This website uses cookies to ensure you get the best experience on our website.
- Table of Contents
OTC / Ornithine transcarbamylase, mitochondrial · IHC design guide
Design Immunohistochemistry for OTC
Plan chromogenic IHC for OTC using liver hepatocytes and intestinal endocrine cells as positive tissue references (HPA tissue IHC). The guide covers fixation, staining interpretation, and a catalog antibody validated for IHC-P (datasheet: IHC-P).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
OTC Immunohistochemistry Experimental Design Guide
Expected localisation, validated protocols, controls and antibodies — the at-a-glance facts below, then the full design guide.
Must know before staining
| Expected localisation | Granular cytoplasm in hepatocytes (HPA tissue IHC) | |
| Staining pattern | Granular cytoplasm in hepatocytes and intestinal endocrine cells (HPA tissue IHC) | |
| Antigen retrieval | Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen) | |
| Positive control | Duodenum+4 more · see all | |
| Negative control | Adipose tissue+4 more · see all |
Important caveats
Reasons your staining may differ from the expected pattern.
| Fixation | Keep formalin fixation consistent across FFPE sections (standard IHC practice; not target-specific) | |
| Caveat | Duodenal and small-intestinal positives are endocrine cells (HPA tissue IHC) | |
| Regulation | Expression regulation is unreported (UniProt) | |
| Isoform / epitope | No annotated isoforms; mature chain spans aa 33–354 (UniProt) |
Section 1
Recommended OTC IHC & IF Protocols
The catalog antibody’s IHC-P protocol is accompanied by one published OTC staining protocol for hepatocellular carcinoma tissue (PMC8426309).
| Sample | FFPE human hepatoarcinoma tissue (datasheet A00721-2) |
| Fixation | Image formalin-fixed; duration unreported (datasheet A00721-2); verify before use. |
| Sectioning | 4–5 µm sections on charged slides (standard) |
| Deparaffinisation | Xylene, graded ethanol series to water (standard) |
| Antigen retrieval | Heat-induced epitope retrieval in citrate buffer, pH 6.0, 20 min at 95–98 °C (standard rule: cytoplasmic / membrane antigen) |
| Peroxidase block | 3% H2O2, 10 min, room temperature (standard) |
| Blocking | 10% normal serum of the secondary host, 30 min, room temperature (standard) |
| Primary antibody | Rabbit anti-OTC, 1:10-1:50 (datasheet A00721-2) |
| Primary incubation | Overnight at 4 °C (standard) |
| Detection | HRP-polymer secondary, DAB chromogen 5–10 min (standard) |
| Counterstain | Hematoxylin, blue, dehydrate and mount (standard) |
| Expected result | OTC-positive staining in endocrine cells of duodenum (HPA tissue IHC: High). HPA tissue profile: Granular cytoplasmic expression in hepatocytes, duodenum and small intestine. No signal in the no-primary control. |
💡Decision noteStart with citrate pH 6.0 HIER at 95–98 °C for 20 min (page retrieval); the published protocol does not specify retrieval (PMC8426309).
Section 2
What Is the Expected OTC Staining Pattern?
OTC is a mitochondrial matrix protein without a transmembrane segment (UniProt P00480 topology). In paraffin-section IHC, expect granular cytoplasmic staining in hepatocytes and intestinal cells (HPA: tissue IHC profile). Liver hepatocytes and duodenal and small-intestinal endocrine cells are high-staining examples (HPA: High); the tissue IHC pattern has Enhanced reliability, reflecting high consistency with RNA expression (HPA: reliability).
