Affinage

LRIT3

Leucine-rich repeat, immunoglobulin-like domain and transmembrane domain-containing protein 3 · UniProt Q3SXY7

Length
679 aa
Mass
74.8 kDa
Annotated
2026-04-28
14 papers in source corpus 11 papers cited in narrative 11 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

LRIT3 is a presynaptic transmembrane protein expressed in rod and cone photoreceptors that functions as a transsynaptic organizer of the postsynaptic glutamate signaling complex on depolarizing bipolar cell (DBC) dendrites, thereby enabling ON-pathway visual signaling. Cell-type-specific AAV rescue in Lrit3-knockout mice demonstrates that LRIT3 expressed in rods or cones is sufficient to restore assembly of the DBC signalplex—including nyctalopin and TRPM1—on postsynaptic dendrites (PMID:31189098, PMID:37091241). LRIT3 interacts with and is required for nyctalopin expression at DBC dendritic tips, and its immunoglobulin domain is specifically required for TRPM1 localization, while its leucine-rich repeat domain mediates transsynaptic interaction with nyctalopin and is necessary for synaptic trafficking in cones (PMID:31959619, PMID:41000924). Loss-of-function mutations in LRIT3 cause complete congenital stationary night blindness (cCSNB) in humans, characterized by abolished ON-bipolar cell responses (PMID:23246293, PMID:24598786).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2012 Medium

    Identification of LRIT3 as a disease gene for cCSNB established that it is required for ON-bipolar cell function and localized it to the outer plexiform layer of the retina, opening the question of its precise molecular role at the photoreceptor–bipolar cell synapse.

    Evidence Whole-exome sequencing of cCSNB families plus immunohistochemistry in human retina

    PMID:23246293

    Open questions at the time
    • Localization appeared postsynaptic at this stage; presynaptic vs. postsynaptic identity unresolved
    • No functional mechanistic dissection beyond disease association
    • Molecular partners unknown
  2. 2014 High

    Generation of an Lrit3-knockout mouse confirmed that LRIT3 loss abolishes ON-bipolar cell signaling (nob ERG phenotype) without causing retinal degeneration, establishing a clean functional model for mechanistic studies.

    Evidence Lrit3-KO mouse with ERG, optomotor testing, SD-OCT, and histology

    PMID:24598786

    Open questions at the time
    • Molecular mechanism by which LRIT3 supports DBC signaling unknown
    • Whether LRIT3 is pre- or postsynaptic unresolved
  3. 2015 High

    Immunolocalization in the KO revealed that LRIT3 is required for TRPM1 targeting to all DBC dendritic tips and for the entire cone DBC signalplex (mGluR6, GPR179, RGS7/11, Gβ5), establishing it as an upstream organizer of the postsynaptic signaling complex.

    Evidence Confocal immunofluorescence for multiple signalplex components in WT vs. Lrit3-KO retinal sections; PNA labeling

    PMID:25997951

    Open questions at the time
    • Whether LRIT3 acts from the pre- or postsynaptic side still unresolved
    • Direct protein–protein interactions not yet demonstrated
    • Role at cone vs. rod synapses only partially distinguished
  4. 2017 High

    Ultrastructural and electrophysiological analysis showed that LRIT3 loss selectively disorganizes ON-bipolar but not OFF-bipolar synaptic contacts at cone pedicles, demonstrating pathway-specific transsynaptic coordination.

    Evidence Electron microscopy, immunostaining for GluR1/GluR5, MEA recordings of retinal ganglion cells in Lrit3-KO mice

    PMID:28334377

    Open questions at the time
    • Mechanism of selective ON-pathway disruption unknown
    • Pre- vs. postsynaptic site of LRIT3 action still unresolved
  5. 2019 High

    AAV-mediated restoration of LRIT3 selectively in rods of Lrit3-KO mice rescued postsynaptic signalplex assembly and rod-driven ERG b-waves, proving that LRIT3 is presynaptic and acts transsynaptically to organize the DBC signaling complex.

