cyp26a1

Summary: Asserts that cyp26a1 participates in the breakdown of retinoic acid. Zebrafish Cyp26a1 is the founding member of the CYP26 clade and the first retinoic-acid-catabolising enzyme cloned: expressed in COS-1 cells it converts all-trans RA to 4-OH-RA and 4-oxo-RA [PMID:8939936], so the gene carries direct experimental grounding for the very process the PAINT node asserts.

Reason: The IBD behind this row places retinoic-acid catabolism on the CYP26 node PTN002386488, and zebrafish cyp26a1 sits squarely inside that clade: the WITH/FROM list is the CYP26A1 orthology group (human O43174, mouse, rat) plus cyp26a1 itself. cyp26a1 appearing among its own sources is expected and is a strength, not circularity - its 1996 enzymatic characterisation is one of the descendant evidences that justified placing the function at that node, and the IBA then adds that the activity is inherited rather than lineage-specific. There is no zebrafish-specific evidence of loss or divergence. Catabolism rather than the broader metabolic term is the right specificity: C-4 hydroxylation is the committed step that routes RA to clearance.

Summary: Asserts cyp26a1 participates in central nervous system development. The requirement is real in zebrafish: the cyp26a1/giraffe null expands rostral spinal cord at the expense of hindbrain [PMID:15680360], and depleting all three cyp26 paralogs makes the entire hindbrain express posteriorly-restricted RA-responsive genes [PMID:17164423].

Reason: Retained, not removed - the node placement is sound and the zebrafish phenotypes are genuine. But it is not a core function. Cyp26a1 does none of the work of building the central nervous system: it performs one chemical step, destruction of retinoic acid, and the neural phenotypes follow from the altered ligand concentration that the retinoic-acid receptors then read out. The term records where the enzyme's product gradient matters, not what the enzyme does, so it belongs outside the core set with the other organ-patterning annotations.

Summary: Generic cytochrome-P450 activity class mapped from InterPro signatures. It is correct for cyp26a1: UniProt records the canonical monooxygenase mechanism, one oxygen atom inserted into the substrate and the other reduced to water, with electrons from NADPH via cytochrome P450 reductase.

Reason: Right but uninformative. GO:0004497 is a true ancestor of this gene's actual activity, which is stated precisely by GO:0062182 and GO:0008401 - both separately annotated here and both accepted. No MODIFY is proposed for exactly that reason: the specific child already exists in the annotation set, so a replacement term would duplicate an existing row rather than add information. Kept as an accurate family-level statement and marked non-core because the specific terms carry the content.

Summary: InterPro P450 signatures assert iron binding. This is directly supported for the zebrafish protein: UniProt annotates heme as cofactor and an axial heme-iron binding residue at position 438.

Reason: Accurate, but a cofactor-level property rather than a function of the gene product. The iron in question is the heme iron of the P450 catalytic centre; holding it is a prerequisite of the 4-hydroxylase activity rather than an activity in its own right, so it is kept as supporting detail outside the core set.

Summary: Places Cyp26a1 in the endoplasmic reticulum membrane, mapped from the UniProt subcellular-location vocabulary. The UniProt SUBCELLULAR LOCATION line assigns the zebrafish protein to the endoplasmic reticulum membrane and microsome membrane as a peripheral membrane protein.

Reason: Correct and mechanistically required: a class II P450 must sit in the ER membrane to receive electrons from membrane-bound NADPH-cytochrome P450 reductase, and the original zebrafish enzymology was performed on microsomal fractions of transfected cells. Accepted with one honest caveat - the underlying zebrafish evidence is by similarity to human CYP26A1 (O43174), not a localisation experiment in zebrafish, so this rests on conserved P450 architecture and the microsomal assay format rather than direct observation in this species.

Summary: ARBA machine-learning rule assigning retinoic acid 4-hydroxylase activity. This lands on precisely the reaction demonstrated for the zebrafish enzyme: 4-OH-RA and 4-oxo-RA are its major products from all-trans RA [PMID:8939936], and UniProt states hydroxylation occurs primarily at C-4.

