This website uses cookies to ensure you get the best experience on our website.
- Table of Contents
ARPP21 / cAMP-regulated phosphoprotein 21 · IHC design guide
Design Immunohistochemistry for ARPP21
Plan chromogenic IHC for ARPP21 in paraffin sections using its reported cytoplasmic tissue pattern (HPA tissue IHC). Compare neuronal and glial staining in brain with skeletal muscle myocytes, and interpret intensity alongside the reported medium consistency between staining and RNA (HPA tissue IHC).
Evidence assembled Oct 2026 · For research use; verify linked source records and product datasheet before use
ARPP21 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 | Cytoplasmic in brain and skeletal muscle (HPA tissue IHC) | |
| Staining pattern | Cytoplasmic signal in brain cells and skeletal myocytes (HPA tissue IHC) | |
| Antigen retrieval | Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen) | |
| Positive control | Appendix+2 more · see all | |
| Negative control | Adipose tissue+4 more · see all |
Important caveats
Reasons your staining may differ from the expected pattern.
| Fixation | Keep fixation conditions consistent across paraffin sections. (standard IHC practice; not target-specific) | |
| Caveat | Staining and RNA show only medium consistency (HPA tissue IHC) | |
| Regulation | Brain-enriched RNA expression (HPA tissue RNA) | |
| Isoform / epitope | Six isoforms; epitope coverage is unspecified (UniProt; datasheets) |
Section 1
Recommended ARPP21 IHC & IF Protocols
Compare the catalog antibody’s IHC-P protocol with the published ARPP21 dual-staining example in patient spinal cord (PMC13545126).
| Sample | Paraffin-embedded human heart tissue; fixative not specified (datasheet A03525-1) |
| Fixation | Image fixative and duration unreported (datasheet A03525-1); 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-ARPP21, 1:100-1:300 (datasheet A03525-1) |
| 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 | ARPP21-positive staining in goblet cells of appendix (HPA tissue IHC: Medium). HPA tissue profile: Cytoplasmic expression in the brain and skeletal muscles. No signal in the no-primary control. |
💡Decision noteStart with citrate pH 6.0 HIER at 95–98 °C for 20 min (page antigen-retrieval rule; UniProt: cytoplasm).
Section 2
What Is the Expected ARPP21 Staining Pattern?
ARPP21 is a cytoplasmic protein with no transmembrane segment (UniProt Q9UBL0 topology). In paraffin-section IHC, expect cytoplasmic staining in cerebral-cortex neurons, caudate glial cells and appendix goblet cells, each reported at medium intensity (HPA tissue IHC). HPA also describes cytoplasmic expression in brain and skeletal muscle, but rates tissue IHC reliability as Enhanced with medium consistency between antibody staining and RNA expression (HPA tissue IHC).
| Medium cytoplasmic staining in cerebral-cortex neurons or caudate glial cells, with tissue detail preserved. | This matches the reported cell types, intensity and tissue-IHC compartment (HPA tissue IHC). Score the named cells separately from neighboring cells; a positive field alone does not establish that every cell in it expresses ARPP21 (general IHC interpretation). |
| Predominantly nuclear or nucleolar staining in paraffin-section IHC, without the expected cytoplasmic pattern. | Treat this as a compartment mismatch against the tissue-IHC profile and UniProt cytoplasmic annotation (HPA tissue IHC; UniProt Q9UBL0). Check morphology and controls before calling it ARPP21; HPA's approved nucleolar observation comes from ICC-IF, a different application (HPA ICC-IF). |
| Strong staining in adipocytes or adrenal glandular cells while the expected positive cells are unstained. | Those cell types are listed as not detected (HPA tissue IHC). Suspect cross-reactivity or endogenous chromogenic activity, then compare a no-primary control and a known-positive section processed in the same run (general IHC practice). |
| Diffuse color across cells, stroma or section edges, obscuring cell boundaries. | This is difficult to score as cytoplasmic ARPP21 (HPA tissue IHC). Review blocking, washes, primary-antibody concentration and detection controls; diffuse deposition can arise from general IHC workflow rather than the reported cell-specific pattern (general IHC practice). |
| No staining in cerebral-cortex neuronal cells or caudate glial cells. | Both are reported at medium intensity, so absence calls for a run-level check before a biological negative call (HPA tissue IHC). Verify that the tissue and target cells are present, then review retrieval, antibody incubation and chromogen performance (general IHC practice). |
💡Expected ARPP21 appearanceCall a positive paraffin-section IHC result when cytoplasm is visibly stained at approximately medium intensity in cerebral-cortex neurons or caudate glial cells; isolated strong signal in HPA-negative cell types or a nucleus-only pattern warrants control review (HPA tissue IHC; UniProt Q9UBL0).
