Recombinant Rat Vomeronasal type-1 receptor A15 (V1ra15)

What is Vomeronasal type-1 receptor A15 (V1ra15) and what is its function?

Vomeronasal type-1 receptor A15 (V1ra15), also known as Vom1r102, is a G protein-coupled receptor found in the vomeronasal organ (VNO) of rats. It functions as a pheromone receptor involved in chemical communication between rats. The full-length protein consists of 336 amino acids and is expressed in vomeronasal sensory neurons located in the apical part of the VNO epithelium . These neurons also express the G protein subunit Gαi2, which is involved in the signal transduction pathway following pheromone binding .

What are the common synonyms and identifiers for V1ra15?

V1ra15 is known by several alternative names and identifiers:

• Vom1r102 (Gene name)

• V1ra15

• Vnr2

• Vomeronasal type-1 receptor 102

• Pheromone receptor VN2

• Vomeronasal receptor 2

• UniProt ID: Q5J3K5

How is recombinant V1ra15 typically produced and purified?

Recombinant V1ra15 can be produced using bacterial expression systems. The standard protocol includes:

• Gene cloning into an appropriate expression vector

• Expression in E. coli with an N-terminal His tag

• Bacterial culture and protein induction

• Cell lysis and protein extraction

• His-tag affinity chromatography purification

• Lyophilization for stable storage

The final product is typically a lyophilized powder with greater than 90% purity as determined by SDS-PAGE analysis .

What are the optimal storage and reconstitution conditions for recombinant V1ra15?

For optimal storage and reconstitution:

• Storage: Store at -20°C/-80°C upon receipt. Aliquoting is necessary for multiple use to avoid repeated freeze-thaw cycles. Working aliquots can be stored at 4°C for up to one week .

• Storage Buffer: Tris/PBS-based buffer containing 6% Trehalose, pH 8.0 .

• Reconstitution:

  • Centrifuge the vial briefly prior to opening

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

  • Add 5-50% glycerol (final concentration) and aliquot for long-term storage

  • The recommended final glycerol concentration is 50%

What quality control measures should be implemented when working with recombinant V1ra15?

Essential quality control measures include:

• Purity assessment: SDS-PAGE to verify >90% purity

• Structural integrity: Western blotting with appropriate antibodies

• Functional verification: Ligand binding or calcium imaging assays

• Solubility testing: Monitoring protein aggregation in reconstitution buffer

• Batch-to-batch consistency: Comparing protein from different expression batches

• Activity retention: Verifying functionality after storage periods

How can researchers verify V1ra15 responsiveness to potential pheromone ligands?

Several techniques can be employed to verify receptor-ligand interactions:

• Heterologous expression systems: Express V1ra15 in HEK293-T cells and perform calcium imaging to measure receptor activation upon ligand binding. This approach has been successfully used for other vomeronasal receptors such as Vom1r68 and Vom2r53 .

• Immunofluorescence: Confirm membrane localization of the receptor by co-localization studies with membrane markers like mTmG. Research has shown this technique is effective for vomeronasal receptors .

• Calcium imaging: Monitor intracellular calcium levels in cells expressing V1ra15 when exposed to potential ligands. Calcium influx indicates receptor activation .

• Electrophysiology: Record electrical responses from cells expressing V1ra15 after ligand application to provide direct evidence of receptor activation.

What is known about ligand specificity among vomeronasal receptors?

While specific ligands for V1ra15 have not been definitively identified in the provided references, research on related receptors provides insights into ligand specificity patterns:

• Vom1r68 has been shown to respond specifically to 2-heptanone, a volatile pheromone .

• Vom2r53 responds to MUP13 (Major Urinary Protein 13) .

• These findings suggest a "one receptor-one ligand" pattern may exist for at least some vomeronasal receptors.

The specificity of receptor-ligand interactions is likely an important factor in the precise detection of species-specific pheromonal signals.

How does the V1R repertoire vary across mammalian species?

The V1R gene repertoire shows dramatic variation across mammalian species:

This 23-fold variation in repertoire size represents the greatest among-species variation in gene family size of all mammalian gene families studied . This diversity likely reflects differences in the importance and complexity of pheromone communication across mammalian species.

What evolutionary patterns are observed in the V1R gene family?

Phylogenetic analysis of V1R genes across mammals reveals:

• Massive gene births and deaths: Multiple losses of ancestral genes in carnivores (e.g., dogs) and artiodactyls (e.g., cows), with extensive gains through gene duplication in rodents .

• Independent expansions: The V1R repertoire has expanded independently in placental mammals and marsupials, suggesting convergent evolution in pheromone detection systems .

• Correlation with VNO complexity: There appears to be a concordance between V1R repertoire size and the complexity of VNO morphology, suggesting that VNO complexity may indicate the sophistication of pheromone communication within a species .

• Rapid evolution: The V1R gene family shows evidence of rapid evolution, likely driven by adaptation to species-specific chemical communication needs.

