SMAD1 (Ab-187) Antibody

What is SMAD1 and what are its primary functions in cellular signaling?

SMAD1 (also known as BSP-1, Dwarfin-A, or JV4-1) is a critical downstream effector in the bone morphogenetic protein (BMP) signaling pathway. It belongs to the SMAD family of proteins, which are mammalian homologs of the Drosophila Mothers against dpp (Mad) proteins. SMAD1, along with SMAD5 and SMAD8, functions specifically as an effector of BMP2 and BMP4 signaling . This distinguishes it from SMAD2 and SMAD3, which primarily mediate TGFβ and activin signaling processes. Upon BMP receptor activation, SMAD1 becomes phosphorylated and translocates to the nucleus where it regulates gene expression patterns that control various cellular processes including proliferation, differentiation, and apoptosis. Recent research has demonstrated that SMAD1 plays a significant role in cancer biology, particularly in glioma where it appears to promote cell proliferation and metastasis when not properly regulated .

What epitope does the SMAD1 (Ab-187) Antibody recognize?

The SMAD1 (Ab-187) Antibody specifically recognizes a synthetic non-phosphopeptide derived from human SMAD1 around the phosphorylation site of serine 187 (P-H-S(p)-P-N) . This antibody was generated by immunizing rabbits with this specific peptide sequence and subsequently purifying the antibody through affinity chromatography using epitope-specific immunogen . It's important to note that while the antibody was raised against a sequence surrounding Ser187, there are different versions available: some detect total SMAD1 protein regardless of phosphorylation status , while phospho-specific variants only recognize SMAD1 when phosphorylated at Serine 187 . This specificity makes the antibody particularly valuable for distinguishing between active and inactive forms of the protein in signaling studies.

What are the recommended applications for SMAD1 (Ab-187) Antibody?

The SMAD1 (Ab-187) Antibody has been validated for multiple applications in molecular and cellular biology research. These include:

• Western Blotting (WB): Effective for detecting SMAD1 protein (approximately 60kDa) in cell and tissue lysates. The antibody provides clear detection of endogenous levels of both total and phosphorylated SMAD1 depending on the specific antibody variant used .

• Immunohistochemistry (IHC): Suitable for analyzing SMAD1 expression and localization in paraffin-embedded tissue sections. The antibody demonstrates both cytoplasmic and nuclear staining patterns, reflecting the protein's translocation during active signaling .

• Immunofluorescence (IF): Allows visualization of SMAD1 subcellular localization in cultured cells, enabling researchers to track dynamic changes in protein distribution upon pathway activation .

• Immunocytochemistry (ICC): Particularly useful for studying SMAD1 in specific cell types under various experimental conditions .

• ELISA: Can be employed for quantitative measurement of SMAD1 protein levels in solution-based assays .

Each application requires optimization of specific parameters including antibody dilution, incubation conditions, and detection methods to achieve optimal signal-to-noise ratios.

How can SMAD1 (Ab-187) Antibody be utilized to investigate the role of SMAD1 in cancer biology?

Recent research has revealed a significant role for SMAD1 in cancer progression, particularly in gliomas. The SMAD1 (Ab-187) Antibody serves as a valuable tool for investigating these relationships through several methodological approaches:

• Expression analysis: Western blotting using this antibody can quantify SMAD1 expression levels across different glioma cell lines (such as U251 and U87MG) compared to normal brain tissue, revealing alterations in protein expression associated with malignancy .

• Functional studies: Following genetic manipulation of SMAD1 expression (via siRNA knockdown or overexpression vectors), the antibody can be used to confirm successful modification of protein levels. Research has demonstrated that overexpression of SMAD1 can rescue the inhibitory effects of miR-187 on glioma cell proliferation and metastasis, highlighting its oncogenic potential .

• Pathway interaction mapping: IHC and IF applications using this antibody can visualize SMAD1 localization changes upon treatment with pathway modulators, revealing mechanistic interactions between SMAD1 and other signaling molecules in cancer cells.

• Phosphorylation dynamics: Using phospho-specific variants, researchers can track activation patterns of SMAD1 signaling in response to potential therapeutic interventions .

This multi-faceted approach has revealed that SMAD1 functions as a direct target of miR-187, which acts as a tumor suppressor in glioma. When miR-187 expression is decreased in glioma tissues, SMAD1 activity increases, promoting cancer cell proliferation, invasion, and migration .