Reason: The electronic rule reaches the right specific activity rather than a generic P450 class, and the identical term is independently supported by a zebrafish IDA from the same paper (reviewed separately in this file). Accepted as a statement of the gene's core molecular function.

Summary: Broad oxidoreductase class from InterPro P450 signatures, covering enzymes that act on paired donors with incorporation or reduction of molecular oxygen. True of cyp26a1, whose UniProt-recorded mechanism inserts one oxygen atom into atRA and reduces the other to water.

Reason: Correct but two levels too general to say anything about this gene, and treated consistently with the sibling generic term GO:0004497 monooxygenase activity. The informative statement is the specific 4-hydroxylase reaction already annotated as GO:0062182/GO:0008401, so no replacement is proposed and the row is kept as accurate family-level background.

Summary: InterPro P450 signatures assert heme binding. UniProt independently records heme as the cofactor of the zebrafish protein and annotates the axial heme-iron ligand at residue 438.

Reason: A genuine and well-evidenced cofactor property, kept for that reason, but not a core function: heme binding is what equips the catalytic centre, and the activity it enables is captured by the specific 4-hydroxylase terms. Treated consistently with GO:0005506 iron ion binding, which describes the same prosthetic group from the metal side.

Summary: ARBA rule asserting involvement in retinoic acid catabolism. This matches the demonstrated biology: the zebrafish enzyme converts all-trans RA to the more polar 4-OH and 4-oxo products that commit it to clearance [PMID:8939936].

Reason: The electronic assertion agrees with direct zebrafish enzymology and with the in vivo genetic evidence reviewed elsewhere in this file, and catabolism is the correct specificity rather than the broader metabolic parent. Accepted as a core biological process for this gene.

Summary: Rhea-derived annotation of the exact catalysed reaction (RHEA:51492): all-trans-retinoate plus O2 and reduced NADPH-hemoprotein reductase give all-trans-(4S)-hydroxyretinoate. This is the reaction UniProt records as the zebrafish enzyme's catalytic activity, with experimental evidence from PMID:8939936.

Reason: The most precise molecular-function statement available for this gene, tied to a balanced reaction and a stereochemically defined product, and grounded in a zebrafish experiment rather than inferred. Accepted as the core molecular function.

Summary: Manual sequence-similarity transfer of endoplasmic reticulum membrane localisation from human CYP26A1 (UniProtKB:O43174). UniProt records the same location for the zebrafish protein, as a peripheral membrane protein of the ER and microsome membrane.

Reason: A sound ortholog transfer: the donor is the direct human ortholog, the ER-membrane anchoring of class II P450s is a deeply conserved architectural feature required for electron delivery from NADPH-cytochrome P450 reductase, and zebrafish Cyp26a1 activity is itself assayed in microsomal preparations. Accepted, noting it duplicates the UniProt-vocabulary IEA row for the same term and rests on similarity rather than direct zebrafish imaging.

Summary: Experimental annotation of the defining reaction from the paper that identified this gene. In COS-1 cells transfected with the zebrafish P450RAI/cyp26a1 cDNA all-trans RA was rapidly converted to more polar metabolites, identified as 4-oxo-RA and 4-OH-RA [PMID:8939936].

Reason: This is the anchor experimental evidence for the gene's core molecular function, and the source of the EC and catalytic-activity statements in UniProt. The activity is isomer-selective - UniProt records no activity toward 9-cis and 13-cis retinoic acid - which makes the all-trans-specific term the correct choice over a generic retinoid-hydroxylase term. Accepted as core.

Summary: Asserts that cyp26a1 acts upstream of or within outflow tract morphogenesis, from a genetic-interaction experiment in which Cyp26a1 and Cyp26c1 were co-depleted and outflow tract defects resulted [PMID:27893754].

