Mechanically activated, Ca2+-permeable cation channel of the TMEM63/OSCA (CSC1) family. TMEM63A is an 11-transmembrane protein that, unusually for its structural superfamily, functions as a monomer with a single highly restricted pore, and it gates by the force-from-lipids principle: membrane stretch or hypo-osmotic swelling opens a small-conductance, high-threshold cation conductance that carries Ca2+ into the cell. Native TMEM63A is predominantly endolysosomal, residing in lysosomal and early endosomal membranes and in the limiting membrane of alveolar lamellar bodies, but it also reaches the plasma membrane in oligodendrocytes and in heterologous expression. In oligodendrocytes it is the mechanosensor that lets the cell gauge axon caliber, converting membrane stretch into Ca2+ signals that set myelin sheath length and thickness; its loss produces shorter and thinner sheaths on large axons, ectopic myelination of very small axons, and increased sheath retraction. In alveolar epithelium TMEM63A acts together with TMEM63B to convert lung inflation into the Ca2+ signal that drives lamellar body exocytosis and pulmonary surfactant secretion, and in Drosophila and mouse the orthologue shapes lysosomal membrane morphology. Heterozygous missense variants in the pore-forming region cause transient infantile hypomyelinating leukodystrophy. Unlike its paralog TMEM63B, TMEM63A does not behave as a phospholipid scramblase in cells: the purified protein can translocate lipids when reconstituted into vesicles and stretched cells expressing it expose phosphatidylserine, but under resting cellular conditions no scrambling is detected, and the disease substitution V53M is notable precisely because it confers constitutive scrambling that the wild-type protein lacks.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005227 calcium-activated cation channel activity | IBA GO_REF:0000033 | MODIFY | Summary: Ca2+-permeable, stretch-gated cation channel annotated with a term that asserts gating by Ca2+ binding. Reason: The essence is right - TMEM63A is a Ca2+-permeable cation channel - but the term names the wrong gating stimulus. GO:0005227 is defined as a channel that opens 'when a calcium cation has been bound by the channel complex or one of its constituent parts', and every experimental user of the term in GOA is a genuinely Ca2+-gated channel (KCNN4, SLO1/SLO2, TRPM4, TMEM16A). TMEM63A opens in response to membrane stretch, with Ca2+ as a permeant ion that carries the resulting signal, as the oligodendrocyte work states directly. The provenance of the slip is visible in the electronic pipeline: the InterPro family behind the IEA row is named 'Calcium permeable stress-gated cation channel 1-like' (IPR045122) yet is mapped to the calcium-activated term, and the same conflation sits behind the plant OSCA annotations that seed the phylogenetic node. Replace with the mechanosensitive cation channel term plus a plain calcium channel term, which together capture what was measured without asserting Ca2+ gating. The identical change is proposed for the paralog TMEM63B. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN001404773 · OSCA/TMEM63 ancestral node SUPPORTS SOURCE BUT NOT TARGET The node correctly captures a conserved stress-gated, Ca2+-permeable cation channel; the GO term chosen for it names Ca2+ as the gating ligand instead. The phylogenetic placement is not being challenged - only the term. MGI:MGI:2387609 · Tmem63b (mouse) SUPPORTS SOURCE BUT NOT TARGET Mouse IDA rests on PMID:31243992, titled 'Overexpression of Osmosensitive Ca(2+)-Permeable Channel TMEM63B', which reports Ca2+ permeability and hyperosmolarity gating, not Ca2+-dependent gating. UniProtKB:Q5T3F8 · TMEM63B (human paralog) SUPPORTS SOURCE BUT NOT TARGET Carries the same term-choice problem; the identical MODIFY is proposed in the TMEM63B review. UniProtKB:Q9P1W3 · TMEM63C (human paralog) SUPPORTS SOURCE BUT NOT TARGET AGI_LocusCode:AT4G04340 · Arabidopsis OSCA SUPPORTS SOURCE BUT NOT TARGET Plant OSCA proteins are hyperosmolality-gated calcium-permeable channels; the same permeable/activated conflation applies at the plant end of the tree. AGI_LocusCode:AT4G22120 · Arabidopsis OSCA SUPPORTS SOURCE BUT NOT TARGET SGD:S000004231 · yeast CSC1-like UNRESOLVED Not individually inspected. Proposed replacements: mechanosensitive monoatomic cation channel activity calcium channel activity |
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: TMEM63A reaches the plasma membrane, where its stretch-activated currents are recorded and where it acts in oligodendrocytes. Reason: Correct. Note that native TMEM63A is predominantly endolysosomal in several cell types, and much of the plasma membrane electrophysiology uses heterologous over-expression; the plasma membrane pool is nonetheless real, being reported in native oligodendrocytes and in neutrophil granule/plasma membrane proteomics. |
