Recombinant Mouse Probable G-protein coupled receptor 149 (Gpr149)

What is Gpr149 and what are its structural characteristics?

GPR149 is classified as a Class-A, rhodopsin-like G-protein coupled receptor (GPCR) with clear orthologs in many vertebrates including mice and humans. Structurally, it is a 732 amino acid protein with a unique and highly conserved 360 amino acid C-terminal domain that has no homology to other proteins and may play a significant role in downstream signaling . Unlike typical Class A GPCRs, GPR149 lacks the first two charged amino acids of the characteristic Asp-Arg-Tyr (DRY) motif found at the end of the third transmembrane helix, which is typically important in G protein coupling . Based on phylogenetic analysis of human GPCRs, GPR149 shows closest sequence homology to receptors that utilize peptides as their ligands, though its endogenous ligand remains unidentified .

Where is Gpr149 expressed in mice?

GPR149 exhibits a distinctive expression pattern with neuronal enrichment. Quantitative PCR analysis has revealed that the strongest expression occurs in central nervous system tissues, particularly in the striatum, hypothalamus, brainstem, and spinal cord . Among non-neuronal tissues, the pituitary gland shows the highest expression levels . Low levels of expression are detected in the gastrointestinal tract and female reproductive organs, while other examined tissues show very low or threshold-level expression .

In situ hybridization studies have further mapped the precise distribution of Gpr149 within the brain, identifying at least 80 brain regions with varying expression levels. The most robust expression is observed in the islands of Calleja, olfactory tubercle, ventromedial hypothalamus, rostral interpeduncular nucleus, and select brainstem nuclei such as the sphenoid nucleus . In the adult mouse brain, Gpr149 expression appears to be restricted to neurons rather than glial cells .

In the reproductive system, Gpr149 is highly expressed in oocytes, particularly at the germinal vesicle and meiosis II stages, but not in granulosa cells . Expression levels are low in newborn ovaries but increase throughout folliculogenesis, then decline after fertilization, becoming undetectable by the two-cell stage .

What knockout models are available for studying Gpr149 function?

Several knockout models have been developed for investigating Gpr149 function:

• Global Gpr149 knockout mice: These were generated by targeting exon 1, resulting in complete deletion of the gene. These knockout mice are viable and display normal folliculogenesis but unexpectedly show enhanced fertility phenotypes .

• Gpr149-Cre line: This transgenic model was created by inserting Cre-P2A at the Gpr149 ATG start sequence, allowing for lineage tracing of Gpr149-expressing cells .

The methodology for generating these models typically involves:

• For the null allele: CRISPR/Cas9-mediated deletion using guide RNAs flanking exon 1, with administration through pronuclear injection in C57Bl/6N mice .

• For the Cre line: Targeting the endogenous Gpr149 locus with guide RNAs and co-injecting pronuclei with DNA encoding homology arms and Cre-P2A sequence .

Genotyping can be performed using specific primers that distinguish between wild-type and knockout alleles, resulting in characteristic band patterns on gel electrophoresis (WT band of 200 bp and Gpr149 KO band of 350 bp) .

How can researchers validate Gpr149 expression in experimental models?

Researchers can employ multiple complementary techniques to validate Gpr149 expression:

• Quantitative PCR (qPCR): For broad tissue screening and relative quantification of expression levels. Primers targeting Gpr149 (e.g., Gpr149-Det-1 forward: 5′-GTTGCCTTCGATGGGAAAAAG and Gpr149-Det-1 reverse: 5′-TGGGACAGTCGTCTCTCTGGA) can be used with appropriate housekeeping genes like Hprt1 and Gapdh as controls .

• In situ hybridization (ISH): To map the precise cellular distribution of Gpr149 mRNA in tissues. RNAscope technology with specific probes (e.g., RNAscope probe #318071) has been successfully applied for detailed brain mapping .

• Transgenic reporter models: Gpr149-Cre-tdTomato mice can be used to visualize Gpr149-expressing cells through fluorescent labeling .

• Validation in knockout models: Comparing expression between wild-type and Gpr149-/- tissues provides crucial specificity controls for antibodies and probes .

For optimal results, researchers should consider combining these approaches to overcome the limitations of individual methods and ensure reliable detection.

How does Gpr149 deletion affect fertility and reproductive functions in mice?

Contrary to initial expectations, Gpr149 knockout mice display enhanced fertility phenotypes. Female Gpr149-/- mice exhibit:

• Increased fertility with enhanced ovulation rates

• Normal folliculogenesis despite the absence of this oocyte-enriched receptor

• Elevated oocyte Gdf9 mRNA levels, which may contribute to the hyperfertility phenotype through improved oocyte quality

• Increased levels of FSH receptor and cyclin D2 mRNA in granulosa cells, suggesting altered follicular sensitivity to gonadotropins

These findings position Gpr149 as a negative regulator of fertility, making it one of the few known genetic models with enhanced reproductive capacity. The molecular mechanisms underlying this phenotype likely involve complex interactions between oocyte-derived factors (like GDF9) and somatic cell responses in the follicle. The potential therapeutic implications for fertility enhancement make this an especially promising area for translational research .

