Recombinant Rat Transmembrane protein 150C (Tmem150c)

What is the primary function of Tmem150c in neuronal tissues?

Tmem150c functions primarily as a regulator of mechano-gated ion channels rather than serving as an independent ion channel itself. Current research indicates that Tmem150c significantly modulates the activity of various mechano-sensitive channels including Piezo1, Piezo2, and the potassium-selective channel TREK-1 . Initially proposed to mediate mechano-activated current in proprioceptive neurons, more recent evidence suggests its role is primarily regulatory - prolonging the duration of mechano-current, decreasing apparent activation thresholds in channels like Piezo2, and inducing persistent current in channels such as Piezo1 . This regulatory function appears to be evolutionarily conserved among vertebrates, as demonstrated by functional similarities between mouse and avian orthologs .

How is Tmem150c expression distributed across neuronal populations?

While initially thought to be primarily expressed in proprioceptive neurons, in situ hybridization studies have revealed broader expression patterns. For example, in duck trigeminal ganglia, approximately 83.3% ± 1.0% of neurons express TMEM150C . The high abundance of both TMEM150C and Piezo2-positive neurons in these ganglia necessitates overlap between the populations, indicating that TMEM150C is co-expressed with Piezo2 in neuronal populations beyond proprioceptors . This expanded distribution suggests a more diverse functional role in sensory systems than previously believed.

What experimental models have been developed to study Tmem150c function?

Two primary mouse models with ablated Tmem150c locus have been developed for functional studies:

• A CRISPR/Cas9-generated mouse model with targeted deletion of the Tmem150c/Ttn3 locus. The primers used for genotyping this model include Tmem150c WT Rev1 (5′-TACCTGATGTATGGAGCATGCTTC-3′) and Tmem150c WT Fw1 (5′-TACTTTATAGCCGTGGAAGATGAC-3′) for wild-type allele amplification, and MEMT 1 Fw (5′-CTCAATAACAGCCACAAGGAAAG-3′) and MEMT 1 Rev (5′-ACTGGCAGGGTTGTGTAAG-3′) for mutant allele detection .

• A Tmem150c KOMP line generated from ES cell clones created by the International Knockout Mouse Project. This model involves insertion of a LacZ cassette with a splice acceptor designed to lead to transcript truncation .

These models provide complementary approaches for studying Tmem150c function, though complete gene ablation was only achieved in the CRISPR/Cas9 model, as analysis indicated the KOMP model retained some TMEM150C expression in sensory neurons .

How does Tmem150c modulate the biophysical properties of mechano-gated ion channels?

Tmem150c significantly alters several key biophysical properties of mechano-gated ion channels:

• Inactivation Kinetics: When co-expressed with Piezo2, mouse TMEM150C prolongs the inactivation time constant (τinact) of mechano-activated currents. This effect is independent of peak MA current amplitude, suggesting it does not result from changes in channel density but rather from altered channel gating properties .

• Activation Threshold: Duck TMEM150C significantly decreases the apparent threshold of mechanical activation in Piezo2 from 5.3 ± 0.3 μm to 3.6 ± 0.5 μm (p = 0.0098, Dunnett's test) . This suggests TMEM150C increases the sensitivity of these channels to mechanical stimuli.

• Current Persistence: TMEM150C induces persistent current in Piezo1, altering the temporal profile of mechano-activated responses .

Notably, these modulatory effects appear consistent across different classes of mechano-gated channels (Piezo1, Piezo2, and TREK-1), suggesting TMEM150C functions as a general regulator of mechano-sensitivity rather than having channel-specific effects .

What methodological approaches are optimal for assessing Tmem150c function in recombinant expression systems?

For optimal assessment of Tmem150c function in recombinant expression systems, researchers should employ:

• Cell Line Selection: HEK293T cells with genomic ablation of endogenous mechanically activated currents (such as HEK293T ΔP1 cells) provide a clean background for mechanosensitivity studies, avoiding potential confounding effects from endogenous channels .

• Mechanical Stimulation Methods: Two independent methods of mechanical stimulation have proven effective:

  • Glass probe indentation for precise spatial control of membrane deformation

  • Whole-cell patch-clamp recording during mechanical stimulation to measure activation thresholds and inactivation kinetics

• Co-expression Analysis: Comparing cells expressing mechano-gated channels alone versus those co-expressing Tmem150c can reveal modulatory effects. Two-way ANOVA analysis with post-hoc tests (like Dunnett's test) can determine statistical significance of observed differences in channel properties .

• Interspecies Comparison: Cloning and expressing Tmem150c orthologs from different species (e.g., mouse, rat, duck) can provide insights into evolutionary conservation of function, with special attention to sequence homology and functional similarities .

How should contradictory findings regarding Tmem150c function be interpreted in light of current evidence?

