compatible fluorophores to detect close molecular interactions in live cells

• Surface expression assays: Comparing Olfr151 surface localization in wild-type vs. RTP knockout models through:

  • Cell surface biotinylation followed by Western blotting

  • Flow cytometry using antibodies against extracellular epitopes

  • Immunocytochemistry with and without permeabilization

• Transgenic mouse models: Creating and analyzing RTP1,2 double knockout mice (RTP1,2DKO) to evaluate changes in Olfr151 expression patterns and axonal targeting

Research has demonstrated that in RTP1,2DKO mice, there are significantly fewer Olfr151-expressing olfactory sensory neurons compared to wild-type mice, indicating that Olfr151 is a uOR (underrepresented olfactory receptor) that requires RTPs for proper expression and trafficking .

What methodologies are available for studying Olfr151 gene choice and expression stability?

Several sophisticated methodologies have been developed to investigate Olfr151 gene choice and expression stability:

• Lineage tracing with Cre-lox system: Using M71-IRES-Cre (where M71 corresponds to Olfr151) crossed with reporter mice containing a Cre-inducible fluorescent marker like Rosa26-lox-stop-lox-tdTomato. This approach permanently labels any cell that has ever expressed Olfr151, allowing researchers to track whether OSNs maintain or switch their OR expression .

• Single-cell RNA sequencing: Allows transcriptome-wide analysis of individual OSNs to identify cells expressing Olfr151 and characterize their molecular signatures.

• In situ hybridization combined with immunohistochemistry: Can be used to simultaneously detect Olfr151 mRNA and protein expression, along with markers of the unfolded protein response (UPR) such as nATF5.

• Quantitative analysis of OR choice stability: By comparing the ratio of cells expressing only the lineage marker (tdTomato) versus those expressing both the lineage marker and Olfr151, researchers can quantify the stability of OR choice:

  Genotype	tdTomato+ cells also expressing Olfr151	Interpretation
  Wild-type	31% (79/258 neurons)	Normal stability of Olfr151 expression
  Heterozygous	38% (66/172 neurons)	Comparable to wild-type stability
  RTP1,2DKO	17% (24/140 neurons)	Significantly reduced stability of Olfr151 expression

These data indicate that the absence of RTPs leads to frequent termination of Olfr151 gene expression, suggesting RTPs play a crucial role in stabilizing OR gene choice .

How can axonal targeting of Olfr151-expressing neurons be visualized and analyzed?

Visualizing and analyzing the axonal targeting of Olfr151-expressing neurons involves several specialized techniques:

• Transgenic reporter mice: Using mouse lines with fluorescent markers expressed under the control of the Olfr151 promoter, such as M71-IRES-tau-GFP, which labels the entire neuron including axonal projections.

• Whole-mount imaging: Preparation of intact olfactory bulbs for visualization of glomerular targeting patterns without sectioning, preserving the three-dimensional organization.

• Immunohistochemistry: Using antibodies against OMP (Olfactory Marker Protein) to visualize all mature OSN axons in combination with specific labeling for Olfr151-expressing neurons.

• Quantitative glomerular analysis: Counting and characterizing glomeruli formed by Olfr151-expressing neurons:

  Genotype	Number of Olfr151 glomeruli	Glomerular formation
  Wild-type	2 per OB	Normal convergence
  RTP1,2DKO	0	Failure of convergence

• Lineage tracing combined with axon imaging: In RTP1,2DKO mice with M71-IRES-Cre and Rosa26-lox-stop-lox-tdTomato, small glomeruli formed by tdTomato-positive axons were observed (in 2 out of 3 mice examined), suggesting that OSNs initially expressing Olfr151 may switch to expressing other OR genes but can still form glomeruli .

These methods provide critical insights into how Olfr151 expression affects axonal guidance and glomerular formation in the olfactory system.

How does Olfr151 expression affect the Unfolded Protein Response (UPR) in olfactory sensory neurons?