What is the role of Gpr149 in energy homeostasis?

Recent evidence suggests Gpr149 involvement in energy metabolism regulation, though the precise mechanisms remain to be fully elucidated:

• Gpr149 expression has been detected in brain regions critical for energy balance and glucose homeostasis, most notably the ventromedial hypothalamus .

• The receptor is enriched in mouse vagal afferents, suggesting potential roles in gut-brain signaling pathways that regulate feeding behavior and energy expenditure .

• Male Gpr149 knockout mice exhibit metabolic phenotypes that indicate involvement in energy homeostasis, though detailed characterization of these effects requires further investigation .

The neuronal enrichment of Gpr149 in regions associated with autonomic regulation, motivated behaviors, and sensory processing supports its potential role as a modulator of metabolic functions. Researchers investigating this aspect should consider comprehensive metabolic phenotyping of knockout models, including:

• Energy expenditure measurements

• Glucose tolerance and insulin sensitivity testing

• Food intake and body composition analysis

• Hypothalamic neuropeptide expression profiling

What are the challenges in identifying potential endogenous ligands for Gpr149?

As an orphan GPCR, identifying the endogenous ligand(s) for Gpr149 presents significant challenges:

What techniques are optimal for mapping Gpr149 expression patterns across tissues?

Comprehensive mapping of Gpr149 expression requires a multi-technique approach:

• Quantitative PCR (qPCR):

  • Advantages: High sensitivity, quantitative, suitable for large-scale tissue screening

  • Methodology: Extract RNA using appropriate kits (e.g., RNeasy mini/microkit for tissues/oocytes), perform reverse transcription with Superscript III, and conduct qPCR with validated primers

  • Limitations: Lacks cellular resolution, may detect low-level expression with unclear biological significance

• In situ hybridization (ISH):

  • Advantages: Provides cellular and subcellular resolution, visualizes spatial distribution

  • Methodology: RNAscope technology with specific Gpr149 probes has been successfully used on fixed tissue sections, with either fluorescent or chromogenic detection systems

  • Protocol details: Apply probe at 40°C for 2 hours, followed by amplification with Opal570 for fluorescence or FastRed for chromogenic detection

  • Validation: Include Gpr149-/- tissues as negative controls to confirm probe specificity

• Single-cell RNA sequencing:

  • Advantages: Reveals cell-type specific expression patterns and potential co-expression with other genes

  • Applications: Particularly valuable for heterogeneous tissues like brain regions where Gpr149 may be expressed in specific neuronal subpopulations

• Transgenic reporter models:

  • Advantages: Allows visualization of Gpr149-expressing cells in intact tissues and potential for live imaging

  • Example: Gpr149-Cre-tdTomato mice provide fluorescent labeling of cells that express or have expressed Gpr149

  • Applications: Useful for developmental studies and lineage tracing

The optimal strategy involves complementary use of these techniques, with qPCR providing broad tissue screening, ISH offering cellular resolution, and transgenic models enabling developmental and functional studies.

How can researchers generate and validate transgenic Gpr149 mouse models?

Generating reliable transgenic Gpr149 mouse models involves several critical steps:

• Design strategy selection:

  • For knockout models: Target critical exons (e.g., exon 1) containing the start codon to ensure complete protein ablation

  • For Cre-driver lines: Insert Cre recombinase at the endogenous Gpr149 locus to maintain physiological expression patterns

• CRISPR/Cas9-based targeting:

  • Design guide RNAs flanking the target region (e.g., guides flanking a 2kb region containing Gpr149 exon 1)

  • For the Gpr149 null allele, use guides such as:

    • 5′ Guide: 5′-CUUAUAACUGGUCACCUAUGUGUUUUAGAGCUAUGCU-3′

    • 3′ Guide: 5′-UUGGUAGUUAACGAGACCCCGUUUUAGAGCUAUGCU-3′

  • Administer guides, tracrRNA, and Cas9 protein through pronuclear injection in appropriate mouse strains (e.g., C57Bl/6N)

• Genotyping strategies:

  • Design primers that can distinguish wild-type and modified alleles:

    • Gpr149 1: 5′-GCTGCTTGTAATGTGTGCAGAGAG-3′

    • Gpr149 2: 5′-GTCTACTCATGGCAGACCAAAGTAATGG-3′

    • Gpr149 3: 5′-GTCTCTTGGTGCTAGAGATGGGTG-3′

  • Expected results: WT band of 200 bp and Gpr149 KO band of 350 bp

• Validation approaches:

  • Molecular validation: Confirm gene deletion/modification at DNA, RNA, and protein levels

  • Functional validation: Assess expected phenotypes based on known Gpr149 functions (e.g., enhanced fertility in females)

  • Expression validation: Use ISH to confirm absence of Gpr149 expression in knockout tissues

What approaches can be used to study Gpr149 signaling mechanisms?

