Affinage

TMEM231

Transmembrane protein 231 · UniProt Q9H6L2

Length
316 aa
Mass
36.1 kDa
Annotated
2026-04-28
21 papers in source corpus 8 papers cited in narrative 8 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TMEM231 is a two-pass transmembrane protein that functions as a core component of the MKS module at the ciliary transition zone, where it forms a diffusion barrier essential for ciliary membrane compartmentalization and signaling. It assembles at the transition zone in a Septin 2-dependent, intraflagellar transport-independent manner, with reciprocal localization dependencies on B9D1, CC2D2A, and MKS1, and its recruitment is organized within an MKS-5/CEP-290-dependent hierarchy conserved from C. elegans to mammals (PMID:22179047, PMID:25869670, PMID:26595381, PMID:26982032). TMEM231 physically interacts with TMEM138 and caveolin 1 at the transition zone, and its loss causes mislocalization of ciliary proteins Arl13b and Inpp5e, abrogation of Hedgehog signaling in craniofacial development, and near-complete loss of primary cilia (PMID:35394880, PMID:37997673, PMID:34672258). Biallelic loss-of-function mutations in TMEM231 cause Meckel syndrome and OFD type VI, ciliopathies characterized by polydactyly, kidney cysts, and midface defects (PMID:25869670, PMID:26982032).

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 2011 High

    The first question was whether the transition zone contains a discrete protein complex that restricts diffusion into cilia; discovery of a nine-protein TZ complex including TMEM231 established that this complex acts as a ciliary membrane diffusion barrier, with TMEM231 localizing to the basal body in a Septin 2-dependent, IFT-independent manner.

    Evidence RNAi screening, proteomics, FRAP diffusion measurements, and mouse knockout genetics in IMCD3 cells and mouse

    PMID:22179047

    Open questions at the time
    • How Septin 2 controls TMEM231 recruitment mechanistically was not resolved
    • The stoichiometry and structural arrangement of the nine-protein complex remained unknown
    • Whether TMEM231 itself directly contacts the membrane barrier or acts as a scaffold was unclear
  2. 2015 High

    The next question was how TMEM231 fits into the assembly hierarchy of the MKS module and what organismal phenotypes its loss produces; studies in mouse and C. elegans showed that TMEM231 and B9D1 are mutually required and both are needed for MKS1 recruitment, while Tmem231 knockout mice exhibit polydactyly and kidney cysts characteristic of Meckel syndrome, and super-resolution imaging revealed periodic, immobile localization of MKS module proteins including TMEM231 at the transition zone.

    Evidence Mouse knockout phenotyping, immunofluorescence localization hierarchy, C. elegans genetics, super-resolution microscopy (STORM/SIM), patient mutation validation

    PMID:25869670 PMID:26595381

    Open questions at the time
    • The structural basis for the periodic arrangement of TZ membrane proteins was not determined
    • Whether TMEM231 has catalytic or purely structural roles remained open
    • The mechanism by which Arl13b and Inpp5e mislocalize upon TMEM231 loss was not dissected
  3. 2016 High

    A remaining question was what sits atop the TZ assembly hierarchy; genetic epistasis in C. elegans placed TMEM-231 localization downstream of CEP-290 and MKS-5, defining a CEP-290/MKS-5-dependent assembly pathway, and patient mutations in TMEM231 were linked to OFD type VI.

    Evidence C. elegans genetic epistasis with localization readouts, patient fibroblast ciliogenesis assays

    PMID:26982032

    Open questions at the time
    • Whether CEP-290 directly contacts TMEM231 or acts indirectly was not determined
    • Functional rescue of patient cells by TMEM231 re-expression was not shown
  4. 2021 Medium

    It was unknown how TMEM231-dependent cilia contribute to craniofacial patterning; Tmem231 mutant mice showed that reduced Hedgehog signaling in the prechordal plate causes midface hypotelorism via increased cell death, placing TMEM231 upstream of HH pathway activation in facial development.

    Evidence Mouse knockout with HH pathway reporters, cell death assays, Ptch1 genetic epistasis

    PMID:34672258

    Open questions at the time
    • Direct rescue of Tmem231 midface phenotype by enhanced HH signaling was not achieved, unlike for Tctn2/Cc2d2a mutants
    • Whether TMEM231 has HH-pathway roles beyond transition zone integrity remains untested
  5. 2022 Medium

    The question of which additional proteins directly interact with TMEM231 at the TZ was addressed by demonstrating that TMEM138 reciprocally co-immunoprecipitates with TMEM231 and is required for TMEM231 localization in photoreceptor connecting cilia.