| Tissue and cell selection | Cortex neurons, caudate glial cells and appendix goblet cells are medium; skeletal-muscle myocytes are low, so a weak muscle result alone is a less decisive positive control (HPA tissue IHC). |
| Antibody validation | HPA017303 has Enhanced IHC validation (HPA antibodies). The tissue-IHC profile still has medium antibody/RNA consistency, so interpret unexpected cells and intensity with controls (HPA tissue IHC). |
| Isoform context | Isoform 2 is expressed in brain; isoform 1 is present in immature thymocytes at protein level (UniProt Q9UBL0). The supplied IHC record does not assign individual tissue-staining observations to an isoform (HPA tissue IHC). |
| Topology and processing | ARPP21 has no transmembrane segment or signal peptide; its listed chain spans residues 2–812 (UniProt Q9UBL0). Interpret a crisp cell-surface-only pattern cautiously against the cytoplasmic tissue-IHC profile (HPA tissue IHC). |
| IF/ICC Q: Should nucleoli stain? | A: HPA ICC-IF lists approved nucleoli as the main location and approved cytosol as an additional location (HPA ICC-IF). That application-specific result does not replace the cytoplasmic paraffin-section IHC expectation (HPA tissue IHC). |
| Situation | Likely cause | Next action |
|---|---|---|
| The known-positive cortex or caudate section has no visible signal. | The target cells may be absent from the field, or an IHC step may have failed (general IHC practice); HPA reports medium staining in these cells (HPA tissue IHC). | Confirm cell identity and section integrity, then check the run's retrieval, primary incubation and detection controls before scoring the sample negative (general IHC practice). |
| Only nuclei or nucleoli are colored in an IHC section. | The pattern conflicts with cytoplasmic tissue IHC and UniProt localization (HPA tissue IHC; UniProt Q9UBL0); ICC-IF has a separate approved nucleolar observation (HPA ICC-IF). | Inspect cell boundaries and a no-primary control, then repeat or confirm with the IHC-validated antibody and an appropriate positive section (general IHC practice; HPA antibodies). |
| Adipocytes or adrenal glandular cells stain strongly. | Both are reported as not detected in those cells (HPA tissue IHC); nonspecific antibody binding or endogenous detection activity is possible (general IHC practice). | Compare no-primary and known-positive controls; review blocking and detection chemistry before assigning ARPP21 positivity (general IHC practice). |
| Background color obscures the cytoplasm in most cells. | Excess primary-antibody signal, incomplete washing or endogenous chromogenic activity may obscure localization (general IHC practice). | Check the no-primary control and reagent instructions; optimize blocking, washes and antibody concentration while retaining a positive-control section (general IHC practice). |
| Skeletal muscle looks faint beside a clearly positive brain section. | Myocytes are listed as low, while cerebral-cortex neuronal cells and caudate glial cells are medium (HPA tissue IHC). | Score each cell population against its reported level and morphology; use the medium brain staining to judge whether the run detected the target (HPA tissue IHC; general IHC interpretation). |
| A stained field is reported positive although the named target cells are unstained. | A field-level impression can conceal staining in another cell type (general IHC interpretation); HPA observations specify cells within each tissue (HPA tissue IHC). | Record tissue, cell identity, compartment and intensity separately, and compare the result with the corresponding HPA cell-level observation (HPA tissue IHC; general IHC interpretation). |
Experiment evidence
IHC & IF images showing ARPP21 staining
A03525-1 · IHCImmunohistochemistry analysis of paraffin-embedded human heart tissue, using ARPP21 Antibody. The picture on the right is blocked with the s
A30584 · IHCImmunohistochemistry analysis of paraffin-embedded human heart tissue, using ARPP21 Antibody. The picture on the right is blocked with the s
HPA · Cerebral cortexHuman Protein Atlas IHC, Cerebral cortex. Source: https://www.proteinatlas.org/ENSG00000172995-ARPP21/tissue/cerebral+cortex#imid_17583478
HPA · CaudateHuman Protein Atlas IHC, Caudate. Source: https://www.proteinatlas.org/ENSG00000172995-ARPP21/tissue/basal+ganglia#imid_17583480
HPA · ColonHuman Protein Atlas IHC, Colon. Source: https://www.proteinatlas.org/ENSG00000172995-ARPP21/tissue/colon#imid_17576009
HPA · LiverHuman Protein Atlas IHC, Liver. Source: https://www.proteinatlas.org/ENSG00000172995-ARPP21/tissue/liver#imid_17576002
HPA · ICC-IF Rh30Human Protein Atlas immunofluorescence, Rh30, antibody HPA017303; green = ARPP21, blue = nucleus, red = microtubules.
