GNAI3 Human
Description
Gene and Protein Overview
Gene Details
| Feature | Description |
|---|---|
| Chromosomal location | 1p13 |
| Transcript | NM_006496.3 (354 amino acids) |
| Protein class | G-protein alpha subunit (inhibitory) |
| Molecular weight | ~43 kDa |
Protein Structure
GNAI3 forms the alpha subunit of heterotrimeric G proteins (Gαi3), which interact with βγ subunits (GNB1, GNB2, GNB4) to regulate downstream signaling . The protein alternates between GDP-bound (inactive) and GTP-bound (active) states, modulating adenylyl cyclase and potassium channels .
Functional Role in Signaling
GNAI3-mediated pathways inhibit adenylyl cyclase, reducing intracellular cAMP levels . Key functions include:
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Developmental regulation: Critical for pharyngeal arch formation, influencing jaw and ear development .
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Cellular processes: Modulates ion channels, mitosis, and receptor signaling .
Regulatory Interactions
| Partner Protein | Function | Source |
|---|---|---|
| GNB1, GNB2, GNB4 | Forms heterotrimeric G-protein complex | |
| RGS2, RGS10 | Enhances GTPase activity to terminate signaling | |
| SSTR2 | Mediates somatostatin receptor signaling |
Clinical Associations
Auriculo-Condylar Syndrome (ARCND1)
Mutations in GNAI3 cause ARCND1, characterized by micrognathia, malformed ears, and fused jaw structures.
| Mutation | Functional Impact | Source |
|---|---|---|
| p.Asn269Lys | Disrupts guanine nucleotide binding | |
| p.Leu53Arg | Alters GTPase activity |
Other Pathologies
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NAFLD: Downregulation linked to lipid metabolism dysregulation in hepatic models .
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Infections: Deamidation by Photorhabdus toxins activates RhoA, impairing host defense .
Research Findings
Developmental Studies
| Model | Observation | Source |
|---|---|---|
| Gnai3-iresGFP mice | GFP expression in Deiter’s cells, Hensen’s cells, and hematopoietic cells | |
| Knock-in mice | Biallelic GFP expression correlates with higher fluorescence intensity |
Disease Mechanisms
| Study | Key Insight | Source |
|---|---|---|
| Whole-exome sequencing | Novel GNAI3 variant (c.807C>A) in Japanese ARCND1 patient | |
| Hepatic models | GNAI3 downregulation exacerbates methionine-choline-deficient diet-induced NAFLD |
Expression Patterns
Tissue Distribution
| Tissue | Expression Level | Source |
|---|---|---|
| Inner ear | High (Deiter’s cells, Hensen’s cells) | |
| Blood | Detected in platelets, B/T cells, macrophages | |
| Liver | Modulated in NAFLD models |
Therapeutic and Diagnostic Implications
Diagnostic Tools
| Method | Application | Source |
|---|---|---|
| Immunofluorescence | Detects Gαi3 in inner ear and hematopoietic cells | |
| Flow cytometry | Quantifies GFP fluorescence in knock-in mice |
Future Directions
Product Specs
Q&A
What is the basic structure and function of the GNAI3 protein?
GNAI3 encodes the inhibitory alpha subunit of heterotrimeric guanine nucleotide-binding proteins (G proteins). The protein consists of 354 amino acids and contains five guanine nucleotide-binding sites (G1-G5 boxes) within its GTP catalytic domain. These G boxes are essential for binding guanine nucleotides and subsequent signaling functions. As part of G protein complexes (composed of alpha, beta, and gamma subunits), GNAI3 serves as a critical signal transducer that inhibits adenylate cyclase activity, leading to decreased intracellular cAMP levels .
How does GNAI3 function in cellular signaling pathways?
GNAI3 functions through a classical G protein signaling mechanism where it cycles between active (GTP-bound) and inactive (GDP-bound) states. When G protein-coupled receptors (GPCRs) are activated by extracellular signals, they promote GDP release and GTP binding to the alpha subunit. In its active form, GNAI3 inhibits adenylate cyclase, reducing cAMP production. The alpha subunit possesses intrinsic GTPase activity that hydrolyzes GTP to GDP, thereby terminating signaling. This cyclical process is tightly regulated by numerous regulatory proteins that modulate both GDP release and GTP hydrolysis rates .