    Evidence Cell-type-specific AAV expression in rods, immunofluorescence for signalplex, ERG rescue

    PMID:31189098

    Open questions at the time
    • Cone-specific rescue not yet performed
    • Direct transsynaptic binding partner not identified
    • Domain requirements unknown
  6. 2020 High

    Co-immunoprecipitation and epistasis analysis placed LRIT3 upstream of nyctalopin in signalplex assembly—LRIT3 interacts with and is required for nyctalopin expression at DBC tips, while DBC components are dispensable for LRIT3 expression—and additionally revealed that LRIT3 loss disrupts OFF-pathway signaling indirectly.

    Evidence Co-IP, immunofluorescence, whole-cell and MEA electrophysiology, glutamate imaging in Lrit3-KO mice

    PMID:31959619

    Open questions at the time
    • Whether LRIT3–nyctalopin interaction is direct or mediated by other synaptic proteins
    • Structural basis of the interaction unknown
    • Mechanism of OFF-pathway disruption not fully delineated
  7. 2023 High

    Cone-specific AAV rescue in Lrit3-KO mice restored cone DBC signalplex and partially recovered photopic ERG and downstream RGC responses, confirming that the transsynaptic organizing principle operates at both rod and cone synapses.

    Evidence rAAV cone-specific LRIT3 expression, ERG, whole-cell electrophysiology, immunofluorescence in Lrit3-KO mice

    PMID:37091241

    Open questions at the time
    • Incomplete functional rescue in cones suggests additional factors
    • Domain requirements for cone vs. rod function unknown
  8. 2024 Medium

    LRIT3-dependent ON-pathway signaling was linked to retinal dopamine regulation and refractive development, revealing a broader physiological consequence of ON-pathway dysfunction beyond night blindness.

    Evidence UPLC dopamine/DOPAC quantification and lens-induced myopia experiments in Lrit3-KO mice

    PMID:39250117

    Open questions at the time
    • Single study; whether dopamine reduction is a direct or indirect consequence of ON-pathway loss is unclear
    • Whether LRIT3 mutations contribute to human myopia not tested
  9. 2025 Medium

    Systematic domain-deletion analysis revealed that the LRR domain mediates synaptic trafficking in cones and transsynaptic signalplex assembly (likely via nyctalopin binding), the IG domain is required specifically for TRPM1 localization and function, and the FN3 domain is dispensable, providing a modular mechanistic model for LRIT3 transsynaptic signaling.

    Evidence rAAV-mediated expression of LRIT3 domain-deletion constructs in Lrit3-KO retinas, immunofluorescence, ERG (preprint)

    PMID:41000924

    Open questions at the time
    • Preprint not yet peer-reviewed
    • Direct binding between LRR domain and nyctalopin or IG domain and TRPM1 not biochemically demonstrated
    • Structural basis for domain-specific interactions unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • Whether LRIT3 directly binds nyctalopin via its LRR domain and TRPM1 via its IG domain in trans remains to be biochemically demonstrated, and no high-resolution structural model of these transsynaptic complexes exists.
  • No reconstituted binding assay for LRIT3–nyctalopin or LRIT3–TRPM1
  • No crystal or cryo-EM structure of LRIT3 or its complexes
  • Mechanism underlying differential trafficking requirements in rods vs. cones unexplained

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098631 cell adhesion mediator activity 4
Localization
GO:0005886 plasma membrane 4
Pathway
R-HSA-112316 Neuronal System 4 R-HSA-162582 Signal Transduction 2
Partners
GRM6NYXTRPM1