    Evidence Reciprocal co-immunoprecipitation, Tmem138 knockout mouse photoreceptor immunofluorescence

    PMID:35394880

    Open questions at the time
    • Whether the TMEM138–TMEM231 interaction is direct or bridged by other MKS components is unknown
    • The interaction was characterized in photoreceptors; generality across other ciliated cell types was not shown
  6. 2023 Medium

    Whether TMEM231 participates in lipid-raft-dependent barrier function was addressed by showing that TMEM231 interacts with caveolin 1 at the TZ and redistributes to the axoneme when the interaction is disrupted by galectin 8-induced cilia elongation.

    Evidence Co-immunoprecipitation, live imaging, recombinant galectin 8 treatment, caveolin 1 knockout

    PMID:37997673

    Open questions at the time
    • Whether the TMEM231–caveolin 1 interaction is direct was not established
    • The physiological relevance of galectin 8-mediated redistribution in vivo is unclear
    • Whether caveolin 1 loss phenocopies TMEM231 loss for ciliary compartmentalization was not tested

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the atomic structure of TMEM231 within the MKS module, whether TMEM231 possesses any enzymatic or lipid-binding activity, and the precise molecular mechanism by which it restricts membrane protein diffusion at the transition zone.
  • No structural model of TMEM231 or reconstituted MKS module exists
  • Whether TMEM231 directly contacts lipids or membrane domains is unknown
  • The mechanism of HH signaling failure in Tmem231 mutants beyond cilia loss is not resolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 3
Localization
GO:0005929 cilium 6 GO:0005886 plasma membrane 2
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 4 R-HSA-1643685 Disease 3 R-HSA-162582 Signal Transduction 1
Partners
B9D1CAV1CC2D2ACEP290MKS1TMEM107TMEM138
Complex memberships
MKS module (transition zone complex)

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2011 TMEM231 is a transmembrane component of a nine-protein complex at the ciliary transition zone; it localizes to the basal body before and independently of intraflagellar transport in a Septin 2 (Sept2)-regulated fashion. The localizations of TMEM231, B9D1, and CC2D2A at the transition zone are dependent on one another and on Sept2. Disruption of the complex increases the rate of diffusion into the ciliary membrane and the amount of plasma-membrane protein in the cilia, demonstrating that the complex acts as a diffusion barrier to maintain the cilia membrane as a compartmentalized signaling organelle. RNAi screening, proteomics, cell biological assays (FRAP/diffusion measurements), and mouse knockout genetics Nature cell biology High 22179047
2015 TMEM231 (a two-pass transmembrane protein) is essential for MKS complex formation at the transition zone: Tmem231 and B9d1 are required for each other and for Mks1 to localize to the transition zone. Loss of mouse Tmem231 disrupts localization of Arl13b and Inpp5e to cilia, causing polydactyly and kidney cysts characteristic of Meckel syndrome. The C. elegans orthologue similarly localizes to and controls transition zone formation and function, indicating an evolutionarily conserved role. Patient-derived TMEM231 mutations compromise transition zone function. Mouse knockout with phenotypic analysis, immunofluorescence localization hierarchy experiments, C. elegans genetics, and patient mutation functional validation The Journal of cell biology High 25869670
2015 TMEM-107 (TMEM107) organizes recruitment of ciliopathy proteins including TMEM-231 (JBTS20) within an intermediate layer of the TZ-localized MKS module. Super-resolution microscopy revealed periodic localizations of MKS module membrane proteins (including TMEM231) within the transition zone, and these proteins are immobile within the TZ. C. elegans genetics, super-resolution microscopy (STORM/SIM), localization hierarchy assays in nematode and mammalian cells Nature cell biology High 26595381
2016 In C. elegans, TZ localization of TMEM-231 depends on CEP-290 and other MKS module components, placing TMEM231 within an MKS-5 and CEP-290-dependent assembly pathway for building a functional transition zone. Human patients with mutations in TMEM231 present with OFD6 phenotypes linked to ciliogenesis defects. C. elegans genetic epistasis (localization hierarchy), patient fibroblast ciliogenesis assays PLoS biology High 26982032
2021 Tmem231 mutant mice display hypotelorism due to reduced Hedgehog (HH) pathway activation in the prechordal plate and adjacent neurectoderm as early as the end of gastrulation, leading to increased cell death in the neurectoderm and facial ectoderm and collapse of the facial midline. Reducing Ptch1 gene dosage (enhancing HH signaling) did not rescue the Tmem231 midface defect directly, but rescued Tctn2 and Cc2d2a mutants, placing TMEM231-dependent cilia function upstream of HH signaling in facial midline development. Mouse knockout genetics, HH pathway activity reporters, cell death assays, genetic epistasis with Ptch1 eLife Medium 34672258
2022 TMEM138 interacts reciprocally with TMEM231 (co-immunoprecipitation), and the ciliary localization of TMEM231 is altered in Tmem138 knockout mouse photoreceptors, demonstrating that TMEM138 is required for proper TMEM231 localization at the photoreceptor connecting cilium. Reciprocal co-immunoprecipitation, mouse knockout with immunofluorescence localization of TMEM231 Proceedings of the National Academy of Sciences of the United States of America Medium 35394880
2023 TMEM231 interacts with caveolin 1 at the transition zone, and this interaction can be perturbed by exogenous galectin 8. As cilia elongate in response to galectin 8, TMEM231 transitions from the TZ to the growing axoneme, indicating that the TMEM231–caveolin 1 interaction is part of the lipid-raft-dependent diffusion barrier mechanism at the transition zone. Co-immunoprecipitation, live imaging of cilia elongation, exogenous recombinant galectin 8 treatment, caveolin 1 knockout FASEB journal Medium 37997673
2021 Loss of TMEM231 expression (splice site variants causing exon 5 deletion and mRNA degradation) results in near-complete absence of primary cilia in human kidney tissue, as shown by immunofluorescence on fetal kidney samples from a Meckel syndrome patient. Patient kidney tissue immunofluorescence, RT-PCR, cDNA TA-cloning sequencing to confirm splice defect Frontiers in genetics Low 37736303

