Affinage

C1QL1

C1q-related factor · UniProt O75973

Length
258 aa
Mass
26.5 kDa
Annotated
2026-06-09
18 papers in source corpus 14 papers cited in narrative 14 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

C1QL1 is a secreted C1q-family protein that functions as a synaptic organizer by binding the adhesion-GPCR BAI3 to control the establishment, maintenance, and elimination of excitatory synapses in the nervous system (PMID:25611509, PMID:25660030). In the cerebellum, C1QL1 is supplied as an anterograde signal by climbing fibers and acts on postsynaptic Purkinje cells to determine and maintain a single-winner climbing fiber, with its restricted expression in inferior olivary neurons defining the climbing-fiber synaptic territory (PMID:25611509, PMID:25660030); this C1QL1-BAI3 axis operates downstream of GluD2-dependent synapse maintenance and drives activity-dependent reinnervation of mature Purkinje cell dendrites (PMID:37488606). Structurally, the trimeric globular gC1q domain undergoes calcium-modulated domain-swapping to assemble into a hexamer that engages the extended CUB domain of BAI3, and full-length C1QL1 forms linear clusters that accumulate BAI3 receptors at the plasma membrane to scaffold the synapse (PMID:41372137). Beyond the cerebellum, C1QL1 interacts with BAI3 in the cochlea to regulate auditory nerve fiber growth and hair-cell afferent innervation via the BAI3-ELMO1-DOCK180-RAC1 cytoskeletal pathway, with global loss causing progressive hearing loss (PMID:34512267, PMID:40193629), and it bidirectionally regulates oligodendrocyte progenitor differentiation and myelination during development and remyelination (PMID:39257292). In non-neural and disease contexts, the globular domain stimulates HUVEC migration and tube formation through ERK1/2 signaling (PMID:27734226), C1QL1 localizes to the endoplasmic reticulum where it binds HSP90α and VCP to promote their degradation and induce ER-stress-dependent apoptosis in breast cancer (PMID:40583061), and glioblastoma-secreted C1QL1 engages BAI3 to drive RAC1-mediated synaptic pruning and tumor microtube outgrowth (PMID:41747254).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2015 High

    Established C1QL1's core function by identifying its receptor BAI3 and showing the pair is required for climbing-fiber synapse selection, answering how a single winner afferent is chosen and maintained.

    Evidence Genetic knockout, reciprocal binding assays, electrophysiology, and immunohistochemistry in mouse cerebellum, replicated across two labs

    PMID:25611509 PMID:25660030

    Open questions at the time
    • Structural basis of C1QL1-BAI3 binding not resolved
    • Downstream intracellular signaling from BAI3 not defined
    • Whether the same axis operates outside cerebellum unknown
  2. 2009 Medium

    Showed C1QL1 pre-mRNA is subject to conserved A-to-I editing producing non-synonymous substitutions, raising the possibility of transcript-level functional diversification.

    Evidence RNA sequencing, comparative genomics, and RNA secondary-structure analysis across human, mouse, and zebrafish

    PMID:19275900

    Open questions at the time
    • Functional consequence of edited residues on protein activity not tested
    • Tissue specificity and regulation of editing not established
  3. 2016 Medium

    Extended C1QL1 function beyond neurons by showing its globular domain drives angiogenesis through ERK1/2 signaling, hinting at BAI3 as a vascular receptor.

    Evidence HUVEC migration/tube-formation assays, phospho-ERK Western blots, U0126 inhibition, chick yolk sac membrane assay

    PMID:27734226

    Open questions at the time
    • BAI3 involvement inferred from immunoreactivity only, not by loss-of-function
    • In vivo angiogenic role not demonstrated
  4. 2021 High

    Generalized the synapse-organizer role to the auditory periphery, showing C1QL1 in hair cells supports afferent synapse maintenance and nerve fiber innervation.

    Evidence Conditional and global knockout mice, ABR/DPOAE, confocal and electron microscopy, voltage-clamp recording

    PMID:33979385 PMID:34512267

    Open questions at the time
    • Receptor mediating cochlear effects not identified in these studies
    • Conditional OHC KO lacked a compelling functional auditory phenotype
  5. 2022 Medium

    Probed non-neural physiology, implicating C1QL1 in ovarian folliculogenesis via granulosa cell autophagy/apoptosis while finding it largely dispensable for systemic metabolic homeostasis.

    Evidence Antibody-mediated blockade with hormone ELISA and IHC (ovary); constitutive KO with metabolic cage, body composition, and tolerance tests (metabolism)

    PMID:35403439 PMID:35560215

    Open questions at the time
    • Ovarian effects rely on antibody blockade rather than genetic KO
    • Downstream signaling linking C1QL1 to autophagy/apoptosis not directly established
    • Receptor mediating reproductive and metabolic effects unknown
  6. 2023 High

    Placed C1QL1-BAI3 in a defined genetic hierarchy, showing it acts downstream of GluD2 to drive activity-dependent climbing-fiber reinnervation of mature dendrites.