HPA · ICC-IF Rh30Human Protein Atlas immunofluorescence, Rh30, antibody HPA017303; green = ARPP21, blue = nucleus, red = microtubules.
← swipe / scroll for more images →
Real IHC / IF data behind the staining-pattern expectations in this section.
Sample controls for ARPP21 IHC & IF
🧪Start with appendix: goblet cells should show medium staining (HPA: Appendix, goblet cells, Medium). Run adipose tissue as the negative tissue (HPA: Adipose tissue, adipocytes, Not detected); on the appendix slide, assess adjacent cells without visible signal as internal background, without assuming that every non-goblet cell is negative.
Positive control tissue: Appendix (Goblet cells, HPA Medium)
Negative control tissue: Adipose tissue (HPA Not detected)
ICC-IF cell lines (HPA subcellular resource): HPA ICC-IF images show ARPP21 in Rh30, U-251MG, U2OS, with annotated localisation: Nucleoli (approved) (HPA subcellular).
Technical controls: Include no-primary (secondary-only) and host- and clonality-matched isotype controls, plus a biological negative such as a knockout specimen or peptide blocking; peptide blocking was shown for the catalog antibody in human heart tissue (SKU A03525-1 caption). For chromogenic appendix IHC, quench endogenous peroxidase and check background in the no-primary section (standard IHC practice).
⚠️Feasibility: A target-specific fixation window or fixation effect is unreported in the supplied evidence; the selected paraffin-section caption does not state the fixative (SKU A03525-1 caption). Retrieval dependence is unreported, so assess retrieval conditions empirically with the positive and negative controls (standard IHC practice). The supplied evidence does not establish whether frozen sections or IF would be easier; for appendix, assess mucin-associated background when scoring goblet-cell staining (standard IHC practice).
HPA tissue IHC evidence for ARPP21
Comprehensive Human Protein Atlas IHC scoring per tissue (reliability: Enhanced — Medium 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 |
|---|---|---|---|---|
| Appendix | Goblet cells | Medium | Protein (IHC) | HPA → |
| Caudate | Glial cells | Medium | Protein (IHC) | HPA → |
| Cerebral cortex | Neuronal cells | 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 ARPP21 IHC Tips
Troubleshoot ARPP21 staining in paraffin sections by checking retrieval, compartment, cell type and controls before comparing signal intensity across samples.
How should I retrieve ARPP21 in paraffin sections when staining is weak?
Use citrate buffer at pH 6.0 for HIER at 95–98 °C for 20 min (page retrieval protocol: A03525-1). If staining remains weak, compare a small retrieval time series on adjacent sections while keeping antibody concentration and detection conditions fixed (standard IHC practice). Include a section expected to contain neuronal cells, since medium staining is reported in cerebral cortex neuronal cells (HPA tissue IHC). Check tissue preservation and the no-primary control before increasing detection strength, because damaged sections and background can make a retrieval change difficult to judge (standard IHC practice).
Could fixation explain weak or uneven ARPP21 staining?
