Recombinant Chicken Transmembrane protein 170A (TMEM170A)

What is the basic function of TMEM170A in cellular biology?

TMEM170A is a transmembrane protein that plays a critical role in endoplasmic reticulum (ER) morphogenesis, specifically promoting ER sheet formation at the expense of ER tubules. Research has demonstrated that TMEM170A localizes in both ER and nuclear envelope membranes, functioning as an ER-sheet-promoting protein . Its expression levels directly influence the ratio between tubular ER and ER sheets in the cell, making it a key regulator of ER membrane organization .

Unlike reticulons (RTNs) and DP1/Yop1p family members which shape ER tubules, TMEM170A works antagonistically to these proteins, specifically promoting the formation and maintenance of ER sheets. This balance between tubular-promoting and sheet-promoting proteins is essential for proper ER morphogenesis and function .

What is the molecular structure of chicken TMEM170A?

Chicken TMEM170A is a small transmembrane protein containing three transmembrane domains. The human homolog is approximately 15.25 kDa, and the chicken variant likely has similar characteristics . Based on computational analysis using TMPRED software, the N-terminus is predicted to be luminal while the C-terminus is cytoplasmic .

The transmembrane topology has been experimentally verified in human TMEM170A using permeabilization experiments with digitonin and Triton X-100, followed by antibody accessibility tests . The protein's structural features are integral to its function in ER membrane organization, and this structure-function relationship appears to be conserved across species, including in chicken TMEM170A .

How does TMEM170A differ from other ER-shaping proteins?

TMEM170A distinguishes itself from other ER-shaping proteins by specifically promoting ER sheet formation rather than tubular structures. This sets it apart from well-characterized proteins like reticulons (RTNs) and DP1/Yop1p family members that induce tubular ER formation .

Key differences include:

• Antagonistic function: TMEM170A works in opposition to tubular-promoting proteins like RTN4. In fact, co-silencing experiments have shown that simultaneous knockdown of TMEM170A and RTN4 rescues the altered ER morphology observed with single TMEM170A silencing .

• Broader cellular impacts: TMEM170A not only affects ER structure but also influences nuclear envelope expansion, nuclear pore complex (NPC) formation, and inner nuclear membrane (INM) protein targeting, suggesting a more comprehensive role in nuclear-ER organization than many other ER-shaping proteins .

• Interaction profile: TMEM170A interacts with RTN4, indicating that a regulatory balance between these opposing factors maintains proper ER membrane morphology .

What are the detailed molecular mechanisms by which TMEM170A promotes ER sheet formation?

The precise molecular mechanisms through which TMEM170A promotes ER sheet formation remain under investigation, but current research provides several insights:

TMEM170A appears to function through a direct interaction with RTN4, a well-established tubular-ER-shaping protein . This interaction suggests a competitive or regulatory relationship between sheet-promoting and tubule-promoting factors. When TMEM170A is present at normal or elevated levels, it may inhibit or counterbalance the tubule-forming activity of RTN4, shifting the equilibrium toward ER sheet formation .

Ultrastructural analysis using transmission electron microscopy (TEM) and 3D electron tomography has revealed that TMEM170A silencing induces tubular ER formation that is predominantly unorganized, with only occasional fusion events leading to partially organized structures . Conversely, overexpression of TMEM170A promotes extensive proliferation of organized ER sheets decorated with membrane-bound ribosomes .

The mechanism likely involves a combination of:

• Direct stabilization of sheet morphology through transmembrane domain interactions

• Antagonistic regulation of tubule-promoting factors

• Potential recruitment of other sheet-stabilizing proteins

Further research is needed to elucidate whether TMEM170A actively promotes sheet formation or primarily acts by inhibiting tubule formation factors .

How does the interaction between TMEM170A and RTN4 affect nuclear pore complex (NPC) formation?

The interaction between TMEM170A and RTN4 has profound implications for nuclear pore complex (NPC) formation, revealing a previously unrecognized connection between ER membrane organization and nuclear envelope architecture .

Research has demonstrated that TMEM170A-silenced cells exhibit a dramatic decrease in NPC density, accompanied by significantly reduced cellular levels of several nucleoporins . Remarkably, co-silencing experiments with TMEM170A and RTN4 restore these NPC-related phenotypes and nucleoporin protein levels, suggesting that these two proteins function antagonistically in NPC assembly .