| GO:0003676 nucleic acid binding | IEA GO_REF:0000002 | REMOVE | Summary: Nucleic acid binding inferred from a structural superfamily match, with no functional basis. Reason: Fold-only electronic inference that is demonstrably inapplicable. The InterPro matches for O94886 include SSF54928 'RNA-binding domain, RBD' mapping to IPR035979 'RNA-binding domain superfamily', and IPR012677 'Nucleotide-binding alpha-beta plait domain superfamily'. Both are homologous-superfamily hits on the CSC1/OSCA1-like cytosolic domain (IPR027815), which adopts an RRM-like alpha-beta plait fold. An RRM-like fold is a common scaffold and carries no implication of nucleic acid binding on its own; no OSCA or TMEM63 protein has ever been reported to bind nucleic acid, and TMEM63A is an 11-transmembrane integral membrane channel of the lysosomal and plasma membranes. The pipeline is not even self-consistent: the paralog TMEM63B, which has the same cytosolic domain, carries no such annotation. This is exactly the class of wrong electronic inference that should be removed rather than demoted. |
| GO:0005227 calcium-activated cation channel activity | IEA GO_REF:0000002 | MODIFY | Summary: Ca2+-permeable, stretch-gated cation channel annotated with a term that asserts gating by Ca2+ binding. Reason: The essence is right - TMEM63A is a Ca2+-permeable cation channel - but the term names the wrong gating stimulus. GO:0005227 is defined as a channel that opens 'when a calcium cation has been bound by the channel complex or one of its constituent parts', and every experimental user of the term in GOA is a genuinely Ca2+-gated channel (KCNN4, SLO1/SLO2, TRPM4, TMEM16A). TMEM63A opens in response to membrane stretch, with Ca2+ as a permeant ion that carries the resulting signal, as the oligodendrocyte work states directly. The provenance of the slip is visible in the electronic pipeline: the InterPro family behind the IEA row is named 'Calcium permeable stress-gated cation channel 1-like' (IPR045122) yet is mapped to the calcium-activated term, and the same conflation sits behind the plant OSCA annotations that seed the phylogenetic node. Replace with the mechanosensitive cation channel term plus a plain calcium channel term, which together capture what was measured without asserting Ca2+ gating. The identical change is proposed for the paralog TMEM63B. Proposed replacements: mechanosensitive monoatomic cation channel activity calcium channel activity |
| GO:0005765 lysosomal membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Lysosomal membrane is the principal native location of TMEM63A. Reason: Well-supported core location, reported by focused imaging studies and by two independent lysosomal membrane proteomics datasets. |
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: TMEM63A reaches the plasma membrane, where its stretch-activated currents are recorded and where it acts in oligodendrocytes. Reason: Correct. Note that native TMEM63A is predominantly endolysosomal in several cell types, and much of the plasma membrane electrophysiology uses heterologous over-expression; the plasma membrane pool is nonetheless real, being reported in native oligodendrocytes and in neutrophil granule/plasma membrane proteomics. |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: Root-level membrane term from an InterPro domain match. Reason: Correct but carries no information beyond 'is a membrane protein'. The specific membranes are known and already annotated. Proposed replacements: lysosomal membrane plasma membrane |
| GO:0031901 early endosome membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Early endosome membrane localisation. Reason: Experimentally observed secondary location, consistent with the endolysosomal distribution of the native protein. |
| GO:0034220 monoatomic ion transmembrane transport | IEA GO_REF:0000108 | MODIFY | Summary: Generic monoatomic ion transport, derived electronically from the mechanosensitive ion channel term. Reason: Correct but under-specific: TMEM63A conducts cations, and the cation-level term is already annotated on this gene. Proposed replacements: monoatomic cation transmembrane transport |
| GO:0098655 monoatomic cation transmembrane transport | IEA GO_REF:0000120 | ACCEPT | Summary: Cation flux across the membrane, the direct consequence of stretch-evoked channel opening. Reason: Core biological process for the channel activity. |
| GO:0007040 lysosome organization | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Lysosome organization, transferred from the single Drosophila ortholog Tmem63 (UniProtKB:Q6NP91). Reason: Biologically plausible and consistent with the endolysosomal localisation of native TMEM63A - the fly and mouse proteins are reported to control lysosomal membrane morphology through lysosomal mechanosensitivity - but this is a downstream organelle-shape consequence of the channel activity rather than the activity itself, and there is no direct human evidence. Retained as non-core. |
