This website uses cookies to ensure you get the best experience on our website.
- Table of Contents
FOXP1 / Forkhead box protein P1 · IHC design guide
Design Immunohistochemistry for FOXP1
Plan FOXP1 paraffin IHC around nuclear staining in most cells (HPA tissue IHC) and the catalog antibody at 2 μg/ml (datasheet A00723). This guide covers positive tissue choice, fixation consistency, and the reported risk of staining proteins from other genes (HPA tissue IHC).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
FOXP1 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 | Nucleus; excluded from nucleolus (UniProt) | |
| Staining pattern | Nuclear staining in most cells (HPA tissue IHC) | |
| Antigen retrieval | EDTA pH 8.0 HIER, heat-mediated (datasheet A00723) | |
| Positive control | Appendix+4 more · see all | |
| Negative control | None in HPA (detected in all 45 tissues); use no-primary + isotype controls |
Important caveats
Reasons your staining may differ from the expected pattern.
| Fixation | Keep fixation consistent across sections. (standard IHC practice; not target-specific) | |
| Caveat | Staining may include proteins from other genes (HPA tissue IHC) | |
| Regulation | Low tissue specificity (HPA tissue RNA) | |
| Isoform / epitope | 7 isoforms; isoform 8 is embryonic stem cell-specific (UniProt) |
Section 1
Recommended FOXP1 IHC & IF Protocols
Compare the catalog antibody’s IHC-P protocol (datasheet: A00723) with published FOXP1 staining protocols for oesophageal tissue, extrahepatic cholangiocarcinoma and mouse brain sections (PMC11037412; PMC6489656; PMC4920670).
| Sample | Paraffin-embedded human mammary cancer tissue; fixative not specified (datasheet A00723) |
| Fixation | Image fixative and duration unreported (datasheet A00723); verify before use. |
| Sectioning | 4–5 µm sections on charged slides (standard) |
| Deparaffinisation | Xylene, graded ethanol series to water (standard) |
| Antigen retrieval | Heat retrieval: EDTA pH 8.0 (datasheet A00723); 20 min, 95–100 °C (standard) |
| Peroxidase block | 3% H2O2, 10 min, room temperature (standard) |
| Blocking | 10% goat serum (datasheet A00723) |
| Primary antibody | Rabbit anti-FOXP1, 2μg/ml (datasheet A00723) |
| Primary incubation | Overnight at 4 °C (datasheet A00723) |
| Detection | Streptavidin-biotin complex (SABC), DAB chromogen (datasheet A00723) |
| Counterstain | Hematoxylin, blue, dehydrate and mount (standard) |
| Expected result | FOXP1-positive staining in endocrine cells of appendix (HPA tissue IHC: High). HPA tissue profile: Nuclear expression in most cells. No signal in the no-primary control. |
💡Decision noteStart with heat-mediated EDTA retrieval at pH 8.0 (datasheet: A00723); the published paraffin-section protocols offer EDTA at pH 9.0 or citrate at pH 6.0 (PMC11037412; PMC6489656).
Section 2
What Is the Expected FOXP1 Staining Pattern?
FOXP1 is a nuclear protein, absent from the nucleolus (UniProt Q9H334). In paraffin sections, expect nuclear staining in many cell types, including respiratory epithelium, breast glands, neurons, and hematopoietic cells (HPA tissue IHC: nuclear expression in most cells; High in the listed populations). Interpret intensity cautiously: HPA rates tissue IHC reliability as Supported, with medium agreement between staining and RNA data and a warning that the antibody signal may include protein from another gene (HPA tissue IHC).
