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FOXP1 / Forkhead box protein P1 · IHC design guide
Design Immunohistochemistry for FOXP1
Plan FOXP1 IHC on paraffin sections around the expected nuclear staining pattern (HPA tissue IHC). Use the catalog antibody’s documented IHC conditions (datasheet A00723) and score nuclear staining across cells (standard IHC practice).
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 | Nuclear in most tissue cells (HPA tissue IHC) | |
| Staining pattern | Nuclear staining across most cell types (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 reflect proteins from more than one gene (HPA tissue IHC) | |
| Regulation | Isoform 8 occurs in embryonic stem cells (UniProt) | |
| Isoform / epitope | Seven isoforms; check which the antibody epitope covers (UniProt) |
Section 1
Recommended FOXP1 IHC & IF Protocols
The catalog antibody uses heat-mediated EDTA retrieval for IHC-P (datasheet: A00723). Published protocols cover paraffin-embedded extrahepatic cholangiocarcinoma tissues (PMC6489656) and mouse whole-brain sections (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 EDTA pH 8.0 for the catalog antibody (datasheet: A00723); citrate pH 6.0 is a published paraffin-section alternative (PMC6489656).
Section 2
What Is the Expected FOXP1 Staining Pattern?
FOXP1 should appear in nuclei, outside nucleoli (UniProt Q9H334: nucleus; absent from nucleolus); it has no transmembrane segment (UniProt Q9H334: topology). In paraffin-section IHC, HPA reports nuclear expression in most cells, with high staining in several epithelial, endocrine, hematopoietic and neuronal cell groups (HPA: tissue IHC). Treat that distribution as a guide: HPA rates the tissue result Supported, with medium consistency between staining and RNA data and a caution that the assay targets protein from more than one gene (HPA: tissue IHC reliability).
| Distinct nuclear chromogen in glandular cells of breast or respiratory epithelial cells of bronchus, with identifiable counterstained tissue architecture (HPA: High in these cell groups). | This matches the expected compartment and documented high-staining cells (UniProt Q9H334: nucleus; HPA: tissue IHC). Score the proportion and intensity of stained nuclei within each identified cell group. HPA's Supported rating and multi-gene-target caution limit claims that every positive nucleus represents FOXP1 alone (HPA: tissue IHC reliability). |
| Predominantly cytoplasmic, membranous or nucleolar signal, with little nuclear signal. | That distribution conflicts with the reported FOXP1 location (UniProt Q9H334: nucleus, absent from nucleolus; HPA: nucleoplasm). Check whether the chromogen follows pigment, tissue edges or background, then reassess detection and antibody specificity. Compartment mismatch alone identifies an unreliable result; it does not establish which technical step failed. |
| Strong staining confined to an unexpected cell group while the documented cells in the same section lack nuclear signal. | Recheck cell identity and compartment before calling the stain positive. HPA reports nuclear expression in most cells and low tissue specificity, so an unlisted cell type is not automatically negative (HPA: tissue IHC). An isolated off-pattern result can reflect cross-reactivity or endogenous detection activity; HPA also cautions that its assay targets protein from more than one gene (HPA: reliability). |
| Diffuse chromogen over nuclei, cytoplasm and extracellular tissue, with no clear nuclear boundaries. | This is background rather than a scorable nuclear pattern (UniProt Q9H334: nucleus; HPA: tissue IHC). Inspect the no-primary control for detection-related signal and the section for residual reagent or tissue pigment. Interpret intensity only after distinct nuclei can be separated from background. |
| No nuclear signal in a documented high-staining control, such as bone marrow hematopoietic cells or breast glandular cells (HPA: High). | The run is inconclusive until the control works. Confirm that the intended cells are present, then review the catalog antibody's IHC-P conditions, retrieval, dilution and detection as general workflow checks. HPA's high designation describes observed staining; it does not establish FOXP1-specific fixation sensitivity (HPA: tissue IHC). |
💡Expected FOXP1 appearanceCall the result positive when identifiable cells show distinct nuclear, non-nucleolar chromogen; high staining is documented in selected cell groups, while diffuse cytoplasmic or extracellular color is suspect (UniProt Q9H334: location; HPA: tissue IHC).