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2012 LRIT3 is expressed in the outer plexiform layer of the human retina in a punctate pattern resembling the dendritic tips of bipolar cells, consistent with a role in ON-bipolar cell signaling, identified via mutations causing complete congenital stationary night blindness (cCSNB) with loss of b-wave amplitude reflecting abnormal ON-bipolar cell function. Whole-exome sequencing, Sanger sequencing, human retinal immunohistochemistry with anti-LRIT3 antibody American journal of human genetics Medium 23246293
2014 Lrit3 knockout mice (nob6) exhibit a no b-wave (nob) ERG phenotype with lacking or severely reduced b-wave amplitudes in scotopic and photopic conditions, thinned inner nuclear layer by SD-OCT, and strongly decreased optomotor responses, establishing LRIT3 loss-of-function causes ON-bipolar cell signaling defect without retinal degeneration. Lrit3 knockout mouse generation, ERG, optomotor testing, SD-OCT, fundus imaging, histology PloS one High 24598786
2015 LRIT3 localizes at the dendritic tips of depolarizing bipolar cells (DBCs) in the outer plexiform layer (OPL) co-localizing with mGluR6, and is required for correct localization of TRPM1 to the dendritic tips of all depolarizing bipolar cells; additionally, mGluR6, GPR179, RGS7, RGS11, and Gβ5 are lost from cone ON-bipolar cell dendritic tips (but not rod bipolar cell tips) in Lrit3 knockout mice, and peanut agglutinin (PNA) labeling is severely reduced in the OPL, suggesting LRIT3 also plays a role in cone synapse formation. Immunofluorescence confocal microscopy of wild-type and Lrit3nob6/nob6 retinal sections using antibodies against LRIT3, TRPM1, mGluR6, GPR179, RGS7, RGS11, Gβ5; PNA labeling The European journal of neuroscience High 25997951
2017 In Lrit3-knockout (nob6) mice, synaptic contacts made by ON-bipolar cells but not OFF-bipolar cells with cone pedicles are structurally disorganized, while molecules essential for OFF-bipolar cell signaling (GluR1, GluR5) are normally targeted to the synapse; multielectrode array recordings confirm complete loss of ON-pathway function but robust (though altered) OFF-pathway signaling, demonstrating LRIT3 selectively coordinates transsynaptic communication between cones and ON-bipolar cells during synapse formation. Electron microscopy, immunostaining and confocal microscopy (GluR1, GluR5), multielectrode array electrophysiology (retinal ganglion cells), ERG in patient with LRIT3 mutations Investigative ophthalmology & visual science High 28334377
2019 LRIT3 is expressed presynaptically in rod photoreceptors (not postsynaptically on depolarizing bipolar cells), and selective restoration of LRIT3 expression in Lrit3-/- rods via AAV rescues postsynaptic glutamate signalplex assembly on DBC dendrites and restores rod-driven vision, demonstrating LRIT3 acts as a transsynaptic organizer of the postsynaptic signaling complex. Cell-type-specific AAV-mediated LRIT3 re-expression in rods of Lrit3-/- mice, immunofluorescence for signalplex components, ERG functional rescue Cell reports High 31189098
2019 In the canine LRIT3-CSNB model, the truncated mutant LRIT3 protein retains correct subcellular localization to the region of ON-bipolar cell dendritic tips (with reduced immunolabeling), establishing that loss of function rather than mislocalization underlies the signaling defect in this in vivo model. Genome-wide association study, whole-genome sequencing, immunohistochemistry in canine retina Scientific reports Medium 31578364
2020 LRIT3 interacts with and is required for expression of nyctalopin at all DBC dendritic tips (thus controlling TRPM1 localization), but DBC signalplex components (including nyctalopin) are not required for LRIT3 expression, placing LRIT3 upstream of nyctalopin in signalplex assembly; loss of LRIT3 also reduces excitatory input to OFF-bipolar cells (type 1 BCs) and disrupts OFF retinal ganglion cell responses. Co-immunoprecipitation, immunofluorescence, whole-cell electrophysiology, multielectrode array (MEA) electrophysiology, glutamate imaging in Lrit3-/- mice eNeuro High 31959619
2012 LRIT3 functions as a modulator of FGFR1, with its LRR and immunoglobulin-like domains interacting with FGFR1 to regulate FGFR-mediated signaling pathways (MAPK, PI3K/AKT, PLC-γ). Co-immunoprecipitation, cell-based signaling assays FEBS letters Low 22673519
2023 rAAV-mediated expression of LRIT3 specifically in cone photoreceptors of Lrit3-/- mice rescues assembly of cone DBC signalplex components and partially restores downstream visual function (light-adapted ERG b-wave, electrophysiological recordings of BCs and RGCs), confirming LRIT3 acts trans-synaptically from cones to organize the postsynaptic signalplex on cone DBCs. rAAV-mediated cone-specific LRIT3 expression in Lrit3-/- mice, ERG, whole-cell electrophysiology of BCs and RGCs, immunofluorescence for signalplex components iScience High 37091241
2024 Loss of LRIT3 in Lrit3-/- mice drastically reduces retinal dopamine and DOPAC levels and impairs recovery from lens-induced myopia, establishing that LRIT3-dependent ON-pathway signaling is required for normal dopaminergic regulation of refractive development. UPLC quantification of dopamine/DOPAC in isolated Lrit3-/- retinas, infrared photorefractometry, lens-induced myopia protocol Investigative ophthalmology & visual science Medium 39250117
2025 Domain-deletion analysis via rAAV expression in Lrit3-/- retinas shows: (1) the LRR domain is required for trafficking LRIT3 to the synapse in cones (but not rods) and for rod bipolar cell signalplex reassembly and function; (2) the IG domain is required for TRPM1 localization to the signalplex and for function, but not for synaptic localization of LRIT3; (3) the FN3 domain is dispensable for signalplex assembly or function. This supports a model in which the LRR domain trans-synaptically binds nyctalopin and the IG domain interacts with TRPM1. rAAV-mediated expression of LRIT3 deletion constructs in Lrit3-/- mouse retinas, immunofluorescence (LRIT3 trafficking, signalplex component localization), ERG functional analysis bioRxivpreprint Medium 41000924

