Recombinant Mouse Transmembrane protein 35 (Tmem35)

What is the expression pattern of Tmem35 in the central nervous system?

Tmem35 exhibits a distinctive expression pattern, with prominent presence in HPA circuitry and limbic areas including the hippocampus and amygdala. These regions are crucial for stress responses and emotional regulation, suggesting Tmem35's involvement in these processes. The protein shows high evolutionary conservation, indicating its biological significance across species . When examining different cell types, Tmem35 expression follows a rank order of GH3 ≥ GH4C1 >> SH-SY5Y with no detectable expression in several other cell lines including SH-EP1, HEK293, RAW264.7 and H9C2 cells .

Research methodologies to detect Tmem35 expression include:

• Western blotting using specific antibodies (such as Sigma rabbit polyclonal antibody catalog HPA048583)

• Immunohistochemistry for tissue localization

• RT-PCR for mRNA expression analysis

What are the known functions of Tmem35?

Tmem35 serves multiple functions based on knockout and knockdown studies:

• Neuroendocrine regulation: Tmem35 knockout mice exhibit elevated basal corticosterone levels, indicating its role in HPA axis regulation .

• Memory consolidation: Although capable of normal memory acquisition, Tmem35 knockout mice show deficits in memory retention, suggesting Tmem35 is required specifically for long-term memory consolidation .

• Anxiety modulation: Knockout mice display increased anxiety-like behavior compared to wild-type controls .

• Nicotinic receptor chaperoning: Also known as NACHO (Novel nAChR regulatOr), Tmem35 functions as a chaperone for α7 nicotinic acetylcholine receptors (nAChRs), facilitating their folding, assembly, and transport to the cell membrane .

How does Tmem35 differ from other transmembrane proteins in the same family?

While Tmem35 shares structural similarities with other transmembrane proteins, it has unique functional properties. Unlike Tmem45b, which is primarily expressed in IB4+ sensory neurons and plays a role in inflammation- and tissue injury-induced mechanical pain hypersensitivity , Tmem35 is predominantly expressed in the central nervous system and focuses on neuroendocrine function and memory processes .

A key structural feature distinguishing Tmem35 is its C-terminal domain, which is critically important for its chaperone function. Modifications to the C-terminal, either through deletion or by adding tags like GFP or Myc-DDK, dramatically reduce its chaperone activity . This suggests that the C-terminal domain is essential for proper protein-protein interactions associated with Tmem35's function.

What molecular mechanisms underlie Tmem35's role in memory consolidation?

Tmem35's role in memory consolidation involves complex molecular mechanisms affecting synaptic plasticity. The knockout mice show a loss of long-term potentiation (LTP) in the Schaffer collateral-CA1 pathway, which is critical for memory formation .

Proteomic analysis reveals that Tmem35 knockout leads to decreased levels of specific postsynaptic molecules essential for synaptic plasticity in the hippocampus, including:

Pathway analysis (via Ingenuity Pathway Analysis) of differentially expressed synaptic proteins in Tmem35 knockout hippocampus reveals molecular networks associated with:

• Decreased long-term potentiation

• Increased startle reactivity

• Increased locomotion

These findings suggest that Tmem35 influences memory consolidation by maintaining adequate levels of key postsynaptic proteins necessary for synaptic plasticity and long-term potentiation.

How does Tmem35 function as a chaperone for nicotinic acetylcholine receptors?

Tmem35 (also known as NACHO) serves as a chaperone protein facilitating the surface expression of α7 nicotinic acetylcholine receptors (nAChRs). Research indicates a direct correlation between endogenous Tmem35 expression levels and the ability of cell lines to express surface α7 when transfected .

The chaperone function appears to be mediated through:

• C-terminal domain interaction: The C-terminal of Tmem35 is critically important for its chaperone activity. Studies show that deleting the last 4 amino acids (VKVS) reduces chaperone efficiency, though some activity remains (approximately 4x above control levels). Since these amino acids help specify an endoplasmic reticulum retention signal, Tmem35 may exert effects beyond the endoplasmic reticulum .

• Cell-type dependent expression: Cell lines with high endogenous Tmem35 expression (GH3, GH4C1) readily express surface α7 nAChRs when transfected, while those lacking Tmem35 expression (SH-EP1, HEK293, RAW264.7, H9C2) show no expression .

• Synergistic action with RIC3: Tmem35 can act alone or synergistically with another chaperone, RIC3 (Resistance to Inhibitors of Cholinesterase 3), particularly in non-permissive cells like HEK293 .

What are the consequences of Tmem35 knockout on synaptosome composition and function?