    Evidence Viral overexpression, conditional knockout, electrophysiology, Ca2+ imaging, and GluD2 KO x Bai3 KO epistasis in mouse cerebellum

    PMID:37488606

    Open questions at the time
    • Molecular link between GluD2 and C1QL1 upregulation not defined
    • How neuronal activity gates the reinnervation not resolved
  7. 2024 High

    Identified a glia-intrinsic function, showing C1QL1 bidirectionally controls oligodendrocyte progenitor differentiation and myelination in development and remyelination.

    Evidence OPC-specific conditional KO, in vivo viral overexpression, cuprizone demyelination model, and primary OPC culture with IHC

    PMID:39257292

    Open questions at the time
    • Receptor and signaling pathway in OPCs not identified
    • Whether OPC effect is cell-autonomous via autocrine signaling unclear
  8. 2025 High

    Resolved the structural mechanism of receptor engagement, showing calcium-modulated hexamerization of the gC1q domain binds the BAI3 CUB domain and clusters receptors to scaffold synapses.

    Evidence Cryo-EM of the C1ql1 gC1q hexamer-BAI3 CUB complex, biochemical assembly assays, and cellular/in vivo validation

    PMID:41372137

    Open questions at the time
    • How calcium concentration is sensed in the synaptic cleft in vivo not established
    • Stoichiometry of full-length linear clusters at native synapses not quantified
  9. 2025 Medium

    Connected the cochlear phenotype to a defined cytoskeletal effector pathway and uncovered an ER-localized, BAI3-independent function in cancer.

    Evidence Co-IP and colocalization with BAI3 plus pathway-component analysis (cochlea); LC-MS/MS, co-IP, methylation-specific PCR, and in vitro/in vivo apoptosis assays identifying HSP90alpha and VCP interactions (breast cancer)

    PMID:40193629 PMID:40583061

    Open questions at the time
    • Cochlear pathway placement not validated by full genetic epistasis
    • ER-localization mechanism for a secreted protein not explained
    • Causality of HSP90alpha/VCP degradation in apoptosis partially inferred
  10. 2026 Medium

    Demonstrated pathological repurposing of the synapse-organizing axis, showing glioblastoma-secreted C1QL1 uses BAI3-RAC1 signaling to prune normal synapses and drive tumor microtube outgrowth.

    Evidence In vitro signaling assays, RAC1 inhibitor rescue, and in vivo glioma models with functional rescue experiments

    PMID:41747254

    Open questions at the time
    • Pathway placement via inhibitor rather than genetic epistasis
    • Source and regulation of tumor C1QL1 expression not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the single C1QL1-BAI3 module is functionally specialized across such diverse contexts (cerebellum, cochlea, oligodendrocytes, vasculature, ovary, tumors) and which contexts engage BAI3 versus alternative receptors or intracellular partners remains unresolved.
  • No unifying account of receptor choice across tissues
  • Intracellular ER-localized functions not reconciled with secreted synaptic role
  • Editing-dependent functional variation untested in vivo

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0048018 receptor ligand activity 3 GO:0005198 structural molecule activity 1
Localization
GO:0005576 extracellular region 2 GO:0005783 endoplasmic reticulum 1 GO:0005886 plasma membrane 1
Pathway
R-HSA-112316 Neuronal System 3 R-HSA-162582 Signal Transduction 3 R-HSA-1266738 Developmental Biology 1 R-HSA-5357801 Programmed Cell Death 1
Partners