| Distinct nuclear staining in expected cells, with little signal outside nuclei. | This matches FOXP1 localisation (UniProt Q9H334: nucleus; HPA tissue IHC: nuclear expression in most cells). Nucleoplasmic staining with a spared nucleolus is also consistent with the independent ICC-IF location (HPA subcellular: nucleoplasm; UniProt Q9H334: not found in nucleolus). Nuclear placement supports the interpretation, but staining alone does not establish that every positive nucleus contains FOXP1 (HPA tissue IHC: antibody signal may include protein from another gene). |
| Predominantly cytoplasmic, membrane-like, or nucleolar staining. | These compartments conflict with the expected nuclear pattern (UniProt Q9H334: nucleus, not nucleolus; HPA tissue IHC: nuclear expression). FOXP1 has no transmembrane segment (UniProt Q9H334 topology). Treat a dominant signal there as suspect; review the counterstain, morphology, detection controls, and antibody validation before scoring it as FOXP1 (general IHC practice). |
| Signal is concentrated in an unexpected cell population while expected high-staining cells are blank. | Compare cell identity on the same section before calling the result positive: HPA reports High staining in bronchial respiratory epithelial cells, breast glandular cells, bone marrow hematopoietic cells, and several listed endocrine or neuronal populations (HPA tissue IHC). An isolated pattern elsewhere could reflect cross-reactivity or endogenous detection activity (general IHC practice), especially given HPA's warning that the antibody signal may include protein from another gene (HPA tissue IHC). |
| Diffuse colour covers nuclei and surrounding tissue without clear cell boundaries. | This obscures the nuclear pattern needed for interpretation (UniProt Q9H334: nucleus; HPA tissue IHC: nuclear expression). Excess primary or detection reagent, incomplete blocking, or inadequate washing can cause nonspecific background (general IHC practice). Reassess controls and staining conditions before assigning positive cells; diffuse colour has no reliable compartment or cell-type information (general IHC practice). |
| No nuclear signal appears in a section chosen for a reported High-staining cell population. | First confirm that the relevant cells are present and preserved on the slide; a tissue label alone does not ensure the sampled field contains them (general IHC practice). HPA reports High staining in specific cells, such as bone marrow hematopoietic cells and bronchial respiratory epithelial cells (HPA tissue IHC). If those cells are present but blank, check the staining run and controls before interpreting the absence biologically (general IHC practice). |
💡Expected FOXP1 appearanceCall a convincing positive result when identifiable cells show predominantly nucleoplasmic nuclear signal, with stronger staining plausible in HPA-listed High populations; dominant cytoplasmic, membrane-like, nucleolar, or diffuse deposit is suspect (UniProt Q9H334: nucleus, not nucleolus; HPA tissue IHC: nuclear expression and listed High populations; HPA subcellular: nucleoplasm; general IHC practice).
| Cell population and comparison tissue | HPA describes nuclear expression in most cells and low tissue specificity at the RNA level, while naming particular High and Low staining populations (HPA tissue IHC). Judge intensity within identified cell populations; a Low designation, such as hippocampal neurons, is not a universal negative control (HPA tissue IHC). |
| Antibody validation and specificity | Two listed antibodies have Supported IHC status, but HPA describes only medium agreement with RNA data and cautions that antibody signal may include protein from another gene (HPA antibodies; HPA tissue IHC). Nuclear staining is therefore compatible with FOXP1, not proof of molecular specificity (HPA tissue IHC; general IHC practice). |
| Isoform and epitope coverage | UniProt lists seven FOXP1 isoforms and reports isoform 8 specifically in embryonic stem cells (UniProt Q9H334). No epitope or isoform coverage is supplied for the IHC antibody here; a stain cannot distinguish those isoforms without additional evidence (general IHC practice). |
| Processing and compartment | FOXP1 is annotated as a nuclear protein with no signal peptide, propeptide, or transmembrane segment (UniProt Q9H334). Those features support a nuclear interpretation; they do not establish a particular retrieval method or a fixation sensitivity (UniProt Q9H334; general IHC practice). Target-specific fixation effects are unreported in the supplied evidence. |
| Situation | Likely cause | Next action |
|---|---|---|
| High-staining reference cells show no nuclear signal. | The expected cells may be absent from the sampled field, or a reagent, retrieval, or detection step may have failed (HPA tissue IHC: cell-specific High staining; general IHC practice). The supplied sources give no FOXP1-specific fixation or retrieval sensitivity. | Verify the cell population on the counterstained section, then review a run control, reagent preparation, and the established IHC-P procedure for the catalog antibody (general IHC practice). Do not infer biological absence from one blank section. |
