{"gene":"GPR156","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":2021,"finding":"GPR156 acts downstream of the transcription factor EMX2 to signal through Gαi, triggering a 180° reversal in hair cell orientation in mechanosensory epithelia. EMX2 polarizes GPR156 distribution at hair cell boundaries, enabling GPR156-Gαi signaling to establish mirror-image hair cell orientations in mouse otolith organs and zebrafish lateral line.","method":"Genetic loss-of-function (mouse and zebrafish knockout), live imaging, epistasis experiments","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — clean KO in two species with defined cellular phenotype, epistasis placing GPR156 downstream of EMX2 and upstream of Gαi, replicated across labs","pmids":["34001891"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures of human GPR156 in apo and Gi3-coupled states reveal that GPR156 forms a TM5/6-TM5/6 dimer interface in both states, explaining its high constitutive activity. ECL2 and the N-terminus form a small extracellular region. The C-terminus of the G-bound subunit plays a dual role: promoting G protein binding within that subunit while preventing the G-free subunit from binding an additional G protein.","method":"Cryo-EM structure determination, functional assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structures in two states with mechanistic interpretation of dimerization and constitutive activity","pmids":["39638804"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures of human GPR156 in Go-free and Go-coupled states reveal that an endogenous phospholipid molecule is located within each TMD of the GPR156 dimer. Asymmetric Gα binding to the phospholipid-bound GPR156 dimer restructures intracellular loops 1 and 2 and the C-terminal part of TM7 without altering dimer conformation, identifying GPR156 as a transducer for phospholipid signaling whose constitutive activity is maintained by constant phospholipid binding.","method":"Cryo-EM structure determination, active-site analysis","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structures in two states with identification of endogenous phospholipid ligand and mechanistic dissection of constitutive activation","pmids":["38332368"],"is_preprint":false},{"year":2021,"finding":"GPR156 exhibits constitutive Gi/o coupling when expressed as an unliganded orphan GPCR, as detected using luciferase reporter assays with G protein chimeras.","method":"Luciferase reporter assay with Gαi/o chimeric G proteins","journal":"British journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — cell-based functional assay with chimeric G proteins, single lab","pmids":["33784795"],"is_preprint":false},{"year":2003,"finding":"GPR156 (termed GABABL) was identified as a novel class C GPCR with sequence homology to GABAB1/GABAB2, containing a C-terminal coiled-coil domain, di-leucine motifs, and RXR(R) ER retention motifs. Expression in isolation or with GABAB1/GABAB2 failed to produce functional GABA-responsive receptor, indicating its endogenous partner was unknown.","method":"Molecular cloning, bioinformatics, functional expression assays","journal":"Brain research. Molecular brain research","confidence":"Medium","confidence_rationale":"Tier 3 — molecular cloning with functional null result; negative data well-controlled","pmids":["12591167"],"is_preprint":false},{"year":2003,"finding":"GPR156 (GABABL) protein is distributed throughout the rat CNS, with dense immunoreactivity in cortex, hippocampus, dentate gyrus, cerebellum (granule cell layer and Purkinje cells), spinal cord substantia gelatinosa, and a subset of parvalbumin-positive hippocampal interneurons, as determined by immunohistochemistry.","method":"Immunohistochemistry with specific rabbit polyclonal antisera","journal":"Brain research","confidence":"Medium","confidence_rationale":"Tier 3 — direct localization experiment with validated antibody, single lab","pmids":["14556935"],"is_preprint":false},{"year":2023,"finding":"STK32A, a serine/threonine kinase negatively regulated by EMX2, reinforces line of polarity reversal formation by regulating the apical localization of GPR156 in mouse inner ear hair cells. Genetic epistasis shows STK32A acts to block GPR156-mediated bundle reversal in EMX2-negative hair cells.","method":"Genetic epistasis (double mutants), conditional expression, immunolocalization","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — epistasis with double mutants and rescue experiments placing STK32A as a regulator of GPR156 apical localization","pmids":["37144879"],"is_preprint":false},{"year":2025,"finding":"Genetic epistasis in mice with combined Gpr156/Stk32a and Emx2/Stk32a mutations established that GPR156 functions to reverse stereociliary bundle orientation relative to the PCP axis, but this can be blocked by STK32A, and that EMX2 establishes the boundary between the two hair cell groups by repressing Stk32a transcription, allowing GPR156 to act.","method":"Genetic epistasis, combined knockout analysis, hair cell orientation quantification","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — multi-allele epistasis experiments defining pathway order among EMX2, STK32A, and GPR156","pmids":["41208475"],"is_preprint":false},{"year":2024,"finding":"In zebrafish, GPR156 loss abolishes the smaller mechanically-evoked signals characteristic of EMX2-positive hair cells, demonstrating GPR156 relays hair cell transduction information downstream of EMX2. In mouse, Gpr156 knockout otolith organs retain normal mechano-electrical