Reason: The observation stands and the interaction is real, but the annotation records a downstream consequence rather than participation. The same paper shows the phenotype is entirely a retinoic-acid-dosage effect: blocking RA synthesis with DEAB, or re-supplying cyp26a1 mRNA, restores heart morphology and cardiomyocyte number in Cyp26-deficient embryos. Cyp26a1 therefore does none of the work of shaping the outflow tract - it sets the RA concentration that outflow tract progenitors respond to. IGI rather than IMP is itself informative here: single depletion is not sufficient, so the requirement is shared across the paralogs. Kept as genuine but non-core developmental context.

Summary: Asserts cyp26a1 acts upstream of or within anterior/posterior pattern specification in the pronephros. Cyp26a1 is expressed in the ventral posterior lateral mesoderm, and its knockdown (morpholino and the pan-Cyp26 inhibitor R115866) shows it is needed there during gastrulation to restrict the anteriorising effect of retinoic acid on kidney progenitors [PMID:27406002].

Reason: Well-evidenced and spatially resolved - one of the better-supported developmental rows in this set, since the authors map cyp26a1 expression onto the kidney progenitor field and perturb it two independent ways. It is nonetheless non-core by the participation test: the authors' own formulation is that posterior kidney progenitors are protected from RA by Cyp26a1, i.e. the enzyme removes a ligand and the patterning is performed by the RA-responsive transcriptional machinery in the progenitors. Kept as a well-supported non-core role.

Summary: Asserts cyp26a1 acts upstream of or within heart development, from morpholino depletion of cyp26a1 in a study of retinoic-acid receptor feedback [PMID:23990796]. Embryos depleted of both RARalphab1 and Cyp26a1 had dysmorphic hearts with reduced ventricular cardiomyocyte number.

Reason: Kept: a ZFIN curator made this experimental annotation having read the full text, and the cardiac phenotype is reproducible across several independent zebrafish studies. It is non-core for the standard reason - the paper's own model is that Cyp26a1 limits embryonic RA levels as the negative-feedback arm of RA signalling, and the cardiac consequences follow from RA excess when that arm is removed. The enzyme contributes no structure, catalysis or cofactor activity to cardiac morphogenesis itself.

Summary: The genetic-interaction counterpart of the heart development IMP row from the same study: the cardiac phenotype is scored in embryos co-depleted for RARalphab1 and Cyp26a1 [PMID:23990796].

Reason: Same action as the IMP row for this term, for consistency, and for the same participation argument: Cyp26a1 controls retinoic-acid concentration and the cardiac defect is the downstream readout. The IGI evidence code is the more accurate description of the experiment - the marked phenotype emerges from co-depletion, which shows the requirement is buffered rather than solely cyp26a1-dependent.

Summary: Asserts cyp26a1 acts upstream of or within midbrain-hindbrain boundary development, from co-depletion of RARalphab1 and Cyp26a1 [PMID:23990796].

Reason: Kept but clearly peripheral, and the paper is explicit about why: in either RARalphab1 or Cyp26a1 deficient embryos alone the authors never observed loss of the midbrain-hindbrain boundary; the phenotype appears only on co-depletion. This is a synthetic, sensitised phenotype reflecting retinoic-acid excess, not evidence that Cyp26a1 does work in building the boundary. Non-core is the appropriate treatment; REMOVE would be wrong because the genetic interaction itself is solidly demonstrated.

Summary: Asserts cyp26a1 acts upstream of or within vasculature development, from co-depletion of Cyp26a1 and Cyp26c1, which reduces cranial vasculature cells while increasing atrial cells [PMID:24667328].

Reason: Kept - the lineage-tracing evidence that the cardiac/vascular progenitor boundary shifts in Cyp26-deficient embryos is strong. But this paper supplies the clearest participation argument in the whole set for treating it as non-core: the authors find Cyp26 enzymes act largely cell non-autonomously, i.e. the enzyme works in one cell population and the vascular deficit appears in another. That is the signature of an enzyme shaping a diffusible ligand, not one executing vascular morphogenesis. Note too that single knockdown of Cyp26a1 does not overtly affect cardiovascular development, which is why the row is IGI.