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2015 C1QL1 (provided by climbing fibers as an anterograde signal) specifically binds to BAI3 (brain-specific angiogenesis inhibitor 3), a cell-adhesion G-protein-coupled receptor expressed on postsynaptic Purkinje cells, and this C1QL1-BAI3 signaling is required to determine and maintain a single-winner climbing fiber in the mouse cerebellum throughout development and adulthood. Genetic knockout, binding assays, electrophysiology, immunohistochemistry Neuron High 25611509
2015 The C1QL1-BAI3 signaling pathway controls the stereotyped pattern of synaptic connectivity established by excitatory afferents (both climbing fibers and parallel fibers) on cerebellar Purkinje cells; restricted expression of C1QL1 in inferior olivary neurons ensures the proper synaptic territory for climbing fibers. Genetic knockout, overexpression, electrophysiology, immunohistochemistry Cell reports High 25660030
2016 The globular domain of C1QL1/CTRP14 directly stimulates migration and capillary tube formation of HUVECs in a dose-dependent manner, activating phosphorylation of c-Raf, MEK1/2, ERK1/2, and p90RSK; MEK1/2 inhibition with U0126 blocks these effects. BAI3 immunoreactivity was detected in HUVECs, suggesting BAI3 mediates this proangiogenic effect. In vitro angiogenesis assay (HUVEC migration and tube formation), Western blot for phospho-ERK pathway components, pharmacological inhibition (U0126), chick yolk sac membrane assay Molecular and cellular biochemistry Medium 27734226
2009 C1QL1 pre-mRNA undergoes A-to-I RNA editing in vivo, causing non-synonymous amino acid substitutions, conserved across human, mouse, and zebrafish; the major editing site had previously been misannotated as a SNP. RNA sequencing, comparative genomics, RNA secondary structure analysis FEBS letters Medium 19275900
2023 Overexpression of C1ql1 in climbing fibers or Bai3 in Purkinje cells causes transverse CF branches to elongate and form new synapses on distal dendrites of mature Purkinje cells; this reinnervation requires neuronal activity and is dependent on Bai3 in Purkinje cells. Additionally, C1ql1 levels in CFs are upregulated in GluD2 knockout mice, and the reinnervation phenotype of GluD2 KO is absent in Bai3 KO mice, placing C1ql1-Bai3 signaling downstream of GluD2-dependent synapse maintenance. Viral overexpression, conditional knockout, electrophysiology, Ca²⁺ imaging, immunohistochemistry, genetic epistasis (GluD2 KO × Bai3 KO double mutant) Molecular brain High 37488606
2021 C1ql1 is expressed in outer hair cells of the cochlea in an adolescence-onset, tonotopic gradient pattern. Conditional knockout of C1ql1 in outer hair cells results in histological evidence of reduced outer hair cell afferent synapse maintenance, though auditory behavioral and physiological phenotypes were not compelling. Fluorescent reporter knockin mouse, conditional knockout, histology/immunohistochemistry, auditory brainstem response testing PloS one Medium 33979385
2021 C1ql1 global knockout mice exhibit progressive hearing loss with reduced auditory nerve fiber innervation of both inner and outer hair cells, and significant outer hair cell loss; however, spiral ganglion neurons are normal ultrastructurally, and IHC presynaptic machinery (synaptic vesicle release, presynaptic proteins) is not significantly affected by C1ql1 deletion. Global knockout mouse, auditory brainstem response, DPOAE, confocal microscopy, electron microscopy, voltage-clamp recording, immunocytochemistry Frontiers in cellular neuroscience High 34512267
2022 C1QL1 deficiency in mice (via intraperitoneal and intrabursal injection of C1QL1 antiserum) impairs folliculogenesis, reduces granulosa cell autophagy, alleviates C1QL1-mediated inhibition of granulosa cell apoptosis, elevates circulating estradiol, reduces hypothalamic KISS1 and GnRH expression, and decreases serum FSH, leading to depletion of ovarian follicle reserve. Antibody-mediated blockade (IP + intrabursal injection), immunohistochemistry, ELISA for hormones, confocal microscopy for follicle staging Endocrinology Medium 35560215
2022 CTRP14/C1QL1 deficiency in mice alters physical activity and food intake in a sex- and nutritional state-dependent manner (lower activity in fed males, increased activity in fasted/refed females, reduced food intake in refed males), but is largely dispensable for metabolic homeostasis, body composition, and insulin sensitivity. Constitutive knockout mouse, metabolic cage analysis (physical activity, food intake), body composition analysis, glucose tolerance test, insulin tolerance test, lipid profiling American journal of physiology. Endocrinology and metabolism Medium 35403439
2024 C1QL1 is expressed in oligodendrocyte progenitor cells (OPCs) and its deficiency (OPC-specific conditional KO) reduces OPC differentiation into oligodendrocytes and myelin production during development and after cuprizone-induced demyelination; conversely, in vivo overexpression of C1QL1 increases oligodendrocyte density and myelination during recovery. C1QL1 levels bidirectionally regulate OPC differentiation in primary culture. OPC-specific conditional knockout, in vivo viral overexpression, cuprizone demyelination model, primary OPC culture, immunohistochemistry The FEBS journal High 39257292
2025 The trimeric globular C1q (gC1q) domain of C1ql1 undergoes calcium-modulated domain-swapping to form a hexamer; cryo-EM reveals calcium ions stabilize the C1ql1_gC1q hexamer in complex with the extended CUB domain of BAI3. Full-length C1ql1 further assembles into linear clusters via the gC1q hexamer, providing a scaffold to accumulate BAI3 receptors on the plasma membrane, supporting synapse maintenance. Cryo-EM structure determination, biochemical assembly assays, computational analysis, cellular and in vivo functional validation Nature communications High 41372137
2025 C1QL1 interacts with BAI3 in the cochlea (confirmed by colocalization and co-immunoprecipitation), and regulates auditory nerve fiber growth via the BAI3-ELMO1-DOCK180-RAC1 pathway; C1ql1 overexpression inhibits expression of the TIAM1-PARD3 pathway. Co-immunoprecipitation, colocalization imaging, overexpression/knockdown with pathway component analysis Acta oto-laryngologica Medium 40193629
2025 In breast cancer, C1QL1 localizes to the endoplasmic reticulum and interacts with HSP90α and VCP (confirmed by co-immunoprecipitation and mass spectrometry), facilitating their ubiquitin-mediated degradation and thereby inducing ER stress/unfolded protein response (ERS/UPR) and caspase-dependent apoptosis. C1QL1 promoter methylation silences its expression in breast cancer. LC-MS/MS, co-immunoprecipitation, Western blot, overexpression/knockdown in vitro and in vivo (nude mice), flow cytometry (apoptosis/cell cycle), TUNEL, methylation-specific PCR Experimental & molecular medicine Medium 40583061
2026 Glioblastoma-secreted C1QL1 binds to BAI3 on neighboring neurons and GBM cells, activating RAC1-mediated cytoskeleton rearrangement to prune normal synapses and promote tumor microtube (TM) outgrowth and malignant synapse formation; a non-GEF-targeting RAC1 inhibitor rescues C1QL1-mediated synaptic pruning and inhibits glioma recurrence. In vitro signaling assays, pharmacological inhibition (RAC1 inhibitor), in vivo glioma models, functional rescue experiments Cancer discovery Medium 41747254