The supplied ARPP21 evidence does not establish target-specific fixation sensitivity, and the catalog antibody’s paraffin-section caption does not state a fixative (A03525-1 caption). Record the fixative and fixation duration for each specimen, then compare similarly processed sections before attributing an intensity difference to biology (standard IHC practice). If processing records differ, test adjacent sections with the same pH 6.0, 95–98 °C, 20 min retrieval and identical detection settings (page retrieval protocol: A03525-1; standard IHC practice). Judge preservation by morphology and control staining; tissue expression patterns alone cannot identify a fixation effect (standard IHC practice).
Should I score nuclear or cytoplasmic ARPP21 staining?
For tissue IHC, assess cytoplasmic staining first: ARPP21 is annotated as cytoplasmic, and the tissue profile describes cytoplasmic expression in brain and skeletal muscle (UniProt Q9UBL0 subcellular location; HPA tissue IHC). Medium staining is reported in cerebral cortex neuronal cells and caudate glial cells, so define the scored cell population before measuring intensity (HPA tissue IHC). Nucleolar staining is also plausible because approved subcellular imaging reports nucleoli as the main location and cytosol as an additional location (HPA subcellular). Score nucleolar and cytoplasmic signals separately, and require appropriate morphology and controls before treating either compartment as specific (standard IHC practice).
Could isoforms or epitope masking change the staining pattern?
ARPP21 has 6 annotated isoforms; isoform 2 is expressed in brain, while isoform 1 is present in immature thymocytes (UniProt Q9UBL0 isoforms and tissue specificity). Check the catalog antibody’s immunogen or mapped epitope against each isoform before interpreting absent staining as absent ARPP21 (standard IHC practice). The protein contains R3H residues 164–227, SUZ residues 228–300, and documented phosphorylation sites, including serines 33 and 300 (UniProt Q9UBL0 domains and modified residues). If an epitope overlaps a splice difference or modified residue, confirm that possibility with epitope information and independent controls; the supplied evidence does not map this antibody’s epitope (standard IHC practice; supplied catalog record).
How can IF help resolve ambiguous ARPP21 IHC staining?
Use the separate IF/ICC guide for method development; here, fluorescence can help assess whether IHC signal follows the expected cell type and compartment (standard IF practice). Multiplex ARPP21 with a neuronal marker when examining cerebral cortex neuronal cells, and interpret the overlap in the context of the reported medium neuronal staining (HPA tissue IHC; standard IF practice). Choose a far-red fluorophore when tissue autofluorescence compromises shorter wavelengths, and include single-label controls for channel bleed-through (standard IF practice). Permeabilisation must allow access to cytosolic and nucleolar epitopes because ARPP21 has no transmembrane segment and both locations are reported; optimise it without assuming this antibody’s epitope is known (UniProt Q9UBL0 topology; HPA subcellular; standard IF practice).
What controls distinguish ARPP21 signal from chromogenic background?
Run a no-primary section to assess detection background, and apply a peroxidase block before DAB when using peroxidase-based detection (standard IHC practice). Compare staining with and without the synthesized blocking peptide if available: the catalog image shows paraffin-embedded human heart tissue with a peptide-blocked companion image (A03525-1 caption). That caption does not report the fixative or establish how the antibody performs across other tissues (A03525-1 caption). Inspect pigment, section folds, damaged edges and precipitate under the same imaging conditions, then adjust blocking or washing only after identifying where the background arises (standard IHC practice).
How should I quantify ARPP21 staining across sections? ⚠ ANSWER MARKED FOR VERIFICATION
Define the tissue compartment and cell population before scoring, since reported ARPP21 levels vary among cerebral cortex neuronal cells, caudate glial cells and other sampled cells (HPA tissue IHC). For a specified population, report the percentage of positive cells and an H-score from 0–300 using the percentages at intensity grades 1–3 (standard IHC scoring practice). If counting discrete positive cells, report density per mm² of evaluable tissue and exclude folds, necrosis and tissue-free space (standard IHC practice). Keep retrieval, chromogen development, imaging and positivity thresholds consistent; normalise counts to the eligible cell population or evaluable area, as appropriate (standard IHC practice).
When is an apparent ARPP21-positive section convincing?