Summary: Asserts cyp26a1 acts upstream of or within atrial cardiac muscle cell development. In Cyp26a1/Cyp26c1 co-depleted embryos the myocardial progenitor field contains excess atrial progenitors and shifts anteriorly into territory that normally gives rise only to vascular progenitors [PMID:24667328].

Reason: Kept for the same reasons as the vasculature row from this paper, and given the same action for consistency: a real, lineage-traced effect on atrial progenitor number that is nonetheless produced cell non-autonomously through retinoic-acid levels rather than by Cyp26a1 acting within differentiating atrial cardiomyocytes. The excess atrial cells and the reduced vascular cells are two readouts of one shifted boundary.

Summary: Asserts cyp26a1 acts upstream of or within the retinoic acid receptor signalling pathway. The cited study shows cyp26a1 is a genuine in vivo target of miR-19 and that failure to repress cyp26a1 properly contributes to RA-induced axis defects [PMID:23975936].

Reason: Kept rather than modified. Cyp26a1's relation to this pathway is that it destroys the receptor ligand, so a narrower regulatory term was considered - but a comparator check argues against replacing this row: in zebrafish GO:0048384 is carried by the RA-handling enzymes and binding proteins generally, including aldh1a2, dhrs3a, crabp2b and the paralog cyp26b1, so GO curation convention already places ligand-availability enzymes under the pathway term rather than reserving it for receptors and coactivators. Treating cyp26a1 as the exception would impose a distinction the comparator class does not make. Marked non-core because the gene's own contribution is catalytic ligand clearance, which the molecular-function terms state directly; a separate NEW row proposes the negative-regulation term that the family also carries.

Summary: Asserts cyp26a1 acts upstream of or within mesodermal-endodermal cell signalling. Cell transplantation showed Cyp26a1 functions directly within endoderm to modulate retinoic-acid signalling and limit the pancreatic field [PMID:19416885].

Reason: This is the strongest cell-autonomy evidence anywhere in this gene's annotation set, and it makes the term defensible: retinoic acid is produced in mesoderm and signals to endoderm, and Cyp26a1 acting inside endodermal cells genuinely modulates that mesoderm-to-endoderm transfer of information. Kept on that basis. Still non-core, because what Cyp26a1 contributes is the destruction of the signalling molecule - it is neither the signal nor the receptor, and the term describes the communication event rather than the enzymology.

Summary: Asserts cyp26a1 acts upstream of or within pancreas development. The cyp26a1/giraffe mutant confirms cyp26a1 plays the primary role in setting the anterior limit of the pancreatic field, and loss of Cyp26 function expands pancreatic cell types anteriorly [PMID:19416885].

Reason: A well-controlled in vivo requirement, established with a genetic null rather than morpholinos alone, and kept for that reason. It is non-core under the participation test: cyp26a1 sets the position of a boundary by clearing retinoic acid from the anterior trunk endoderm, and the specification of pancreatic fates is carried out by the RA-responsive transcriptional programme in the endoderm. The enzyme determines where that programme is permitted to run, not how it runs.

Summary: Genetic-interaction counterpart of the pancreas development row: analysis of giraffe mutants shows cyp26b1 and cyp26c1 function redundantly to partially compensate for loss of Cyp26a1 [PMID:19416885].

Reason: Given the same action as the IMP row for this term, for consistency. The IGI evidence adds the useful detail that the requirement is partially buffered by the other two cyp26 paralogs, which is exactly the pattern seen for hindbrain and cardiovascular phenotypes and reinforces that what matters is total retinoic-acid-clearing capacity in the tissue rather than a cyp26a1-specific developmental activity.

Summary: In vivo genetic evidence that cyp26a1 carries out retinoic-acid catabolism: the giraffe mutant and Cyp26-depleted embryos show expanded retinoic-acid-dependent pancreatic fates, the expected consequence of failing to degrade RA in the anterior trunk endoderm [PMID:19416885].

