spns1 (nrs/spinl) encodes a lysosomal-membrane major facilitator superfamily (spinster-family) transporter, experimentally deorphanized as a proton-dependent lysophospholipid efflux transporter with substrate specificity for the zwitterionic lysophospholipids lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE) (He et al. 2022 PNAS, PMID:36161949). It exports these lysolipids from the lysosomal lumen to the cytosolic side, enabling lysosomal phospholipid salvage and maintaining lysosomal homeostasis. Transport is pH-dependent (acidic optimum ~5-6), consistent with proton coupling for an MFS transporter at the lysosome. A mammalian genetics study additionally proposes a role in lysosomal sphingosine release (Ha et al. 2024 JCI Insight, PMID:38451736), but the highest-confidence substrate assignment remains LPC/LPE. Autophagy, autophagosome maturation, cardiac valve morphogenesis (via notch1 signaling; Chávez et al. 2024 iScience, PMID:39720516), and cellular/developmental senescence are downstream consequences of impaired lysosomal lipid efflux rather than the molecular core, which is lysosomal lysophospholipid transmembrane transport.
Definition: Catalysis of the proton-dependent transfer of lysophospholipids (e.g. lysophosphatidylcholine and lysophosphatidylethanolamine) from the lysosomal lumen across the lysosomal membrane to the cytosolic side.
Justification: Spns1 is experimentally demonstrated to be a proton-dependent lysosomal efflux transporter selective for the zwitterionic lysophospholipids LPC and LPE (PMID:36161949 He et al. 2022 PNAS; falcon deep research). No existing GO molecular-function term captures this activity: GO:0022857 (transmembrane transporter activity) is far too broad, and GO:0051978 (the only lysophospholipid transporter MF term) is specifically a lysophospholipid:SODIUM symporter, whereas Spns1 is proton-coupled and operates in the efflux direction. The proposed parent GO:0015562 (efflux transmembrane transporter activity) is OLS-verified as a valid, non-obsolete MF term (child of transmembrane transporter activity GO:0022857 under transporter activity GO:0005215), making it an appropriate is_a parent.
Parent term: efflux transmembrane transporter activity
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0022857 transmembrane transporter activity | IBA GO_REF:0000033 | ACCEPT | Summary: transmembrane transporter activity (GO:0022857) is supported for zebrafish spns1 and is coherent with the synthesized gene function. Falcon deep research confirms the substrate-level specificity: Spns1 was experimentally deorphanized as a proton-dependent lysophospholipid transporter selective for LPC and LPE. GO:0022857 is correct but very general; a substrate-specific term is preferred (see proposed_new_terms). Reason: Transmembrane transporter activity is the best available general MF annotation for the lysosomal transporter role; no existing GO MF term captures proton-coupled lysophospholipid efflux (GO:0051978 is sodium-symport specific). Supporting Evidence: file:DANRE/spns1/spns1-uniprot.txt Mediates the rate-limiting, proton-dependent, lysosomal file:DANRE/spns1/spns1-uniprot.txt efflux of lysophospholipids PMID:36161949 indicating that Spns1 is a proton-coupled LPC transporter PMID:36161949 Lipidomic analysis on Spns1-deficient whole embryos revealed significant accumulation of LPC and LPE species relative to control embryos |
| GO:0016020 membrane | IBA GO_REF:0000033 | MODIFY | Summary: membrane (GO:0016020) captures the right general area for zebrafish spns1, but lysosomal membrane (GO:0005765) is the better supported term. Falcon deep research independently confirms that Spns1 is primarily a lysosomal/ late-endosomal membrane protein (colocalizing with LAMP1 and Rab7), supporting the narrower term. Reason: The broad membrane location should be narrowed to lysosomal membrane. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000605425 · Spinster/SPNS MFS transporter family node SUPPORTS TRANSFER Membrane localization is real, but the generic membrane term is uninformative; the supported compartment for Spns1 is the lysosomal membrane. UniProtKB:O96156 · Drosophila Spinster donor SUPPORTS TRANSFER Donor supports membrane residence; specific lysosomal membrane location is preferred. Proposed replacements: lysosomal membrane Supporting Evidence: file:DANRE/spns1/spns1-uniprot.txt SUBCELLULAR LOCATION: Lysosome membrane file:DANRE/spns1/spns1-deep-research-falcon.md SPNS1/Spns1 is primarily a **lysosomal/late endosomal membrane protein** file:DANRE/spns1/spns1-deep-research-falcon.md colocalizes with LAMP1 (lysosomes) and Rab7 (late endosomes) |