What methodological considerations are important when studying SMAD1 phosphorylation dynamics?

Investigating SMAD1 phosphorylation dynamics requires careful methodological considerations to obtain reliable and meaningful results:

• Antibody selection: Use phospho-specific SMAD1 (Ser187) antibodies for detecting activated forms, while total SMAD1 antibodies should be employed as controls to normalize for protein expression levels . This combination allows calculation of activation ratios.

• Phosphatase inhibition: Sample preparation must include comprehensive phosphatase inhibitor cocktails to prevent artificial dephosphorylation during extraction. This typically includes sodium fluoride, sodium orthovanadate, and β-glycerophosphate at appropriate concentrations.

• Temporal considerations: BMP-induced SMAD1 phosphorylation occurs rapidly (within 15-30 minutes) and may be transient. Time-course experiments are essential to capture the full dynamics of activation and subsequent deactivation.

• Subcellular fractionation: Since phosphorylated SMAD1 translocates to the nucleus, separate analysis of cytoplasmic and nuclear fractions provides insight into pathway activation beyond mere phosphorylation status.

• Validation strategies: Confirming phospho-specific antibody fidelity through lambda phosphatase treatment of control samples ensures signal specificity. Loss of detection after phosphatase treatment confirms the phospho-specificity of the antibody.

• Quantification methods: For western blotting applications, densitometric analysis should calculate the ratio of phospho-SMAD1 to total SMAD1, rather than comparing to housekeeping proteins, to accurately reflect activation rather than expression changes.

These methodological approaches enable precise tracking of SMAD1 activity states during experimental manipulations or disease progression.

How can researchers effectively use SMAD1 (Ab-187) Antibody in studying the relationship between miR-187 and SMAD1?

The relationship between miR-187 and SMAD1 represents an important regulatory mechanism in glioma biology that can be effectively studied using the SMAD1 (Ab-187) Antibody through several methodological approaches:

• Target validation: Western blot analysis using this antibody can confirm SMAD1 protein downregulation following miR-187 overexpression. Research has demonstrated that U251 cells transfected with miR-187 mimics express significantly lower levels of SMAD1 protein, while SMAD1 expression is upregulated in U87MG cells treated with miR-187 inhibitor .

• Rescue experiments: The antibody can verify SMAD1 protein restoration in co-treatment experiments (miR-187 mimics + pcDNA-SMAD1) compared to miR-187 mimics alone . This approach confirms the specificity of miR-187's effects on SMAD1.

• Functional correlation: By pairing SMAD1 protein detection with functional assays (proliferation, migration, invasion), researchers can correlate protein expression levels with phenotypic outcomes. Studies have shown that restoration of SMAD1 expression rescues cell growth and metastasis inhibited by miR-187 mimics .

• Mechanism exploration: Combining the antibody with luciferase reporter assays for the SMAD1 3'-UTR can confirm direct binding of miR-187 to SMAD1 mRNA. Research confirmed this interaction, showing that co-transfection with miR-187 mimics significantly reduced luciferase activity with wild-type 3'-UTR but not with the mutant group .

These methodologies have collectively established that miR-187 functions as a tumor suppressor in glioma by directly targeting and repressing SMAD1 expression, subsequently inhibiting cell proliferation and metastasis.

What experimental controls are essential when using SMAD1 (Ab-187) Antibody in phosphorylation studies?

When conducting phosphorylation studies with SMAD1 (Ab-187) Antibody, implementing appropriate controls is crucial for result validity and interpretation:

• Positive controls: Include samples treated with known SMAD1-activating stimuli (e.g., BMP2/4 treatment of responsive cell lines) to confirm antibody functionality. For phospho-specific variants, this demonstrates the ability to detect the activated form .

• Negative controls:

  • Phosphatase-treated samples: Treating positive control lysates with lambda phosphatase should eliminate detection by phospho-specific antibodies.

  • Pathway inhibition: Samples treated with BMP receptor kinase inhibitors should show reduced phospho-SMAD1 signal.

  • SMAD1 knockdown/knockout: Genetic depletion of SMAD1 through siRNA or CRISPR approaches verifies antibody specificity.

• Loading controls: Always include detection of total SMAD1 protein alongside phospho-SMAD1 detection to normalize for expression level variations. Additionally, standard housekeeping proteins (GAPDH, β-actin) should be used to ensure equal total protein loading .

