Recombinant Mouse Transmembrane protein 110 (Tmem110)

What is TMEM110 and where is it primarily localized in cells?

TMEM110 is an endoplasmic reticulum membrane protein that plays a crucial role in maintaining ER-plasma membrane junctions. The protein is primarily localized in the cortical endoplasmic reticulum, the endoplasmic reticulum membrane, and at the contact sites between the endoplasmic reticulum and plasma membrane. Research using fluorescence microscopy techniques has demonstrated that TMEM110 can be visualized at these junctions, particularly after store depletion when it colocalizes with STIM1 at ER-plasma membrane junctions. Understanding this localization is essential for designing experiments to study TMEM110's functions in calcium signaling and membrane dynamics.

What are the key structural domains of mouse TMEM110?

Mouse TMEM110 contains specific functional domains that are critical for its activity at ER-plasma membrane junctions. The C-terminal region (residues 210-294) plays a particularly important role in the protein's function. Studies using truncated TMEM110 constructs (TMEM110ΔC) have shown that deletion of this C-terminal region prevents proper localization to the ER-plasma membrane junctions and abolishes its ability to support store-dependent rearrangement of cortical ER. The C-terminal region likely mediates interactions with other junction components or regulatory factors. For effective recombinant protein design, researchers should ensure that full-length constructs including this critical C-terminal domain are used to preserve TMEM110's native functions.

How does TMEM110 interact with calcium signaling pathways?

TMEM110 plays a fundamental role in calcium signaling by supporting STIM1 relocalization to ER-plasma membrane junctions. Upon store depletion, STIM1 moves to these junctions to interact with ORAI1 channels, facilitating calcium influx. Research shows that TMEM110 depletion significantly impairs STIM1 movement to the TIRF (Total Internal Reflection Fluorescence) layer, indicating reduced relocalization to junctions. This effect occurs even with the constitutively active STIM1(D76A) mutant and in cells depleted of ORAI1, suggesting TMEM110 directly facilitates STIM1 relocalization rather than acting through ORAI1. Experiments designed to study calcium signaling must consider TMEM110's role, as its depletion can alter experimental outcomes by fundamentally affecting store-operated calcium entry mechanisms.

What are the recommended approaches for generating recombinant mouse TMEM110 constructs?

To generate effective recombinant mouse TMEM110 constructs, researchers should follow these methodological steps based on established protocols:

• Start with full-length mouse TMEM110 cDNA as your template.

• Design PCR primers that encompass the complete coding sequence, including the critical C-terminal domain (residues 210-294).

• For fusion protein constructs, use a standard linker sequence (e.g., ggcggaggaagc) between TMEM110 and your tag of choice.

• Clone the PCR product into an appropriate mammalian expression vector (e.g., modified pMax).

• For fluorescent tagging, successful constructs have been generated with GFP, BFP, RFP, and mCherry tags at either the N- or C-terminus.

The choice of vector and tag position should be determined by your experimental needs. For functional studies, both N-terminal (GFP-TMEM110, pTagRFP-TMEM110) and C-terminal (TMEM110-pTagGFP2, TMEM110-BFP) fusion constructs have been successfully used in previous research. When creating truncated variants, carefully consider which domains you are removing, as the C-terminal region is essential for proper localization and function.

What technical approaches are most effective for detecting and monitoring TMEM110 localization?

For optimal detection and monitoring of TMEM110 localization, researchers should employ these technical approaches:

• TIRF Microscopy: The most effective method for visualizing TMEM110 at ER-plasma membrane junctions, as it selectively illuminates fluorophores within ~100-200 nm of the coverslip.

• Confocal Microscopy: Useful for determining colocalization of TMEM110 with other proteins like STIM1 or ER markers.

• Electron Microscopy: Essential for direct visualization of ER-plasma membrane junctions (defined as ER-plasma membrane contacts with spacing less than 20 nm).

• Fluorescent Protein Tagging: TMEM110 can be effectively tagged with fluorescent proteins at either terminus, with GFP-TMEM110, TMEM110-pTagGFP2, pTagRFP-TMEM110, or TMEM110-BFP all having been successfully used.

• Quantification Methods: When analyzing TIRF data, calculate the ratio of TIRF-layer fluorescence to total cellular fluorescence to quantitatively assess junction presence.

For accurate results, researchers must ensure minimal photobleaching during imaging and should include appropriate controls, such as imaging the general ER marker (DsRed-ER or RFP-ER) simultaneously to distinguish TMEM110-specific effects from general ER changes.

How should researchers design siRNA experiments to effectively deplete TMEM110?

