NEO1

Neogenin (NEO1) is a multifunctional transmembrane receptor that integrates guidance, morphogenetic, and survival signals by binding Netrin-1, RGM family members, and BMPs through its four immunoglobulin-like and six fibronectin type III extracellular domains (PMID:9169140, PMID:25938661). In the absence of ligand, neogenin functions as a dependence receptor, triggering caspase-mediated apoptosis via cleavage of its intracellular domain, whereas RGM binding suppresses this pro-apoptotic output and instead drives intramembrane proteolysis to generate a nuclear fragment required for neuroepithelial cell elongation (PMID:15258591, PMID:31399534). Formation of a ternary Netrin-1–NEO1–RGM super-assembly reciprocally silences both attractive and repulsive guidance signals, providing a structural mechanism for integrating opposing cues at the cell surface (PMID:33740419). Beyond axon guidance, NEO1 activates FAK–β-catenin and RhoA pathways in contexts ranging from pluripotency maintenance in embryonic stem cells to promotion of epithelial-mesenchymal transition in pancreatic cancer, and in astrocytes it regulates blood–brain barrier integrity through iron-hepcidin homeostasis and controls neuroinflammatory A1 polarization via cPLA2–MAVS–NF-κB signaling (PMID:32231305, PMID:41474982, PMID:39107268, PMID:41345945).

1. 1997 High

   Cloning of human NEO1 established its domain architecture (4 Ig + 6 FNIII + TM + ICD) and ~50% identity to DCC, defining it as a distinct member of the DCC receptor family rather than a DCC orthologue.

   Evidence cDNA cloning, sequencing, Northern blot, and FISH mapping to 15q22.3-q23

   PMID:9121761 PMID:9169140

   Open questions at the time

   • No ligand had been identified
   • Function of the intracellular domain was unknown
2. 2004 High

   Demonstration that neogenin is a dependence receptor — inducing caspase-mediated apoptosis in the absence of its ligand RGM — revealed a survival-checkpoint function beyond guidance, while identification of neogenin–CDO complex formation in myoblasts showed it also operates outside the nervous system to promote netrin-dependent myogenesis.

   Evidence Chick neural tube electroporation and cell-based apoptosis/caspase cleavage assays (dependence receptor); co-immunoprecipitation and CDO-null myoblast differentiation assays (myogenesis)

   PMID:15258591 PMID:15520228

   Open questions at the time

   • Downstream apoptotic cascade components beyond caspase cleavage were not identified
   • How CDO–neogenin cis-interaction modulates intracellular signaling remained unclear
3. 2005 High

   Identification of PITPα as a netrin-1-recruited effector of neogenin/DCC linked receptor activation to phospholipid metabolism (PIP2 hydrolysis), providing the first intracellular signaling mechanism for netrin-1-induced neurite outgrowth.

   Evidence Co-immunoprecipitation, in vitro lipid-transfer assay, zebrafish morpholino knockdown, and cortical explant neurite assay

   PMID:16244667

   Open questions at the time

   • Whether PITPα acts on neogenin and DCC independently or in a shared complex was unresolved
   • Downstream targets of PIP2 hydrolysis were not mapped
4. 2009 High

   Resolution of the contested role of neogenin in iron homeostasis: neogenin physically interacts with hemojuvelin (HJV) and is required for BMP4-induced hepcidin expression in hepatocytes, placing it as a co-receptor in the HJV–BMP–hepcidin axis despite an earlier report of HJV-BMP signaling independence.

   Evidence Co-immunoprecipitation, siRNA knockdown, soluble neogenin fragment blocking in vivo, and qRT-PCR for hepcidin

   PMID:18326817 PMID:19564337

   Open questions at the time

   • Whether neogenin contacts BMP ligands directly in this context was unknown
   • In vivo hepatic phenotype of neogenin loss was not characterized
5. 2010 High

   Direct binding of neogenin to BMP-2, -4, -6, and -7 was demonstrated, and a signaling bifurcation was identified: neogenin suppresses Smad1/5/8-dependent osteoblastic differentiation while simultaneously activating RhoA, establishing it as a BMP co-receptor that redirects pathway output.

   Evidence Ligand binding assays, siRNA knockdown and overexpression, phospho-Smad and RhoA activity assays in C2C12 cells

   PMID:21149453

   Open questions at the time

   • Structural basis of direct neogenin–BMP interaction was missing
   • How neogenin toggles between Smad suppression and RhoA activation was mechanistically unresolved
6. 2015 High

   Crystal structures of RGM–BMP2 and the ternary BMP2–RGM–NEO1 complex revealed that RGM bridges NEO1 and BMP signaling as a central structural scaffold, and BMP-induced clustering of this complex was validated at the cell surface.

