Recombinant Human Spermatogenesis-associated protein 9 (SPATA9)

What is SPATA9 and what is its genomic location?

SPATA9 (spermatogenesis associated 9), also known as NYD-SP16, is a 254 amino acid single-pass membrane protein primarily involved in testicular development and spermatogenesis. It is encoded by a gene located on human chromosome 5q15, which consists of about 181 million base pairs and represents approximately 6% of human genomic DNA . SPATA9 functions as a component of the sperm acrosome and may participate in sperm capacitation and acrosome reaction, processes that are necessary for fertilization .

What is the tissue expression profile of SPATA9?

SPATA9 exhibits a selective tissue expression pattern:

This expression profile supports its primary role in reproductive functions, particularly in spermatogenesis . Notably, no expression of SPATA9 has been found in patients affected by Sertoli-cell-only syndrome (also known as Del Castillo syndrome or germ cell aplasia), which is characterized by male sterility without sexual abnormality .

How does SPATA9 differ from other spermatogenesis-associated proteins?

While several spermatogenesis-associated proteins (SPATA) exist, SPATA9 has distinctive characteristics. Unlike SPATS1 (spermatogenesis-associated, serine-rich 1), which knockout studies have shown is not individually essential for male fertility in mice , SPATA9 appears to be more directly involved in sperm capacitation and the acrosome reaction .

A comparative analysis of spermatogenesis-associated proteins shows:

What non-reproductive functions has SPATA9 been associated with?

Beyond its reproductive functions, SPATA9 has been implicated in:

• Liver enzyme regulation: The SPATA9 variant rs72783407 has been significantly associated with maximum level of alanine aminotransferase (ALT) (p = 2.58 × 10^-8) in rheumatoid arthritis patients treated with methotrexate .

• Hypoxic adaptation: SPATA9 has been identified as a potential gene directly or indirectly related to hypoxic adaptation . Four SNPs located on Oar5 (markers 5_92277630, 5_92265355, 5_92276610, and 5_92256711) associated with the RWD_CV trait were found within SPATA9 . Research suggests SPATA9 is expressed in lungs, airway smooth muscle, bronchial epithelial cells, and peripheral blood mononuclear cells, and is associated with forced expiratory volume in 1s (FEV1) and the ratio of FEV1 to forced vital capacity (FVC) .

What methodologies are recommended for studying SPATA9 expression in human tissues?

For comprehensive analysis of SPATA9 expression in human tissues, a multi-modal approach is recommended:

• RT-PCR Methodology:

  • Use gene-specific primers for SPATA9 detection through end-point PCR.

  • Reaction setup: 20 μl of diluted AccuPrime Super Mix II containing 1 μl of cDNA and SPATA9-specific primers.

  • Thermal cycling: 94°C for 2 minutes, then 35 cycles of (94°C for 20 seconds, 58°C for 20 seconds, 68°C for 30 seconds) .

  • Visualize PCR products on 1.75% agarose gels containing ethidium bromide.

• Quantitative Real-Time PCR (qRT-PCR):

  • Design cDNA primers using established databases like Primerbank.

  • Use a high-capacity cDNA reverse transcription kit for generating cDNA from total RNA.

  • Utilize SYBR Green Master Mix in the qPCR reaction with appropriate endogenous controls (e.g., GAPDH) .

  • Perform reactions in triplicate for statistical validity.

  • Analyze results using appropriate software (e.g., Expression Suite software v1.1) .

• Single-Cell RNA Sequencing (scRNA-seq):

  • For high-resolution profiling of SPATA9 in heterogeneous testicular cell populations.

  • This approach can identify discrete testicular cell states and stages of differentiation not discernible by regular immunohistochemistry .

  • Data analysis requires specialized bioinformatic pipelines to identify cell-type specific expression patterns.

How can GWAS approaches be effectively implemented to study SPATA9 variants?

When conducting Genome-Wide Association Studies (GWAS) involving SPATA9:

• Sample Size Determination:

  • Ensure adequate statistical power by calculating minimum sample size requirements based on expected effect sizes.

  • For detecting associations similar to the rs72783407 variant, studies should include at least 300-400 individuals .

• Statistical Analysis Framework:

  • Implement the Bonferroni calibrated multiple tests method to determine significance thresholds (e.g., genome-wide significance level of 0.05) .

  • Use generalized linear models (GLM) for regression analysis with appropriate covariates.

  • For SNP analysis, the following model is recommended:
    $y = bX + vQ + e$
    where y is the corrected phenotype, b is the regression coefficient, X represents the vector of SNP indicators, v represents population structure effects, Q is the principal components matrix, and e is the residual error vector .

• Haplotype Analysis:

  • Implement the standard expectation-maximization (EM) algorithm to detect individual haplotype blocks and frequencies.

  • Use software such as TASSEL 5.2.43 for both single-marker and haplotype-based analyses .

  • Create Manhattan plots and quantile-quantile (Q-Q) plots using the R package "CMplot" to visualize GWAS results .

• Integration with Functional Data:

  • Correlate genetic variants with expression data using eQTL analysis.

  • Consider implementing spatial transcriptomic approaches to understand tissue-specific effects of variants .

What experimental approaches are recommended for investigating SPATA9's role in sperm function?