| GO:0005765 lysosomal membrane | IEA GO_REF:0000044 | ACCEPT | Summary: lysosomal membrane (GO:0005765) is supported for zebrafish spns1 and is coherent with the synthesized gene function. Falcon deep research corroborates lysosomal/late-endosomal membrane localization (LAMP1/Rab7 colocalization in mammalian systems; autolysosomal/lysosomal compartments in zebrafish tissues). Reason: The lysosomal membrane location is directly supported and represents the site of action of the transporter. Supporting Evidence: file:DANRE/spns1/spns1-uniprot.txt SUBCELLULAR LOCATION: Lysosome membrane file:DANRE/spns1/spns1-deep-research-falcon.md SPNS1/Spns1 is primarily a **lysosomal/late endosomal membrane protein** |
| GO:0022857 transmembrane transporter activity | IEA GO_REF:0000002 | ACCEPT | Summary: transmembrane transporter activity (GO:0022857) is supported for zebrafish spns1 and is coherent with the synthesized gene function. This InterPro-based prediction is consistent with the experimentally demonstrated proton-coupled lysophospholipid efflux activity reported in the falcon deep research synthesis. Reason: Transmembrane transporter activity is the best available general MF annotation for the lysosomal transporter role; a substrate-specific term is proposed in proposed_new_terms. Supporting Evidence: file:DANRE/spns1/spns1-uniprot.txt Mediates the rate-limiting, proton-dependent, lysosomal file:DANRE/spns1/spns1-uniprot.txt efflux of lysophospholipids PMID:36161949 indicating that Spns1 is a proton-coupled LPC transporter PMID:36161949 Lipidomic analysis on Spns1-deficient whole embryos revealed significant accumulation of LPC and LPE species relative to control embryos |
| GO:0055085 transmembrane transport | IEA GO_REF:0000002 | MODIFY | Summary: transmembrane transport (GO:0055085) is supported for zebrafish spns1 and is coherent with the synthesized gene function. The direct biological process is lysosomal efflux of lysophospholipids, which is more precisely captured by lysophospholipid transport (GO:0051977; OLS-verified, a child of lipid transport GO:0006869 under transport GO:0006810). The falcon synthesis identifies lysosomal lysophospholipid export as the best-supported primary function. Reason: Transmembrane transport is correct but overly general; the substrate-specific process term lysophospholipid transport (GO:0051977) is a better, same-aspect (BP) description of spns1's direct biological process. Proposed replacements: lysophospholipid transport Supporting Evidence: file:DANRE/spns1/spns1-uniprot.txt Mediates the rate-limiting, proton-dependent, lysosomal PMID:36161949 Lipidomic analysis on Spns1-deficient whole embryos revealed significant accumulation of LPC and LPE species relative to control embryos |
| GO:0006914 autophagy | IGI PMID:24967584 Aberrant autolysosomal regulation is linked to the induction... | KEEP AS NON CORE | Summary: autophagy (GO:0006914) is supported or plausible for zebrafish spns1, but it is not the most informative core function. Falcon deep research frames the autophagy/autolysosomal phenotype as a downstream consequence of impaired lysosomal lipid efflux: loss of Spns1 causes enlarged/abnormal lysosomes and perturbed autophagic flux. Reason: Autophagy is affected by Spns1 loss but is downstream of the lysosomal transporter core (acts_upstream_of_or_within). Supporting Evidence: PMID:24967584 which functions at a late stage file:DANRE/spns1/spns1-deep-research-falcon.md Loss of Spns1 causes **enlarged/abnormal lysosomes** |
| GO:0090398 cellular senescence | IMP PMID:24967584 Aberrant autolysosomal regulation is linked to the induction... | KEEP AS NON CORE | Summary: cellular senescence (GO:0090398) is supported or plausible for zebrafish spns1, but it is not the most informative core function. Falcon deep research describes spns1 as involved in the regulation of developmental senescence, a downstream phenotype of impaired lysosomal/autolysosomal function rather than the molecular core. Reason: Cellular senescence is a downstream phenotype of Spns1 deficiency (acts_upstream_of_or_within). Supporting Evidence: PMID:24967584 Beclin 1 suppression ameliorates Spns1 loss-mediated senescence file:DANRE/spns1/spns1-deep-research-falcon.md developmental senescence |
| GO:0090398 cellular senescence | IGI PMID:24967584 Aberrant autolysosomal regulation is linked to the induction... | KEEP AS NON CORE | Summary: cellular senescence (GO:0090398) is supported or plausible for zebrafish spns1, but it is not the most informative core function. Falcon deep research describes spns1 as involved in the regulation of developmental senescence, a downstream phenotype of impaired lysosomal/autolysosomal function rather than the molecular core. Reason: Cellular senescence is a downstream phenotype of Spns1 deficiency (acts_upstream_of_or_within). Supporting Evidence: PMID:24967584 Beclin 1 suppression ameliorates Spns1 loss-mediated senescence file:DANRE/spns1/spns1-deep-research-falcon.md developmental senescence |