A convincing result has reproducible staining in a defined cell population and a plausible compartment, such as cytoplasm in cerebral cortex neuronal cells or caudate glial cells (HPA tissue IHC; standard IHC practice). Nucleolar signal warrants separate assessment because it is reported in subcellular imaging, while diffuse extracellular staining lacks support from the annotated cytoplasmic location (HPA subcellular; UniProt Q9UBL0 subcellular location). Reject edge-only staining, necrotic regions and signal reproduced in the no-primary control as evidence of specific expression (standard IHC practice). Peptide blocking supports the catalog heart image’s interpretation but cannot alone validate a new tissue or exclude endogenous enzyme activity; use morphology and detection controls together (A03525-1 caption; standard IHC practice).
Boster reagents
Best ARPP21 / cAMP-regulated phosphoprotein 21 IHC Antibodies
Two anti-ARPP21 antibodies have paraffin-section IHC images from human heart (each SKU’s IHC image caption); both list IF and human/mouse reactivity (catalog applications/reactivity).
Real IHC data
Anti-ARPP-21 Antibody
Cat # A03525-1
Real IHC data
Anti-ARPP21 Antibody
Cat # A30584
A03525-1 lists IHC and IF, with an IHC image of paraffin-embedded human heart tissue (A03525-1 catalog applications; IHC image caption). A30584 lists IHC, IF and ICC, with its own IHC image of paraffin-embedded human heart tissue (A30584 catalog applications; IHC image caption).
Which to pick: For tissue IHC, either A03525-1 or A30584 has an image supporting paraffin sections; the fixative is unreported in both captions (each SKU’s IHC image caption). For IF/ICC, choose A30584 if ICC is required because it lists both applications; A03525-1 lists IF but not ICC (catalog applications). Both are rabbit polyclonals listed as reactive with human and mouse, though their IHC images show human tissue only (catalog host/dilution data and reactivity; each SKU’s IHC image caption).
Each figure is that product's own IHC / IF validation image from its datasheet.
References
- UniProt Consortium. UniProt entry Q9UBL0 (ARP21_HUMAN, cAMP-regulated phosphoprotein 21).
- Human Protein Atlas. ARPP21 tissue IHC expression (reliability: Enhanced).
- Human Protein Atlas. ARPP21 subcellular location (ICC-IF): Mainly localized to the nucleoli. In addition localized to the cytosol..
- Human Protein Atlas. ARPP21 antibody validation summary (1 antibodies).
- Familial, neuropathological and cellular analysis identify ARPP21 as a major amyotrophic lateral sclerosis associated gene in French cohorts. Acta neuropathologica 2026 — PMC13545126.
- PubMed PMID:8120638 — UniProt-cited evidence.
- PubMed PMID:10931946 — UniProt-cited evidence.
- PubMed PMID:14702039 — UniProt-cited evidence.
Immunohistochemistry protocol sheet for ARPP21 (cAMP-regulated phosphoprotein 21). Expected localisation Cytoplasmic in brain and skeletal muscle (HPA tissue IHC). Antigen retrieval: Citrate pH 6.0 HIER, 95–98 °C, 20 min (rule: cytoplasmic / membrane antigen). Validated IHC antibody: A03525-1 at 1:100-1:300 (the product's own IHC validation image is shown). Controls (HPA): positive Appendix (Goblet cells); negative Adipose tissue. IHC-P workflow on paraffin sections; fixative unspecified. Protocol steps: 1. Sample: Paraffin-embedded human heart tissue; fixative not specified (datasheet A03525-1); 2. Fixation: Image fixative and duration unreported (datasheet A03525-1); 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-ARPP21, 1:100-1:300 (datasheet A03525-1); 9. Primary incubation: Overnight at 4 °C (standard). Watch for: Fixation: Keep fixation conditions consistent across paraffin sections. (standard IHC practice; not target-specific); Caveat: Staining and RNA show only medium consistency (HPA tissue IHC); Isoform / epitope: Six isoforms; epitope coverage is unspecified (UniProt; datasheets); Regulation: Brain-enriched RNA expression (HPA tissue RNA). Evidence: UniProt Q9UBL0, HPA tissue IHC · Enhanced, HPA ICC-IF · Mainly localized to the nucleoli. In addition localized to the…, Datasheet A03525-1, PMC13545126. QR code links to https://www.bosterbio.com/bosterbio-gene-info-cards/ARPP21/immunohistochemistry-ihc-guide.