| Compartment and scoring | FOXP1 is nuclear and excluded from nucleoli (UniProt Q9H334: subcellular location). Score stained nuclei within identified cell groups; do not count diffuse color as equivalent nuclear staining. |
| Choice of tissue control | HPA reports High staining in appendix endocrine cells, bone marrow hematopoietic cells, breast glandular cells and bronchial respiratory epithelial cells (HPA: tissue IHC). Its Low entries, including hippocampal neuronal cells and liver cholangiocytes, are weak comparators, not validated negative controls (HPA: tissue IHC). |
| Antibody interpretation | Two listed antibodies have Supported IHC status (HPA: HPA003876 and CAB011501). The tissue profile has medium staining–RNA consistency and a multi-gene-target caution (HPA: reliability); agreement with location and controls strengthens interpretation but does not prove unique FOXP1 recognition. |
| Isoforms and epitope coverage | UniProt lists seven FOXP1 isoforms (UniProt Q9H334: isoforms 1, 3, 4, 5, 6, 7, 8). No antibody epitope or isoform coverage is supplied here, so differences between specimens cannot be assigned to a particular isoform from staining alone. |
| IF/ICC Q&A: where should signal appear? | In IF/ICC, expect nucleoplasmic localization (HPA: subcellular ICC-IF, Nucleoplasm supported). HPA lists images from A-431, U-251MG, U2OS and KOLF2.1J (HPA: subcellular ICC-IF). This localization cross-check supplies no IF/ICC protocol for this IHC-P guide. |
| Situation | Likely cause | Next action |
|---|---|---|
| The high-staining tissue control has no nuclear chromogen (HPA: tissue IHC). | The target cell group may be absent, or a general IHC step may have underperformed; these data do not identify a FOXP1-specific fixation effect. | Verify the cell group on the counterstain, then compare the run with the catalog antibody's IHC-P instructions for retrieval, dilution and detection. Repeat with a documented high-staining control. |
| Signal is mainly cytoplasmic or nucleolar. | The compartment conflicts with FOXP1's reported nuclear, non-nucleolar location (UniProt Q9H334: subcellular location). | Check nuclear morphology and tissue pigment; compare a no-primary control and an established high-staining control before interpreting the suspect signal. |
| Broad brown haze obscures nuclear boundaries. | Excess background can arise from general blocking, washing, detection or chromogen conditions; the pattern cannot be scored as nuclear FOXP1. | Inspect the no-primary control, optimize blocking and washes, and adjust detection conditions using the catalog IHC-P guidance. Reassess only clearly delimited nuclei. |
| Unexpected cells stain strongly while documented cells do not. | Cell identification may be wrong, or staining may reflect cross-reactivity or endogenous detection activity. HPA reports broad nuclear expression and cautions about multi-gene targeting (HPA: tissue IHC reliability). | Identify the cells on the counterstain, assess whether signal is nuclear, and check a no-primary control. Avoid declaring an unlisted cell group negative solely from HPA's examples. |
| Only faint staining appears in hippocampal neuronal cells or liver cholangiocytes. | HPA lists these cell groups as Low, so faint signal can fit the reported tissue pattern (HPA: tissue IHC). | Compare nuclear localization and background against a documented High control before changing assay conditions. Do not use a Low entry as a proven negative control. |
| Replicate sections or antibodies give different nuclear fractions. | HPA rates the tissue profile Supported with medium staining–RNA consistency and warns of multi-gene targeting (HPA: reliability); the supplied data cannot assign discordance to an isoform or fixation effect. | Score the same identified cell group across sections and check each antibody's control pattern and IHC-P instructions. Report unresolved differences without assigning a molecular cause. |
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 and score glandular cells for nuclear staining (HPA: High in breast glandular cells; UniProt Q9H334: nucleus). 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 staining on the positive slide to show counterstain without nuclear DAB signal (HPA: no negative tissue; standard IHC control practice).
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 control, a concentration-matched rabbit IgG isotype control matched to the primary antibody’s clonality, and FOXP1 knockout material as a biological negative (caption: rabbit primary; standard IHC control practice). Check endogenous peroxidase and biotin background in the breast section because the reported detection uses a biotinylated secondary, streptavidin–biotin complex and DAB (caption: A00723 detection).