   Evidence X-ray crystallography, SAXS, and live-cell super-resolution fluorescence microscopy

   PMID:25938661

   Open questions at the time

   • Signaling consequences of cluster formation were not directly measured
   • Stoichiometry and dynamics of full-length receptor assemblies in native membranes remained undefined
7. 2019 High

   RGMa-induced intramembrane proteolysis of Neo1 generates a nuclear intracellular domain fragment (NeoICD) that is essential for microtubule-dependent neuroepithelial cell elongation during neural tube morphogenesis, revealing a regulated intramembrane proteolysis (RIP) signaling mode for neogenin.

   Evidence Zebrafish morpholino knockdown, cell transplantation for cell autonomy, NeoICD rescue construct overexpression

   PMID:31399534

   Open questions at the time

   • Nuclear targets of NeoICD were not identified
   • The protease(s) mediating intramembrane cleavage were not characterized
8. 2020 High

   Netrin-1–NEO1 signaling was placed at the center of naive pluripotency maintenance by showing that NEO1 activates FAK to inactivate GSK3 and stabilize β-catenin while modulating MAPK through PP2A, with the balance between NEO1 and UNC5B receptors determining pathway output.

   Evidence Chemical inhibitor rescue, phospho-Western blot signaling analysis, receptor OE/KD, transcriptomic profiling in mouse ESCs

   PMID:32231305

   Open questions at the time

   • Direct physical interaction between NEO1 and PP2A was not demonstrated
   • Whether these pathways operate in human ESCs was untested
9. 2021 High

   Structural determination of the Netrin-1–NEO1–RGM ternary complex and its higher-order 'trimer-of-trimers' super-assembly provided a molecular mechanism for reciprocal silencing: the super-assembly sequesters both attractive and repulsive signaling-competent receptor states, explaining how opposing guidance cues are integrated at the membrane.

   Evidence X-ray crystallography, cryo-electron microscopy, growth cone collapse and cell migration assays, super-resolution microscopy

   PMID:33740419

   Open questions at the time

   • In vivo validation of the super-assembly in developing organisms was lacking
   • How cells dissolve the super-assembly to re-enable signaling was unknown
10. 2024 Medium

    Astrocyte-specific NEO1 conditional knockout demonstrated that NEO1 maintains blood–brain barrier integrity after injury through iron–hepcidin homeostasis, and subsequent work showed NEO1 drives neuroinflammatory A1 astrocyte polarization via a cPLA2–MAVS–NF-κB pathway.

    Evidence GFAP-Cre;NEO1fl/fl conditional knockout mice, Evans Blue/dextran permeability assays, hepcidin rescue, scRNA-seq, lentiviral cPLA2 OE rescue in SAH model

    PMID:39107268 PMID:41345945

    Open questions at the time

    • How NEO1 activates cPLA2 biochemically is undefined
    • Whether the iron-homeostasis and neuroinflammatory functions are mechanistically coupled is unknown
    • Findings are from a single laboratory
11. 2025 High

    In pancreatic cancer, Netrin-1–NEO1 signaling through FAK was shown to drive EMT, cancer stemness (via ZEB1/SOX9), and liver metastasis, and to promote sympathetic axonogenesis that supports tumor growth — extending the FAK-dependent signaling axis to tumor biology.

    Evidence Pdx1-Cre;KrasG12D mouse model with Neo1 knockout, liver metastasis neutralizing antibody model, ex vivo celiac ganglia axonogenesis assay, FAK phosphorylation analysis

    PMID:41474982

    Open questions at the time

    • Whether NEO1 is the sole Netrin-1 receptor mediating these tumor effects or acts redundantly with DCC/UNC5 is unclear
    • Therapeutic relevance of NEO1 inhibition versus FAK inhibition was not compared

• Key unresolved questions include the identity of nuclear targets of the NeoICD fragment, the protease(s) responsible for intramembrane cleavage, the structural basis for how the super-assembly is dynamically regulated in vivo, and whether the astrocytic iron-homeostasis and neuroinflammatory functions represent the same or distinct signaling branches.
• Nuclear targets of NeoICD unknown
• Protease mediating RIP cleavage unidentified
• Super-assembly dynamics in vivo uncharacterized
• Relationship between iron-homeostasis and cPLA2-MAVS pathways in astrocytes unresolved