SEMA5A

SEMA5A (M-SemF) is a transmembrane class-5 semaphorin that functions as a bifunctional axon guidance cue and a regulator of vascular and neuronal patterning during development (PMID:12506007, PMID:15743826). As an inhibitory ensheathing cue, Sema5A is expressed by neuroepithelial cells and oligodendrocytes flanking developing axon tracts, where it triggers growth cone collapse and restrains axon elongation to maintain pathway integrity, and contributes to the inhibitory glial environment that limits CNS axon regeneration (PMID:12506007, PMID:15163691). Its short cytoplasmic C-terminal ESSV motif binds the single PDZ domain of SEMCAP-1/GIPC, which redistributes the protein into detergent-resistant surface aggregates and thereby controls its subcellular distribution (PMID:10318831). Genetic ablation in mice is embryonic lethal at E11.5–E12.5 with defective remodeling of cranial vasculature, establishing an essential role in vascular patterning (PMID:15743826), and its thrombospondin (TSP1) repeat domain is required for pro-angiogenic, pro-inflammatory activity driving pannus formation in rheumatoid arthritis (PMID:33616619). SEMA5A also acts non-cell-autonomously in cancer: M2 macrophage-derived SEMA5A engages tumor-cell PLXNB3 to enhance aerobic glycolysis and promote pancreatic adenocarcinoma liver metastasis (PMID:36741230). Autism-spectrum-disorder-associated gain-of-function variants (R676C, S951C) drive excessive neuronal process elongation through autocrine Plexin-B3 signaling that converges on Rho-family GTPase activation via JNK/RhoG-Elmo1, ErbB2-Dock7-Rac1/Cdc42, and Arf6/FE65/ELMO2-Rac1 cascades (PMID:38133141, PMID:41226692, PMID:41703006).

1. 1999 Medium

   Established how the cytoplasmic tail of SEMA5A is read out intracellularly, identifying a PDZ-domain adaptor that controls receptor surface organization.

   Evidence Yeast two-hybrid, HEK293 co-expression with detergent-resistance/fluorescence assay, and PDZ/C-terminal mutagenesis

   PMID:10318831

   Open questions at the time

   • Functional consequence of GIPC-mediated clustering for in vivo signaling not tested
   • No link to a specific receptor or downstream pathway established here
2. 2003 High

   Defined SEMA5A as an inhibitory ensheathing guidance cue, showing it produces an invariant repulsive growth cone response that confines retinal axons to their pathway in vivo.

   Evidence In situ/IHC localization, growth cone collapse and outgrowth assays, and function-blocking antibody perturbation in ex vivo embryo preparations

   PMID:12506007

   Open questions at the time

   • Receptor mediating the inhibitory response not identified
   • Bifunctional context-dependence (attractive vs repulsive) not resolved
3. 2004 High

   Extended the inhibitory role to glia, showing oligodendrocyte-derived SEMA5A contributes to the non-permissive environment limiting CNS axon regeneration.

   Evidence Glial RNA analysis, substrate-bound collapse and outgrowth assays with RGCs, and neutralizing antibody on optic nerve explants

   PMID:15163691

   Open questions at the time

   • Receptor and intracellular signaling in RGCs not identified
   • Relevance to in vivo regeneration after injury not tested
4. 2005 High

   Demonstrated an essential, non-neuronal developmental requirement by showing SEMA5A loss causes embryonic lethality with defective cranial vascular remodeling.

   Evidence Targeted knockout in mice with embryo morphology and cranial vein branching analysis

   PMID:15743826

   Open questions at the time

   • Receptor and effector pathway in vascular cells not defined
   • Whether vascular and axonal roles use shared signaling unknown
5. 2019 Medium

   Placed Sema5a as a downstream target of an RNA-binding regulator, linking its dose to synaptic plasticity and cognition.

   Evidence FUS transgenic mouse transcriptomics, RNA immunoprecipitation, hippocampal LTP and spine density measurement

   PMID:31509188

   Open questions at the time

   • Direct causal contribution of reduced Sema5a to the cognitive phenotype not isolated
   • Mechanism linking surface SEMA5A to spine density not established
6. 2021 High

   Identified the TSP1 domain as the functionally essential module for SEMA5A pro-angiogenic and pro-inflammatory activity in arthritis pathogenesis.

   Evidence FLS transcriptomics, proliferation and angiogenesis assays, anti-SEMA5A mAb in CIA mice, and TSP1-deletion rescue in Sema5a-/- CIA mice

   PMID:33616619

   Open questions at the time

   • Receptor engaged by the TSP1 domain in synoviocytes/endothelium not defined
   • Downstream angiogenic signaling pathway not mapped
7. 2023 Medium

   Established a non-cell-autonomous oncogenic axis in which macrophage-derived SEMA5A signals through tumor PLXNB3 to reprogram metabolism in metastasis.

   Evidence PDAC patient samples, intrasplenic injection and KPC mouse models, receptor-ligand studies, and glycolysis assays

   PMID:36741230

   Open questions at the time

   • Molecular link between PLXNB3 engagement and glycolytic enzymes not detailed
   • Reciprocal/structural validation of the SEMA5A-PLXNB3 interaction limited
8. 2023 Medium

   Showed ASD-associated SEMA5A gain-of-function variants drive aberrant neurite elongation via autocrine Plexin-B3 signaling converging on JNK through RhoG-Elmo1.

   Evidence Mutant Sema5A expression in N1E-115 cells, confocal localization, JNK activity assay, Plexin-B3 blocking antibody, JNK inhibitor, and Elmo1 RhoG-binding domain construct

   PMID:38133141

   Open questions at the time

   • Mechanism by which point mutations create gain-of-function not resolved
   • Confined to cell-line model; in vivo relevance not tested
9. 2025 Medium

   Resolved a second effector branch for the R676C variant, identifying the ErbB2-Dock7 axis as a driver of Rac1/Cdc42 overactivation underlying excessive elongation.

   Evidence shRNA knockdown of Dock7, ErbB2 kinase inhibition, and Rac1/Cdc42 activity assays in primary cortical neurons and N1E-115 cells

   PMID:41226692

   Open questions at the time

   • How SEMA5A/Plexin-B3 engages ErbB2 mechanistically not defined
   • Relationship between this branch and the JNK/RhoG branch not integrated
10. 2026 Medium

    Defined a third converging branch in which R676C signals through an Arf6/FE65/ELMO2 signalosome to elevate Rac1, with FE65 as the specific coupler.

    Evidence CRISPR/Cas13 knockdown of Arf6 and FE65, ELMO2-binding domain rescue, and Rac1 activity assay in primary cortical neurons and N1E-115 cells

    PMID:41703006

    Open questions at the time

    • How multiple parallel cascades (JNK, ErbB2-Dock7, Arf6-FE65) are coordinated unknown
    • In vivo confirmation in ASD models lacking

• How SEMA5A's shared structural elements (TSP1 domain, ESSV/GIPC tail) and receptor (Plexin-B3) are deployed across its distinct roles in axon guidance, vascular patterning, angiogenic inflammation, and tumor metabolism remains unresolved.
• No unifying receptor/effector framework connecting developmental, inflammatory, and oncogenic contexts
• Structural basis for ligand-receptor engagement uncharacterized in the corpus
• Mechanism distinguishing inhibitory (guidance) from elongation-promoting (mutant) outputs unclear