Source papers

Stage 0 corpus · 14 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2012 Whole-exome sequencing identifies LRIT3 mutations as a cause of autosomal-recessive complete congenital stationary night blindness. American journal of human genetics 108 23246293
2014 Lrit3 deficient mouse (nob6): a novel model of complete congenital stationary night blindness (cCSNB). PloS one 49 24598786
2015 LRIT3 is essential to localize TRPM1 to the dendritic tips of depolarizing bipolar cells and may play a role in cone synapse formation. The European journal of neuroscience 48 25997951
2019 Presynaptic Expression of LRIT3 Transsynaptically Organizes the Postsynaptic Glutamate Signaling Complex Containing TRPM1. Cell reports 42 31189098
2022 Targeting ON-bipolar cells by AAV gene therapy stably reverses LRIT3-congenital stationary night blindness. Proceedings of the National Academy of Sciences of the United States of America 28 35316139
2020 LRIT3 is Required for Nyctalopin Expression and Normal ON and OFF Pathway Signaling in the Retina. eNeuro 27 31959619
2017 LRIT3 Differentially Affects Connectivity and Synaptic Transmission of Cones to ON- and OFF-Bipolar Cells. Investigative ophthalmology & visual science 23 28334377
2019 Genome-wide association study and whole-genome sequencing identify a deletion in LRIT3 associated with canine congenital stationary night blindness. Scientific reports 17 31578364
2012 Leucine-rich repeat, immunoglobulin-like and transmembrane domain 3 (LRIT3) is a modulator of FGFR1. FEBS letters 14 22673519
2024 Loss of ON-Pathway Function in Mice Lacking Lrit3 Decreases Recovery From Lens-Induced Myopia. Investigative ophthalmology & visual science 7 39250117
2023 Extended functional rescue following AAV gene therapy in a canine model of LRIT3-congenital stationary night blindness. Vision research 6 37220680
2023 LRIT3 expression in cone photoreceptors restores post-synaptic bipolar cell signalplex assembly and partial function in Lrit3 mice. iScience 4 37091241
2016 Mutation screening of the LRIT3, CABP4, and GPR179 genes in Chinese patients with Schubert-Bornschein congenital stationary night blindness. Ophthalmic genetics 4 27428514
2025 Domain-specific functions of LRIT3 in synaptic assembly and retinal signal transmission. bioRxiv : the preprint server for biology 0 41000924