Proteomic analysis of synaptosomes from Tmem35 knockout mice reveals significant alterations in protein composition compared to wild-type controls. Key findings include:

• Reduced postsynaptic density proteins: Analysis of synaptosomal proteins shows lower levels of postsynaptic molecules important for synaptic plasticity in knockout mice hippocampus, including PSD95 and N-methyl-d-aspartate receptors .

• Pathway disruptions: Ingenuity Pathway Analysis of differentially expressed synaptic proteins in Tmem35 knockout hippocampus implicates molecular networks associated with specific cellular and behavioral functions .

• Functional consequences: These molecular changes manifest as:

  • Decreased long-term potentiation

  • Impaired memory consolidation

  • Increased startle reactivity

  • Altered locomotion

These findings suggest that Tmem35 plays a crucial role in maintaining normal synaptosome composition, which in turn affects synaptic plasticity and related behaviors.

What are the optimal methods for generating and validating Tmem35 knockout models?

Creating effective Tmem35 knockout models requires careful consideration of several methodological approaches:

Generation Techniques:

• Conventional knockout: Complete deletion of the tmem35 gene has been successfully used to characterize endocrine, behavioral, electrophysiological, and proteomic alterations .

• Conditional knockout: For tissue-specific or temporally-controlled deletion, Cre-loxP systems can be employed to avoid potential developmental compensation.

• Acute knockdown: siRNA-mediated knockdown can be used to study acute effects without potential developmental influences of gene knockout .

Validation Methods:

• Genomic verification: PCR analysis of genomic DNA to confirm gene deletion.

• Protein expression analysis: Western blotting using specific antibodies (such as Sigma rabbit polyclonal antibody catalog HPA048583) to confirm protein absence .

• Functional validation: Phenotypic assessment focusing on:

  • HPA axis function (corticosterone levels)

  • Anxiety-like behaviors

  • Memory retention tests

  • Electrophysiological assessment of LTP in the Schaffer collateral-CA1 pathway

• Receptor expression analysis: For NACHO function, assessment of surface α7 nAChR expression using 125I-α-bungarotoxin binding assays .

What expression systems are most effective for producing recombinant Tmem35 protein?

Based on the research data, several expression systems have been employed for Tmem35 production, each with specific advantages:

Mammalian Cell Expression Systems:

• GH4C1 and GH3 cells: These rat pituitary-derived cell lines show high endogenous Tmem35 expression and readily produce surface α7 nAChRs when transfected with appropriate DNA. They represent effective systems for studying Tmem35 function in a near-native environment .

• HEK293 cells: While these cells lack endogenous Tmem35 expression, they can be engineered to co-express Tmem35 along with target proteins like α7 nAChRs and RIC3, making them useful for controlled studies of Tmem35 function .

Plasmid Considerations:
For optimal expression, researchers have successfully used:

• Full-length Tmem35 in standard expression vectors

• Caution with C-terminal tags: TMEM35-GFP shows approximately 25% activity compared to wild-type TMEM35

• Plasmids encoding rat α7 in pRep4, and human TMEM35

Expression Validation:

• Western blotting for protein expression

• Functional assays such as 125I-α-bungarotoxin binding to measure surface α7 nAChR expression

• Immunofluorescence to assess cellular localization

What experimental approaches effectively measure Tmem35's impact on memory consolidation?

Investigating Tmem35's role in memory consolidation requires a multi-faceted experimental approach:

Behavioral Assessments:

• Fear conditioning tests: Especially useful since knockout mice display impairment of hippocampus-dependent fear memories .

• Spatial memory tests: Morris water maze or radial arm maze to assess hippocampus-dependent spatial memory, which is impaired in Tmem35 knockout mice .

• Novel object recognition: To distinguish between effects on memory acquisition versus memory retention.

Electrophysiological Approaches:

• Long-term potentiation (LTP) recording: Particularly in the Schaffer collateral-CA1 pathway, which shows loss of LTP in Tmem35 knockout mice .

• Field potential recordings: To assess synaptic transmission changes.

• Patch-clamp recordings: For detailed analysis of channel properties affected by Tmem35 absence.

Molecular and Proteomic Analysis:

• Synaptosome isolation and proteomic analysis: To identify changes in postsynaptic molecules important for synaptic plasticity, such as PSD95 and NMDA receptors .

• Pathway analysis: Using tools like Ingenuity Pathway Analysis to identify affected molecular networks .

• Immunohistochemistry: To visualize changes in protein expression and localization in relevant brain regions.

Temporal Intervention Studies:

• Acute knockdown experiments: Using siRNA to distinguish between developmental and acute effects of Tmem35 loss .

• Time-course studies: To determine critical periods for Tmem35 function in memory consolidation.

How can researchers address the challenges of Tmem35 protein modification while maintaining functionality?