| GO:0008381 mechanosensitive monoatomic ion channel activity | IEA GO_REF:0000107 | MODIFY | Summary: Mechanosensitive ion channel activity, correct but under-specific. Reason: Correct in kind but under-specific. TMEM63A is a mechanosensitive CATION channel: it is Ca2+-permeable and translates membrane stretch into Ca2+ signals in oligodendrocytes, and the family conducts Na+, K+ and Cs+. GO:0140135 mechanosensitive monoatomic cation channel activity is available and is what the paralog TMEM63B already carries from an IDA, so using the ion-agnostic parent here loses information the recordings establish and makes the two paralogs look different when they are not. This is the core molecular function of TMEM63A and the only molecular function for which the evidence is unambiguous. Proposed replacements: mechanosensitive monoatomic cation channel activity |
| GO:0160069 surfactant secretion | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Surfactant secretion from alveolar type 2 cells, downstream of stretch-activated TMEM63A/B currents. Reason: A well-documented in vivo role - Tmem63a/b double knockout mice die of atelectasis and respiratory failure - but a tissue-specific secretory process downstream of the channel activity rather than something the protein does directly. |
| GO:1990760 osmolarity-sensing monoatomic cation channel activity | IEA GO_REF:0000107 | ACCEPT | Summary: Osmolarity-gated cation channel activity; the same conductance described by its osmotic gating stimulus. Reason: Core. The osmotic and mechanical descriptions are two views of one force-from-lipids gating mechanism rather than two activities, and hypo-osmotic activation of TMEM63A currents is established for the orthologue. Retained alongside the mechanosensitive cation channel term. |
| GO:0034451 centriolar satellite | IDA GO_REF:0000052 | MARK AS OVER ANNOTATED | Summary: Centriolar satellite localisation from a single high-throughput immunofluorescence dataset. Reason: Incompatible with everything else known about the protein: TMEM63A is an 11-transmembrane integral membrane protein of the lysosomal, endosomal and plasma membranes, and centriolar satellites are non-membranous pericentriolar granules. This is a single-antibody HPA immunofluorescence call with no corroboration from any focused study or from the paralog. Marked as over-annotated rather than removed, since it carries an experimental evidence code and the underlying image may reflect a real but incidental juxtanuclear vesicle pool. |
| GO:0007040 lysosome organization | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: Lysosome organization, transferred from the single Drosophila ortholog Tmem63 (UniProtKB:Q6NP91). Reason: Biologically plausible and consistent with the endolysosomal localisation of native TMEM63A - the fly and mouse proteins are reported to control lysosomal membrane morphology through lysosomal mechanosensitivity - but this is a downstream organelle-shape consequence of the channel activity rather than the activity itself, and there is no direct human evidence. Retained as non-core. |
| GO:0005765 lysosomal membrane | IDA PMID:39716028 Membrane structure-responsive lipid scramblase activity of t... | ACCEPT | Summary: Lysosomal membrane is the principal native location of TMEM63A. Reason: Well-supported core location, reported by focused imaging studies and by two independent lysosomal membrane proteomics datasets. |
| GO:0017128 phospholipid scramblase activity | IDA NOT PMID:39716028 Membrane structure-responsive lipid scramblase activity of t... | ACCEPT | Summary: NOT annotation: in a scramblase-null cellular background, human TMEM63A - unlike TMEM63B - did not confer phospholipid scrambling. Reason: This is a negative assertion (NOT|enables) and it is correct as made. The source study deliberately compared paralogs in Tmem63b-deficient pro-B cells and found that scramblase activity tracked with TMEM63B orthology rather than with family membership, which is why the paralog carries the positive annotation and TMEM63A the negative one. The 2026 reconstitution work initially looks contradictory, since purified hTMEM63A does translocate lipids in giant unilamellar vesicles, but the same paper states that this is not the case in the cellular context, and reports cellular phosphatidylserine exposure only when cells are actively stretched. The two results are therefore about gating state rather than identity: TMEM63A retains the structural capacity to scramble but does not do so under resting cellular conditions. The V53M channelopathy substitution