What are the known physiological roles of GNAI3?
GNAI3 plays essential roles in:
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Inhibiting adenylate cyclase activity, which decreases intracellular cAMP levels
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Stimulating activity of receptor-regulated K+ channels
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Regulating cell division processes
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Contributing to embryonic development, particularly in the formation of first and second pharyngeal arches, which ultimately develop into jawbones, facial muscles, middle ear bones, ear canals, and outer ears
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Participating in the endotherin-Dlx5/Dlx6 signaling pathway during mandibular development
What experimental models are available for studying GNAI3 expression and function?
Researchers have developed several valuable models for studying GNAI3, most notably the Gnai3-iresGFP reporter mouse line. This model features an internal ribosomal entry site (IRES) inserted behind the stop-codon of the Gnai3 gene, initiating simultaneous translation of GFP alongside Gαi3. Importantly, this genetic modification does not alter Gαi3 expression levels compared to wild-type littermates, making it an ideal tool for precise analysis of expression patterns. This reporter system allows visualization of Gαi3 expression in various tissues including spleen, thymus, and the inner ear .
What methods are most effective for detecting GNAI3 expression in different tissues?
Multiple complementary approaches can be employed:
| Method | Application | Advantages | Limitations |
|---|---|---|---|
| Flow cytometry | Cell-specific expression | High throughput, quantitative | Requires single-cell suspensions |
| Immunofluorescence | Tissue localization | Preserves spatial context | Antibody specificity challenges |
| Immunoblot analysis | Protein expression levels | Quantitative, detects total protein | Loses spatial information |
| Reporter systems (e.g., Gnai3-iresGFP) | Live tracking | Non-invasive, real-time | Requires genetic modification |
The Gnai3-iresGFP reporter mouse has been successfully used with flow cytometry to detect GFP fluorescence in B cells, T cells, macrophages, granulocytes, and platelets, while immunofluorescent staining has revealed expression in the inner ear, particularly in Deiter's cells and Hensen's cells .
What diseases are associated with GNAI3 mutations?
Mutations in GNAI3 cause auriculo-condylar syndrome type 1 (ARCND1), a rare disorder primarily affecting the development of the ears and lower jaw (mandible). This condition is characterized by micrognathia (abnormally small jaw), external ear malformations, and prominent cheeks. ARCND1 represents one of three genetically distinct forms of auriculo-condylar syndrome, with the others caused by mutations in PLCB4 (ARCND2) and EDN1 (ARCND3) .
How do specific mutations in the GNAI3 gene affect protein function?
At least six pathogenic variants in GNAI3 have been identified in patients with ARCND1:
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Three mutations in the G1 box (p.Gly40Arg, p.Gly45Val, and p.Ser47Arg)
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One mutation adjacent to the G1 box (p.Thr48Asn)
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Two mutations in the G4 box (p.Asn269Tyr and p.Asn269Lys)
The most recently reported variant, p.Asn269Lys, disrupts a hydrogen bond with the N7 atom of the guanine moiety, likely interfering with downstream Gαi3 signaling. In silico structural analysis suggests this substitution impairs guanine nucleotide binding, which explains the observed developmental abnormalities. These mutations likely alter the structure of the inhibitory alpha subunit and impair normal G protein signaling .
How do the phenotypic manifestations of GNAI3 mutations differ from other forms of auriculo-condylar syndrome?
ARCND1 caused by GNAI3 mutations exhibits distinguishable craniofacial features compared to ARCND2 and ARCND3:
| Feature | ARCND1 (GNAI3) | ARCND2/3 (PLCB4/EDN1) |
|---|---|---|
| Mandibular hypoplasia | Severe | Mild to moderate |
| Mandibular angle | Unclear/absent | Clear |
| Fusion | Between mandibular rami and pterygoid plate | Not described |
| Mandibular condyle | Often absent | Present but hypoplastic |
Three-dimensional computed tomography (3D-CT) of ARCND1 patients typically shows agenesis of the mandibular condyle, retrognathia, excessively short mandibular rami, and fusion with the medial and lateral pterygoid plates. This severe mandibular phenotype may be due to additional dysregulation of Sox9 expression, which is regulated by Gnai3 via PKA and cAMP during embryonic development .