Source papers

Stage 0 corpus · 21 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2011 A ciliopathy complex at the transition zone protects the cilia as a privileged membrane domain. Nature cell biology 286 22179047
2016 MKS5 and CEP290 Dependent Assembly Pathway of the Ciliary Transition Zone. PLoS biology 108 26982032
2015 TMEM107 recruits ciliopathy proteins to subdomains of the ciliary transition zone and causes Joubert syndrome. Nature cell biology 108 26595381
2017 Fifteen years of research on oral-facial-digital syndromes: from 1 to 16 causal genes. Journal of medical genetics 85 28289185
2015 TMEM231, mutated in orofaciodigital and Meckel syndromes, organizes the ciliary transition zone. The Journal of cell biology 81 25869670
2012 Mutations in TMEM231 cause Joubert syndrome in French Canadians. Journal of medical genetics 62 23012439
2013 Mutations in TMEM231 cause Meckel-Gruber syndrome. Journal of medical genetics 31 23349226
2020 Network study of nasal transcriptome profiles reveals master regulator genes of asthma. The Journal of allergy and clinical immunology 27 32828590
2022 Tmem138 is localized to the connecting cilium essential for rhodopsin localization and outer segment biogenesis. Proceedings of the National Academy of Sciences of the United States of America 21 35394880
2019 Long-read nanopore sequencing resolves a TMEM231 gene conversion event causing Meckel-Gruber syndrome. Human mutation 20 31663672
2020 Genetic tests aid in counseling of fetuses with cerebellar vermis defects. Prenatal diagnosis 18 32386258
2019 High Functioning Autism with Missense Mutations in Synaptotagmin-Like Protein 4 (SYTL4) and Transmembrane Protein 187 (TMEM187) Genes: SYTL4- Protein Modeling, Protein-Protein Interaction, Expression Profiling and MicroRNA Studies. International journal of molecular sciences 17 31323913
2016 TMEM231 Gene Conversion Associated with Joubert and Meckel-Gruber Syndromes in the Same Family. Human mutation 15 27449316
2017 (Pro)renin receptor (ATP6AP2) depletion arrests As4.1 cells in the G0/G1 phase thereby increasing formation of primary cilia. Journal of cellular and molecular medicine 12 28215051
2021 Ciliary Hedgehog signaling regulates cell survival to build the facial midline. eLife 8 34672258
2021 A Novel Homozygous Variant of TMEM231 in a Case With Hypoplasia of the Cerebellar Vermis and Polydactyly. Frontiers in pediatrics 6 34912761
2021 The diagnostic yield of whole exome sequencing as a first approach in consanguineous Omani renal ciliopathy syndrome patients. F1000Research 4 34354814
2023 Lipid raft interacting galectin 8 regulates primary ciliogenesis. FASEB journal : official publication of the Federation of American Societies for Experimental Biology 3 37997673
2025 Whole-exome sequencing screening for candidate genes and potential pathogenic variants associated with early-onset high myopia in 47 Chinese families. Scientific reports 2 40175531
2019 Tectocerebellar dysraphia with occipital encephalocele: a phenotypic variant of the TMEM231 gene mutation induced Joubert syndrome. Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery 2 30617574
2023 Identification of novel TMEM231 gene splice variants and pathological findings in a fetus with Meckel Syndrome. Frontiers in genetics 0 37736303