The research literature contains apparently contradictory findings regarding Tmem150c function that require careful analysis:

These contradictions may stem from:

• Methodological differences in assessing mechanosensitivity

• Incomplete gene ablation in some models (as observed in the KOMP model)

• Potential compensatory mechanisms in knockout animals

• Tissue-specific requirements for TMEM150C function

To resolve these contradictions, future studies should employ multiple independent methodologies and knockout models with verified complete gene ablation, along with tissue-specific conditional knockouts to assess potential compensatory mechanisms.

What techniques are most effective for characterizing the interaction between Tmem150c and Piezo channels?

To effectively characterize Tmem150c-Piezo interactions, researchers should employ:

• Electrophysiological Methods:

  • Whole-cell patch-clamp recordings during mechanical stimulation to quantify changes in activation thresholds, inactivation kinetics, and current persistence

  • Systematic analysis across different indentation ranges (e.g., 5-10 μm) to capture threshold-dependent effects

• Molecular Biology Approaches:

  • Co-immunoprecipitation to assess physical interaction between TMEM150C and Piezo channels

  • Domain swapping or truncation experiments to identify specific regions of TMEM150C responsible for channel modulation

• Imaging Techniques:

  • Fluorescence resonance energy transfer (FRET) to analyze protein-protein proximity in live cells

  • Super-resolution microscopy to visualize co-localization patterns at submicron scales

• Biomechanical Measurements:

  • Assessment of membrane mechanical properties in the presence and absence of TMEM150C to determine if modulation occurs through direct channel interaction or via changes in membrane properties

These complementary approaches can provide comprehensive insights into the molecular mechanisms underlying TMEM150C's modulatory effects on Piezo channels.

What are the critical controls needed when assessing Tmem150c function in knockout models?

When designing experiments to assess Tmem150c function in knockout models, the following controls are critical:

• Verification of Complete Gene Ablation:

  • RT-PCR analysis of multiple exon regions (e.g., Ex4-Ex6 fragment, Ex7-Ex8 fragment) using specific primers to confirm complete transcript loss

  • Western blot analysis using antibodies against the C-terminal part of TMEM150C (e.g., ABN2266, Millipore) with appropriate loading controls (β-actin)

  • Verification across multiple tissues (DRGs, epididymis, liver) to confirm tissue-specific ablation patterns

• Genotyping Accuracy:

  • Multiplex PCR using primers targeting both wild-type and mutant alleles

  • Verification of expected Mendelian frequencies in progeny from heterozygous matings

• Physiological Assessments:

  • Comparison across multiple modalities (e.g., ex vivo skin nerve preparation, locomotion analysis) to capture potential compensation mechanisms

  • Age-matched wild-type controls to account for developmental differences

  • Multiple sensory fiber subtypes examination (mechanoreceptors, nociceptors) in peripheral tissues

• Ultrastructural Analysis:

  • Electron microscopy of peripheral nerves to assess fiber composition (C:A-fibers ratio)

  • Measurement of myelin thickness and g-ratio in knockout versus wild-type animals to detect potential secondary effects

These controls help distinguish direct effects of Tmem150c ablation from potential compensatory mechanisms or incomplete gene targeting.

What experimental parameters should be optimized when studying the modulatory effects of Tmem150c on mechano-gated channels?

To optimize experimental parameters when studying Tmem150c modulatory effects:

• Expression Level Calibration:

  • Titrate expression levels of both TMEM150C and channel proteins to physiologically relevant ranges

  • Monitor expression using fluorescent tags or quantitative Western blotting

  • Analyze effects across different expression ratios to determine stoichiometric relationships

• Stimulus Optimization:

  • Calibrate mechanical stimulation parameters (indentation depth, speed, duration)

  • Apply stimulus ranges that span both sub-threshold and saturating levels (e.g., 5-10 μm indentation range)

  • Implement standardized stimulus protocols for reproducibility across experiments

• Recording Configuration:

  • Optimize whole-cell recording parameters (series resistance, capacitance compensation)

  • Control membrane potential to assess voltage-dependent modulation effects

  • Use consistent analysis parameters for inactivation kinetics (τinact) and activation thresholds

• Environmental Factors:

  • Control temperature, which affects channel kinetics

  • Standardize extracellular and intracellular ionic compositions

  • Maintain consistent cell density and recording timepoints post-transfection

Careful optimization of these parameters enhances reproducibility and physiological relevance of the observed modulatory effects.

What is the optimal protocol for generating functional recombinant rat Tmem150c protein?