⚠️Feasibility: A target-specific fixation window or fixation effect is unreported, and the selected A00723 paraffin-section caption does not state the fixative (caption: fixative unreported). The reported IHC procedure uses heat retrieval in EDTA at pH 8.0, but the evidence does not establish whether frozen sections or IF would be easier (caption: A00723 retrieval; HPA: ICC-IF nucleoplasm). No breast-specific artefact is reported; assess background from the biotin-based DAB detection on the chosen section (caption: A00723 detection; standard IHC practice).
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
Troubleshoot FOXP1 staining in paraffin sections by checking retrieval, nuclear localisation, antibody specificity and cell-based scoring before interpreting chromogenic signal.
What should I adjust when FOXP1 nuclear staining is weak after retrieval?
Use heat-mediated antigen retrieval in EDTA at pH 8.0 for paraffin sections (datasheet A00723). The selected tissue image used that retrieval, followed by 2 μg/ml primary antibody overnight at 4°C (datasheet A00723). If nuclei remain weak, check that sections were fully deparaffinised and heated evenly, then compare retrieval duration across matched sections while keeping detection conditions fixed (standard IHC practice). Score nuclear signal against local background; FOXP1 is expected in nuclei and excluded from nucleoli (UniProt Q9H334). Keep the same retrieval conditions across sections being compared so changes in intensity remain interpretable (standard IHC practice).
Could fixation explain inconsistent FOXP1 staining between paraffin blocks?
FOXP1-specific sensitivity to fixation is unknown because the selected paraffin-section caption does not state a fixative (datasheet A00723). Record each block’s fixative and processing history, then compare sections with matched retrieval in EDTA at pH 8.0 (datasheet A00723; standard IHC practice). Include a similarly processed control with expected nuclear staining, such as breast glandular cells, which show high staining in the tissue profile (HPA: High in breast glandular cells). If blocks differ, assess nuclear signal and tissue preservation together before changing antibody concentration (standard IHC practice). Neither the reported tissue pattern nor FOXP1’s molecular features establish a fixation effect (HPA: tissue IHC; UniProt Q9H334).
How should I assess cytoplasmic or nucleolar FOXP1 staining?
Score convincing FOXP1 signal in nuclei: the protein is nuclear and is reported outside the nucleolus (UniProt Q9H334). The tissue profile describes nuclear expression in most cells, while the subcellular profile supports nucleoplasmic localisation (HPA: tissue IHC; HPA: subcellular). If DAB predominates in cytoplasm or nucleoli, inspect the counterstain and compare those regions with an antibody-omission control before calling them positive (standard IHC practice). Record nuclear and nonnuclear staining separately, since combining them would obscure the expected compartment (UniProt Q9H334; standard IHC practice). Repeat questionable staining on a nearby section with the documented EDTA pH 8.0 retrieval (datasheet A00723).
Can this stain distinguish FOXP1 isoforms or modified epitopes?
Do not assign an isoform from nuclear chromogenic staining alone: FOXP1 has 7 listed isoforms, and the selected image does not identify the antibody’s epitope (UniProt Q9H334; datasheet A00723). Isoform 8 is specifically expressed in embryonic stem cells, but that record does not establish what this antibody detects in paraffin sections (UniProt Q9H334). FOXP1 also has reported phosphorylation sites at residues 83, 653 and 658; their presence does not establish modification-specific staining (UniProt Q9H334). Check documented epitope coverage before making an isoform claim, and report the observed result as FOXP1 immunoreactivity unless specificity has been independently established (standard IHC practice).
How can IF help resolve an ambiguous chromogenic FOXP1 pattern?
Use IF as a separate localisation check, with FOXP1 assigned to a fluorophore distinguishable from tissue autofluorescence and a marker identifying the cell population under study (standard IF practice). Choose and validate that marker for the specimen; the tissue profile reports high FOXP1 staining in breast glandular cells and bone-marrow hematopoietic cells (HPA: tissue IHC). Because FOXP1 is nuclear and has no transmembrane segment, permeabilisation should permit antibody access to nuclear epitopes (UniProt Q9H334; standard IF practice). Include a nuclear counterstain, single-colour controls and an antibody-omission control when assessing overlap (standard IF practice). The supported nucleoplasmic location offers a compartment check, while IF conditions require their own validation (HPA: subcellular; standard IF practice).