makes the same point from the other direction - it CREATES constitutive scrambling, which presupposes that the wild-type protein does not scramble. The NOT annotation is accepted, with the condition-dependence recorded here and the unresolved question moved to suggested_questions rather than being used to overturn a curator's IDA. Supporting Evidence: PMID:39716028 We expressed human TMEM63 paralogs, TMEM63B orthologs, and plant OSCA1.1 in Tmem63b-deficient mouse pro-B cells and found that vertebrate TMEM63B orthologs exhibit scramblase activity at the PM. PMID:41617699 Results from our experimental scrambling assays show that WT TMEM63A translocates lipids in GUVs but this is not the case in the cellular context. |
| GO:0160069 surfactant secretion | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: Surfactant secretion from alveolar type 2 cells, downstream of stretch-activated TMEM63A/B currents. Reason: A well-documented in vivo role - Tmem63a/b double knockout mice die of atelectasis and respiratory failure - but a tissue-specific secretory process downstream of the channel activity rather than something the protein does directly. Supporting Evidence: PMID:38127458 we show that loss of the mechanosensitive channels TMEM63A and TMEM63B (TMEM63A/B) resulted in atelectasis and respiratory failure in mice due to a deficit of surfactant secretion |
| GO:0005765 lysosomal membrane | IDA PMID:38127458 Mechanosensitive channels TMEM63A and TMEM63B mediate lung i... | ACCEPT | Summary: Lysosomal membrane is the principal native location of TMEM63A. Reason: Well-supported core location, reported by focused imaging studies and by two independent lysosomal membrane proteomics datasets. Supporting Evidence: PMID:38127458 TMEM63A/B were predominantly localized at the limiting membrane of the lamellar body (LB), a lysosome-related organelle that stores pulmonary surfactant and ATP in AT2 cells. |
| GO:0031901 early endosome membrane | IDA PMID:38127458 Mechanosensitive channels TMEM63A and TMEM63B mediate lung i... | ACCEPT | Summary: Early endosome membrane localisation. Reason: Experimentally observed secondary location, consistent with the endolysosomal distribution of the native protein. |
| GO:0005886 plasma membrane | IDA PMID:37543036 TMEM63 proteins function as monomeric high-threshold mechano... | ACCEPT | Summary: TMEM63A reaches the plasma membrane, where its stretch-activated currents are recorded and where it acts in oligodendrocytes. Reason: Correct. Note that native TMEM63A is predominantly endolysosomal in several cell types, and much of the plasma membrane electrophysiology uses heterologous over-expression; the plasma membrane pool is nonetheless real, being reported in native oligodendrocytes and in neutrophil granule/plasma membrane proteomics. |
| GO:0008381 mechanosensitive monoatomic ion channel activity | IDA PMID:37543036 TMEM63 proteins function as monomeric high-threshold mechano... | MODIFY | Summary: Mechanosensitive ion channel activity, correct but under-specific. Reason: Correct in kind but under-specific. TMEM63A is a mechanosensitive CATION channel: it is Ca2+-permeable and translates membrane stretch into Ca2+ signals in oligodendrocytes, and the family conducts Na+, K+ and Cs+. GO:0140135 mechanosensitive monoatomic cation channel activity is available and is what the paralog TMEM63B already carries from an IDA, so using the ion-agnostic parent here loses information the recordings establish and makes the two paralogs look different when they are not. This is the core molecular function of TMEM63A and the only molecular function for which the evidence is unambiguous. Proposed replacements: mechanosensitive monoatomic cation channel activity Supporting Evidence: PMID:37543036 Functional analyses demonstrated that TMEM63s are bona fide mechanosensitive ion channels, characterized by small conductance and high thresholds. |
| GO:0005886 plasma membrane | ISS GO_REF:0000024 | ACCEPT | Summary: TMEM63A reaches the plasma membrane, where its stretch-activated currents are recorded and where it acts in oligodendrocytes. Reason: Correct. Note that native TMEM63A is predominantly endolysosomal in several cell types, and much of the plasma membrane electrophysiology uses heterologous over-expression; the plasma membrane pool is nonetheless real, being reported in native oligodendrocytes and in neutrophil granule/plasma membrane proteomics. |