• Cross-reactivity controls: As SMAD family members share sequence similarity, include samples with isolated SMAD5 and SMAD8 proteins to verify antibody specificity to SMAD1.

• Temporal controls: For pathway dynamics studies, include multiple time points (0, 15, 30, 60, 120 minutes) following stimulation to capture the complete phosphorylation profile.

• Subcellular fractionation controls: When examining nuclear translocation, verify fractionation quality using cytoplasmic (e.g., GAPDH) and nuclear (e.g., Lamin B) markers alongside SMAD1 detection.

These controls collectively ensure that observed changes in phospho-SMAD1 signals represent genuine biological events rather than technical artifacts.

What are the recommended sample preparation techniques for Western blotting with SMAD1 (Ab-187) Antibody?

Optimal sample preparation for Western blotting with SMAD1 (Ab-187) Antibody requires careful attention to several critical factors:

• Lysis buffer composition: Use a buffer containing:

  • 50 mM Tris-HCl (pH 7.4)

  • 150 mM NaCl

  • 1% NP-40 or Triton X-100

  • 0.5% sodium deoxycholate

  • 0.1% SDS

  • 1 mM EDTA

  • Protease inhibitor cocktail

  • Phosphatase inhibitors (10 mM NaF, 1 mM Na₃VO₄, 10 mM β-glycerophosphate) - essential for preserving phosphorylation

• Sample handling: Maintain samples on ice throughout processing to minimize protein degradation and dephosphorylation. Rapid processing after cell/tissue collection is critical, especially for phosphorylation studies.

• Protein quantification: Perform accurate protein determination (BCA or Bradford assay) to ensure equal loading (typically 20-50 μg per lane).

• Denaturation conditions: Heat samples at 95°C for 5 minutes in Laemmli buffer containing SDS and β-mercaptoethanol. For phospho-epitopes, avoid excessive heating which can promote dephosphorylation.

• Gel selection: Use 10% SDS-PAGE gels for optimal SMAD1 separation (MW approximately 60 kDa) .

• Transfer conditions: Employ wet transfer to PVDF membranes (rather than nitrocellulose) at 100V for 90 minutes in transfer buffer containing 20% methanol to maximize protein retention.

• Blocking conditions: Block membranes with 5% non-fat dry milk (for total SMAD1) or 5% BSA (for phospho-specific detection) in TBST for 1 hour at room temperature.

• Antibody dilution: Dilute primary antibody typically at 1:500 to 1:1000 in blocking buffer and incubate overnight at 4°C .

This methodical approach ensures optimal detection sensitivity and specificity for SMAD1 protein in Western blotting applications.

What considerations are important for immunohistochemical detection of SMAD1?

Successful immunohistochemical detection of SMAD1 in tissue samples requires attention to several critical methodological factors:

• Fixation protocol: Optimal results are typically achieved with formalin-fixed, paraffin-embedded (FFPE) tissues fixed in 10% neutral buffered formalin for 24-48 hours. Overfixation can mask epitopes, while underfixation may compromise tissue morphology.

• Antigen retrieval: Heat-induced epitope retrieval (HIER) is essential for SMAD1 detection in FFPE tissues. Use citrate buffer (pH 6.0) or EDTA buffer (pH 9.0) with heating to 95-100°C for 15-20 minutes, followed by gradual cooling. This critical step unmasks epitopes that become crosslinked during fixation .

• Blocking parameters: Perform dual blocking:

  • Endogenous peroxidase blocking with 3% hydrogen peroxide for 10 minutes

  • Nonspecific protein blocking with 5-10% normal serum (from the same species as the secondary antibody) for 30-60 minutes at room temperature

• Antibody dilution and incubation: Typically use a 1:50 to 1:100 dilution of SMAD1 (Ab-187) Antibody with overnight incubation at 4°C in a humidified chamber . Optimization may be required for each tissue type.

• Detection system: HRP-polymer detection systems generally provide superior sensitivity and reduced background compared to traditional ABC methods. DAB (3,3'-diaminobenzidine) substrate produces a brown precipitate that clearly visualizes SMAD1 expression.

• Counterstaining: Light hematoxylin counterstaining (30 seconds) provides nuclear context while maintaining visibility of the SMAD1 signal.