Reason: Accepted as core. This complements the biochemical evidence by showing the catabolic activity operating on endogenous retinoic acid in the intact embryo, in a defined tissue, with a genetic null rather than only in transfected cells. Together with the COS-1 enzymology this makes retinoic-acid catabolism the best-supported biological process for this gene.

Summary: Asserts cyp26a1 acts upstream of or within forebrain anterior/posterior pattern specification, from a study of Tgif in which loss of cyp26a1 produced a forebrain phenotype mimicking tgif morphants [PMID:17998248].

Reason: Kept: cyp26a1 is expressed in the forebrain and midbrain and the phenotype is reproducible, so the requirement is genuine. Non-core because the mechanism the paper proposes is explicitly one of ligand exclusion - RA-degrading enzymes are expressed in forebrain and midbrain to protect those regions from retinoic acid, and Tgif patterns the forebrain by regulating that degradation. Cyp26a1 is the effector that removes RA, not a component of the patterning machinery.

Summary: Asserts cyp26a1 acts upstream of or within brain morphogenesis, scored in the cyp26a1/giraffe mutant in the same holoprosencephaly study [PMID:17998248].

Reason: Kept, and treated consistently with the forebrain patterning row from this paper. This is the broadest of the neural annotations for this gene and the furthest from its enzymology; the morphogenetic defect is a consequence of elevated forebrain retinoic acid rather than of any structural or catalytic contribution by Cyp26a1 to brain morphogenesis. Non-core rather than over-annotated, since the mutant phenotype is directly observed.

Summary: Asserts a cellular response to vitamin A. The direct evidence is transcriptional: exogenous all-trans-retinol and the dihydroretinols strongly induced expression of Cyp26A1 in zebrafish [PMID:17253779], consistent with UniProt's record that the gene is induced by retinoic acid.

Reason: Kept, and the IDA is properly grounded - induction of cyp26a1 transcript by a vitamin A stimulus is a bona fide cellular response, and this paper also places Cyp26 enzymes downstream as the oxidisers of the resulting dihydroretinoic acid. Marked non-core because the annotation captures how the gene is regulated rather than what the protein does; the induction is the sensing arm of the retinoid feedback loop whose effector arm is the catabolic activity annotated separately.

Summary: Asserts cyp26a1 acts upstream of or within somitogenesis. Su(H) controls cyp26a1 expression in the tailbud, and morpholino knockdown of cyp26a1 alone caused asymmetric cyclic dlc expression [PMID:17098223].

Reason: Kept - unusually for the developmental rows this is a single-gene requirement rather than a synthetic one, so the IMP is well placed. It remains non-core because the authors' own interpretation is that excess retinoic acid in the tailbud drives the cyclic asymmetries, and they show exogenous RA alone is sufficient to generate asymmetric expression of the cyclic genes. Cyp26a1 sets tailbud RA levels; the segmentation clock does the segmenting.

Summary: Asserts cyp26a1 acts upstream of or within rhombomere 4 morphogenesis, scored in the cyp26a1 mutant background [PMID:17164423].

Reason: Kept, but this paper is itself the reason to treat it as peripheral: the authors note that cyp26a1 mutants in fish and mouse show relatively subtle hindbrain patterning defects, inconsistent with a global role for cyp26a1 in hindbrain patterning, and that the dramatic phenotype requires depleting all three cyp26 paralogs. The annotation therefore records a modest, redundancy-buffered contribution to a rhombomere boundary, produced by retinoic-acid clearance rather than by any activity of Cyp26a1 within rhombomere 4.

Summary: Genetic-interaction row for rhombomere 4 morphogenesis, from co-depletion of cyp26a1 with a second cyp26 paralog [PMID:17164423].

Reason: Same action as the IMP row for this term. The IGI codes the central finding of the paper - that the three cyp26 genes function redundantly to shape retinoic-acid-dependent gene expression in the hindbrain - and reinforces that no single paralog, cyp26a1 included, owns this developmental process.