| Granular cytoplasmic staining in hepatocytes, with appropriately stained intestinal cells. | This fits the mitochondrial matrix location (UniProt P00480) and HPA's tissue pattern. Hepatocytes and duodenal and small-intestinal endocrine cells are reported as High (HPA: tissue IHC). Judge the granules within identified cells; the expected result does not require uniform staining across every cell in the section (HPA: cell-specific levels). |
| Predominantly nuclear, membranous, or extracellular staining, especially without cytoplasmic granules. | These compartments conflict with the mitochondrial matrix assignment and lack of a transmembrane segment (UniProt P00480 topology). Treat an isolated wrong-compartment signal as suspect, then compare it with a known-positive hepatocyte region and a detection control before assigning it to OTC (HPA: High in hepatocytes; standard IHC practice). |
| Strong staining in cells reported as negative, such as adipocytes in adipose tissue. | HPA reports OTC as Not detected in those adipocytes (HPA: adipose tissue IHC). Reproducible signal there warrants a specificity check; antibody cross-reactivity or endogenous chromogenic activity are possible explanations, not conclusions established by HPA (standard IHC practice). Check cell identity and detection controls before scoring that signal as OTC. |
| Diffuse color across cells and tissue, with little distinction between granules and background. | A diffuse deposit obscures the granular cytoplasmic pattern used to interpret OTC staining (HPA: tissue IHC profile). It can reflect nonspecific reagent binding or the chromogenic detection system (standard IHC practice). Compare a primary-antibody omission control and tissue-free areas; neither background appearance nor a single control establishes OTC specificity by itself. |
| No staining in well-preserved hepatocytes on a putative positive-control section. | Hepatocytes are reported as High and are a useful positive reference (HPA: liver IHC). An absent result calls for a workflow check, including control-section identity, reagent performance, antigen retrieval, and detection steps (standard IHC practice). HPA's tissue pattern does not identify which step failed or establish OTC-specific fixation sensitivity. |
💡Expected OTC appearanceCall positive OTC IHC when identified hepatocytes show convincing granular cytoplasmic staining, with strong signal consistent with HPA's High rating; an isolated nuclear, membranous, or diffuse deposit is suspect against the mitochondrial matrix assignment (HPA: liver IHC; UniProt P00480 topology).
| Tissue and cell selection (HPA: tissue IHC). | Liver hepatocytes, duodenal endocrine cells, and small-intestinal endocrine cells are High; appendix endocrine cells and rectal enterocytes are Medium (HPA: tissue IHC). Use the stated cell type when comparing sections: an HPA level for one population does not describe every neighboring cell. |
| Compartment and molecular form (UniProt P00480). | OTC occupies the mitochondrial matrix, has no transmembrane segment, and has an annotated mature chain at residues 33–354 (UniProt P00480). These facts support intracellular granular interpretation; they do not locate the catalog antibody's epitope or predict its retrieval requirement. |
| Strength of the tissue-pattern evidence (HPA: reliability and antibodies). | HPA calls the tissue IHC pattern Enhanced and lists 2 antibodies with Enhanced IHC status, HPA000243 and HPA000570 (HPA: tissue IHC; HPA: antibodies). That supports the reported distribution, but it does not validate an unspecified catalog antibody or every staining run. |
| IF/ICC expectation? (HPA: subcellular ICC-IF). | For the separate IF/ICC application, expect mitochondrial localization: HPA reports Mitochondria (supported) and lists images from A-431, U-251MG, and U2OS (HPA: subcellular ICC-IF). This localization cross-check does not supply an IHC-P protocol or predict fluorescence intensity in paraffin tissue. |
| Situation | Likely cause | Next action |
|---|---|---|
| Hepatocyte staining is absent or very weak. | Hepatocytes should be High (HPA: liver IHC); the cause of a failed run is not specified by that rating. | Verify control-tissue identity and morphology, then review the catalog antibody's IHC-P instructions, retrieval, dilution, and detection records (standard IHC practice). Avoid attributing failure to OTC-specific fixation effects without evidence. |
| Staining appears mainly nuclear or along cell borders. | That location conflicts with mitochondrial matrix OTC and its lack of a transmembrane segment (UniProt P00480 topology). | Recheck compartment against stained hepatocytes, inspect counterstain and section morphology, and repeat with appropriate detection controls if the pattern persists (HPA: High in hepatocytes; standard IHC practice). |
| An HPA-negative cell population stains strongly. | For example, adipose-tissue adipocytes are Not detected (HPA: adipose tissue IHC); cross-reactivity or endogenous detection activity may contribute (standard IHC practice). | Confirm the stained cell type, compare the same run's positive tissue, and use a primary-antibody omission control to assess detection-derived color (standard IHC practice). Do not score unexpected color as OTC solely from intensity. |
| The whole section has diffuse chromogenic background. | Diffuse color can hide the reported granular cytoplasmic profile (HPA: tissue IHC); nonspecific binding or detection background is possible (standard IHC practice). | Inspect the omission control and review blocking, antibody concentration, washing, and chromogen development under the established IHC-P workflow (standard IHC practice). Reassess cellular localization after background is controlled. |
| Intestinal staining seems inconsistent between sections or cell groups. | HPA reports High duodenal and small-intestinal endocrine cells, but Medium rectal enterocytes and appendix endocrine cells (HPA: tissue IHC). | Record the tissue site and identified cell population before comparing intensity; include hepatocytes as a High reference when available (HPA: tissue IHC). Avoid treating all intestinal cells as an equivalent positive control. |
| A granular signal appears, but its specificity remains uncertain. | Granularity agrees with the HPA profile, yet morphology alone cannot establish antibody specificity (HPA: tissue IHC profile; standard IHC practice). | Compare positive and HPA Not detected reference populations, inspect the omission control, and document whether staining follows the expected cells and compartment (HPA: tissue IHC; UniProt P00480 topology; standard IHC practice). |
Experiment evidence
IHC & IF images showing OTC staining
A00721-2 · IHCFormalin-fixed and paraffin-embedded human hepatoarcinoma with OTC Antibody (Center), which was peroxidase-conjugated to the secondary antib
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000036473-OTC/tissue/cerebral+cortex#imid_104034
HPA · DuodenumHuman Protein Atlas IHC, Duodenum. Source: https://www.proteinatlas.org/ENSG00000036473-OTC/tissue/duodenum#imid_103975
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000036473-OTC/tissue/colon#imid_103976
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000036473-OTC/tissue/liver#imid_103977
HPA · ICC-IF A-431Human Protein Atlas immunofluorescence, A-431, antibody HPA000243; green = OTC, blue = nucleus, red = microtubules.