| Colour is mainly cytoplasmic or outlines cell membranes. | The distribution disagrees with nuclear FOXP1 and its lack of a transmembrane segment (UniProt Q9H334; HPA tissue IHC). Nonspecific binding or detection artefact is possible (general IHC practice). | Inspect morphology and the counterstain, compare the expected nuclear compartment, and check appropriate staining controls (general IHC practice). Withhold a FOXP1-positive call if the abnormal compartment dominates. |
| Scattered deposits or widespread colour make nuclei hard to score. | Background from blocking, reagent concentration, washing, or the chromogenic detection system can obscure cellular localisation (general IHC practice). | Review a no-primary control and the established blocking, dilution, washing, and detection steps (general IHC practice). Score only interpretable cells with nuclear signal; do not count diffuse deposits as positive. |
| An unexpected population stains strongly while the expected population is blank. | Cell identity may have been misread, or the signal may arise from cross-reactivity or endogenous detection activity (general IHC practice). HPA specifically cautions that antibody signal may include protein from another gene (HPA tissue IHC). | Recheck the cell population against the counterstain and HPA's cell-specific examples, then compare appropriate detection controls and independent antibody evidence where available (HPA tissue IHC; general IHC practice). |
| A purported negative tissue contains some nuclear-positive cells. | FOXP1 has broad reported nuclear expression, and HPA's Low entries describe particular cell populations rather than absence throughout a tissue (HPA tissue IHC). | Record which cells stain and compare intensity with a reported High population processed in the same run (HPA tissue IHC; general IHC practice). Avoid treating a Low population as an absolute negative control. |
| IF/ICC: what pattern should be expected? | The separate ICC-IF evidence places FOXP1 in the nucleoplasm, consistent with the nuclear IHC pattern (HPA subcellular: supported nucleoplasm; HPA tissue IHC: nuclear expression). | Look for nucleoplasmic signal aligned with the nuclear counterstain and assess background with appropriate IF controls (HPA subcellular; general IF practice). Interpret IF/ICC using its separate guide; this IHC section supplies no IF protocol. |
Experiment evidence
IHC & IF images showing FOXP1 staining
A00723 · IHCIHC analysis of FOXP1 using anti-FOXP1 antibody (A00723). FOXP1 was detected in paraffin-embedded section of human mammary cancer tissue. He
A00723 · IHCIHC analysis of FOXP1 using anti-FOXP1 antibody (A00723). FOXP1 was detected in paraffin-embedded section of human mammary cancer tissue. He
A00723-1 · IHCImmunohistochemical analysis of paraffin-embedded H. thymus section using FOXP1 Antibody (C-term). A00723-1 was diluted at 1:25 dilution. A
A00723-1 · IHCFOXP1 Antibody (C-term) IHC analysis in formalin fixed and paraffin embedded lung tissue followed by peroxidase conjugation of the secondary
PA1593 · IHCAnti-FOXP1 antibody, PA1593, IHC(P) IHC(P): Human Rectal Cancer Tissue
M00723 · IFIF analysis of FOXP1 using anti-FOXP1 antibody (M00723) and anti-Beta Tubulin antibody (M01857-3). FOXP1 was detected in immunocytochemical
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000114861-FOXP1/tissue/cerebral+cortex#imid_3035240
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000114861-FOXP1/tissue/colon#imid_3035174
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000114861-FOXP1/tissue/liver#imid_3035175
HPA · KidneyHuman Protein Atlas IHC, Kidney. Source: https://www.proteinatlas.org/ENSG00000114861-FOXP1/tissue/kidney#imid_3035168
HPA · ICC-IF A-431Human Protein Atlas immunofluorescence, A-431, antibody CAB011501; green = FOXP1, blue = nucleus, red = microtubules.
HPA · ICC-IF A-431Human Protein Atlas immunofluorescence, A-431, antibody CAB011501; green = FOXP1, blue = nucleus, red = microtubules.
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for FOXP1 IHC & IF
🧪Run breast first: glandular cells should show FOXP1 staining (HPA: High in breast glandular cells). HPA detects FOXP1 in all 45 scored tissues, so there is no supported negative tissue; use no-primary and isotype controls, and expect cells without specific nuclear signal on the positive slide to retain only counterstain (HPA: no negative tissue rows; UniProt Q9H334: nucleus).
Positive control tissue: Appendix (Endocrine cells, HPA High)
Negative control tissue: None in HPA: FOXP1 is detected in all 45 scored tissues. Use a no-primary (secondary-only) and an isotype control instead.
ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show FOXP1 in A-431, U-251MG, U2OS, KOLF2.1J, with annotated localisation: Nucleoplasm (supported) (HPA subcellular).