What causes diffuse DAB signal around FOXP1-positive nuclei?
First distinguish crisp nuclear staining from diffuse pigment using a counterstain and an antibody-omission section (UniProt Q9H334; standard IHC practice). The selected image used 10% goat serum blocking and a biotinylated secondary antibody with a streptavidin–biotin complex and DAB (datasheet A00723). Endogenous peroxidase or biotin can contribute chromogenic background in such workflows, so evaluate appropriate blocking and detection controls for the tissue (standard IHC practice). Check section edges and poorly preserved areas separately, where nonspecific signal can complicate scoring (standard IHC practice). Retitrate detection against a positive nuclear control while preserving the documented EDTA pH 8.0 retrieval (datasheet A00723; standard IHC practice).
How should I quantify FOXP1 staining across tissue sections? ⚠ ANSWER MARKED FOR VERIFICATION
Define the cell population and score nuclear DAB signal, consistent with FOXP1’s expected compartment (UniProt Q9H334; standard IHC practice). Report the percentage of positive nuclei and, if intensity matters, an H-score using intensity grades 0–3 for a possible range of 0–300 (standard IHC practice). For spatial comparisons, report positive nuclei per mm² of viable tissue and the total nuclei assessed in each region (standard IHC practice). Normalise to eligible nuclei or viable area, and apply the same positivity threshold, counterstain and imaging settings across sections (standard IHC practice). Keep cell populations separate because the tissue profile describes broad nuclear expression (HPA: tissue IHC).
When is an apparent FOXP1-positive cell likely an artefact?
Treat a sharply defined nuclear signal in an intact cell as more consistent with FOXP1 than isolated cytoplasmic pigment or nucleolar staining (UniProt Q9H334; standard IHC practice). Verify the cell identity against the tissue context; the profile reports high staining in several populations, including breast glandular cells and bone-marrow hematopoietic cells (HPA: tissue IHC). Recheck signal restricted to cut edges, necrotic areas or an antibody-omission control, and assess endogenous enzyme activity in the DAB workflow (standard IHC practice). The tissue IHC profile is rated Supported but notes medium RNA–staining consistency and possible detection of protein from more than one gene (HPA: tissue IHC). Corroborate consequential cell-specific claims with an independent specificity control (standard IHC practice).
Boster reagents
Best FOXP1 / Forkhead box protein P1 IHC Antibodies
Anti-FOXP1 antibodies have IHC images from human paraffin sections and rectal cancer tissue, plus an IF image from HeLa cells (catalog image captions). Listed reactivity includes human, monkey, mouse and rat (catalog applications and reactivity).
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 has IHC images from human mammary and rectal cancer paraffin sections; A00723-1 has IHC images from human thymus paraffin sections and paraffin-section, paraffin-embedded lung tissue (catalog image captions). PA1593 has an IHC-P image from human rectal cancer tissue, while M00723 has an IF image from HeLa cells (catalog image captions).
Which to pick: For tissue IHC, choose A00723 when its documented EDTA pH 8 retrieval and 2 μg/ml incubation suit the experiment; its mammary and rectal cancer captions specify paraffin sections but do not report the fixative (A00723 image captions). A00723-1 offers a human IHC-P dilution range of 1:50–1:100 (catalog: A00723-1); its thymus image uses 1:25 on a paraffin section with fixative unreported, while its separate lung caption specifies fixation (A00723-1 image captions). For IF/ICC, choose rabbit monoclonal M00723, shown in HeLa cells at 1:50 (catalog: M00723; M00723 image caption); for broader listed species reactivity in tissue IHC, consider A00723, with human, monkey, mouse and rat reactivity listed but IHC images shown only in human tissue (catalog: A00723; A00723 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 Nuclear in most tissue cells (HPA tissue IHC). 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 reflect proteins from more than one gene (HPA tissue IHC); Isoform / epitope: Seven isoforms; check which the antibody epitope covers (UniProt); Regulation: Isoform 8 occurs in embryonic stem cells (UniProt). Evidence: UniProt Q9H334, HPA tissue IHC · Supported, HPA ICC-IF · nucleoplasm., Datasheet A00723, PMC6489656, PMC4920670. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/FOXP1/immunohistochemistry-ihc-guide.