transduction properties, zonal organization, and type I-II hair cell distribution, but show altered swimming and off-vertical-axis rotation performance.","method":"Electrophysiology (mechano-electrical transduction), mouse and zebrafish knockout behavioral assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function in two species with electrophysiological and behavioral readouts, replicated in peer-reviewed and preprint versions","pmids":["39531034","39282410"],"is_preprint":false},{"year":2026,"finding":"Conditional inactivation of Gpr156 specifically in postmitotic hair cells recapitulated the hair cell misorientation phenotype of null mutants and produced similar auditory and vestibular dysfunction, demonstrating that GPR156 is required in hair cells themselves for orientation. Hair cells can carry out mechano-electrical transduction without GPR156, indicating sensory deficits result from the orientation function rather than a direct role in transduction.","method":"Conditional knockout (hair cell-specific Cre), auditory brainstem response, vestibulo-ocular reflex, hair cell orientation analysis","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with multiple functional readouts and direct comparison to null, showing cell-autonomous role","pmids":["41547998"],"is_preprint":false},{"year":2023,"finding":"GPR156 is identified as a key inducer of lipid droplet accumulation in MMGT1-deficient macrophages during Mycobacterium tuberculosis infection, placing GPR156 in an MMGT1-GPR156-lipid droplet axis that promotes Mtb persistence.","method":"Genome-wide CRISPR screen, macrophage knockout validation, lipid droplet quantification","journal":"Cell host & microbe","confidence":"Medium","confidence_rationale":"Tier 2 — CRISPR screen hit validated in macrophage KO with specific phenotypic readout, single lab","pmids":["37269834"],"is_preprint":false},{"year":2025,"finding":"A rare missense variant in GPR156 (p.Glu533Asp), when knocked into the murine locus, induces medial habenula hyperactivity and abnormal stress-related behaviors, localizing GPR156 function to the medial habenula for mood regulation.","method":"Knock-in mouse model, electrophysiology (habenula activity), behavioral stress assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — humanized knock-in mouse with electrophysiological and behavioral validation, moderate evidence from single study","pmids":["40228124"],"is_preprint":false}],"current_model":"GPR156 is a constitutively active class C orphan GPCR that signals through Gαi/o proteins; structurally, it forms a TM5/6-TM5/6 dimer stabilized by endogenous phospholipid binding that drives constitutive activity, and its G protein coupling involves asymmetric Gα binding that reshapes intracellular loops without disrupting the dimer. In the inner ear, EMX2-dependent polarized localization of GPR156 at hair cell junctions enables Gαi signaling to reverse the interpretation of planar cell polarity cues—a process negatively regulated by STK32A—establishing mirror-image hair cell orientations essential for auditory and vestibular function; loss of GPR156 causes sensorineural hearing loss in mice and humans. In the medial habenula, a disease-associated GPR156 variant causes habenula hyperactivity and stress-related behavior, implicating it in mood regulation. Additionally, GPR156 promotes lipid droplet accumulation in macrophages as part of an MMGT1-GPR156 axis that supports Mycobacterium tuberculosis persistence."},"narrative":{"teleology":[{"year":2003,"claim":"Molecular cloning established GPR156 as a novel class C GPCR related to GABAB receptors, but with no identified ligand or functional signaling partner, defining it as an orphan receptor.","evidence":"Cloning, sequence analysis, and functional expression assays in heterologous cells","pmids":["12591167"],"confidence":"Medium","gaps":["No ligand identified","No signaling output detected in heterologous expression","Physiological function unknown"]},{"year":2003,"claim":"Mapping GPR156 protein distribution across the rat CNS revealed expression in cortex, hippocampus, cerebellum, and spinal cord, establishing it as a broadly expressed neuronal receptor.","evidence":"Immunohistochemistry with validated polyclonal antibodies in rat brain sections","pmids":["14556935"],"confidence":"Medium","gaps":["Single antibody approach without independent validation method","Function in any of these brain regions unknown","Expression outside CNS not examined"]},{"year":2021,"claim":"The central biological role of GPR156 was revealed when genetic loss-of-function in mice and zebrafish showed it acts downstream of EMX2 to activate Gαi signaling and reverse hair cell orientation by 180°, solving how mirror-image hair cell patterns are established in mechanosensory organs.","evidence":"Mouse and zebrafish knockouts with epistasis experiments, live imaging of hair cell orientation","pmids":["34001891"],"confidence":"High","gaps":["Mechanism of EMX2-dependent polarized localization unresolved","Direct protein-protein interactions mediating pathway not shown","Downstream effectors of Gαi in orientation reversal unknown"]},{"year":2021,"claim":"Cell-based signaling assays demonstrated that GPR156 constitutively couples to Gi/o proteins without an exogenous ligand, establishing it as a constitutively active orphan GPCR.","evidence":"Luciferase reporter assay with Gαi/o chimeric G proteins in transfected cells","pmids":["33784795"],"confidence":"Medium","gaps":["Chimeric G protein assay may not reflect native coupling","Single-lab