• Controls: Include both positive controls (tissues known to express SMAD1) and negative controls (primary antibody replaced with PBS or nonimmune IgG) in each staining run .

• Interpretation guidelines: SMAD1 typically shows both cytoplasmic and nuclear staining, with increased nuclear localization indicating active signaling . Scoring should consider both staining intensity and percentage of positive cells.

These methodological considerations ensure reliable and reproducible SMAD1 detection in immunohistochemical applications.

What dilution and incubation conditions are optimal for different applications of SMAD1 (Ab-187) Antibody?

Optimal dilution and incubation conditions for SMAD1 (Ab-187) Antibody vary based on the specific application and sample type:

Additional methodological considerations include:

• Validation testing: Perform initial titration experiments (serial dilutions) to determine the optimal concentration for each specific application and sample type.

• Signal enhancement: For low abundance targets, consider signal amplification systems (TSA, polymer-based detection) or extended substrate development times.

• Background reduction: For high background, adjust blocking conditions (increase blocking agent concentration or time) and incorporate additional washing steps.

• Incubation temperature effects: While overnight incubation at 4°C generally provides optimal signal-to-noise ratio, room temperature incubations may be suitable for stronger signals with shortened duration (2-4 hours).

• Optimization for phospho-specific detection: When using phospho-specific variants, always include phosphatase inhibitors throughout the protocol and use BSA rather than milk for blocking and antibody dilution.

These optimized conditions ensure reliable detection while minimizing nonspecific background signals across various experimental platforms.

What validation strategies should researchers employ to confirm SMAD1 (Ab-187) Antibody specificity?

Rigorous validation of SMAD1 (Ab-187) Antibody specificity is essential for generating reliable research data. Researchers should implement multiple complementary approaches:

• Genetic manipulation controls:

  • siRNA/shRNA knockdown: Reduced signal intensity should be observed in SMAD1-depleted samples compared to controls.

  • Overexpression: Increased signal should be detected in samples transfected with SMAD1 expression vectors .

  • CRISPR/Cas9 knockout: Complete signal elimination in SMAD1 knockout cells provides definitive specificity confirmation.

• Peptide competition assays:

  • Pre-incubate antibody with excess immunizing peptide before sample application.

  • Specific binding should be blocked, resulting in signal reduction or elimination.

  • A control peptide with unrelated sequence should not affect antibody binding.

• Cross-reactivity assessment:

  • Test antibody against recombinant SMAD family proteins (SMAD5, SMAD8) to confirm specificity.

  • Evaluate reactivity across multiple sample types from relevant species to confirm predicted cross-reactivity .

• Phospho-specificity validation (for phospho-specific variants):

  • Lambda phosphatase treatment of positive control samples should eliminate signal.

  • Pathway stimulation (BMP treatment) should increase phospho-SMAD1 signal.

  • Pathway inhibition (kinase inhibitors) should reduce phospho-SMAD1 signal.

• Molecular weight verification:

  • Confirm detection at the expected molecular weight (approximately 60 kDa for SMAD1) .

  • Any additional bands should be investigated and explained (potential isoforms, degradation products, or post-translational modifications).

• Multiple detection methods:

  • Confirm findings using alternative antibodies targeting different SMAD1 epitopes.

  • Verify results using complementary techniques (mass spectrometry, RNA expression).

• Application-specific controls:

  • For IHC/IF: Include known positive and negative tissue controls in each experiment .

  • For WB: Include positive control cell lines with confirmed SMAD1 expression.

These comprehensive validation strategies ensure that experimental findings truly reflect SMAD1 biology rather than antibody artifacts or cross-reactivity.

What are common challenges in Western blotting with SMAD1 (Ab-187) Antibody and how can they be addressed?