Summary: Asserts cyp26a1 acts upstream of or within hindbrain development, from combined depletion of the cyp26 paralogs, after which the entire hindbrain expresses retinoic-acid-responsive genes normally confined to nested posterior domains [PMID:17164423].

Reason: Kept: this is a striking and well-controlled phenotype, and hindbrain patterning is the best-studied context in which cyp26a1 matters. Non-core nonetheless, and for a reason the paper itself supplies - its model is that differential RA responsiveness along the hindbrain axis is shaped by the dynamic expression of RA-degrading enzymes. Cyp26a1 supplies degrading capacity; the Hox network performs the patterning. The single-mutant phenotype is described as subtle, so this is a shared, redundancy-buffered role.

Summary: Asserts cyp26a1 acts in retinoic-acid metabolism, from the cyp26a1 mutant in the hindbrain study. Cyp26 enzymes are characterised there as metabolising retinoic acid into polar derivatives, and loss of that activity expands RA-responsive gene expression across the hindbrain [PMID:17164423].

Reason: Accepted. This is in vivo evidence, in the intact embryo, that removing cyp26a1 raises effective retinoic-acid levels - the functional signature of a retinoic-acid-metabolising enzyme. It is the correct term for this row even though the more specific catabolic term also applies elsewhere, since the assay reads out retinoid turnover rather than a defined catabolic product.

Summary: Asserts cyp26a1 acts upstream of or within metabolism of retinal - the C20 aldehyde that retinaldehyde dehydrogenase Aldh1a2 oxidises to retinoic acid. ZFIN made this IMP from the cyp26a1/giraffe mutant alongside GO:0042573 retinoic acid metabolic process from the same paper and evidence code [PMID:17164423]. The mutant's retinoid-dependent patterning is genuinely disturbed, but retinal is one metabolite upstream of the species this enzyme turns over.

Reason: Re-adjudicated from a previous REMOVE, which was not defensible. This is an experimental annotation made by a ZFIN curator who read the full text, whereas the cached copy of PMID:17164423 contains only the abstract and introduction - the mutant retinoid measurements cannot be checked from here, and nothing accessible contradicts the observation. A cyp26a1 mutant plainly perturbs embryonic retinoid flux, so REMOVE is the wrong instrument. What the accessible evidence does establish is that the term overreaches by one metabolite. Direct zebrafish enzymology finds CYP26 enzymes metabolise retinoic-acid isomers but cannot metabolise retinol or retinal [PMID:16455818], and UniProt confines the zebrafish reaction to all-trans-retinoate; this paper's own introduction assigns retinal oxidation to a different enzyme, Aldh1a2. A comparator check shows this is an established convention rather than an oversight: GO:0042574 is held across human, mouse and zebrafish essentially only by enzymes and carriers that directly make or consume retinal - the retinol/retinaldehyde dehydrogenases (RDH10, RDH11, RDH13, DHRS4, dhrs9, rdh1, ALDH1A3), the carotenoid cleavage oxygenases BCO1 and BCO2, RPE65 and ABCA4 - and no CYP26 carries it in human or mouse, while in zebrafish cyp26a1 is the only one of the three paralogs with it. The family convention is GO:0042573 retinoic acid metabolic process, which all three zebrafish cyp26 genes carry and which is separately annotated to cyp26a1 from this very paper. No replacement term is proposed for exactly that reason - a MODIFY would duplicate an existing row. Flagged as over-annotation so the retinoic-acid-specific terms carry the claim.

Summary: Asserts cyp26a1 acts in retinoic-acid metabolism, from HPLC analysis in a paper whose primary subject is the paralog Cyp26D1. The abstract confirms cyp26a1 was assayed alongside it: the all-trans RA metabolites produced by Cyp26D1 were the same as those produced by Cyp26A1, mainly 4-hydroxy- and 4-oxo-all-trans-RA, and the overexpression phenotypes were compared directly with those of cyp26a1 [PMID:16455818].