observation at this time point","Molecular basis of constitutive activity unknown"]},{"year":2023,"claim":"Identification of STK32A as a negative regulator of GPR156 apical localization completed the EMX2→STK32A⊣GPR156→Gαi pathway hierarchy for hair cell orientation, explaining how boundary formation between hair cell groups is achieved.","evidence":"Genetic epistasis with double-mutant mice, conditional expression, and immunolocalization","pmids":["37144879"],"confidence":"High","gaps":["Whether STK32A directly phosphorylates GPR156 is not shown","Mechanism by which STK32A controls GPR156 apical trafficking unknown"]},{"year":2023,"claim":"A genome-wide CRISPR screen in macrophages revealed an unexpected non-neuronal role: GPR156 drives lipid droplet accumulation downstream of MMGT1, creating a lipid-rich niche that supports Mycobacterium tuberculosis persistence.","evidence":"CRISPR screen in macrophages, KO validation with lipid droplet quantification during Mtb infection","pmids":["37269834"],"confidence":"Medium","gaps":["Mechanism linking GPR156 signaling to lipid droplet biogenesis unclear","Whether Gαi coupling is involved in macrophage context not tested","Single study; not independently replicated"]},{"year":2024,"claim":"Two independent cryo-EM studies resolved the structural basis of GPR156 constitutive activity: the receptor forms a TM5/6-mediated homodimer with endogenous phospholipids bound within each TMD, and asymmetric Gα binding reshapes intracellular loops without disrupting the dimer architecture.","evidence":"Cryo-EM structures in apo, Go-free, Gi3-coupled, and Go-coupled states with functional assays","pmids":["38332368","39638804"],"confidence":"High","gaps":["Identity of the endogenous phospholipid not definitively assigned","Whether phospholipid binding is regulated in vivo unknown","No structure of GPR156 in complex with potential allosteric modulators"]},{"year":2024,"claim":"Electrophysiological and behavioral studies in zebrafish and mouse clarified that GPR156 controls the functional readout of hair cell orientation rather than mechano-electrical transduction itself, as knockout hair cells retain normal transduction properties.","evidence":"Mechano-electrical transduction recordings and behavioral assays in Gpr156 knockout mice and zebrafish","pmids":["39531034"],"confidence":"High","gaps":["How misorientation leads to altered signal integration at the circuit level is unexplored","Whether compensatory mechanisms exist in mature animals unknown"]},{"year":2025,"claim":"Multi-allele epistasis experiments refined the pathway model, establishing that EMX2 represses Stk32a transcription to permit GPR156-mediated bundle reversal, and confirmed GPR156's role is to reverse orientation relative to the PCP axis.","evidence":"Combined Gpr156/Stk32a and Emx2/Stk32a knockout mice with hair cell orientation quantification","pmids":["41208475"],"confidence":"High","gaps":["Direct transcriptional regulation of Stk32a by EMX2 not shown at promoter level","Whether additional regulators modulate GPR156 surface expression unknown"]},{"year":2025,"claim":"A human disease-associated GPR156 missense variant (E533D) knocked into mice caused medial habenula hyperactivity and stress-related behavioral abnormalities, extending GPR156 function beyond the inner ear to mood regulation in the brain.","evidence":"Knock-in mouse with electrophysiology of habenula neurons and behavioral stress assays","pmids":["40228124"],"confidence":"High","gaps":["Mechanism by which E533D alters receptor function (gain vs. loss of activity) not resolved","Whether this variant affects Gαi coupling specifically not tested","Relevance to human psychiatric phenotypes not clinically validated"]},{"year":2026,"claim":"Conditional inactivation of Gpr156 specifically in postmitotic hair cells demonstrated that the orientation function is cell-autonomous and confirmed that sensory deficits arise from misorientation rather than impaired transduction.","evidence":"Hair cell-specific conditional knockout with ABR, VOR, and hair cell orientation analysis","pmids":["41547998"],"confidence":"High","gaps":["Whether GPR156 has additional non-cell-autonomous roles in surrounding support cells not excluded","Temporal window during which GPR156 acts is not defined"]},{"year":null,"claim":"Key unresolved questions include the identity and regulatory significance of the endogenous phospholipid bound within the GPR156 dimer, the downstream effectors of Gαi that execute cytoskeletal remodeling for bundle reversal, whether STK32A directly phosphorylates GPR156, and the mechanism by which GPR156 promotes lipid droplet formation in macrophages.","evidence":"","pmids":[],"confidence":"High","gaps":["No substrate/effector downstream of Gαi in hair cells identified","Phospholipid identity and regulation unresolved","STK32A-GPR156 direct interaction not demonstrated","Macrophage signaling mechanism unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,2,3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,6,9]}],"pathway":[{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[0,8,9]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,6,7]}],"complexes":["GPR156 homodimer"],"partners":["GNAI3","GNAO1","STK32A","EMX2","MMGT1"],"other_free_text":[]},"mechanistic_narrative":"GPR156 is a constitutively active class C orphan GPCR that couples to Gαi/o proteins to establish mirror-image hair cell orientations in mechanosensory epithelia and modulates neuronal activity in the brain. In the inner ear, EMX2-dependent