To investigate SPATA9's functional role in sperm:

• Recombinant Protein Production and Purification:

  • Express recombinant human SPATA9 in E. coli systems.

  • Purify using affinity chromatography methods, following protocols similar to those used for other recombinant proteins .

  • For carrier-free preparations, lyophilize from a 0.2 μm filtered solution in PBS and DTT.

  • Reconstitute at 250 μg/mL in PBS for functional assays .

• Functional Assays:

  • Sperm Capacitation Assessment: Measure protein phosphorylation and lipid remodeling pathways in the presence and absence of recombinant SPATA9 .

  • Acrosome Reaction Quantification: Use fluorescent markers to track acrosomal changes following exposure to recombinant SPATA9.

  • ED50 determination: Establish dose-response curves to determine effective concentrations (ED50) for biological activities .

• CRISPR/Cas9 Gene Editing:

  • Generate SPATA9 knockout models using CRISPR/Cas9 technology, similar to approaches used for SPATS1 .

  • Analyze phenotypic effects through:

    • Flow cytometry analysis of testicular cell populations

    • Histological analysis of testicular architecture

    • Sperm concentration, motility, and morphology assessments

    • Fertility trials to evaluate functional impacts

How can protein-protein interactions of SPATA9 be effectively studied?

For comprehensive analysis of SPATA9 protein interactions:

• 3D Protein Modeling and Interaction Prediction:

  • Use tools like AlphaFold Protein Structure Database and Swiss-Model to generate structural models of SPATA9 .

  • Employ Ramachandran plot servers and ERRAT for model validation.

  • Use STRING database to predict protein-protein interactions .

• Multiplex Immunohistochemistry (mIHC) Approach:

  • Develop antibody panels similar to those used in testicular proteome studies .

  • Implement a cyclic 6-plex workflow to determine cell state-specific localization.

  • Use automated image analysis pipelines for quantitative protein expression readouts .

  • Analyze co-expression patterns to identify functional protein networks.

• RNA-Protein Expression Correlation Analysis:

  • Investigate correlation coefficients between mRNA and protein levels.

  • Identify cases of both concordant and discordant expression to understand post-transcriptional regulation .

  • This approach can reveal temporal differences between gene and protein expression during spermatogenesis.

What approaches should be used to investigate SPATA9's potential role in non-reproductive functions?

To investigate SPATA9's emerging role in non-reproductive contexts:

• Hypoxic Adaptation Studies:

  • Culture cells expressing SPATA9 under normoxic and hypoxic conditions.

  • Measure parameters related to oxygen utilization and respiratory function.

  • Design experiments to test the relationship between SPATA9 expression and FEV1/FVC parameters in relevant cell types .

• Liver Enzyme Regulation:

  • In vitro models using hepatic cell lines with SPATA9 overexpression or knockdown.

  • Measure ALT levels under various conditions, including exposure to methotrexate.

  • Perform pathway analysis to understand the mechanism behind SPATA9's association with liver enzyme levels .

• Integrative Multi-Omics Approach:

  • Combine transcriptomic, proteomic, and epigenomic data to build comprehensive models of SPATA9 function.

  • Implement methods similar to those used in single-cell studies of genomic architecture .

  • Analyze chromatin accessibility peaks in relation to SPATA9 expression to understand regulatory mechanisms.

How should contradictory results in SPATA9 research be addressed?

When faced with contradictory findings:

• Systematic Analysis Framework:

  • Compare methodological differences between studies (sample preparation, detection methods, statistical approaches).

  • Consider species-specific differences – findings in mouse models may not directly translate to humans.

  • Evaluate cell/tissue type specificity – SPATA9 may function differently in various cellular contexts.

• Technical Validation Approaches:

  • Confirm antibody specificity through appropriate controls (knockout validation, peptide competition).

  • Verify protein expression using multiple antibodies targeting different epitopes.

  • Validate functional findings using complementary approaches (e.g., both gain and loss of function).

• Statistical Reassessment:

  • Review statistical power calculations to ensure studies were adequately powered.

  • Consider multiple testing corrections in genomic studies (e.g., Bonferroni calibration as used in GWAS studies) .

  • Implement meta-analysis approaches when multiple small studies exist.

What are the critical quality control measures for recombinant SPATA9 production?

For ensuring high-quality recombinant SPATA9:

• Expression System Selection:

  • E. coli systems are suitable for basic structural studies.

  • Mammalian expression systems may be preferred when post-translational modifications are critical.

• Purity Assessment:

  • SDS-PAGE analysis with Coomassie or silver staining (target >95% purity).

  • Western blot verification using specific antibodies.

  • Mass spectrometry confirmation of protein identity.

• Functional Validation:

  • Verify biological activity through functional assays relevant to known SPATA9 roles.

  • Compare activity to established benchmarks or reference standards.

  • Assess protein stability through thermal shift assays or limited proteolysis.

• Storage and Handling Recommendations:

  • Store lyophilized protein at -20°C to -80°C.

  • For reconstituted protein, use a manual defrost freezer and avoid repeated freeze-thaw cycles .

  • Consider addition of stabilizing agents (e.g., BSA) for long-term storage unless carrier-free preparation is specifically required.