Researchers face significant challenges when modifying Tmem35 for study, as alterations particularly to the C-terminal domain can dramatically reduce its functionality:

Challenges and Solutions:

• C-terminal modifications:

  • Research shows that TMEM35-GFP fusion proteins retain only about 25% of wild-type activity

  • TMEM35-Myc-DDK tags similarly reduce functionality

  • Alternative approach: Use small epitope tags (e.g., FLAG, HA) positioned at internal permissive sites identified through alanine scanning mutagenesis

• C-terminal deletions:

  • Deletion of the last 4 amino acids (VKVS) reduces activity by approximately 50%

  • Recommendation: Maintain intact C-terminus when possible, or use truncation series to identify minimal functional domains

• Expression level optimization:

  • Titrate expression plasmid concentrations to achieve physiologically relevant levels

  • Use inducible expression systems to control protein production levels

• Functional validation:

  • Always include wild-type controls alongside modified proteins

  • Quantify chaperone activity through 125I-α-bungarotoxin binding assays

  • Assess receptor functionality using electrophysiological techniques

Experimental data comparing Tmem35 variants:

What are the most reliable antibodies and detection methods for Tmem35 research?

Based on published research, several validated approaches exist for Tmem35 detection:

Antibodies:

• Sigma rabbit polyclonal antibody (catalog HPA048583): Successfully used for western blotting and immunofluorescence detection of Tmem35 in multiple cell lines

• Considerations for antibody selection:

  • Epitope location: Avoid antibodies targeting the C-terminal region if studying functional protein

  • Cross-reactivity: Validate specificity using knockout tissue/cells as negative controls

  • Application compatibility: Ensure suitability for western blotting, immunofluorescence, or immunoprecipitation as needed

Detection Methods:

• Western blotting protocol optimization:

  • Sample preparation: Use appropriate detergents for membrane protein extraction

  • Loading controls: Select membrane-appropriate controls (e.g., Na+/K+ ATPase)

  • Detection systems: Enhanced chemiluminescence or infrared detection systems

• Immunofluorescence microscopy:

  • Fixation: Paraformaldehyde fixation (typically 4%) preserves membrane protein structure

  • Permeabilization: Mild detergents like 0.1% Triton X-100

  • Co-staining: Combine with organelle markers to determine subcellular localization

• Functional detection methods:

  • Surface α7 nAChR binding assays using 125I-α-bungarotoxin to indirectly measure Tmem35 chaperone activity

  • GFP-expressing Ad35 vector (Ad35-GFP) transduction studies for functional assessment

How might understanding Tmem35's dual roles in neuroendocrine function and receptor chaperoning lead to novel therapeutic approaches?

Tmem35's involvement in both neuroendocrine regulation and receptor chaperoning presents intriguing therapeutic possibilities:

Potential Therapeutic Applications:

• Anxiety and stress-related disorders:

  • Tmem35 knockout mice show elevated basal corticosterone and increased anxiety-like behavior

  • Targeting Tmem35 could potentially modulate HPA axis activity in anxiety and stress-related disorders

  • Research direction: Develop compounds that enhance Tmem35 function to potentially reduce anxiety symptoms

• Memory enhancement and cognitive disorders:

  • Given Tmem35's role in memory consolidation and LTP , enhancing its function might improve memory in cognitive disorders

  • The protein's involvement in maintaining postsynaptic density proteins suggests potential for addressing synaptic deficits in conditions like Alzheimer's disease

  • Research direction: Screen for small molecules that enhance Tmem35-mediated synaptic plasticity

• Nicotinic receptor modulation:

  • As a chaperone for α7 nAChRs , Tmem35 offers a novel approach to modulating these receptors

  • Potential applications in schizophrenia, Alzheimer's disease, and inflammation, where α7 nAChRs play important roles

  • Research direction: Develop tools to selectively enhance Tmem35's chaperone function in specific tissues

• Pain management approaches:

  • While Tmem35 itself may not be directly implicated in pain processing, the related protein Tmem45b is involved in mechanical pain hypersensitivity

  • Understanding the functional differences between these related proteins may provide insights into selective pain modulation

  • Research direction: Comparative studies between Tmem family members to identify selective therapeutic targets

What are the experimental considerations for investigating potential compensatory mechanisms in Tmem35 knockout models?