| GO:0097352 autophagosome maturation | IMP PMID:24967584 Aberrant autolysosomal regulation is linked to the induction... | KEEP AS NON CORE | Summary: autophagosome maturation (GO:0097352) is supported or plausible for zebrafish spns1, but it is not the most informative core function. Falcon deep research supports the interpretation that defective autolysosomal processing follows from impaired lysosomal lipid efflux, placing this term downstream of the transporter core. Note: the original PMID:24967584 hypothesis of an H+-carbohydrate transporter is now superseded by the experimental demonstration that Spns1 is a proton-coupled lysophospholipid (LPC/LPE) transporter. Reason: Autophagosome maturation is a process consequence of lysosomal transport/homeostasis defects, not the molecular core. Supporting Evidence: PMID:24967584 putative lysosomal H+-carbohydrate transporter PMID:24967584 which functions at a late stage file:DANRE/spns1/spns1-deep-research-falcon.md Loss of Spns1 causes **enlarged/abnormal lysosomes** |
| GO:0006914 autophagy | IGI PMID:24967584 Aberrant autolysosomal regulation is linked to the induction... | KEEP AS NON CORE | Summary: autophagy (GO:0006914) is annotated by IGI from morphant/mutant genetic interaction studies. spns1 (nrs) mutants show accumulation of autolysosomes and autophagosomes and defective autophagosome-lysosome fusion (PMID:24967584). This is a downstream consequence of the lysosomal transporter defect, not a molecular function spns1 executes within autophagy. Reason: spns1's core activity is lysosomal lysophospholipid efflux (PMID:36161949); the autophagic-flux defect follows from impaired lysosomal lipid homeostasis, so this is retained as acts_upstream_of_or_within rather than a core function. Same action as the sibling GO:0006914 IGI row. Supporting Evidence: PMID:24967584 indicating defects in both fusion of autophagosomes with lysosomes and autolysosomal maturation |
| GO:0090398 cellular senescence | IGI PMID:24967584 Aberrant autolysosomal regulation is linked to the induction... | KEEP AS NON CORE | Summary: cellular senescence (GO:0090398) is annotated by IGI. nrs/spns1 mutants were identified in a senescence (SA-beta-gal) screen and Beclin 1 suppression ameliorates the senescence phenotype (PMID:24967584). Senescence is a downstream organismal consequence of impaired lysosomal function, not a molecular process spns1 carries out. Reason: Developmental/embryonic senescence is a phenotype of spns1 deficiency, downstream of the lysosomal lysophospholipid transporter core (PMID:36161949); retained as non-core (acts_upstream_of_or_within), consistent with the sibling GO:0090398 rows. Supporting Evidence: PMID:24967584 inhibition of Beclin 1 can attenuate the yolk opacity and senescence caused by the Spns1 defect |
| GO:0090398 cellular senescence | IGI PMID:24967584 Aberrant autolysosomal regulation is linked to the induction... | KEEP AS NON CORE | Summary: cellular senescence (GO:0090398) is annotated by IGI. nrs/spns1 mutants were identified in a senescence (SA-beta-gal) screen and Beclin 1 suppression ameliorates the senescence phenotype (PMID:24967584). Senescence is a downstream organismal consequence of impaired lysosomal function, not a molecular process spns1 carries out. Reason: Developmental/embryonic senescence is a phenotype of spns1 deficiency, downstream of the lysosomal lysophospholipid transporter core (PMID:36161949); retained as non-core (acts_upstream_of_or_within), consistent with the sibling GO:0090398 rows. Supporting Evidence: PMID:24967584 inhibition of Beclin 1 can attenuate the yolk opacity and senescence caused by the Spns1 defect |
| GO:0097352 autophagosome maturation | IMP PMID:24967584 Aberrant autolysosomal regulation is linked to the induction... | KEEP AS NON CORE | Summary: autophagosome maturation (GO:0097352) is annotated by IMP. spns1 mutants show defective autophagosome-lysosome fusion and autolysosomal maturation (PMID:24967584). This late-stage autophagy defect is downstream of the lysosomal transport/acidification defect rather than an activity spns1 performs during maturation. Reason: The maturation defect is a consequence of impaired lysosomal function caused by loss of the lysophospholipid efflux transporter (PMID:36161949); retained as non-core, consistent with the sibling GO:0097352 IMP row. Supporting Evidence: PMID:24967584 indicating defects in both fusion of autophagosomes with lysosomes and autolysosomal maturation |
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