The precise mechanism linking TMEM170A/RTN4 balance to NPC formation remains to be fully characterized, but several hypotheses exist:

• The altered membrane curvature resulting from TMEM170A/RTN4 imbalance may directly affect NPC insertion sites

• Changes in ER-nuclear envelope connections might disrupt nucleoporin trafficking

• TMEM170A may play a more direct role in NPC assembly independent of its ER-shaping function

This relationship represents an important area for future research, as it connects fundamental cellular processes of ER morphogenesis and nucleocytoplasmic transport .

What phenotypic changes occur at the cellular level when TMEM170A is silenced or overexpressed?

TMEM170A manipulation produces distinct and dramatic phenotypic changes at the cellular level:

TMEM170A Silencing Effects:

• Increased cell death: Only approximately 10±2% of silenced cells survive 72 hours post-transfection .

• Altered ER morphology: The ER becomes atypical in >80% of surviving cells, appearing asymmetrically distributed around the nucleus or dispersed, with a tendency to aggregate .

• Nuclear abnormalities: Nuclei become irregularly shaped and enlarged, with frequent nuclear envelope invaginations or evaginations .

• Tubular ER induction: Ultrastructural analysis reveals extensive formation of unorganized tubular ER .

• Reduced CLIMP-63 levels: An ER-sheet-specific marker shows reduced immunofluorescence and protein levels (28.47±2.25% of control) .

• Decreased NPC density: Nuclear pore complexes are dramatically reduced .

• INM protein mislocalization: Inner nuclear membrane proteins are either reduced at the nuclear rim or mislocalized to the ER .

TMEM170A Overexpression Effects:

• Expanded ER sheet volume: CLIMP-63-positive ER shows significant expansion .

• Proliferation of organized ER sheets: High-resolution imaging reveals extensive, well-organized ER sheet stacks with membrane-bound ribosomes .

• Reduced nuclear size: Nuclear surface area decreases to 83.9±1.9% and volume to 73.97±19.82% of control cells .

These phenotypic changes highlight TMEM170A's role in maintaining proper ER sheet-tubule balance and nuclear envelope architecture .

What are the optimal conditions for storing and reconstituting recombinant chicken TMEM170A protein?

Based on current research standards for recombinant chicken TMEM170A, the following storage and reconstitution protocols are recommended:

Storage Conditions:

• For liquid formulations: Store at -20°C/-80°C with a shelf life of approximately 6 months .

• For lyophilized formulations: Store at -20°C/-80°C with a shelf life of approximately 12 months .

• Avoid repeated freezing and thawing cycles as this may compromise protein integrity .

• Working aliquots can be stored at 4°C for up to one week .

Reconstitution Protocol:

• Briefly centrifuge the vial prior to opening to bring contents to the bottom .

• Reconstitute the protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL .

• Add glycerol to a final concentration of 5-50% (with 50% being the default recommendation) for long-term storage .

• Aliquot the reconstituted protein to minimize freeze-thaw cycles .

This protocol is designed to maintain protein stability and activity, critical for experimental reproducibility. The addition of glycerol serves as a cryoprotectant to prevent protein denaturation during freeze-thaw cycles .

What experimental approaches can be used to study TMEM170A interactions with other proteins like RTN4?

Several experimental approaches have proven effective for studying TMEM170A interactions with proteins like RTN4:

1. Immunoprecipitation coupled with mass spectrometry (IP-MS):
This approach has successfully identified RTN4 as a TMEM170A-interacting protein. The protocol involves:

• Generating stable cell lines expressing tagged TMEM170A (e.g., TMEM170A-GFP)

• Lysing cells in appropriate buffer (20 mM Tris pH 7.5, 150 mM NaCl, 1% v/v NP40 with protease inhibitors)

• Incubating lysates with GFP-Trap beads to pull down TMEM170A complexes

• Washing beads extensively and eluting bound proteins

• Analyzing samples by SDS-PAGE followed by silver staining

• Excising unique bands, performing in-gel trypsin digestion, and identifying peptides by liquid chromatography-tandem mass spectrometry (LC-MS/MS)

2. Co-immunoprecipitation (Co-IP) assays:
These can validate specific interactions identified by IP-MS and determine if they are direct or indirect.

3. Functional rescue experiments:
Co-silencing experiments (e.g., simultaneous knockdown of TMEM170A and RTN4) can demonstrate functional relationships between interacting proteins . This approach revealed that TMEM170A and RTN4 act antagonistically in ER membrane organization, nuclear envelope formation, and NPC assembly .