For effective siRNA-mediated depletion of TMEM110, researchers should follow this methodological approach:

• Design multiple siRNA sequences targeting different regions of the TMEM110 mRNA to identify the most effective construct. Previous research has successfully designed specific siRNAs targeting TMEM110.

• Include appropriate controls:

  • Negative control (non-targeting siRNA)

  • RNAi-resistant TMEM110 rescue construct to confirm specificity

• Validate knockdown efficiency using:

  • qRT-PCR to measure mRNA levels

  • Western blotting to confirm protein depletion

• Optimal transfection conditions for TMEM110 siRNA:

  • For HeLa cells: Transfect using Lipofectamine at 20-50 nM siRNA concentration

  • Allow 48-72 hours for effective protein depletion

• Functional validation:

  • Measure TIRF-layer ER fluorescence

  • Assess STIM1 relocalization after store depletion

  • Quantify ER-plasma membrane junctions by electron microscopy

When interpreting results, researchers should note that complete TMEM110 knockdown significantly reduces ER-plasma membrane junctions and impairs STIM1 relocalization, while partial knockdown may produce intermediate phenotypes. For definitive loss-of-function studies, CRISPR-Cas9 targeting has been successfully used to generate TMEM110-/- HEK293 cells as an alternative to siRNA approaches.

How does TMEM110 influence ER-plasma membrane junctions?

TMEM110 plays a dual role in ER-plasma membrane junction biology, affecting both their maintenance and dynamic remodeling. Quantitative studies using TIRF microscopy and electron microscopy have provided clear evidence of these functions:

• Junction Maintenance: TMEM110 depletion by siRNA in HeLa cells or CRISPR-Cas9 knockout in HEK293 cells significantly reduces the number of ER-plasma membrane junctions. Electron microscopy reveals that TMEM110-depleted cells have fewer junctions per μm of plasma membrane compared to control cells. This effect is observed in both unstimulated and store-depleted conditions, indicating TMEM110's fundamental role in maintaining junction integrity.

• Dynamic Remodeling: Time-series analysis shows that TMEM110 is required for the acute rearrangement of cortical ER following store depletion. In control cells, TIRF-layer ER signal increases during the first several minutes after store depletion, reflecting cortical ER reorganization. This dynamic response is completely abolished in TMEM110-depleted or knockout cells.

• Rescue Experiments: Expression of RNAi-resistant TMEM110 in depleted cells restores both the basal level of junctions and the dynamic increase following store depletion, confirming specificity.

• Domain Specificity: The C-terminal region (residues 210-294) of TMEM110 is essential for these functions, as TMEM110ΔC fails to rescue junction formation or remodeling.

These findings demonstrate that TMEM110 is not merely a passive component of ER-plasma membrane junctions but actively participates in their formation, maintenance, and stimulus-dependent reorganization.

What is the relationship between TMEM110 and autophagy regulation?

Recent research has revealed a significant role for TMEM110 in autophagy regulation, particularly in the context of melatonin-induced autophagy in inflammatory conditions:

• Autophagy Activation: TMEM110 is involved in the initiation of autophagy. RNA sequencing, KEGG, GO, and GESA analyses identified TMEM110 as one of the autophagy-related genes significantly upregulated after melatonin treatment, with TMEM110-MUSTN1 showing the most significant increase.

• Autophagy Marker Regulation: Blocking TMEM110 with siRNA significantly affects the expression of key autophagy markers:

  • LC3II/I ratio decreases (impaired autophagosome formation)

  • Beclin1 expression decreases (reduced autophagy initiation)

  • p62 accumulates (impaired autophagy flux)

• Morphological Evidence: Transmission electron microscopy (TEM) analysis confirms that TMEM110 knockdown reduces the formation of autophagosomes, providing structural evidence of its role in autophagy.

• Mechanism: The involvement of TMEM110 in autophagy may be related to its role in membrane remodeling and trafficking, as autophagy requires extensive membrane reorganization. TMEM110's position at ER-plasma membrane junctions places it at a critical interface for membrane dynamics and vesicle formation.

This relationship between TMEM110 and autophagy opens new research directions, particularly in understanding how membrane contact sites contribute to autophagosome formation and maturation.

How does TMEM110 contribute to osteogenic differentiation of stem cells?

TMEM110 plays a critical role in osteogenic differentiation of stem cells, particularly in inflammatory environments, through the following mechanisms:

• Melatonin-Induced Osteogenesis: Research on inflamed periodontal ligament stem cells (Inf-PDLSCs) demonstrates that melatonin treatment upregulates TMEM110 expression, which corresponds with enhanced osteogenic differentiation.