Western blotting with SMAD1 (Ab-187) Antibody may present several technical challenges that researchers can systematically address through methodological adjustments:

• Weak or absent signal:

  • Increase antibody concentration (try 1:250 dilution if 1:500 is insufficient)

  • Extend primary antibody incubation time to overnight at 4°C

  • Increase protein loading (up to 50-75 μg per lane)

  • Enhance signal using more sensitive detection reagents (ECL-Plus or chemiluminescent substrates)

  • Verify sample integrity by probing for abundant housekeeping proteins

  • For phospho-specific detection, confirm pathway activation in positive controls

• High background/non-specific bands:

  • Increase blocking time (2 hours) and washing duration (5 x 5 minutes with TBST)

  • Reduce primary antibody concentration (try 1:1000 or 1:2000 dilution)

  • Switch blocking reagent (from milk to BSA or commercial blockers)

  • Use fresher antibody aliquots (avoid repeated freeze-thaw cycles)

  • Prepare fresh buffers and use ultrapure water

  • Include 0.05% Tween-20 in washing and antibody dilution buffers

• Multiple bands or unexpected molecular weight:

  • Verify SMAD1 expression in your specific cell type

  • Consider post-translational modifications altering migration pattern

  • Use freshly prepared samples with complete protease inhibitors

  • Optimize gel percentage for better resolution around 60 kDa

  • Run longer SDS-PAGE separation to resolve closely migrating bands

• Inconsistent results between experiments:

  • Standardize lysate preparation protocol with precise timing

  • Aliquot antibodies to avoid freeze-thaw degradation

  • Maintain consistent exposure times between experiments

  • Use internal loading controls for normalization

  • Standardize culture conditions prior to cell harvesting

• Phospho-specific detection issues:

  • Ensure complete phosphatase inhibition during sample preparation

  • Use phosphatase inhibitor cocktails containing sodium fluoride, sodium orthovanadate, and β-glycerophosphate

  • Process samples rapidly and maintain cold temperature throughout

  • Use BSA instead of milk for blocking and antibody dilution

These systematic troubleshooting approaches address the most common technical challenges encountered with SMAD1 (Ab-187) Antibody in Western blotting applications.

How can researchers optimize immunofluorescence protocols for SMAD1 localization studies?

Optimizing immunofluorescence protocols for SMAD1 localization studies requires careful attention to several methodological parameters:

• Fixation optimization:

  • Compare 4% paraformaldehyde (10-15 minutes) versus methanol fixation (-20°C, 10 minutes)

  • For phospho-epitopes, PFA fixation generally preserves phosphorylation better than methanol

  • Include phosphatase inhibitors in wash buffers when studying phosphorylated SMAD1

• Permeabilization parameters:

  • For cytoplasmic/nuclear proteins like SMAD1, use 0.2-0.3% Triton X-100 for 10 minutes

  • Alternative: 0.1-0.5% saponin for gentler permeabilization that better preserves membrane structures

  • Adjust permeabilization time based on cell type (longer for dense cell types)

• Blocking optimization:

  • Extended blocking (1-2 hours) with 5-10% normal serum from secondary antibody species

  • Include 1% BSA to reduce nonspecific binding

  • Consider commercial blocking reagents specifically designed for IF applications

• Antibody concentration and incubation:

  • Test dilution series (1:50, 1:100, 1:200, 1:500) to determine optimal concentration

  • Extend primary antibody incubation to overnight at 4°C for maximum sensitivity

  • Use antibody dilution buffer containing 1% BSA and 0.3% Triton X-100

• Signal amplification strategies:

  • Tyramide signal amplification for low-abundance targets

  • Brightness-enhanced fluorophores (Alexa Fluor series instead of traditional FITC/TRITC)

  • Optimize exposure settings during image acquisition

• Nuclear translocation visualization:

  • Counterstain nuclei with DAPI or Hoechst (1 μg/ml, 5 minutes)

  • Use confocal microscopy for precise subcellular localization

  • Perform Z-stack imaging to confirm nuclear versus perinuclear localization

• Quantification approaches:

  • Measure nuclear/cytoplasmic signal ratio across multiple cells (>50 per condition)

  • Use automated image analysis software for unbiased quantification

  • Apply consistent thresholding parameters between experimental conditions

• Multi-labeling considerations:

  • When co-staining with other antibodies, verify absence of cross-reactivity

  • Select fluorophores with minimal spectral overlap

  • Include single-stained controls to confirm specificity

These optimized protocols enable precise visualization of SMAD1 subcellular distribution and translocation dynamics in response to pathway activation or experimental manipulation.

What strategies can improve detection of low-abundance SMAD1 in challenging samples?