Reason: Accepted, and specifically not treated as a paralog mis-attribution. The title foregrounds Cyp26D1, but the cached abstract itself states that Cyp26A1 products and cyp26a1 overexpression phenotypes were measured in the same study, so the ZFIN curator had direct grounds for annotating cyp26a1 from this paper. The result also supplies the substrate-specificity evidence used elsewhere in this review: these enzymes act on retinoic-acid isomers and not on retinol or retinal.

Summary: Asserts cyp26a1 acts upstream of or within blood vessel development, scored in the cyp26a1/giraffe mutant, which shows defects of the common cardinal vein among other organs [PMID:15680360].

Reason: Kept - a genetic null with a clearly documented vascular phenotype. Non-core because the authors themselves place two steps between the enzyme and the vessel: molecular markers indicate the lateral plate mesoderm is posteriorised in the mutant, and they attribute the common cardinal vein defect to that posteriorisation. So the causal chain is failure to clear retinoic acid, then mispatterned mesoderm, then a vascular defect - Cyp26a1 contributes no activity to blood vessel morphogenesis itself.

Summary: Asserts cyp26a1 acts upstream of or within hindbrain development, from the giraffe mutant, in which the rostral spinal cord territory expands at the expense of the hindbrain [PMID:15680360].

Reason: Kept, and consistent with the other hindbrain rows in this file. The phenotype is a genuine homeotic shift of the hindbrain/spinal cord boundary in a genetic null, and it is the mirror image of the raldh2 mutant, which is strong evidence that it is driven by retinoic-acid dosage. The paper's model states the mechanism plainly: Cyp26a1 attenuates RA signalling in the prospective rostral spinal cord to limit hox gene expression. Boundary position is set by the Hox network; Cyp26a1 sets the ligand level that positions it.

Summary: Zebrafish IDA for retinoic acid 4-hydroxylase activity from the paper that identified the enzyme: transfected cells converted all-trans RA to more polar metabolites identified as 4-OH-RA and 4-oxo-RA [PMID:8939936].

Reason: Accepted as a core molecular function. This and the all-trans-specific term GO:0062182 describe the same demonstrated reaction at slightly different granularity, and both are retained deliberately - the ZFIN IDA records the assayed 4-hydroxylation, while the Rhea-linked term adds the balanced equation and product stereochemistry. Given consistently the same action as the ARBA-derived IEA row for this term.

Summary: Zebrafish IDA placing cyp26a1 in retinoic-acid metabolism, from the original characterisation in which all-trans RA was rapidly metabolised to more polar products in cells transfected with the cyp26a1 cDNA [PMID:8939936].

Reason: Accepted, consistent with the other GO:0042573 rows in this file. The paper describes this enzyme as the first component of retinoic-acid metabolism isolated at the molecular level, and its induction by retinoic acid - also recorded by UniProt - is what makes it the feedback arm of retinoid homeostasis rather than merely a degradative enzyme.

Summary: Morpholino-based counterpart of the blood vessel development annotation from the same study, independent of the giraffe mutant allele [PMID:15680360]. Resolved from PENDING in this re-review.

Reason: Given the same action as the mutant-based row for this term, for consistency. Having both a genetic null and an independent knockdown supporting the same vascular phenotype strengthens the case that the requirement is real rather than an allele-specific or off-target artefact - which is why the row is kept rather than removed. It remains non-core for the reason given on the mutant row: the vascular defect follows from posteriorisation of the lateral plate mesoderm caused by excess retinoic acid.

Summary: A second genetic-interaction row for vasculature development from the cardiac/vascular lineage study, using a different combination of cyp26a1 and cyp26c1 morpholinos [PMID:24667328]. Resolved from PENDING in this re-review.

Reason: Given the same action as the other vasculature development row from this paper. The additional morpholino combination is corroborating evidence for the same cell-non-autonomous effect on the cranial vasculature, and single knockdown of Cyp26a1 alone does not overtly affect cardiovascular development - so this records a shared, retinoic-acid-mediated contribution rather than a cyp26a1-specific vascular function.