polarized localization of GPR156 at hair cell junctions activates Gαi signaling to reverse stereociliary bundle orientation relative to the planar cell polarity axis, a process negatively regulated by STK32A; loss of GPR156 causes sensorineural hearing loss and vestibular dysfunction in mice and is linked to hearing loss in humans [PMID:34001891, PMID:37144879, PMID:41547998]. Structurally, GPR156 forms a TM5/6-mediated homodimer stabilized by endogenous phospholipid binding within each transmembrane domain, and asymmetric Gα coupling reshapes intracellular loops without disrupting the dimer, explaining high constitutive activity [PMID:38332368, PMID:39638804]. A rare missense variant in GPR156 causes medial habenula hyperactivity and stress-related behavioral abnormalities, implicating GPR156 in mood regulation [PMID:40228124]."},"prefetch_data":{"uniprot":{"accession":"Q8NFN8","full_name":"Probable G-protein coupled receptor 156","aliases":["G-protein coupled receptor PGR28","GABAB-related G-protein coupled receptor"],"length_aa":814,"mass_kda":89.1,"function":"Orphan G-protein coupled receptor involved in the regulation of hair cell orientation in mechanosensory organs of the inner ear. It is required to trigger a 180 degree reversal in hair cell orientation, creating a virtual line of polarity reversal (LPR) across which stereociliary bundles are arranged in opposite orientations","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q8NFN8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GPR156","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GPR156","total_profiled":1310},"omim":[{"mim_id":"621310","title":"SERINE-THREONINE KINASE 32A; STK32A","url":"https://www.omim.org/entry/621310"},{"mim_id":"620551","title":"DEAFNESS, AUTOSOMAL RECESSIVE 121; DFNB121","url":"https://www.omim.org/entry/620551"},{"mim_id":"610464","title":"G PROTEIN-COUPLED RECEPTOR 156; GPR156","url":"https://www.omim.org/entry/610464"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"testis","ntpm":2.5}],"url":"https://www.proteinatlas.org/search/GPR156"},"hgnc":{"alias_symbol":["PGR28","GABABL"],"prev_symbol":[]},"alphafold":{"accession":"Q8NFN8","domains":[{"cath_id":"1.20.1070.10","chopping":"45-189_233-332","consensus_level":"high","plddt":83.3006,"start":45,"end":332}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NFN8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NFN8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NFN8-F1-predicted_aligned_error_v6.png","plddt_mean":55.47},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GPR156","jax_strain_url":"https://www.jax.org/strain/search?query=GPR156"},"sequence":{"accession":"Q8NFN8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8NFN8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8NFN8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NFN8"}},"corpus_meta":[{"pmid":"36928819","id":"PMC_36928819","title":"Genetic association analysis of 77,539 genomes reveals rare disease etiologies.","date":"2023","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/36928819","citation_count":58,"is_preprint":false},{"pmid":"33784795","id":"PMC_33784795","title":"In vitro profiling of orphan G protein coupled receptor (GPCR) constitutive activity.","date":"2021","source":"British journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/33784795","citation_count":50,"is_preprint":false},{"pmid":"34001891","id":"PMC_34001891","title":"EMX2-GPR156-Gαi reverses hair cell orientation in mechanosensory epithelia.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/34001891","citation_count":49,"is_preprint":false},{"pmid":"12591167","id":"PMC_12591167","title":"Molecular cloning and characterisation of a novel GABAB-related G-protein coupled receptor.","date":"2003","source":"Brain research. Molecular brain research","url":"https://pubmed.ncbi.nlm.nih.gov/12591167","citation_count":42,"is_preprint":false},{"pmid":"14556935","id":"PMC_14556935","title":"Distribution of a GABAB-like receptor protein in the rat central nervous system.","date":"2003","source":"Brain research","url":"https://pubmed.ncbi.nlm.nih.gov/14556935","citation_count":42,"is_preprint":false},{"pmid":"15067715","id":"PMC_15067715","title":"Differential expression of gamma-aminobutyric acid type B receptor subunit mRNAs in the developing nervous system and receptor coupling to adenylyl cyclase in embryonic neurons.","date":"2004","source":"The Journal of comparative neurology","url":"https://pubmed.ncbi.nlm.nih.gov/15067715","citation_count":16,"is_preprint":false},{"pmid":"34446027","id":"PMC_34446027","title":"Decoding pathogenesis factors involved in the progression of ATLL or HAM/TSP after infection by HTLV-1 through a systems virology study.","date":"2021","source":"Virology journal","url":"https://pubmed.ncbi.nlm.nih.gov/34446027","citation_count":14,"is_preprint":false},{"pmid":"39638804","id":"PMC_39638804","title":"Molecular insights into the activation mechanism of GPR156 in maintaining auditory function.