How do V1R expression patterns differ between rat subspecies?

Research comparing two subspecies of brown rats (Rattus norvegicus) has revealed significant differences in vomeronasal receptor expression:

• Differential expression: RNA-seq and qPCR analyses identified several differentially expressed vomeronasal receptor genes between the North China subspecies [R. n. humiliatus (RNH)] and the Northeast China subspecies [R. n. caraco (RNC)] .

• V1R family differences: In the V1R family, Vom1r68 was expressed at significantly higher levels in RNH females than in RNC females, while Vom1r60 and Vom1r81 showed the opposite pattern .

• V2R family differences: In the V2R family, Vom2r53 and a Vom2r pseudogene were expressed at higher levels in RNH females, while Vom2r43 was lower in RNH compared to RNC females .

These expression differences may reflect adaptation to detect subspecies-specific pheromonal signals.

How do differences in pheromone production correlate with receptor expression?

Comparative studies between rat subspecies have found a potential co-evolution of pheromone production and detection systems:

• Coordinated differences: RNH males showed higher levels of two predominant male pheromones (2-heptanone and MUP13) compared to RNC males .

• Receptor sensitivity correlation: Correspondingly, the vomeronasal receptors that detect these pheromones (Vom1r68 for 2-heptanone and Vom2r53 for MUP13) were expressed at higher levels in RNH females compared to RNC females .

• Functional confirmation: Calcium imaging experiments confirmed that Vom1r68 responds to 2-heptanone and Vom2r53 responds to MUP13, providing evidence for a functional link between pheromone production and detection differences .

This coordination suggests genetic coupling or coadaptation between pheromone signaling and reception systems within subspecies.

What approaches can be used to overcome expression challenges for vomeronasal receptors?

Vomeronasal receptors, like many GPCRs, can be challenging to express in heterologous systems. Strategies to improve expression include:

• Optimized expression systems: Select appropriate host cells such as HEK293-T cells that have been successfully used for vomeronasal receptor expression .

• Codon optimization: Adapt the coding sequence to the preferred codon usage of the expression host.

• Fusion tags: Use tags that enhance solubility and membrane targeting, such as His-tags for purification .

• Membrane targeting signals: Include signals that improve receptor trafficking to the cell membrane.

• Expression verification: Use immunofluorescence to confirm proper membrane localization, as demonstrated for vomeronasal receptors like Vom1r68 .

What techniques are used to study vomeronasal receptor transcriptomes?

Several genomic and transcriptomic approaches have been employed to study vomeronasal receptors:

• RNA-seq analysis: Used to identify differentially expressed vomeronasal receptor genes between samples. For example, RNA-seq revealed 180 VRs (93 V1Rs and 87 V2Rs) in rat VNO tissues .

• GO enrichment analysis: Molecular Function (MF) Gene Ontology analysis identified VR genes involved in response to stimuli. This approach revealed three V1r genes (Vom1r60, Vom1r68, and Vom1r81) and three V2r genes (Vom2r53, Vom2r-ps1, and Vom2r43) with differential expression between rat subspecies .

• qPCR validation: Quantitative PCR confirms expression differences identified by RNA-seq. This technique verified that Vom1r68 and Vom2r53 were expressed at significantly higher levels in RNH females compared to RNC females .

What are the remaining challenges in understanding V1ra15 function?

Despite advances in vomeronasal receptor research, several challenges remain in understanding V1ra15 function:

• Ligand identification: The specific pheromone(s) that activate V1ra15 have not been definitively identified, requiring systematic screening approaches.

• Structural characterization: The three-dimensional structure of V1ra15 has not been determined, limiting our understanding of ligand binding mechanisms.

• In vivo function: The precise behavioral and physiological responses mediated by V1ra15 activation remain to be fully characterized.

• Integration with neural circuits: How V1ra15 signaling integrates with broader neural circuits to influence behavior needs further investigation.

• Species-specific functions: The role of V1ra15 might differ between rat subspecies or strains, requiring comparative functional studies.

What emerging technologies might advance vomeronasal receptor research?

Emerging technologies that could advance our understanding of V1ra15 and other vomeronasal receptors include:

• CRISPR-Cas9 gene editing: Creation of receptor knockout or reporter animals to study receptor function in vivo.

• Single-cell RNA-seq: Characterization of receptor expression patterns at the single-cell level to understand cellular heterogeneity.

• Cryo-EM: Determination of receptor structures at high resolution to understand ligand binding mechanisms.

• Optogenetics: Selective activation of receptor-expressing neurons to study downstream circuit responses.

• Computational modeling: Prediction of receptor-ligand interactions based on structural information and molecular dynamics simulations.

• Organoids: Development of vomeronasal organ organoids to study receptor function in a more physiological context than cell lines.

These technologies could help resolve outstanding questions about V1ra15 function and the broader role of vomeronasal receptors in pheromone communication.