4. Fluorescence microscopy with tagged proteins:
This allows visualization of potential co-localization in cellular compartments.

5. Proximity ligation assays:
These can detect protein-protein interactions in situ with high sensitivity.

When designing interaction studies, consider using both overexpression and endogenous protein detection approaches to validate physiologically relevant interactions .

What methodologies are effective for analyzing the effects of TMEM170A manipulation on ER morphology?

Multiple complementary methodologies have proven effective for analyzing TMEM170A's effects on ER morphology:

1. Immunofluorescence microscopy:

• Use antibodies against ER markers such as calnexin (general ER), CLIMP-63 (ER sheets), RTN4 (tubular ER), and LEM4

• Compare control cells with TMEM170A-silenced or overexpressing cells

• Quantify the distribution patterns and signal intensity of these markers

• This approach revealed that >80% of TMEM170A-silenced cells show atypical ER distribution

2. Transmission Electron Microscopy (TEM):

• Fix cells with appropriate fixatives for EM (typically glutaraldehyde/paraformaldehyde)

• Process samples for TEM analysis

• Examine at high resolution to distinguish between tubular and sheet forms of ER

• This technique demonstrated that TMEM170A silencing induces tubular ER formation, while overexpression promotes ER sheet formation

3. 3D Electron Tomography:

• Allows reconstruction of three-dimensional views of ER structures

• Particularly valuable for distinguishing between true sheets and tightly packed tubules

• Revealed that in TMEM170A-silenced cells, aggregates that appeared organized at first glance were actually tubules separated into small sections rather than joined cisternal stacks

4. Western Blot Analysis:

• Quantify levels of ER structure-specific proteins like CLIMP-63

• TMEM170A silencing reduced CLIMP-63 protein levels to 28.47±2.25% of control samples

5. Rescue Experiments:

• Perform silencing followed by re-expression of siRNA-resistant TMEM170A

• Co-silencing of TMEM170A with potential antagonists like RTN4

• These experiments demonstrated the functional relationship between TMEM170A and RTN4 in ER morphology

The combination of these approaches provides comprehensive insights into how TMEM170A influences ER structural organization at multiple scales of resolution .

How can researchers effectively study the impact of TMEM170A on nuclear pore complex formation?

To effectively study TMEM170A's impact on nuclear pore complex (NPC) formation, researchers can employ these methodological approaches:

1. Immunofluorescence microscopy with nucleoporin-specific antibodies:

• Use antibodies against various nucleoporins (e.g., Nup153, Nup62, mAb414)

• Compare staining patterns and intensities between control and TMEM170A-manipulated cells

• Quantify NPC density at the nuclear envelope

• This approach revealed significantly reduced nucleoporin staining in TMEM170A-silenced cells

2. Western blot analysis of nucleoporin levels:

• Prepare whole cell lysates from control and TMEM170A-manipulated cells

• Analyze protein levels of multiple nucleoporins

• TMEM170A silencing was shown to reduce cellular levels of several nucleoporins

3. Electron microscopy techniques:

• Conventional TEM to visualize NPCs in cross-section

• Scanning electron microscopy (SEM) of the nuclear surface

• These methods provide direct visualization of NPC density and distribution

4. Functional assays for nucleocytoplasmic transport:

• Import/export assays using fluorescent reporter proteins

• Measure transport efficiency as an indicator of functional NPC density

• Correlate transport rates with TMEM170A expression levels

5. Co-silencing experiments:

• Simultaneously silence TMEM170A and potential interactors (e.g., RTN4)

• Assess rescue of NPC-related phenotypes

• This approach demonstrated that TMEM170A and RTN4 act antagonistically in NPC formation

6. Super-resolution microscopy:

• Techniques like STORM or PALM for high-resolution imaging of individual NPCs

• Quantify spatial distribution and density with nanometer precision

7. Proximity ligation assays:

• Detect potential direct interactions between TMEM170A and nucleoporins or NPC assembly factors

By combining these approaches, researchers can comprehensively characterize how TMEM170A influences NPC formation, providing insights into the connection between ER morphogenesis and nuclear envelope architecture .

Impact of TMEM170A Manipulation on Cellular Parameters

Source: Data compiled from references and

Recommended Storage Conditions for Recombinant Chicken TMEM170A

Source: Data compiled from references and

TMEM170A Interaction Partners Identified by Mass Spectrometry

Source: Data compiled from references and