HPA · ICC-IF A-431Human Protein Atlas immunofluorescence, A-431, antibody HPA000243; green = OTC, blue = nucleus, red = microtubules.
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for OTC IHC & IF
🧪Run liver first: hepatocytes should stain (HPA: High in hepatocytes). Use adipose tissue as the negative tissue, focusing on adipocytes (HPA: Not detected in adipocytes); on the liver slide, treat non-hepatocyte cells as internal negative comparators only after confirming that they lack specific staining, because the supplied HPA row establishes staining for hepatocytes only (HPA: High in hepatocytes).
Positive control tissue: Duodenum (Endocrine cells, HPA High)
Negative control tissue: Adipose tissue (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show OTC in A-431, U-251MG, U2OS, with annotated localisation: Mitochondria (supported) (HPA subcellular).
Technical controls: Include a no-primary, secondary-only control and an isotype control matched to the primary antibody’s host species, immunoglobulin class, and monoclonal or polyclonal format; use OTC knockout material or peptide blocking, if available, as a biological specificity control. For liver DAB staining, block endogenous peroxidase and assess endogenous biotin if using avidin–biotin detection (selected-SKU caption: DAB staining).
⚠️Feasibility: The selected-SKU caption reports formalin-fixed, paraffin-embedded human hepatoarcinoma with DAB staining, but reports no target-specific fixation window or antigen retrieval requirement (selected-SKU caption). The supplied evidence does not establish whether frozen sections or IF/ICC are easier; for IF/ICC, check for mitochondrial localization (HPA: Mitochondria supported). Assess liver background from endogenous peroxidase in chromogenic IHC and autofluorescence in IF.
HPA tissue IHC evidence for OTC
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Enhanced — High consistency between antibody staining and RNA expression data.). Rows are taken directly from the HPA tissue chart — click any row's HPA link to view the source.
Positive expression · recommended positive controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| Duodenum | Endocrine cells | High | Protein (IHC) | HPA → |
| Liver | Hepatocytes | High | Protein (IHC) | HPA → |
| Small intestine | Endocrine cells | High | Protein (IHC) | HPA → |
| Appendix | Endocrine cells | Medium | Protein (IHC) | HPA → |
| Rectum | Enterocytes | Medium | Protein (IHC) | HPA → |
Undetected expression · recommended negative controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| Adipose tissue | Adipocytes | Not detected | Protein (IHC) | HPA → |
| Adrenal gland | Glandular cells | Not detected | Protein (IHC) | HPA → |
| Bone marrow | Hematopoietic cells | Not detected | Protein (IHC) | HPA → |
| Breast | Adipocytes | Not detected | Protein (IHC) | HPA → |
| Bronchus | Respiratory epithelial cells | Not detected | Protein (IHC) | HPA → |
Section 3
Advanced OTC IHC Tips
Troubleshoot chromogenic OTC staining in paraffin sections by checking retrieval, cell type, mitochondrial pattern, and matched controls.
How should I retrieve OTC antigen when staining is weak in paraffin sections?
Use citrate buffer at pH 6.0 for HIER at 95–98 °C for 20 min before chromogenic OTC IHC (page retrieval setting). Compare retrieved sections with a known positive liver section, where hepatocytes show high OTC staining, using the same detection run (HPA tissue IHC). Evaluate granular cytoplasmic staining rather than total brown signal, because OTC resides in the mitochondrial matrix and HPA reports a granular cytoplasmic pattern (UniProt P00480; HPA tissue IHC). If staining remains weak, adjust heating or cooling one variable at a time while keeping the citrate condition as the reference, and inspect tissue integrity alongside signal (standard IHC practice).