Technical controls: Include a no-primary, secondary-only slide, a concentration-matched rabbit IgG isotype control, and a FOXP1 knockout specimen or validated peptide-block control (IHC control practice; caption: rabbit anti-FOXP1). Quench endogenous peroxidase and assess endogenous biotin background when using the caption’s streptavidin–biotin/DAB detection system (caption: SABC with DAB; IHC control practice).
⚠️Feasibility: No target-specific fixation window or fixation effect is reported in the supplied evidence, and the selected A00723 paraffin-section caption does not state a fixative (caption: fixative unreported). The caption uses heat retrieval in EDTA pH 8.0; whether retrieval is required for other preparations, or whether frozen sections or IF are easier, is unreported (caption: EDTA retrieval). Breast tissue is a practical positive choice (HPA: High in breast glandular cells); check background from the biotin-based detection system before scoring nuclear staining (caption: SABC with DAB; UniProt Q9H334: nucleus).
HPA tissue IHC evidence for FOXP1
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Supported — Medium consistency between antibody staining and RNA expression data. Caution, targets protein from more than one gene.). 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 |
|---|---|---|---|---|
| Appendix | Endocrine cells | High | Protein (IHC) | HPA → |
| Bone marrow | Hematopoietic cells | High | Protein (IHC) | HPA → |
| Breast | Glandular cells | High | Protein (IHC) | HPA → |
| Bronchus | Respiratory epithelial cells | High | Protein (IHC) | HPA → |
| Caudate | Neuronal cells | High | Protein (IHC) | HPA → |
Undetected expression · recommended negative controls
| Tissue | Cell type | Level | Evidence | Source |
|---|---|---|---|---|
| None in HPA: FOXP1 is detected in all 45 scored tissues. Use a no-primary (secondary-only) and an isotype control instead. | ||||
Section 3
Advanced FOXP1 IHC Tips
Use nuclear staining, matched controls and the A00723 paraffin-section example to troubleshoot FOXP1 chromogenic IHC; assess IF/ICC separately.
Which retrieval condition should I start with for FOXP1 paraffin-section IHC?
Start with heat-mediated antigen retrieval in EDTA at pH 8.0 (datasheet A00723). The A00723 paraffin-section image used that condition before an overnight incubation at 4°C with 2 μg/mL primary antibody (datasheet A00723). If nuclear staining is weak, check that sections were fully dewaxed and that heating and cooling were consistent across the run before changing retrieval conditions (standard IHC practice). If you then test another buffer or pH, compare it side by side with EDTA at pH 8.0 using the same tissue and controls, because the alternative has no supplied A00723 validation (datasheet A00723).
How should I investigate weak FOXP1 staining when fixation history differs between samples?
The A00723 image identifies a paraffin-embedded section, but its fixative and fixation duration are unreported; FOXP1-specific fixation sensitivity is therefore unknown (datasheet A00723). Record each sample’s fixative, time before fixation and fixation duration, then compare sections processed and stained together to reduce handling differences (standard IHC practice). Keep retrieval at EDTA pH 8.0 and the initial antibody condition at 2 μg/mL overnight at 4°C while assessing those differences (datasheet A00723). If staining tracks with processing history, test a controlled fixation series before attributing the loss to FOXP1 abundance; neither tissue expression patterns nor phosphorylation sites establish a fixation effect (HPA: tissue IHC profile; UniProt Q9H334: modified residues).
What FOXP1 staining pattern should I expect, and how should I handle cytoplasmic signal?
Score nuclear staining first: FOXP1 is assigned to the nucleus and excluded from the nucleolus, while HPA reports nuclear expression in most cells (UniProt Q9H334: subcellular location; HPA: tissue IHC profile). HPA also supports nucleoplasmic localisation in its cell images, providing a compartment check when reviewing a chromogenic section (HPA: subcellular location). If diffuse cytoplasmic DAB dominates, inspect the no-primary control, counterstain and section edges, then repeat with the documented EDTA pH 8.0 retrieval (standard IHC practice; datasheet A00723). Record cytoplasmic signal separately from nuclear positivity until independent specificity evidence supports assigning it to FOXP1 (UniProt Q9H334: subcellular location).
Could an isoform or epitope difference explain discordant FOXP1 nuclear staining?