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/39638804","citation_count":13,"is_preprint":false},{"pmid":"15702867","id":"PMC_15702867","title":"[History and the present of metabotropic GABAB receptor].","date":"2004","source":"Ceskoslovenska fysiologie","url":"https://pubmed.ncbi.nlm.nih.gov/15702867","citation_count":12,"is_preprint":false},{"pmid":"35938679","id":"PMC_35938679","title":"Hear the sounds: the role of G protein-coupled receptors in the cochlea.","date":"2022","source":"American journal of physiology. Cell physiology","url":"https://pubmed.ncbi.nlm.nih.gov/35938679","citation_count":11,"is_preprint":false},{"pmid":"37144879","id":"PMC_37144879","title":"The dark kinase STK32A regulates hair cell planar polarity opposite of EMX2 in the developing mouse inner ear.","date":"2023","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/37144879","citation_count":11,"is_preprint":false},{"pmid":"38332368","id":"PMC_38332368","title":"Constitutive activation mechanism of a class C GPCR.","date":"2024","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/38332368","citation_count":11,"is_preprint":false},{"pmid":"37269834","id":"PMC_37269834","title":"Identification of host regulators of Mycobacterium tuberculosis phenotypes uncovers a role for the MMGT1-GPR156 lipid droplet axis in persistence.","date":"2023","source":"Cell host & microbe","url":"https://pubmed.ncbi.nlm.nih.gov/37269834","citation_count":10,"is_preprint":false},{"pmid":"37814107","id":"PMC_37814107","title":"Novel GPR156 variants confirm its role in moderate sensorineural hearing loss.","date":"2023","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/37814107","citation_count":7,"is_preprint":false},{"pmid":"39531034","id":"PMC_39531034","title":"Contributions of mirror-image hair cell orientation to mouse otolith organ and zebrafish neuromast function.","date":"2024","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/39531034","citation_count":5,"is_preprint":false},{"pmid":"39300279","id":"PMC_39300279","title":"Brainstem transcriptomic changes in male Wistar rats after acute stress, comparing the use of duplex specific nuclease (DSN).","date":"2024","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/39300279","citation_count":5,"is_preprint":false},{"pmid":"39587238","id":"PMC_39587238","title":"Instrumented swim test for quantifying motor impairment in rodents.","date":"2024","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/39587238","citation_count":2,"is_preprint":false},{"pmid":"40228124","id":"PMC_40228124","title":"A rare variant in GPR156 associated with depression in a Mennonite pedigree causes habenula hyperactivity and stress sensitivity in mice.","date":"2025","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/40228124","citation_count":1,"is_preprint":false},{"pmid":"39760840","id":"PMC_39760840","title":"A Novel Homozygous Loss-of-Function Variant in GPR156 Delineates Non-syndromic Hearing Loss.","date":"2025","source":"Biochemical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39760840","citation_count":1,"is_preprint":false},{"pmid":"41208475","id":"PMC_41208475","title":"Planar polarized organization of mouse hair cells is established and maintained by STK32A, GPR156 and EMX2.","date":"2025","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/41208475","citation_count":0,"is_preprint":false},{"pmid":"41547998","id":"PMC_41547998","title":"GPR156 is required in sensory hair cells for proper auditory and vestibular function.","date":"2026","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/41547998","citation_count":0,"is_preprint":false},{"pmid":"39282410","id":"PMC_39282410","title":"Contributions of mirror-image hair cell orientation to mouse otolith organ and zebrafish neuromast function.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/39282410","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11178,"output_tokens":2878,"usd":0.038352},"stage2":{"model":"claude-opus-4-6","input_tokens":6259,"output_tokens":2647,"usd":0.146205},"total_usd":0.184557,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2021,\n      \"finding\": \"GPR156 acts downstream of the transcription factor EMX2 to signal through Gαi, triggering a 180° reversal in hair cell orientation in mechanosensory epithelia. EMX2 polarizes GPR156 distribution at hair cell boundaries, enabling GPR156-Gαi signaling to establish mirror-image hair cell orientations in mouse otolith organs and zebrafish lateral line.\",\n      \"method\": \"Genetic loss-of-function (mouse and zebrafish knockout), live imaging, epistasis experiments\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO in two species with defined cellular phenotype, epistasis placing GPR156 downstream of EMX2 and upstream of Gαi, replicated across labs\",\n      \"pmids\": [\"34001891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures of human GPR156 in apo and Gi3-coupled states reveal that GPR156 forms a TM5/6-TM5/6 dimer interface in both states, explaining its high constitutive activity. ECL2 and the N-terminus form a small extracellular region. The C-terminus of the G-bound subunit plays a dual role: promoting G protein binding within that subunit while preventing the G-free subunit from binding an additional G protein.\",\n      \"method\": \"Cryo-EM structure determination, functional assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structures in two states with mechanistic interpretation of dimerization and constitutive activity\",\n      \"pmids\": [\"39638804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures of human GPR156 in Go-free and Go-coupled states reveal that an endogenous phospholipid molecule is located within each TMD of the GPR156 dimer. Asymmetric Gα binding to the phospholipid-bound GPR156 dimer restructures intracellular loops 1 and 2 and the C-terminal part of TM7 without altering dimer conformation, identifying GPR156 as a transducer for phospholipid signaling whose constitutive activity is maintained by constant phospholipid binding.