Could fixation explain weak or uneven OTC staining?
Target-specific OTC sensitivity to fixation is unknown from the supplied evidence, so do not assign weak staining to a particular fixation duration or chemistry (supplied evidence). An OTC antibody image uses formalin-fixed, paraffin-embedded human hepatoarcinoma with DAB detection, but its caption does not compare fixation conditions (caption: A00721-2). Record the fixative and fixation interval for each specimen, then compare sections processed with the same retrieval and detection conditions (standard IHC practice). Include a positive liver control in each run and judge staining in viable hepatocytes, which are reported as high for OTC, before changing retrieval or antibody conditions (HPA tissue IHC).
Where should convincing OTC staining appear within positive cells?
Expect granular cytoplasmic OTC staining in positive cells, consistent with mitochondrial matrix localisation and the HPA tissue pattern (UniProt P00480; HPA tissue IHC). In liver, assess hepatocytes first because HPA reports high staining there, while its profile also describes staining in duodenum and small intestine (HPA tissue IHC). A diffuse nuclear or surface-membrane pattern does not match the reported compartment and needs comparison with a matched negative control (UniProt P00480; standard IHC practice). Check whether the granules are reproducible across viable cell interiors rather than confined to section edges or pigment deposits, and assess the pattern before scoring overall DAB intensity (standard IHC practice).
How do OTC processing and modifications affect epitope interpretation?
OTC is recorded as a 354 aa precursor with a mature chain spanning residues 33–354, and no isoforms are annotated (UniProt P00480). Its mitochondrial matrix location and absence of a transmembrane segment support looking for intracellular granular staining after retrieval (UniProt P00480; HPA tissue IHC). The record lists acetylation and succinylation sites, but it supplies no antibody epitope map or evidence that these modifications alter IHC staining (UniProt P00480; supplied evidence). If two antibodies disagree, compare their documented immunogens or epitopes, if available, and repeat staining with the same positive tissue and detection conditions before assigning the difference to processing or modification (standard IHC practice).
How can I assess OTC localisation by IF alongside chromogenic IHC?
For the separate IF/ICC assay, pair OTC with a marker that identifies the expected cell type, such as hepatocytes in liver sections, and assess whether OTC forms intracellular puncta (HPA tissue IHC; HPA subcellular). Choose fluorophores after checking tissue autofluorescence in an unstained section, and reserve the cleaner spectral channel for the weaker signal (standard IF practice). OTC is in the mitochondrial matrix, so a matrix-facing epitope requires permeabilisation, although the catalog antibody’s epitope side is not specified here (UniProt P00480; supplied evidence). Optimise permeabilisation against cell preservation and include single-stain controls for multiplex separation; keep IF results distinct from the catalog antibody’s chromogenic IHC evidence (standard IF practice; caption: A00721-2).
What should I check when DAB background obscures OTC granules?
Start with a no-primary control and compare its DAB deposition with the OTC-stained section under the same counterstain and imaging conditions (standard IHC practice). Block endogenous peroxidase before secondary detection, then check whether secondary reagent, incomplete washing, or excessive DAB development contributes to background (standard IHC practice). The selected OTC image used a peroxidase-conjugated secondary antibody followed by DAB, but that caption does not establish which blocking conditions are optimal (caption: A00721-2). Reassess staining in viable hepatocytes, where high OTC expression is reported, and require granular cytoplasmic signal above the matched control before calling a cell positive (HPA tissue IHC; standard IHC practice).
How should I quantify OTC staining across paraffin sections? ⚠ ANSWER MARKED FOR VERIFICATION
Define the scored cell population and viable tissue area before measuring OTC, using hepatocytes for liver sections because HPA reports high staining in those cells (HPA tissue IHC). Report the percentage of positive cells and an H-score from 0–300 based on intensity classes, with thresholds set from matched negative controls (standard IHC practice). If counting positive cells per mm², normalise to the viable area occupied by the scored cell type rather than total section area (standard IHC practice). Keep retrieval, DAB development, imaging, and counterstain consistent, and score granular cytoplasmic signal separately from pigment or diffuse background (page retrieval setting; HPA tissue IHC; standard IHC practice).
How can I distinguish true OTC staining from artefact?
A credible OTC-positive cell shows granular cytoplasmic staining compatible with mitochondrial localisation, particularly in hepatocytes, which HPA reports as high (UniProt P00480; HPA tissue IHC). Treat dominant nuclear or surface staining as discordant with that location, and compare it with no-primary and known positive controls before interpreting it (UniProt P00480; standard IHC practice). Exclude section edges, necrotic regions, and deposits also present in the no-primary control; endogenous peroxidase can otherwise produce misleading DAB signal (standard IHC practice). The formalin-fixed hepatoarcinoma image demonstrates IHC use of SKU A00721-2, but its caption explicitly leaves clinical relevance unevaluated, so morphology alone cannot establish clinical meaning (caption: A00721-2).