FOXP1 has 7 listed isoforms, and isoform 8 is specifically expressed in embryonic stem cells (UniProt Q9H334: isoforms and tissue specificity). The supplied A00723 caption does not identify its epitope or establish which isoforms it detects, so staining cannot be assigned to an isoform from this IHC image (datasheet A00723). When results disagree across antibodies, compare documented immunogen or epitope information with the isoforms being studied, and assess each reagent against the same sections and controls (standard IHC practice). FOXP1 also has reported phosphorylation sites at residues 83, 653 and 658, but the supplied evidence does not show that these alter A00723 staining (UniProt Q9H334: modified residues; datasheet A00723).
How can I check FOXP1 by multiplex IF/ICC without misreading nuclear signal?
Plan IF/ICC as a separate validation: the A00723 example is chromogenic paraffin-section IHC, while HPA supports FOXP1 localisation in the nucleoplasm by cell imaging (datasheet A00723; HPA: subcellular location). Multiplex with a marker for the expected cell population and a nuclear counterstain, then ask whether FOXP1 signal falls within the appropriate nuclei (standard IF practice; UniProt Q9H334: subcellular location). Select a fluorophore and detection channel after checking the specimen’s autofluorescence and single-colour controls, particularly where tissue fluorescence obscures weak nuclear signal (standard IF practice). FOXP1 has no transmembrane segment and is nuclear, so choose permeabilisation that permits antibody access to the nuclear epitope and optimise IF/ICC fixation independently; no IF/ICC fixation condition is supplied here (UniProt Q9H334: topology and subcellular location).
How do I reduce diffuse DAB or secondary-antibody background without losing FOXP1 staining?
First compare the stained section with a no-primary control and inspect whether background follows tissue edges, damaged areas or the entire section (standard IHC practice). The A00723 example used 10% goat serum block, 2 μg/mL rabbit primary overnight at 4°C, and a biotinylated secondary for 30 minutes at 37°C (datasheet A00723). In a chromogenic peroxidase workflow, check the peroxidase block, washing and DAB development on matched sections before increasing primary concentration (standard IHC practice). Because the documented detection used a streptavidin–biotin complex, investigate endogenous biotin if background persists, while retaining nuclear localisation as the criterion for FOXP1 scoring (datasheet A00723; UniProt Q9H334: subcellular location).
How should I quantify FOXP1 IHC when cell populations differ across sections? ⚠ ANSWER MARKED FOR VERIFICATION
Define the cell population and analysis region before scoring, then count nuclei rather than total brown area because FOXP1 is nuclear (UniProt Q9H334: subcellular location; standard IHC practice). Report the percentage of positive nuclei and staining intensity, or calculate an H-score from intensity categories and their percentages using one threshold across the comparison (standard IHC practice). For spatial analyses, report positive nuclei per mm² and normalise to the number of eligible nuclei or the area of the same annotated compartment (standard IHC practice). Stratify cell populations when needed: HPA reports high staining in breast glandular cells and bone-marrow hematopoietic cells, so mixed-cell fields can change an aggregate score (HPA: tissue IHC profile).
When is a FOXP1-positive IHC result convincing rather than an artefact?
A convincing result shows interpretable nuclear staining in the cell population being scored, with nucleoli spared, and a clean no-primary control (UniProt Q9H334: subcellular location; standard IHC practice). Check cell identity rather than assuming every stained cell has the same biological meaning: HPA reports high staining in several distinct cell populations and nuclear expression in most cells (HPA: tissue IHC profile). Exclude edge effects, necrotic regions and endogenous peroxidase signal from scoring, and investigate diffuse cytoplasmic DAB separately (standard IHC practice; UniProt Q9H334: subcellular location). Treat a single antibody result cautiously because HPA rates its tissue evidence “Supported” with medium RNA–staining consistency and warns that the antibody targets protein from more than one gene (HPA: tissue IHC reliability).
Boster reagents
Best FOXP1 / Forkhead box protein P1 IHC Antibodies
The catalog includes FOXP1 antibodies with IHC images from human paraffin sections and an IF image from HeLa cells; listed reactivity also covers mouse, rat, and, for A00723, monkey (catalog applications/reactivity; image captions).