\",\n      \"method\": \"Cryo-EM structure determination, active-site analysis\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structures in two states with identification of endogenous phospholipid ligand and mechanistic dissection of constitutive activation\",\n      \"pmids\": [\"38332368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GPR156 exhibits constitutive Gi/o coupling when expressed as an unliganded orphan GPCR, as detected using luciferase reporter assays with G protein chimeras.\",\n      \"method\": \"Luciferase reporter assay with Gαi/o chimeric G proteins\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-based functional assay with chimeric G proteins, single lab\",\n      \"pmids\": [\"33784795\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"GPR156 (termed GABABL) was identified as a novel class C GPCR with sequence homology to GABAB1/GABAB2, containing a C-terminal coiled-coil domain, di-leucine motifs, and RXR(R) ER retention motifs. Expression in isolation or with GABAB1/GABAB2 failed to produce functional GABA-responsive receptor, indicating its endogenous partner was unknown.\",\n      \"method\": \"Molecular cloning, bioinformatics, functional expression assays\",\n      \"journal\": \"Brain research. Molecular brain research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — molecular cloning with functional null result; negative data well-controlled\",\n      \"pmids\": [\"12591167\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"GPR156 (GABABL) protein is distributed throughout the rat CNS, with dense immunoreactivity in cortex, hippocampus, dentate gyrus, cerebellum (granule cell layer and Purkinje cells), spinal cord substantia gelatinosa, and a subset of parvalbumin-positive hippocampal interneurons, as determined by immunohistochemistry.\",\n      \"method\": \"Immunohistochemistry with specific rabbit polyclonal antisera\",\n      \"journal\": \"Brain research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — direct localization experiment with validated antibody, single lab\",\n      \"pmids\": [\"14556935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"STK32A, a serine/threonine kinase negatively regulated by EMX2, reinforces line of polarity reversal formation by regulating the apical localization of GPR156 in mouse inner ear hair cells. Genetic epistasis shows STK32A acts to block GPR156-mediated bundle reversal in EMX2-negative hair cells.\",\n      \"method\": \"Genetic epistasis (double mutants), conditional expression, immunolocalization\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis with double mutants and rescue experiments placing STK32A as a regulator of GPR156 apical localization\",\n      \"pmids\": [\"37144879\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Genetic epistasis in mice with combined Gpr156/Stk32a and Emx2/Stk32a mutations established that GPR156 functions to reverse stereociliary bundle orientation relative to the PCP axis, but this can be blocked by STK32A, and that EMX2 establishes the boundary between the two hair cell groups by repressing Stk32a transcription, allowing GPR156 to act.\",\n      \"method\": \"Genetic epistasis, combined knockout analysis, hair cell orientation quantification\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multi-allele epistasis experiments defining pathway order among EMX2, STK32A, and GPR156\",\n      \"pmids\": [\"41208475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In zebrafish, GPR156 loss abolishes the smaller mechanically-evoked signals characteristic of EMX2-positive hair cells, demonstrating GPR156 relays hair cell transduction information downstream of EMX2. In mouse, Gpr156 knockout otolith organs retain normal mechano-electrical transduction properties, zonal organization, and type I-II hair cell distribution, but show altered swimming and off-vertical-axis rotation performance.\",\n      \"method\": \"Electrophysiology (mechano-electrical transduction), mouse and zebrafish knockout behavioral assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function in two species with electrophysiological and behavioral readouts, replicated in peer-reviewed and preprint versions\",\n      \"pmids\": [\"39531034\", \"39282410\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Conditional inactivation of Gpr156 specifically in postmitotic hair cells recapitulated the hair cell misorientation phenotype of null mutants and produced similar auditory and vestibular dysfunction, demonstrating that GPR156 is required in hair cells themselves for orientation. Hair cells can carry out mechano-electrical transduction without GPR156, indicating sensory deficits result from the orientation function rather than a direct role in transduction.\",\n      \"method\": \"Conditional knockout (hair cell-specific Cre), auditory brainstem response, vestibulo-ocular reflex, hair cell orientation analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with multiple functional readouts and direct comparison to null, showing cell-autonomous role\",\n      \"pmids\": [\"41547998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GPR156 is identified as a key inducer of lipid droplet accumulation in MMGT1-deficient macrophages during Mycobacterium tuberculosis infection, placing GPR156 in an MMGT1-GPR156-lipid droplet axis that promotes Mtb persistence.