• Autophagy-Dependent Mechanism: TMEM110's contribution to osteogenesis appears to be mediated through its role in autophagy activation. Melatonin-induced autophagy activation is necessary for enhanced osteogenic differentiation, and TMEM110 is a key component in this pathway.

• Functional Validation: Blocking TMEM110 expression with siRNA significantly decreases melatonin-induced osteogenesis of Inf-PDLSCs, as demonstrated by:

  • Reduced alkaline phosphatase (ALP) staining and activity

  • Decreased Alizarin Red S (ARS) staining and mineralized nodule formation

  • Downregulation of osteogenesis-related genes at both mRNA and protein levels

• Potential Applications: These findings suggest that targeting TMEM110 could be a strategy for enhancing stem cell-based therapies for periodontal regeneration and potentially other bone-related disorders.

The dual role of TMEM110 in both autophagy and osteogenesis highlights the interconnection between these processes and positions TMEM110 as a potential therapeutic target for regenerative medicine applications.

How does TMEM110 interact with the STIM-ORAI calcium signaling axis?

TMEM110 plays a sophisticated role in the STIM-ORAI calcium signaling pathway, with multiple levels of interaction revealed through advanced imaging and molecular techniques:

• STIM1 Relocalization: TMEM110 specifically supports STIM1 movement to ER-plasma membrane junctions after store depletion. This function is independent of ORAI1, as TMEM110 depletion impairs STIM1 relocalization even in ORAI1-depleted cells.

• Mechanistic Independence: The effect on STIM1 is not secondary to STIM1 activation, as TMEM110 depletion also impairs localization of constitutively active STIM1(D76A) to the TIRF layer.

• Temporal Dynamics: TMEM110 and STIM1 colocalize at ER-plasma membrane junctions in stimulated cells, suggesting potential direct or indirect molecular interactions during the signaling process.

• Spatial Organization: Rather than directly activating STIM1, TMEM110 appears to organize the structural platform (ER-plasma membrane junctions) required for efficient STIM1-ORAI1 coupling.

• Functional Hierarchy: While STIM1 and ORAI1 are the core machinery for store-operated calcium entry, TMEM110 functions as an essential architectural component that enables their efficient interaction.

For researchers studying calcium signaling, these findings highlight the need to consider junction components like TMEM110 when interpreting calcium signaling phenotypes, as defects may arise from structural reorganization failures rather than direct signaling protein dysfunction.

What is the relationship between TMEM110-MUSTN1 read-through transcription and functional outcomes?

The TMEM110-MUSTN1 read-through transcription represents an intriguing aspect of TMEM110 biology with specific research considerations:

• Genomic Organization: TMEM110-MUSTN1 shows naturally occurring read-through transcription between the neighboring TMEM110 and MUSTN1 genes, as determined with NCBI RefSeq.

• Differential Functions: While TMEM110 is involved in ER-membrane organization and calcium signaling, MUSTN1 (musculoskeletal, embryonic nuclear protein 1) is highly expressed in bone, skeletal muscle, cartilage, and tendon tissues, functioning as a pan-musculoskeletal cell marker.

• Response to Melatonin: RNA sequencing data shows that TMEM110-MUSTN1 exhibits significant upregulation following melatonin treatment, more so than either gene individually.

• Functional Implications: The read-through transcript may represent a specialized form with enhanced activity in autophagy and osteogenesis pathways compared to the individual gene products.

• Research Approach: When studying TMEM110 functions, researchers should design experiments that can distinguish between effects of TMEM110 alone versus the TMEM110-MUSTN1 read-through product:

  • Design primers that specifically detect the read-through transcript

  • Use siRNAs targeting different regions to selectively knock down TMEM110 alone or the read-through transcript

  • Consider the potential for tissue-specific expression patterns of the read-through transcript

This molecular complexity adds an important dimension to TMEM110 research, particularly in musculoskeletal contexts where both genes may have relevant functions.

How do different experimental models affect TMEM110 function and research outcomes?

Different experimental models can significantly impact TMEM110 research outcomes, requiring careful consideration when designing studies:

Researchers should select models based on their specific research questions, with awareness that TMEM110 functions may vary between systems. For example, the reduction in TIRF-layer ER signal appears more pronounced in TMEM110-depleted HeLa cells than in TMEM110-/- HEK293 cells when assessed by certain techniques, highlighting the importance of using multiple complementary approaches.

What are common challenges in recombinant TMEM110 expression and how can they be addressed?