Boster reagents
Best OTC / Ornithine transcarbamylase, mitochondrial IHC Antibodies
A00721-2 has real IHC data from formalin-fixed, paraffin-embedded human hepatoarcinoma (IHC image caption); the catalog lists Human, Mouse, and Rat reactivity (catalog: reactivity).
Real IHC data
Anti-OTC Antibody (Center)
Cat # A00721-2
A00721-2 will render with an IHC-P image of formalin-fixed, paraffin-embedded human hepatoarcinoma stained with a peroxidase-conjugated secondary antibody and DAB (IHC image caption). The catalog lists IHC-P and Human, Mouse, and Rat reactivity for A00721-2; it provides no IF image or IF/ICC application for this SKU (catalog: applications, reactivity, IF images).
Which to pick: Choose A00721-2 for tissue IHC-P: its own image documents staining in formalin-fixed, paraffin-embedded human hepatoarcinoma, and the antibody is rabbit polyclonal (IHC image caption; catalog: host, dilution_raw). For cross-species work, the catalog lists Human, Mouse, and Rat reactivity, while the supplied IHC image documents only the human sample (catalog: reactivity; IHC image caption). No IF/ICC choice is supported by this payload because A00721-2 has no listed IF/ICC application or IF image (catalog: applications, IF images).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry P00480 (OTC_HUMAN, Ornithine transcarbamylase, mitochondrial).
- Human Protein Atlas. OTC tissue IHC expression (reliability: Enhanced).
- Human Protein Atlas. OTC subcellular location (ICC-IF): Localized to the mitochondria..
- Human Protein Atlas. OTC antibody validation summary (2 antibodies).
- A phase II clinical study on the efficacy and predictive biomarker of pegylated recombinant arginase on hepatocellular carcinoma. Investigational new drugs 2021 — PMC8426309.
- Aberrant expression and distribution of enzymes of the urea cycle and other ammonia metabolizing pathways in dogs with congenital portosystemic shunts. PloS one 2014 — PMC4063766.
- Organotypic Co-Cultures as a Novel 3D Model for Head and Neck Squamous Cell Carcinoma. Cancers 2020 — PMC7463661.
- Personalizing the treatment of head and neck cancer in vitro: The 3D-OTC model. BMC medicine 2026 — PMC13123083.
- PubMed PMID:6372096 — UniProt-cited evidence.
- PubMed PMID:2836378 — UniProt-cited evidence.
- PubMed PMID:14702039 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for OTC (Ornithine transcarbamylase, mitochondrial). Expected localisation Granular cytoplasm in hepatocytes (HPA tissue IHC). Antigen retrieval: Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen). Validated IHC antibody: A00721-2 at 1:10-1:50 (the product's own IHC validation image is shown). Controls (HPA): positive Duodenum (Endocrine cells); negative Adipose tissue. IHC workflow; specimen preparation unspecified. Protocol steps: 1. Sample: FFPE human hepatoarcinoma tissue (datasheet A00721-2); 2. Fixation: Image formalin-fixed; duration unreported (datasheet A00721-2); verify before use.; 3. Sectioning: 4–5 µm sections on charged slides (standard); 4. Deparaffinisation: Xylene, graded ethanol series to water (standard); 5. Antigen retrieval: Heat-induced epitope retrieval in citrate buffer, pH 6.0 , 20 min at 95–98 °C…; 6. Peroxidase block: 3% H2O2, 10 min , room temperature (standard); 7. Blocking: 10% normal serum of the secondary host, 30 min , room temperature (standard); 8. Primary antibody: Rabbit anti-OTC, 1:10-1:50 (datasheet A00721-2); 9. Primary incubation: Overnight at 4 °C (standard). Watch for: Fixation: Keep formalin fixation consistent across FFPE sections (standard IHC practice; not target-specific); Caveat: Duodenal and small-intestinal positives are endocrine cells (HPA tissue IHC); Isoform / epitope: No annotated isoforms; mature chain spans aa 33–354 (UniProt); Regulation: Expression regulation is unreported (UniProt). Evidence: UniProt P00480, HPA tissue IHC · Enhanced, HPA ICC-IF · mitochondria., Datasheet A00721-2, PMC8426309. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/OTC/immunohistochemistry-ihc-guide.