Investigating the signaling mechanisms of an orphan GPCR like Gpr149 requires specialized approaches:

• G-protein coupling assays:

  • BRET/FRET-based assays to measure interactions between Gpr149 and different G-protein subtypes

  • GTPγS binding assays to detect G-protein activation in membrane preparations

  • Second messenger measurements (cAMP, Ca²⁺, IP₃) in response to potential ligands

• β-arrestin recruitment assays:

  • Measure recruitment of fluorescently-tagged β-arrestin to Gpr149 in heterologous expression systems

  • Assess receptor internalization and trafficking patterns

• Interactome analysis:

  • Proximity labeling techniques (BioID, APEX) to identify proteins interacting with Gpr149's unique C-terminal domain

  • Co-immunoprecipitation followed by mass spectrometry to identify protein complexes

  • Yeast two-hybrid screening to identify intracellular binding partners

• Comparative transcriptomics/proteomics:

  • RNA-seq comparison between wild-type and Gpr149-/- tissues to identify downstream transcriptional effects

  • Phosphoproteomics to detect signaling cascades affected by Gpr149 deletion

  • Single-cell approaches to capture cell-type specific signaling events

• Functional rescue experiments:

  • Re-expression of wild-type or mutant Gpr149 in knockout backgrounds to identify critical signaling domains

  • Creation of chimeric receptors to determine G-protein coupling specificity

Given the unique structural features of Gpr149, particularly its atypical DRY motif and extended C-terminal domain, researchers should consider the possibility of non-canonical signaling mechanisms that may not be captured by standard GPCR assays.

What is the potential role of Gpr149 in pathological conditions?

Emerging evidence suggests potential involvement of Gpr149 in several pathological contexts:

• Reproductive disorders:

  • Given its role as a negative regulator of fertility in mice, Gpr149 polymorphisms or expression alterations might contribute to fertility variations in humans

  • Potential relevance to premature ovarian failure or polycystic ovarian syndrome warrants investigation

• Oncology:

  • Methylation patterns of GPR149 have been identified as potential prognostic markers for clear cell renal cell carcinoma (ccRCC)

  • Significantly higher methylation levels of GPR149 were observed in ccRCC specimens compared to normal controls

  • Increased methylation levels of GPR149 were significantly associated with advanced pathological T stage in ccRCC

  • GPR149 methylation exhibited a tendency to increase with higher tumor grade, though differences were not statistically significant (P=0.052)

• Neurological conditions:

  • Gpr149 has been identified as a negative regulator of myelinization, suggesting potential relevance to demyelinating disorders

  • Its expression in brain regions involved in motivated behaviors and sensory processing may implicate it in neuropsychiatric conditions

• Metabolic disorders:

  • Expression in hypothalamic regions controlling energy balance and in vagal afferents suggests possible roles in metabolic regulation that could be relevant to obesity or diabetes

How might epigenetic regulation affect Gpr149 expression and function?

Epigenetic regulation appears to play an important role in modulating Gpr149 expression:

• DNA methylation patterns:

  • Differential methylation of GPR149 has been observed in ccRCC compared to normal kidney tissue

  • Methylation levels correlate with disease progression markers such as pathological T stage

• Methodological approaches for studying Gpr149 methylation:

  • Pyrosequencing (PSQ) analysis on bisulfite-modified genomic DNA has been successfully employed to assess GPR149 methylation status

  • Specific CpG island regions (e.g., Infinium HumanMethylation450 target ID: cg00046499) have been identified as relevant for GPR149 methylation analysis

• Potential regulatory mechanisms:

  • Tissue-specific expression patterns of Gpr149 may be maintained through epigenetic mechanisms

  • Developmental regulation of Gpr149 expression (e.g., during folliculogenesis and after fertilization) might involve dynamic epigenetic modifications

What are the therapeutic implications of Gpr149 research?

The unique characteristics and functions of Gpr149 suggest several potential therapeutic applications:

• Fertility enhancement:

  • As one of the few genetic models with enhanced fertility, Gpr149 antagonists could potentially serve as novel treatments for certain forms of infertility

  • The Gpr149 signaling pathway might be targeted for improving assisted reproductive technology outcomes

• Cancer diagnostics and prognostics:

  • GPR149 methylation patterns could serve as biomarkers for ccRCC progression and prognosis

  • The study by Spandidos Publications concluded that "novel methylation markers ZNF492 and GPR149 could be independent prognostic indicators in patients with ccRCC"

• Neurological applications:

  • Given its role as a negative regulator of myelinization, Gpr149 antagonists might have potential in promoting remyelination in demyelinating disorders

  • Expression in specific brain circuits suggests possible applications in neuropsychiatric or neurodevelopmental conditions

• Metabolic regulation:

  • If further research confirms roles in energy homeostasis, Gpr149-targeted therapies might have applications in metabolic disorders

• Drug development considerations:

  • The orphan status of Gpr149 presents challenges for traditional drug development approaches

  • Structure-based drug design will be complicated by the unique features of Gpr149, including its atypical DRY motif and extended C-terminal domain

  • High-throughput screening of compound libraries using Gpr149-expressing cell lines could identify lead molecules for antagonist development