How does GNAI3 interact with other proteins in signaling cascades?
GNAI3 functions within complex protein interaction networks, particularly in the context of GPCR signaling pathways. The active GTP-bound form prevents the association of RGS14 with centrosomes and facilitates its translocation from the cytoplasm to the plasma membrane. In the context of craniofacial development, Gnai3 acts upstream in the endotherin-Dlx5/Dlx6 signaling pathway, where dysregulation causes the mandibular abnormalities observed in ARCND1. Additionally, GNAI3 interacts with regulatory proteins that modulate its GTPase activity and GDP/GTP exchange .
What are the tissue-specific expression patterns of GNAI3?
Analysis of the Gnai3-iresGFP reporter mouse has revealed previously unknown expression patterns. GFP fluorescence, reflecting Gαi3 expression, has been detected in:
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Immune cells: B cells, T cells, macrophages, and granulocytes from both spleen and blood
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Platelets in blood samples
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Inner ear structures, with highest expression in Deiter's cells and the first row of Hensen's cells in the organ of Corti
These findings demonstrate that GNAI3 is expressed in diverse cell types and tissues, suggesting broader physiological roles than previously recognized .
What approaches can be used to measure changes in GNAI3 activity in response to stimuli?
Researchers can employ multiple complementary methods to assess GNAI3 activity:
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GTPγS binding assays to measure activation state
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FRET-based sensors to detect conformational changes in real-time
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Measurement of downstream effectors (e.g., cAMP levels, adenylate cyclase activity)
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Electrophysiological recordings of K+ channel activity, which is stimulated by GNAI3
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Phosphorylation assays of downstream targets regulated by GNAI3-dependent pathways
How can researchers effectively study the role of GNAI3 in embryonic development?
Researchers investigating GNAI3's developmental roles should consider:
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Temporal-spatial gene expression analysis during embryogenesis, particularly in craniofacial structures
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Conditional knockout models to study tissue-specific effects
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Reporter systems (like Gnai3-iresGFP) to track expression throughout development
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Analysis of Sox9 expression in relation to Gnai3 activity, as this relationship appears critical for proper mandibular development
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Comparative analysis between wild-type and mutant phenotypes using 3D-CT or other imaging techniques to characterize structural abnormalities in the developing mandible and associated structures
Product Science Overview
Guanine nucleotide-binding proteins, commonly known as G proteins, play a crucial role in various transmembrane signaling pathways. These proteins are composed of three subunits: alpha, beta, and gamma. The alpha subunit, in particular, is responsible for binding guanine nucleotides and is pivotal in the regulation of signal transduction.
The GNAI3 gene encodes the alpha subunit of the inhibitory G protein (Gαi3). This gene is part of the G-alpha family and is involved in modulating or transducing signals across cell membranes . The GNAI3 gene is located on chromosome 1 and has been associated with several important cellular functions and pathways.
The alpha subunit encoded by GNAI3 alternates between an active, GTP-bound state and an inactive, GDP-bound state. When a G protein-coupled receptor (GPCR) is activated, it promotes the release of GDP and the binding of GTP to the alpha subunit. This activation triggers the alpha subunit to interact with various effector proteins, such as adenylyl cyclase, which in turn influences numerous cellular activities .
The Gαi3 subunit specifically inhibits the activity of adenylyl cyclase, reducing the production of cyclic AMP (cAMP) within the cell. This inhibition is crucial for regulating various physiological processes, including cell growth, division, and differentiation .
Mutations in the GNAI3 gene have been linked to auriculocondylar syndrome (ARCND), a rare genetic disorder characterized by craniofacial abnormalities such as question mark ears, mandibular condyle hypoplasia, and micrognathia . These mutations can affect the downstream targets in the G protein-coupled endothelin receptor pathway, leading to the clinical manifestations of the syndrome.
Human recombinant GNAI3 proteins are widely used in research to study the mechanisms of G protein signaling and their role in various diseases. These recombinant proteins are produced using advanced biotechnological methods, ensuring high purity and activity. They serve as valuable tools for investigating the molecular interactions and regulatory mechanisms of G proteins in cellular signaling pathways.