\",\n      \"method\": \"Genome-wide CRISPR screen, macrophage knockout validation, lipid droplet quantification\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR screen hit validated in macrophage KO with specific phenotypic readout, single lab\",\n      \"pmids\": [\"37269834\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A rare missense variant in GPR156 (p.Glu533Asp), when knocked into the murine locus, induces medial habenula hyperactivity and abnormal stress-related behaviors, localizing GPR156 function to the medial habenula for mood regulation.\",\n      \"method\": \"Knock-in mouse model, electrophysiology (habenula activity), behavioral stress assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — humanized knock-in mouse with electrophysiological and behavioral validation, moderate evidence from single study\",\n      \"pmids\": [\"40228124\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GPR156 is a constitutively active class C orphan GPCR that signals through Gαi/o proteins; structurally, it forms a TM5/6-TM5/6 dimer stabilized by endogenous phospholipid binding that drives constitutive activity, and its G protein coupling involves asymmetric Gα binding that reshapes intracellular loops without disrupting the dimer. In the inner ear, EMX2-dependent polarized localization of GPR156 at hair cell junctions enables Gαi signaling to reverse the interpretation of planar cell polarity cues—a process negatively regulated by STK32A—establishing mirror-image hair cell orientations essential for auditory and vestibular function; loss of GPR156 causes sensorineural hearing loss in mice and humans. In the medial habenula, a disease-associated GPR156 variant causes habenula hyperactivity and stress-related behavior, implicating it in mood regulation. Additionally, GPR156 promotes lipid droplet accumulation in macrophages as part of an MMGT1-GPR156 axis that supports Mycobacterium tuberculosis persistence.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GPR156 is a constitutively active class C orphan GPCR that couples to Gαi/o proteins to establish mirror-image hair cell orientations in mechanosensory epithelia and modulates neuronal activity in the brain. In the inner ear, EMX2-dependent polarized localization of GPR156 at hair cell junctions activates Gαi signaling to reverse stereociliary bundle orientation relative to the planar cell polarity axis, a process negatively regulated by STK32A; loss of GPR156 causes sensorineural hearing loss and vestibular dysfunction in mice and is linked to hearing loss in humans [PMID:34001891, PMID:37144879, PMID:41547998]. Structurally, GPR156 forms a TM5/6-mediated homodimer stabilized by endogenous phospholipid binding within each transmembrane domain, and asymmetric Gα coupling reshapes intracellular loops without disrupting the dimer, explaining high constitutive activity [PMID:38332368, PMID:39638804]. A rare missense variant in GPR156 causes medial habenula hyperactivity and stress-related behavioral abnormalities, implicating GPR156 in mood regulation [PMID:40228124].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Molecular cloning established GPR156 as a novel class C GPCR related to GABAB receptors, but with no identified ligand or functional signaling partner, defining it as an orphan receptor.\",\n      \"evidence\": \"Cloning, sequence analysis, and functional expression assays in heterologous cells\",\n      \"pmids\": [\"12591167\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No ligand identified\", \"No signaling output detected in heterologous expression\", \"Physiological function unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Mapping GPR156 protein distribution across the rat CNS revealed expression in cortex, hippocampus, cerebellum, and spinal cord, establishing it as a broadly expressed neuronal receptor.\",\n      \"evidence\": \"Immunohistochemistry with validated polyclonal antibodies in rat brain sections\",\n      \"pmids\": [\"14556935\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single antibody approach without independent validation method\", \"Function in any of these brain regions unknown\", \"Expression outside CNS not examined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The central biological role of GPR156 was revealed when genetic loss-of-function in mice and zebrafish showed it acts downstream of EMX2 to activate Gαi signaling and reverse hair cell orientation by 180°, solving how mirror-image hair cell patterns are established in mechanosensory organs.\",\n      \"evidence\": \"Mouse and zebrafish knockouts with epistasis experiments, live imaging of hair cell orientation\",\n      \"pmids\": [\"34001891\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of EMX2-dependent polarized localization unresolved\", \"Direct protein-protein interactions mediating pathway not shown\", \"Downstream effectors of Gαi in orientation reversal unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Cell-based signaling assays demonstrated that GPR156 constitutively couples to Gi/o proteins without an exogenous ligand, establishing it as a constitutively active orphan GPCR.\",\n      \"evidence\": \"Luciferase reporter assay with Gαi/o chimeric G proteins in transfected cells\",\n      \"pmids\": [\"33784795\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Chimeric G protein assay may not reflect native coupling\", \"Single-lab observation at this time point\", \"Molecular basis of constitutive activity unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identification of STK32A as a negative regulator of GPR156 apical localization completed the EMX2→STK32A⊣GPR156→Gαi pathway hierarchy for hair cell orientation, explaining how boundary formation between hair cell groups is achieved.