The relationship between Olfr151 expression and the Unfolded Protein Response (UPR) represents an important area of investigation in olfactory research:

• UPR markers in Olfr151-expressing neurons: Research has shown that the number of OSNs co-expressing Olfr151 and nATF5 (a marker of active UPR) is significantly higher in RTP1,2DKO mice compared to wild-type (p<0.05, Fisher's exact test) .

• Comparison with non-OR GPCRs: When β2AR (β2-adrenergic receptor) is expressed from the Olfr151 locus, co-expression with nATF5 in β2AR-expressing neurons shows no difference between RTP1,2DKO and wild-type mice. This suggests that:

  • The UPR is specifically elevated in neurons expressing ORs that require RTPs for trafficking

  • Surface trafficking of the receptor may play a role in UPR termination

• Experimental approaches to study UPR in relation to Olfr151:

  • Immunohistochemistry for UPR markers (nATF5, BiP, XBP1)

  • RNA-seq analysis of UPR-related gene expression

  • Pharmacological manipulation of the UPR pathway

• Functional implications: The persistent UPR in Olfr151-expressing neurons lacking RTPs correlates with instability of OR gene choice, suggesting a mechanistic link between protein trafficking, UPR resolution, and stable OR expression .

What are the implications of Olfr151 gene switching in RTP1,2DKO mice for understanding OR gene choice mechanisms?

The phenomenon of Olfr151 gene switching in RTP1,2DKO mice provides fascinating insights into the mechanisms governing OR gene choice:

• Evidence for gene switching: Lineage tracing experiments show that in RTP1,2DKO mice, only 17% of cells that had ever expressed Olfr151 (tdTomato positive) maintained Olfr151 expression, compared to 31% in wild-type mice .

• Switching patterns: Analysis of whether Olfr151 switches to other ORs within the same genomic locus (such as Olfr143) revealed no co-localization between Olfr143 and tdTomato in lineage-traced neurons. This suggests that:

  • Gene switching is not preferentially directed toward ORs in the same genomic locus

  • The switching mechanism likely involves genome-wide selection rather than local regulatory effects

• Molecular model of OR gene choice stability:

  • Successful trafficking of an OR to the cell surface may provide feedback to stabilize its expression

  • RTPs facilitate this process for a subset of ORs (uORs, including Olfr151)

  • In the absence of RTPs, uORs fail to traffic properly, leading to:

    • Persistent UPR

    • Failure to stabilize initial OR choice

    • Switching to alternative OR genes

• Experimental design considerations: When using Olfr151 as a model OR, researchers should be aware that experimental manipulations affecting trafficking (such as RTP knockout) will impact not only protein localization but also gene expression stability .

How do transgenic models expressing Olfr151 contribute to understanding olfactory system organization?

Transgenic mouse models expressing Olfr151 have provided valuable insights into the organization and development of the olfactory system:

• Glomerular map formation: Transgenic 4x21-Olfr151b mice show multiple Olfr151b-innervated glomeruli in specific domains of the dorsal bulb, breaking the class-based cell-type restriction normally observed. These innervation patterns are remarkably similar to those seen with other ORs like 5x21-OR1A1 .

• Topographical organization: Crossing 4x21-Olfr151b line with ΔTAAR4-YFP mice revealed that TAAR axons lay next to a red Olfr151b-enervated glomerulus centered between the DI and DII domains of the olfactory bulb .

• Experimental applications of Olfr151 transgenic models:

  • Investigating the principles governing axon sorting and glomerular formation

  • Studying the impact of receptor sequence vs. genomic locus on OSN identity

  • Analyzing the effect of altered receptor expression levels on the olfactory map

• Replacement experiments: Studies using β2AR-IRES-LacZ expressed from the Olfr151 locus demonstrate that:

  • More β2AR-positive OSNs are present in RTP1,2DKO compared to wild-type

  • β2AR-expressing neurons form glomeruli in both wild-type and RTP1,2DKO mice, although ectopic glomeruli are observed in the knockout

  • These findings suggest that protein sequence rather than genomic locus determines whether a receptor requires RTPs for proper expression and targeting

These transgenic approaches provide powerful tools for dissecting the complex relationship between receptor identity, expression patterns, and circuit formation in the olfactory system.

What are common pitfalls when working with recombinant Olfr151 and how can they be addressed?

