fads2 encodes zebrafish fatty acid desaturase 2, an endoplasmic-reticulum membrane front-end acyl-CoA desaturase with bifunctional delta-6 and delta-5 (and in-vivo delta-8) activities in polyunsaturated fatty-acid biosynthesis. Yeast expression assays confirmed delta-6 desaturation of C18 PUFA (LA to GLA, ALA to SDA) and delta-5 desaturation of C20 PUFA (to ARA and EPA), and the enzyme also acts on C24 substrates to support Sprecher-pathway DHA synthesis. It contributes to liver development, and partial loss of function impairs female reproduction (egg quality).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016020 membrane | IBA GO_REF:0000033 | MODIFY | Summary: membrane (GO:0016020) is too general for Fads2; the supported location is the endoplasmic reticulum membrane. Falcon deep research notes that most biochemical and review evidence supports Fads2 as an ER membrane enzyme. Reason: The supported location is endoplasmic reticulum membrane. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN002321280 Β· FADS fatty acid desaturase family node SUPPORTS TRANSFER Membrane localization is real, but the generic membrane term is uninformative; the supported compartment for Fads2 is the endoplasmic reticulum membrane. MGI:MGI:1923517 Β· mouse Fads desaturase donor SUPPORTS TRANSFER Donor supports membrane residence; specific ER membrane location is preferred. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: file:DANRE/fads2/fads2-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane file:DANRE/fads2/fads2-deep-research-falcon.md Most biochemical and review evidence supports Fads2 as an **ER membrane** enzyme. |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: endoplasmic reticulum membrane (GO:0005789) is supported for Fads2. Falcon deep research confirms ER localization by co-localization of zebrafish Fads2 with the ER marker ERp57 and by FRET-detected proximity to its cytochrome b5 reductase partners (CYB5R2/3) and ELOVL elongases in an ER lipid-synthetic module. A mitochondrial membrane signal was also reported in a heterologous HeLa system but is interpreted cautiously as a possible overexpression/cell-type artifact. Reason: Fads2 is an ER membrane fatty acid desaturase, corroborated by ERp57 co-localization and proximity to ER reductase/elongase partners. Supporting Evidence: file:DANRE/fads2/fads2-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane file:DANRE/fads2/fads2-deep-research-falcon.md Co-localization with an ER marker (ERp57) supports ER association. file:DANRE/fads2/fads2-deep-research-falcon.md the ER association and proximity to reductases/elongases is strongly supported |
| GO:0006629 lipid metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: lipid metabolic process (GO:0006629) is too broad for the Fads2 pathway role. The specific supported biological process is unsaturated/polyunsaturated fatty-acid biosynthesis. Falcon deep research describes Fads2 as the key desaturase in endogenous LC-PUFA biosynthesis, linking dietary C18 essential fatty acids (LA/ALA) to ARA, EPA, and DHA production. Reason: The specific supported biological process is unsaturated/polyunsaturated fatty-acid biosynthesis. Proposed replacements: unsaturated fatty acid biosynthetic process Supporting Evidence: file:DANRE/fads2/fads2-uniprot.txt PATHWAY: Lipid metabolism; polyunsaturated fatty acid biosynthesis. file:DANRE/fads2/fads2-deep-research-falcon.md Catalyzes early and mid-pathway steps converting dietary **LA/ALA** into longer-chain PUFA intermediates and ultimately supporting **ARA/EPA** production and **DHA** synthesis via a Sprecher-like route. |
| GO:0016213 acyl-CoA 6-desaturase activity | IEA GO_REF:0000120 | ACCEPT | Summary: acyl-CoA 6-desaturase activity (GO:0016213) is supported for Fads2. Falcon deep research confirms the seminal yeast heterologous-expression study directly demonstrated Delta-6 desaturation of C18 PUFA (18:2n-6 to 18:3n-6; 18:3n-3 to 18:4n-3) with GC-MS-validated products, with the Delta-6 step being the rate-limiting first step of LC-PUFA biosynthesis. Reason: Delta-6/acyl-CoA desaturase activity is a central, experimentally validated biochemical function of Fads2. Supporting Evidence: file:DANRE/fads2/fads2-uniprot.txt Fatty acid desaturase with bifunctional delta-5 and delta-6 file:DANRE/fads2/fads2-uniprot.txt biosynthesis of polyunsaturated fatty acids file:DANRE/fads2/fads2-deep-research-falcon.md The seminal yeast heterologous expression study demonstrated that zebrafish Fads2 catalyzes: file:DANRE/fads2/fads2-deep-research-falcon.md introduces a double bond at the 6th carbon from the carboxyl end and is commonly the **rate-limiting first step** for converting dietary essential PUFA precursors into longer-chain PUFA. |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000002 | MODIFY | Summary: oxidoreductase activity (GO:0016491) is too broad for Fads2. The molecular function is better represented by the specific acyl-CoA desaturase activities. Falcon deep research confirms zebrafish Fads2 is a non-heme diiron front-end desaturase that receives electrons via the NADH-cytochrome b5 reductase / cytochrome b5 system and uses molecular oxygen during double-bond insertion, and that the enzyme is bifunctional with both Delta-6 and Delta-5 activities. Reason: The molecular function should be represented by the specific acyl-CoA desaturase activities. Proposed replacements: acyl-CoA 6-desaturase activity acyl-CoA (8-3)-desaturase activity Supporting Evidence: file:DANRE/fads2/fads2-uniprot.txt Fatty acid desaturase with bifunctional delta-5 and delta-6 file:DANRE/fads2/fads2-uniprot.txt biosynthesis of polyunsaturated fatty acids file:DANRE/fads2/fads2-deep-research-falcon.md Front-end desaturases are non-heme diiron enzymes that require an electron-transfer chain involving **NADHβcytochrome b5 reductase**, **cytochrome b5**, and the desaturase, using **molecular oxygen** during double-bond insertion. |
| GO:0062076 acyl-CoA (8-3)-desaturase activity | IEA GO_REF:0000120 | ACCEPT | Summary: acyl-CoA (8-3)-desaturase activity (GO:0062076) is supported for Fads2 and captures the Delta-5 / Delta-8 side of this bifunctional enzyme. Falcon deep research shows the original yeast assay directly demonstrated Delta-5 desaturation of C20 PUFA (20:3n-6 to 20:4n-6 / arachidonic acid; 20:4n-3 to 20:5n-3 / EPA) with GC-MS-validated products, and that partial in-vivo knockout reroutes synthesis through an alternative Delta-8 desaturation pathway, so the enzyme behaves as Delta-6/Delta-5/Delta-8 in the in-vivo pathway context. Reason: UniProt lists this specific desaturase activity as part of the Fads2 catalytic repertoire, and falcon deep research corroborates the Delta-5 (C20 to ARA/EPA) and in-vivo Delta-8 activities of the bifunctional zebrafish enzyme. Supporting Evidence: file:DANRE/fads2/fads2-uniprot.txt Fatty acid desaturase with bifunctional delta-5 and delta-6 file:DANRE/fads2/fads2-uniprot.txt biosynthesis of polyunsaturated fatty acids file:DANRE/fads2/fads2-deep-research-falcon.md Zebrafish are a canonical example: they carry a single **bifunctional Ξ6/Ξ5 Fads2** that supports multiple LC-PUFA biosynthetic steps. file:DANRE/fads2/fads2-deep-research-falcon.md The authors interpret this as evidence that zebrafish Fads2 behaves as **Ξ6/Ξ5/Ξ8** within the in vivo pathway context. |
| GO:0006636 unsaturated fatty acid biosynthetic process | IEA GO_REF:0000041 | ACCEPT | Summary: unsaturated fatty acid biosynthetic process (GO:0006636) is supported for Fads2. Falcon deep research confirms zebrafish Fads2 is the key desaturase in endogenous LC-PUFA biosynthesis, with experimentally validated production of C18 (GLA/SDA) and C20 (ARA/EPA) intermediates and participation in the Sprecher pathway for DHA via Delta-6 desaturation of C24 substrates. Reason: Fads2 acts in polyunsaturated fatty-acid biosynthesis. Supporting Evidence: file:DANRE/fads2/fads2-uniprot.txt PATHWAY: Lipid metabolism; polyunsaturated fatty acid biosynthesis. file:DANRE/fads2/fads2-deep-research-falcon.md These findings support that zebrafish Fads2 can participate in the C24 Ξ6 step required for Sprecher-pathway DHA biosynthesis. |
| GO:0001889 liver development | IMP PMID:23813869 Functional validation of GWAS gene candidates for abnormal l... | KEEP AS NON CORE | Summary: liver development (GO:0001889) is supported as a knockdown-screen phenotype but is not the core molecular role. The direct conserved function is fatty-acid desaturation in PUFA biosynthesis; liver development is a downstream/organismal phenotype. Falcon deep research reinforces that the best-characterized in-vivo loss-of-function phenotype is reproductive: partial CRISPR disruption of fads2 in adult females altered egg LC-PUFA composition and produced poor-quality eggs, consistent with fads2 acting as a metabolic enzyme whose organismal phenotypes (liver, reproduction) are secondary to its desaturase activity. Reason: The direct conserved function is fatty-acid desaturation in PUFA biosynthesis; liver development is a downstream or organismal phenotype. Supporting Evidence: PMID:23813869 function of gene candidates during liver development PMID:23813869 smaller livers at 72 hpf file:DANRE/fads2/fads2-deep-research-falcon.md Partial CRISPR disruption of fads2 in adult females altered egg LC-PUFA signatures and was associated with **poor-quality eggs**, consistent with a requirement for properly balanced LC-PUFA production/availability during oogenesis and egg provisioning. |
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