Source papers

Stage 0 corpus · 18 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2015 Anterograde C1ql1 signaling is required in order to determine and maintain a single-winner climbing fiber in the mouse cerebellum. Neuron 152 25611509
2015 The Secreted Protein C1QL1 and Its Receptor BAI3 Control the Synaptic Connectivity of Excitatory Inputs Converging on Cerebellar Purkinje Cells. Cell reports 112 25660030
2018 CRABP1, C1QL1 and LCN2 are biomarkers of differentiated thyroid carcinoma, and predict extrathyroidal extension. BMC cancer 30 29321030
2016 C1ql1/Ctrp14 and C1ql4/Ctrp11 promote angiogenesis of endothelial cells through activation of ERK1/2 signal pathway. Molecular and cellular biochemistry 25 27734226
2023 C1ql1-Bai3 signaling is necessary for climbing fiber synapse formation in mature Purkinje cells in coordination with neuronal activity. Molecular brain 17 37488606
2021 C1ql1 is expressed in adult outer hair cells of the cochlea in a tonotopic gradient. PloS one 16 33979385
2021 Deletion of C1ql1 Causes Hearing Loss and Abnormal Auditory Nerve Fibers in the Mouse Cochlea. Frontiers in cellular neuroscience 14 34512267
2009 Conserved recoding RNA editing of vertebrate C1q-related factor C1QL1. FEBS letters 13 19275900
2022 Deficiency of C1QL1 Reduced Murine Ovarian Follicle Reserve Through Intraovarian and Endocrine Control. Endocrinology 12 35560215
2022 CTRP14 inactivation alters physical activity and food intake response to fasting and refeeding. American journal of physiology. Endocrinology and metabolism 11 35403439
2024 C1ql1 expression in oligodendrocyte progenitor cells promotes oligodendrocyte differentiation. The FEBS journal 10 39257292
2023 Mapping and targeting of C1ql1-expressing cells in the mouse. Scientific reports 9 37845276
2025 C1QL1 inhibits breast cancer through the HSP90α/VCP-ERS/UPR axis. Experimental & molecular medicine 3 40583061
2022 C1QL1/CTRP14 Is Largely Dispensable for Atherosclerosis Formation in Apolipoprotein-E-Deficient Mice. Journal of cardiovascular development and disease 2 36286293
2025 Role of CTRP14/C1QL1 in motor coordination and learning across the lifespan. Physiology & behavior 1 39761721
2025 C1QL1 regulates auditory nerve fibers growth via ELMO1-DOCK180-RAC1 integrin. Acta oto-laryngologica 1 40193629
2025 Structural basis of calcium-dependent C1ql1/BAI3 assemblies in synaptic connectivity. Nature communications 1 41372137
2026 Glioblastoma-Secreted C1QL1 Orchestrates Tumor Microtube Expansion and Neural Synaptic Pruning to Drive Malignant Synapse Formation and Recurrence. Cancer discovery 0 41747254

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