When working with Tmem35 knockout models, researchers must carefully consider potential compensatory mechanisms that may mask or alter phenotypes:

Recommended Experimental Approaches:

• Temporal knockout strategies:

  • Inducible knockout systems allow deletion of Tmem35 at different developmental stages

  • Comparing embryonic versus adult knockout can reveal developmental compensation

  • Acute knockdown using siRNA approaches can further distinguish between acute effects and compensatory adaptations

• Analysis of related protein expression:

  • Quantify expression changes in related transmembrane proteins and chaperones

  • Particular focus on RIC3, which can act synergistically with Tmem35

  • Examine changes in other potential α7 nAChR chaperones

• Cell-type specific deletion:

  • Conditional knockout in specific neuronal populations using Cre-loxP systems

  • Compare phenotypes between global and cell-type specific knockouts

  • Identify potential compensatory mechanisms specific to certain cell types

• Proteomic time-course studies:

  • Analyze protein expression changes at multiple time points following Tmem35 deletion

  • Identify early versus late adaptations in synaptic protein composition

  • Focus on PSD95, NMDA receptors, and other proteins affected in constitutive knockouts

• Functional compensation assessment:

  • Electrophysiological recordings to detect homeostatic synaptic plasticity

  • Calcium imaging to assess altered signaling dynamics

  • Behavioral assays at multiple time points to track potential recovery of function

How does Tmem35 (NACHO) compare with other identified nicotinic receptor chaperones in terms of mechanism and specificity?

Understanding Tmem35's unique properties as a nicotinic receptor chaperone requires comparative analysis with other known chaperones:

Comparison with RIC3:

Mechanistic Distinctions:

What insights can be gained from comparing the phenotypes of Tmem35 versus Tmem45b knockout models?

While Tmem35 and Tmem45b belong to the same protein family, their knockout phenotypes reveal distinct functional roles:

Phenotypic Comparison:

Research Implications:

• Functional divergence within protein family:

  • Despite structural similarities, these proteins have evolved distinct functions

  • Tmem35 primarily affects central nervous system processes

  • Tmem45b mainly influences peripheral sensory mechanisms

• Complementary therapeutic targets:

  • Tmem35 may be targeted for central disorders (anxiety, memory)

  • Tmem45b provides potential peripheral target for pain without affecting central functions

  • Combined approach might address comorbid conditions (e.g., pain with anxiety)

• Structural-functional relationships:

  • Comparative analysis of domains and motifs could reveal determinants of functional specificity

  • Research direction: Domain-swapping experiments between family members to identify functional regions

How can Tmem35 research be leveraged to develop improved cell models for nicotinic receptor studies?

The discovery of Tmem35's role as a chaperone for nicotinic acetylcholine receptors offers significant opportunities for developing enhanced cellular models:

Strategies for Improved Cell Models:

• Engineered cell lines with controlled Tmem35 expression:

  • Develop HEK293 or SH-EP1 cell lines with stable, regulatable Tmem35 expression

  • Use inducible promoters to control expression levels

  • Co-express with RIC3 for synergistic enhancement of receptor expression

• Optimized expression constructs:

  • Maintain intact C-terminal for maximum chaperone activity

  • Use appropriate promoters for sustained expression

  • Incorporate reporter genes (separate from protein fusion) to track transfection efficiency

• Multi-receptor expression systems:

  • Leverage Tmem35's ability to enhance both α7 and α4β2 receptors

  • Create cell lines expressing multiple receptor subtypes for comparative pharmacology

  • Enable studies of receptor interactions and cross-talk

• Validation protocols:

  • Standardized 125I-α-bungarotoxin binding assays for α7 expression

  • 3H-cytisine binding for α4β2 expression

  • Electrophysiological characterization of functional receptors

Practical Applications Data:

What methodological considerations are essential when developing pharmacological compounds targeting Tmem35 function?

The development of compounds targeting Tmem35 requires careful consideration of several methodological aspects:

Target Validation Approaches:

• Structural characterization:

  • Determine critical domains, particularly the C-terminal region's structure

  • Identify binding partners through techniques like co-immunoprecipitation

  • Develop structural models to guide rational drug design

• Functional assays for compound screening:

  • Primary assays: α7 nAChR surface expression measured by 125I-α-bungarotoxin binding

  • Secondary assays: Electrophysiological function of enhanced receptors

  • Tertiary assays: Effects on downstream signaling pathways

• Specificity considerations:

  • Counter-screening against related transmembrane proteins

  • Evaluation of effects on other chaperones like RIC3

  • Assessment of non-specific membrane effects

• Delivery challenges for membrane protein targets:

  • Compound lipophilicity and membrane permeability

  • Bioavailability to intracellular compartments where Tmem35 functions

  • Blood-brain barrier penetration for central nervous system applications

Translational Research Considerations:

• In vivo target engagement biomarkers:

  • Expression levels of surface α7 nAChRs in accessible tissues

  • Functional measures of receptor activity (e.g., calcium signaling)

  • Downstream effects on memory consolidation or anxiety behaviors

• Safety considerations:

  • Potential off-target effects on related proteins

  • Developmental impacts given Tmem35's role in neural function

  • Assessment across multiple receptor systems affected by Tmem35