Researchers working with recombinant Olfr151 often encounter several technical challenges that can be addressed through specific protocols:

• Poor protein solubility and aggregation:

  • Use detergents specifically optimized for GPCRs (DDM, LMNG, or MNG-3)

  • Consider incorporating the protein into nanodiscs or liposomes

  • Maintain strict temperature control during purification (4°C)

• Loss of activity during storage:

  • Strictly follow storage recommendations (-20°C/-80°C)

  • Use single-use aliquots to avoid freeze-thaw cycles

  • Include 50% glycerol in storage buffer as a cryoprotectant

• Poor expression in heterologous systems:

  • Co-express with accessory proteins like RTPs

  • Optimize codon usage for the expression system

  • Consider fusion partners that enhance expression (SUMO, MBP)

• Functional assays challenges:

  • Test multiple readout systems (calcium imaging, cAMP assays)

  • Ensure proper membrane localization before functional testing

  • Include positive controls with known activity

How can inconsistencies in Olfr151 expression patterns between studies be reconciled?

When faced with discrepancies in reported Olfr151 expression patterns across different studies, researchers should consider several factors:

• Methodological differences:

  • Detection methods (antibodies vs. genetic reporters)

  • Tissue preparation protocols (fixation times, embedding methods)

  • Age of animals studied (developmental changes in OR expression)

• Genetic background effects:

  • Strain-specific variations in OR expression

  • Presence of modifier genes affecting OR choice probability

  • Generation of transgenic line (potential position effects)

• Data analysis approaches:

  • Quantification methods (manual vs. automated counting)

  • Statistical approaches for determining significance

  • Criteria for identifying positive cells

• Experimental validation strategies:

  • Use multiple detection methods in parallel

  • Cross-validate findings across different genetic backgrounds

  • Employ single-cell sequencing to provide unbiased assessment

By systematically addressing these factors, researchers can better understand the sources of variation and design experiments that yield more consistent and interpretable results.

What emerging technologies might enhance research on Olfr151 function and expression?

Several cutting-edge technologies hold promise for advancing research on Olfr151:

• CRISPR-based approaches:

  • Precise genome editing to create knock-in reporter lines

  • Base editing for introducing specific mutations in Olfr151

  • CRISPRa/CRISPRi for modulating endogenous Olfr151 expression

• Advanced imaging techniques:

  • Super-resolution microscopy for visualizing Olfr151 trafficking

  • Light-sheet microscopy for whole-olfactory system imaging

  • In vivo imaging with genetically encoded sensors

• Structural biology advancements:

  • Cryo-EM for determining Olfr151 structure

  • Computational modeling based on AlphaFold2 predictions

  • Structure-based virtual screening for ligand discovery

• Single-cell multi-omics:

  • Integration of transcriptomics, proteomics, and epigenomics

  • Spatial transcriptomics to preserve anatomical context

  • Longitudinal single-cell analysis to track OR choice dynamics

These technologies will enable more precise manipulation and analysis of Olfr151, potentially revealing new aspects of its function and regulation.

What are the most promising areas for future investigation regarding Olfr151?

Based on current knowledge gaps, several research directions appear particularly promising:

• Structure-function relationships:

  • Identification of protein domains critical for RTP interaction

  • Determination of ligand binding sites and activation mechanisms

  • Engineering of Olfr151 variants with altered trafficking properties

• Developmental biology:

  • Temporal dynamics of Olfr151 expression during development

  • Mechanisms linking OR choice to axon guidance

  • Environmental influences on Olfr151 expression patterns

• Comparative studies:

  • Evolution of Olfr151 across species

  • Comparison of "uORs" vs. "oORs" to identify determinants of RTP dependency

  • Cross-species functional conservation and divergence

• Translational applications:

  • Using Olfr151 as a model for understanding GPCR trafficking disorders

  • Development of high-throughput screening systems based on Olfr151

  • Application of OR trafficking principles to therapeutic protein delivery

These research directions build upon existing knowledge while addressing fundamental questions about olfactory receptor biology that have broader implications for understanding GPCR function and regulation.