| GO:0008381 mechanosensitive monoatomic ion channel activity | IDA PMID:30382938 OSCA/TMEM63 are an Evolutionarily Conserved Family of Mechan... | MODIFY | Summary: Mechanosensitive ion channel activity, correct but under-specific. Reason: Correct in kind but under-specific. TMEM63A is a mechanosensitive CATION channel: it is Ca2+-permeable and translates membrane stretch into Ca2+ signals in oligodendrocytes, and the family conducts Na+, K+ and Cs+. GO:0140135 mechanosensitive monoatomic cation channel activity is available and is what the paralog TMEM63B already carries from an IDA, so using the ion-agnostic parent here loses information the recordings establish and makes the two paralogs look different when they are not. This is the core molecular function of TMEM63A and the only molecular function for which the evidence is unambiguous. Proposed replacements: mechanosensitive monoatomic cation channel activity Supporting Evidence: PMID:30382938 Here, we show that various members of the OSCA and TMEM63 family of proteins from plants, flies, and mammals confer mechanosensitivity to naïve cells. |
| GO:0008381 mechanosensitive monoatomic ion channel activity | IMP PMID:31587869 Heterozygous Variants in the Mechanosensitive Ion Channel TM... | MODIFY | Summary: Mechanosensitive ion channel activity, correct but under-specific. Reason: Correct in kind but under-specific. TMEM63A is a mechanosensitive CATION channel: it is Ca2+-permeable and translates membrane stretch into Ca2+ signals in oligodendrocytes, and the family conducts Na+, K+ and Cs+. GO:0140135 mechanosensitive monoatomic cation channel activity is available and is what the paralog TMEM63B already carries from an IDA, so using the ion-agnostic parent here loses information the recordings establish and makes the two paralogs look different when they are not. This is the core molecular function of TMEM63A and the only molecular function for which the evidence is unambiguous. Proposed replacements: mechanosensitive monoatomic cation channel activity Supporting Evidence: PMID:31587869 Here we report heterozygous missense mutations in the gene encoding the MA ion channel TMEM63A that result in an infantile disorder resembling a hypomyelinating leukodystrophy. |
| GO:1990760 osmolarity-sensing monoatomic cation channel activity | ISS GO_REF:0000024 | ACCEPT | Summary: Osmolarity-gated cation channel activity; the same conductance described by its osmotic gating stimulus. Reason: Core. The osmotic and mechanical descriptions are two views of one force-from-lipids gating mechanism rather than two activities, and hypo-osmotic activation of TMEM63A currents is established for the orthologue. Retained alongside the mechanosensitive cation channel term. |
| GO:0005515 protein binding | IPI PMID:28870237 The N- and C-terminal carbohydrate recognition domains of Ha... | REMOVE | Summary: Bare protein binding from a single interaction study with a parasitic nematode galectin. Reason: No more informative molecular function is supportable from this evidence, so the row is removed rather than rewritten. Here the partner is the N-terminal carbohydrate recognition domain of a Haemonchus contortus galectin binding goat peripheral blood mononuclear cells - a host-parasite interaction that says nothing about the normal activity of human TMEM63A. Removal does not imply the reported interaction is false. Supporting Evidence: PMID:28870237 transmembrane protein 63A (TMEM63A) was a binding receptor of MNh |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-6798747 | ACCEPT | Summary: TMEM63A reaches the plasma membrane, where its stretch-activated currents are recorded and where it acts in oligodendrocytes. Reason: Correct. Note that native TMEM63A is predominantly endolysosomal in several cell types, and much of the plasma membrane electrophysiology uses heterologous over-expression; the plasma membrane pool is nonetheless real, being reported in native oligodendrocytes and in neutrophil granule/plasma membrane proteomics. |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-6799350 | ACCEPT | Summary: TMEM63A reaches the plasma membrane, where its stretch-activated currents are recorded and where it acts in oligodendrocytes. Reason: Correct. Note that native TMEM63A is predominantly endolysosomal in several cell types, and much of the plasma membrane electrophysiology uses heterologous over-expression; the plasma membrane pool is nonetheless real, being reported in native oligodendrocytes and in neutrophil granule/plasma membrane proteomics. |
| GO:0035579 specific granule membrane | TAS Reactome:R-HSA-6799350 | KEEP AS NON CORE | Summary: Specific granule membrane, from Reactome's neutrophil degranulation pathway. Reason: Reactome's neutrophil degranulation membership derives from granule proteomics; a plausible membrane pool in neutrophils but not a site where a function of TMEM63A has been demonstrated. |
| GO:0070821 tertiary granule membrane | TAS Reactome:R-HSA-6798747 | KEEP AS NON CORE | Summary: Tertiary granule membrane, from Reactome's neutrophil degranulation pathway. Reason: Same basis as the specific granule membrane annotation: granule proteomics captured by Reactome, with no functional demonstration in this compartment. |