Real IHC data
Anti-FOXP1 Antibody ®
Cat # A00723
Real IHC data
Anti-FOXP1 Antibody (C-term)
Cat # A00723-1
Real IHC data
Anti-Forkhead box protein P1 FOXP1 Antibody ®
Cat # PA1593
Real IF data
Anti-FOXP1 Rabbit Monoclonal Antibody
Cat # M00723
A00723 shows IHC in human mammary and rectal cancer sections, while A00723-1 shows IHC in human thymus and lung sections (A00723 and A00723-1 image captions). PA1593 shows IHC in human rectal cancer tissue, and M00723 shows IF/ICC in HeLa cells (PA1593 and M00723 image captions).
Which to pick: For tissue IHC, A00723 has paraffin-section images with EDTA retrieval, while A00723-1 has a paraffin-section, paraffin-embedded lung image; the fixative is unreported for A00723 and for A00723-1’s thymus image (A00723 and A00723-1 image captions). PA1593 is another IHC option with a human rectal cancer image, but its fixative is unreported; choose M00723 for IF/ICC based on its HeLa IF image and listed IF/ICC applications (PA1593 and M00723 image captions; M00723 catalog applications). For cross-species planning, A00723 lists human, monkey, mouse, and rat reactivity and IHC/IF applications, while the monoclonal M00723 lists human, mouse, and rat reactivity and IF/ICC applications; the pictured IHC and IF results are human only (catalog reactivity/applications; image captions). The selected A00723 tissue-IHC caption documents paraffin sections, but does not specify the fixative (selected-SKU IHC image A00723).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry Q9H334 (FOXP1_HUMAN, Forkhead box protein P1).
- Human Protein Atlas. FOXP1 tissue IHC expression (reliability: Supported).
- Human Protein Atlas. FOXP1 subcellular location (ICC-IF): Localized to the nucleoplasm..
- Human Protein Atlas. FOXP1 antibody validation summary (2 antibodies).
- An integrated analysis of the anticarcinogenic role of forkhead box protein 1 in oesophageal squamous cell carcinoma. Journal of cellular and molecular medicine 2024 — PMC11037412.
- Gene Expression Profiling of Head and Neck Tumors Identifies FOXP1 and SOX10 Expression as Useful for Distinguishing Ameloblastoma From Basaloid Salivary Gland Tumors. The American journal of surgical pathology 2020 — PMC7156310.
- Expression of FOXP1 and FOXO3a in extrahepatic cholangiocarcinoma and the implications in clinicopathological significance and prognosis. OncoTargets and therapy 2019 — PMC6489656.
- FoxP1 marks medium spiny neurons from precursors to maturity and is required for their differentiation. Experimental neurology 2016 — PMC4920670.
- PubMed PMID:11751404 — UniProt-cited evidence.
- PubMed PMID:14702039 — UniProt-cited evidence.
- PubMed PMID:16641997 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for FOXP1 (Forkhead box protein P1). Expected localisation Nucleus; excluded from nucleolus (UniProt). Antigen retrieval: EDTA pH 8.0 HIER, heat-mediated (datasheet A00723). Validated IHC antibody: A00723 at 2μg/ml (the product's own IHC validation image is shown). Controls (HPA): positive Appendix (Endocrine cells); negative None in HPA (detected in all 45 tissues); use no-primary + isotype controls. IHC-P workflow on paraffin sections; fixative unspecified. Protocol steps: 1. Sample: Paraffin-embedded human mammary cancer tissue; fixative not specified (datasheet A00723); 2. Fixation: Image fixative and duration unreported (datasheet A00723); 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 retrieval: EDTA pH 8.0 (datasheet A00723); 20 min, 95–100 °C (standard); 6. Peroxidase block: 3% H2O2, 10 min , room temperature (standard); 7. Blocking: 10% goat serum (datasheet A00723); 8. Primary antibody: Rabbit anti-FOXP1, 2μg/ml (datasheet A00723); 9. Primary incubation: Overnight at 4 °C (datasheet A00723). Watch for: Fixation: Keep fixation consistent across sections. (standard IHC practice; not target-specific); Caveat: Staining may include proteins from other genes (HPA tissue IHC); Isoform / epitope: 7 isoforms; isoform 8 is embryonic stem cell-specific (UniProt); Regulation: Low tissue specificity (HPA tissue RNA). Evidence: UniProt Q9H334, HPA tissue IHC · Supported, HPA ICC-IF · nucleoplasm., Datasheet A00723, PMC11037412, PMC6489656. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/FOXP1/immunohistochemistry-ihc-guide.