Researchers working with recombinant TMEM110 may encounter several challenges that can be systematically addressed:

• Low Expression Levels: As a membrane protein, TMEM110 may express poorly in heterologous systems.

  • Solution: Optimize codon usage for the expression system, use strong promoters suitable for membrane proteins, and consider using specialized expression vectors designed for membrane proteins.

• Mislocalization: Recombinant TMEM110 may fail to properly localize to ER-PM junctions.

  • Solution: Ensure the C-terminal domain (residues 210-294) is intact, as this region is critical for proper localization. Verify localization using TIRF microscopy with appropriate ER markers as controls.

• Tag Interference: Fusion tags may interfere with TMEM110 function or localization.

  • Solution: Compare N-terminal and C-terminal tagging approaches. If function is compromised, consider smaller tags or cleavable linker systems. Validate function using rescue experiments in TMEM110-depleted cells.

• Protein Aggregation: Overexpressed TMEM110 may form aggregates that do not represent physiological structures.

  • Solution: Titrate expression levels by using inducible promoters or transfecting lower amounts of DNA. Monitor expression using live-cell imaging to identify optimal expression conditions.

• Functional Validation: Confirming that recombinant TMEM110 is functionally equivalent to endogenous protein.

  • Solution: Perform rescue experiments in TMEM110-depleted or knockout cells, measuring specific readouts such as ER-PM junction formation, STIM1 relocalization, or calcium signaling.

By anticipating these challenges and implementing appropriate solutions, researchers can improve the reliability of their TMEM110 experimental systems.

How can researchers validate the quality and functionality of recombinant mouse TMEM110?

To ensure high-quality recombinant mouse TMEM110 for experimental use, researchers should implement a comprehensive validation protocol:

• Expression Verification:

  • Western blot analysis to confirm protein expression at the expected molecular weight

  • Immunofluorescence to verify cellular localization to ER membranes and ER-PM junctions

• Structural Integrity:

  • SDS-PAGE under reducing and non-reducing conditions to assess proper folding

  • N-terminal sequencing to confirm the correct start of the protein (if applicable for the construct)

• Functional Validation:

  • Rescue experiments in TMEM110-depleted cells measuring:

    • TIRF-layer ER fluorescence (should restore to control levels)

    • Store-dependent increase in TIRF-layer ER signal (should be restored)

    • STIM1 relocalization efficiency (should be normalized)

• Specificity Controls:

  • Negative control: TMEM110ΔC lacking the C-terminal domain should fail to rescue the depleted phenotype

  • Positive control: Wild-type TMEM110 should restore function in depleted cells

• Biochemical Quality:

  • Endotoxin testing (<0.10 EU per 1 μg protein using LAL method)

  • Purity assessment (>90% by SDS-PAGE with silver staining)

This systematic approach ensures that recombinant TMEM110 preparations meet the necessary quality standards for reliable experimental results. Researchers should document these validation steps and include them in their experimental reports to support reproducibility.

What considerations are important when studying TMEM110 in inflammatory contexts?

When investigating TMEM110 in inflammatory contexts, researchers should address these specific considerations:

• Inflammatory Model Standardization:

  • For in vitro inflammation models (e.g., Inf-PDLSCs), use standardized protocols for inflammatory stimulus exposure:

    • Consistent concentrations of inflammatory mediators (e.g., TNF-α, IL-1β)

    • Defined exposure duration

    • Validated cellular responses to confirm inflammatory state

• Temporal Dynamics:

  • TMEM110 expression and function may change during different phases of inflammation

  • Design time-course experiments to capture acute versus chronic effects

  • Consider both immediate signaling events and long-term adaptations

• Pathway Interactions:

  • In inflammatory environments, multiple signaling pathways are activated simultaneously

  • Use pathway inhibitors to dissect specific contributions of TMEM110

  • Consider potential crosstalk between inflammation, calcium signaling, and autophagy pathways

• Tissue-Specific Effects:

  • TMEM110 functions may vary by tissue in inflammatory contexts

  • Compare responses across different cell types when possible

  • Consider tissue-specific interaction partners

• Therapeutic Interventions:

  • When studying melatonin or other modulators:

    • Use concentration-response curves to determine optimal dosing

    • For melatonin specifically, 5 μM has been identified as effective for promoting Inf-PDLSCs osteogenic differentiation

    • Include appropriate vehicle controls

    • Consider potential receptor-dependent and receptor-independent effects

These methodological considerations help ensure robust and reproducible results when studying TMEM110 in complex inflammatory environments, particularly important for translational research applications.