Detecting low-abundance SMAD1 protein in challenging samples requires implementing several specialized enhancement strategies:

• Sample enrichment techniques:

  • Immunoprecipitation: Concentrate SMAD1 from larger sample volumes before Western blotting

  • Subcellular fractionation: Isolate nuclear fractions where activated SMAD1 accumulates

  • Phosphoprotein enrichment: Use phosphoprotein purification kits for phospho-SMAD1 detection

  • TCA precipitation: Concentrate proteins from dilute samples

• Signal amplification methods:

  • Western blotting:

    • Use high-sensitivity chemiluminescent substrates (femtogram detection range)

    • Employ polymer-HRP conjugated secondary antibodies

    • Increase exposure time with low-noise detection systems

    • Consider biotin-streptavidin amplification systems

  • Immunohistochemistry/Immunofluorescence:

    • Implement tyramide signal amplification (TSA) technology (10-100× signal enhancement)

    • Utilize quantum dot conjugates for higher signal stability and brightness

    • Apply multiple-layer detection systems (biotin-streptavidin or polymer-based)

• Background reduction strategies:

  • Extended blocking (2-3 hours) with specialized blocking reagents

  • Additional washing steps with increased duration (5-6 washes, 10 minutes each)

  • Include 0.1-0.3% Tween-20 in all wash buffers

  • Use highly purified antibody preparations to minimize non-specific binding

• Protocol modifications:

  • Extend primary antibody incubation to 48-72 hours at 4°C for maximum binding

  • Reduce wash stringency to preserve low-abundance signals

  • Optimize antigen retrieval parameters (extended HIER for IHC applications)

  • Use carrier proteins (0.1-0.5% BSA) in dilution buffers to prevent antibody loss

• Specialized detection techniques:

  • Proximity ligation assay (PLA) for visualizing protein interactions at single-molecule sensitivity

  • Digital droplet PCR for absolute quantification of mRNA as a surrogate marker

  • Mass spectrometry-based targeted proteomics for absolute quantification

• Enhanced imaging approaches:

  • Confocal microscopy with photomultiplier tube detectors for improved sensitivity

  • Extended exposure time coupled with background subtraction algorithms

  • Computational enhancement through deconvolution processing

These specialized approaches can significantly improve detection sensitivity for low-abundance SMAD1 protein while maintaining specificity and result reliability.

How should researchers address potential cross-reactivity with other SMAD family members?

Addressing potential cross-reactivity with other SMAD family members is critical for experimental validity when using SMAD1 (Ab-187) Antibody. Researchers should implement several methodological strategies to ensure specificity:

• Epitope analysis and selection:

  • Choose antibodies targeting unique regions of SMAD1 distinct from other SMAD proteins

  • The Ab-187 epitope (around serine 187) resides in a region with sequence divergence from SMAD5/8

  • Phospho-specific antibodies may offer higher specificity when the phosphorylation site and surrounding sequence are unique to SMAD1

• Comprehensive validation approaches:

  • Express recombinant SMAD1, SMAD5, and SMAD8 proteins separately and test antibody reactivity

  • Create peptide competition assays with peptides derived from equivalent regions of SMAD5/8

  • Perform immunoprecipitation followed by mass spectrometry to identify all proteins captured

• Genetic modification controls:

  • Conduct parallel experiments in SMAD1 knockout/knockdown systems

  • Create selective overexpression of each SMAD family member to assess cross-reactivity

  • Use siRNA targeting SMAD1, SMAD5, or SMAD8 individually to determine signal specificity

• Detection optimization:

  • Increase antibody dilution to favor high-affinity binding to the specific epitope

  • Optimize washing stringency (salt concentration, detergent percentage)

  • Consider alternative buffer compositions that may enhance specificity

• Analytical approaches:

  • Always run positive controls with known SMAD1 expression

  • Include negative controls lacking SMAD1 but expressing other SMAD proteins

  • Use precise molecular weight discrimination (SMAD1: 60 kDa, SMAD5: 52 kDa, SMAD8: 51 kDa)

  • When detecting phosphorylated forms, verify with pathway-specific activations

• Complementary techniques:

  • Confirm key findings with alternative SMAD1 antibodies targeting different epitopes

  • Correlate protein detection with mRNA expression (qPCR with gene-specific primers)

  • Use multiple antibodies in parallel experiments as technical validation

• Reporting guidelines:

  • Explicitly acknowledge potential cross-reactivity limitations in publications

  • Document all validation steps performed to confirm specificity

  • Consider showing blots probed for multiple SMAD proteins to demonstrate distinction