Summary: Phylogenetic assertion of generic monooxygenase activity, propagated from the pan-cytochrome-P450 node PANTHER:PTN000669383 - a very deep node whose donor set spans animal CYP26s and thirteen Arabidopsis cytochrome P450s. Resolved from PENDING in this re-review.

Reason: The node placement is not in dispute: monooxygenase activity is ancestral to the entire P450 superfamily, and zebrafish Cyp26a1 is a P450 whose UniProt-recorded mechanism is exactly that reaction, so the inference is sound. The issue is informativeness, not correctness - at this depth the term cannot distinguish a retinoic-acid hydroxylase from a plant sterol oxidase. Given the same action as the InterPro-derived IEA row for the identical term, and kept rather than modified because the specific activity is already annotated as GO:0062182 and GO:0008401.

Summary: A further genetic-interaction row for rhombomere 4 morphogenesis from the hindbrain redundancy study, using a different combination of cyp26 morpholinos on the mutant background [PMID:17164423]. Resolved from PENDING in this re-review.

Reason: Given the same action as the other rhombomere 4 rows in this file. The several IGI rows from this paper differ only in which cyp26 paralogs were co-depleted, and together they make the paper's central point: the hindbrain phenotype scales with total cyp26 capacity, while cyp26a1 mutants alone show relatively subtle hindbrain defects.

Summary: A further genetic-interaction row for rhombomere 4 morphogenesis from the same study with another cyp26 morpholino combination [PMID:17164423]. Resolved from PENDING in this re-review.

Reason: Given the same action as the other rhombomere 4 rows, for consistency. Like them it records a redundancy-buffered contribution to a rhombomere boundary that arises from retinoic-acid clearance rather than from any activity of Cyp26a1 within rhombomere 4 itself.

Summary: A second genetic-interaction row for atrial cardiac muscle cell development, using a different cyp26a1/cyp26c1 morpholino combination [PMID:24667328]. Resolved from PENDING in this re-review.

Reason: Given the same action as the other atrial cardiac muscle cell development row from this paper. The excess atrial progenitors are produced by an anterior shift of the myocardial progenitor field in the anterior lateral plate mesoderm, driven cell non-autonomously through retinoic-acid levels - so Cyp26a1 positions the field boundary rather than doing work within developing atrial cardiomyocytes.

Summary: NEW (proposed). Cyp26a1 reduces retinoic-acid receptor pathway output by catalytically destroying the pathway's ligand. In zebrafish this is shown directly: cyp26a1 knockdown and pan-Cyp26 inhibition both show Cyp26a1 is required in the posterior lateral mesoderm to restrict the anteriorising effects of retinoic acid, with posterior kidney progenitors described as protected from RA by Cyp26a1 [PMID:27406002], and re-supplying cyp26a1 mRNA rescues retinoic-acid-excess phenotypes [PMID:27893754].

Reason: Proposed after both tests in the curation guidance. Participation: the gene product itself performs the step that lowers pathway activity - it hydroxylates all-trans retinoic acid at C-4, converting the receptor ligand into polar products that no longer signal. This is catalysis by Cyp26a1, not a downstream phenotype and not mere necessity. Comparator check: the term is carried by the gene products standing in exactly this role, including human CYP26A1, CYP26B1 and CYP26C1, mouse Cyp26b1 and the retinoic-acid-reducing enzyme Dhrs3, and in zebrafish by the paralog cyp26b1 - so here the comparator class systematically does carry the term and zebrafish cyp26a1 is the anomalous absence, the opposite of the pattern that should block a NEW. It is not an ancestor or descendant of GO:0048384, which the gene already holds and which is retained: that row records participation in the pathway, whereas this one records the direction of the effect. Proposed conservatively as IMP from the kidney-patterning study, whose morpholino and independent chemical-inhibitor evidence directly demonstrates restriction of retinoic-acid signalling.