For optimal production of functional recombinant rat Tmem150c:

• Cloning Strategy:

  • Amplify full-length rat Tmem150c cDNA from appropriate tissue (DRGs, trigeminal ganglia)

  • Insert into mammalian expression vector with appropriate tags (e.g., His, FLAG) for detection and purification

  • Verify sequence integrity with complete sequencing

• Expression System Selection:

  • For functional studies: HEK293T cells with ablated endogenous mechanosensitive channels (e.g., HEK293T ΔP1)

  • For protein production: HEK293F suspension cells for higher yield

  • Alternative: Insect cell expression systems (Sf9, High Five) for mammalian membrane proteins

• Transfection and Culture Conditions:

  • Optimize transfection reagent and DNA ratios

  • Culture at reduced temperature (30-32°C) following transfection to enhance proper folding

  • Add chemical chaperones if misfolding is observed

• Protein Extraction and Purification:

  • Use mild detergents (DDM, LMNG) for membrane protein solubilization

  • Implement two-step purification (affinity chromatography followed by size exclusion)

  • Verify protein integrity by Western blotting using antibodies against the C-terminal part of TMEM150C

• Functional Verification:

  • Co-expression with known interacting partners (Piezo1/2) followed by electrophysiological assessment

  • Compare modulatory effects with those reported for mouse and duck orthologs

This protocol should yield functional recombinant rat Tmem150c suitable for detailed biochemical and functional characterization.

What are the most sensitive methods for detecting Tmem150c expression in different tissue types?

For sensitive detection of Tmem150c expression across tissues:

• Quantitative RT-PCR:

  • Design primers targeting conserved regions (Ex4-Ex6, Ex7-Ex8 fragments)

  • Use reference genes with stable expression (e.g., Hprt1) for normalization

  • Implement absolute quantification with standard curves for cross-tissue comparison

• In Situ Hybridization:

  • RNAscope technology provides single-cell resolution and higher sensitivity than traditional ISH

  • Multiplex with probes for interacting partners (e.g., Piezo2) to assess co-expression

  • Quantify percentage of positive cells in each tissue (e.g., 83.3% ± 1.0% in duck TG neurons)

• Immunohistochemistry and Western Blotting:

  • Use validated antibodies against the C-terminal part of TMEM150C (e.g., ABN2266, Millipore)

  • Include appropriate positive and negative controls (tissues from knockout animals)

  • Combine with cell-type specific markers for co-localization studies

• Single-Cell RNA Sequencing:

  • Provides comprehensive expression profiles across diverse cell populations

  • Enables correlation of Tmem150c expression with other genes in specific cell types

  • Allows identification of potential regulatory networks

A combination of these approaches provides comprehensive characterization of Tmem150c expression patterns with cellular resolution across different tissues.

How should researchers interpret conflicting electrophysiological data regarding Tmem150c function?

When interpreting conflicting electrophysiological data regarding Tmem150c function:

• Context Specificity:

  • Consider the specific experimental context (cell type, expression system, co-expressed proteins)

  • Evaluate whether native versus recombinant systems were used, as native complexes may contain additional regulatory factors

  • Assess whether studies examined the same functional properties (threshold, kinetics, persistence)

• Technical Variation Analysis:

  • Compare stimulation parameters (indentation depth, speed) across studies

  • Evaluate recording configurations (whole-cell vs. outside-out patches)

  • Consider differences in analysis methods for inactivation kinetics or threshold determination

• Experimental Controls:

  • Assess whether appropriate controls for gene ablation verification were implemented

  • Evaluate whether compensation mechanisms were addressed in knockout models

  • Consider developmental timing in knockout studies versus acute manipulation

• Resolution Framework:

  • Design experiments that directly address contradictions

  • Implement multiple methodologies within the same study

  • Consider tissue-specific or context-dependent functions as potential explanations for different observations

By systematically evaluating these factors, researchers can develop more nuanced interpretations of seemingly contradictory findings regarding Tmem150c function.

What statistical approaches are most appropriate for analyzing Tmem150c effects on channel properties?

For statistically robust analysis of Tmem150c effects on channel properties:

• For Threshold Comparisons:

  • One-way ANOVA followed by Dunnett's test when comparing multiple conditions to a control

  • Report precise p-values (e.g., p = 0.0098 for threshold comparisons)

  • Include 95% confidence intervals for threshold values

• For Kinetic Parameters Analysis:

  • Two-way ANOVA to assess multiple factors (e.g., expression construct and stimulus intensity)

  • Report both main effects and interaction terms (e.g., p < 0.0001 for expression construct effect)

  • Perform post-hoc comparisons with appropriate correction for multiple testing

• For Stimulus-Response Relationships:

  • Fit data to appropriate mathematical models (Boltzmann, Hill equation)

  • Compare fitted parameters (EC50, Hill coefficient) between conditions

  • Use extra sum-of-squares F test to determine if separate curves for each condition provide better fits than a shared curve

• For Variability Assessment:

  • Report both central tendency and dispersion measures

  • Consider non-parametric approaches for non-normally distributed data

  • Implement bootstrapping approaches for robust confidence interval estimation

• Sample Size Considerations:

  • Conduct power analysis to determine appropriate sample sizes

  • Report exact n values for each experimental condition

  • Consider hierarchical statistical approaches when multiple measurements come from the same preparation

These statistical approaches enhance reproducibility and interpretability of findings related to Tmem150c modulation of channel properties.