\",\n      \"evidence\": \"Genetic epistasis with double-mutant mice, conditional expression, and immunolocalization\",\n      \"pmids\": [\"37144879\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether STK32A directly phosphorylates GPR156 is not shown\", \"Mechanism by which STK32A controls GPR156 apical trafficking unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A genome-wide CRISPR screen in macrophages revealed an unexpected non-neuronal role: GPR156 drives lipid droplet accumulation downstream of MMGT1, creating a lipid-rich niche that supports Mycobacterium tuberculosis persistence.\",\n      \"evidence\": \"CRISPR screen in macrophages, KO validation with lipid droplet quantification during Mtb infection\",\n      \"pmids\": [\"37269834\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking GPR156 signaling to lipid droplet biogenesis unclear\", \"Whether Gαi coupling is involved in macrophage context not tested\", \"Single study; not independently replicated\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Two independent cryo-EM studies resolved the structural basis of GPR156 constitutive activity: the receptor forms a TM5/6-mediated homodimer with endogenous phospholipids bound within each TMD, and asymmetric Gα binding reshapes intracellular loops without disrupting the dimer architecture.\",\n      \"evidence\": \"Cryo-EM structures in apo, Go-free, Gi3-coupled, and Go-coupled states with functional assays\",\n      \"pmids\": [\"38332368\", \"39638804\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the endogenous phospholipid not definitively assigned\", \"Whether phospholipid binding is regulated in vivo unknown\", \"No structure of GPR156 in complex with potential allosteric modulators\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Electrophysiological and behavioral studies in zebrafish and mouse clarified that GPR156 controls the functional readout of hair cell orientation rather than mechano-electrical transduction itself, as knockout hair cells retain normal transduction properties.\",\n      \"evidence\": \"Mechano-electrical transduction recordings and behavioral assays in Gpr156 knockout mice and zebrafish\",\n      \"pmids\": [\"39531034\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How misorientation leads to altered signal integration at the circuit level is unexplored\", \"Whether compensatory mechanisms exist in mature animals unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Multi-allele epistasis experiments refined the pathway model, establishing that EMX2 represses Stk32a transcription to permit GPR156-mediated bundle reversal, and confirmed GPR156's role is to reverse orientation relative to the PCP axis.\",\n      \"evidence\": \"Combined Gpr156/Stk32a and Emx2/Stk32a knockout mice with hair cell orientation quantification\",\n      \"pmids\": [\"41208475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct transcriptional regulation of Stk32a by EMX2 not shown at promoter level\", \"Whether additional regulators modulate GPR156 surface expression unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A human disease-associated GPR156 missense variant (E533D) knocked into mice caused medial habenula hyperactivity and stress-related behavioral abnormalities, extending GPR156 function beyond the inner ear to mood regulation in the brain.\",\n      \"evidence\": \"Knock-in mouse with electrophysiology of habenula neurons and behavioral stress assays\",\n      \"pmids\": [\"40228124\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which E533D alters receptor function (gain vs. loss of activity) not resolved\", \"Whether this variant affects Gαi coupling specifically not tested\", \"Relevance to human psychiatric phenotypes not clinically validated\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Conditional inactivation of Gpr156 specifically in postmitotic hair cells demonstrated that the orientation function is cell-autonomous and confirmed that sensory deficits arise from misorientation rather than impaired transduction.\",\n      \"evidence\": \"Hair cell-specific conditional knockout with ABR, VOR, and hair cell orientation analysis\",\n      \"pmids\": [\"41547998\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GPR156 has additional non-cell-autonomous roles in surrounding support cells not excluded\", \"Temporal window during which GPR156 acts is not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the identity and regulatory significance of the endogenous phospholipid bound within the GPR156 dimer, the downstream effectors of Gαi that execute cytoskeletal remodeling for bundle reversal, whether STK32A directly phosphorylates GPR156, and the mechanism by which GPR156 promotes lipid droplet formation in macrophages.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No substrate/effector downstream of Gαi in hair cells identified\", \"Phospholipid identity and regulation unresolved\", \"STK32A-GPR156 direct interaction not demonstrated\", \"Macrophage signaling mechanism unexplored\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 6, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [0, 3, 11]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [0, 8, 9]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 6, 7]}\n    ],\n    \"complexes\": [\n      \"GPR156 homodimer\"\n    ],\n    \"partners\": [\n      \"GNAI3\",\n      \"GNAO1\",\n      \"STK32A\",\n      \"EMX2\",\n      \"MMGT1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}