| GO:0070062 extracellular exosome | HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos... | MARK AS OVER ANNOTATED | Summary: Extracellular exosome, from large-scale urinary exosome shotgun proteomics. Reason: A high-throughput co-purification term. Urinary exosomes originate as intraluminal vesicles of multivesicular bodies, so detecting an endolysosomal membrane protein there is expected and adds no functional information. Supporting Evidence: PMID:19056867 Normal human urine contains large numbers of exosomes, which are 40- to 100-nm vesicles that originate as the internal vesicles in multivesicular bodies from every renal epithelial cell type facing the urinary space. |
| GO:0005765 lysosomal membrane | HDA PMID:17897319 Integral and associated lysosomal membrane proteins. | ACCEPT | Summary: Lysosomal membrane is the principal native location of TMEM63A. Reason: Well-supported core location, reported by focused imaging studies and by two independent lysosomal membrane proteomics datasets. Supporting Evidence: PMID:17897319 We searched for novel proteins in lysosomal membranes, tentatively participating in molecular transport across the membrane and/or in interactions with other compartments. |
| GO:0005765 lysosomal membrane | IDA PMID:20957757 The proteome of lysosomes. | ACCEPT | Summary: Lysosomal membrane is the principal native location of TMEM63A. Reason: Well-supported core location, reported by focused imaging studies and by two independent lysosomal membrane proteomics datasets. Supporting Evidence: PMID:20957757 the knowledge about the protein composition of the lysosomal membrane has remained fragmentary for a long time |
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Download this section (compressed HTML)Q: Is the NOT|enables phospholipid scramblase annotation on TMEM63A best read as 'this protein is not a scramblase' or as 'this protein does not scramble under resting cellular conditions'? Purified hTMEM63A translocates lipids in giant unilamellar vesicles and stretched cells expressing mTMEM63A expose phosphatidylserine, yet the same 2026 study reports no scrambling in the unstimulated cellular context, and the paralog survey that grounds the NOT annotation used a resting pro-B cell assay.
Suggested experts: Katsumori Segawa, Charles D Cox, Ben Corry, Yuta Miyata
Q: If TMEM63A can scramble lipids when sufficiently stretched, does that contribute to the oligodendrocyte and lysosomal-morphology phenotypes, which both involve large membrane shape changes? The Neuron 2026 account is framed purely in terms of Ca2+ signalling.
Suggested experts: Amit Agarwal, Charles D Cox
Q: Why does the TMEM63A V53M disease substitution cause a transient hypomyelinating leukodystrophy that resolves in childhood, while the homologous TMEM63B V44M causes a progressive epileptic encephalopathy, when both substitutions disrupt the same hydrophobic latch and both create constitutive scrambling?
Suggested experts: Wang Zheng, Jeffrey R Holt, Huanghe Yang
Q: Where does TMEM63A act in oligodendrocytes - at the plasma membrane of the growing sheath, or in the endolysosomal compartment where the native protein is most abundant?
Suggested experts: Amit Agarwal, Mitra Djannatian
Experiment: Repeat the pro-B cell paralog comparison that grounds the NOT annotation while applying calibrated mechanical stimulation (cyclic uniaxial stretch or high-speed pressure clamp) rather than assaying at rest, scoring annexin V binding for TMEM63A, TMEM63B and TMEM63C side by side in the same Tmem63b-null background.
Hypothesis: TMEM63A scrambling is force-gated rather than absent, so the NOT annotation is condition-specific.
Type: comparative cellular scramblase assay under controlled mechanical load
Experiment: Rescue Tmem63a-null oligodendrocytes with wild-type TMEM63A, with a pore mutant that abolishes cation conduction, and with a groove mutant that abolishes lipid translocation while preserving current (using the separable bottleneck residues identified by coarse-grained MD), then measure sheath length, g-ratio and retraction frequency in vivo.
Hypothesis: The oligodendrocyte myelination phenotype depends on TMEM63A ion conduction and not on any lipid-translocation activity.
Type: structure-function rescue in oligodendrocyte lineage cells
Experiment: If any confirmation is thought necessary before removal, perform RNA immunoprecipitation or CLIP on tagged TMEM63A and an electrophoretic mobility shift assay with the purified CSC1/OSCA1-like cytosolic domain. The expected and predicted outcome is no specific nucleic acid binding.
Hypothesis: The nucleic acid binding annotation is a fold artefact with no experimental correlate.
Type: RNA immunoprecipitation and in vitro binding assay
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