NOMO2

NOMO2 (Nodal modulator) is a type I ER-resident transmembrane protein that operates within a hierarchically assembled complex with Nicalin and TMEM147, where Nicalin is the limiting factor controlling assembly and mutual stabilization of all three subunits (PMID:17261586, PMID:20538592). Through this Nicalin-NOMO complex, NOMO antagonizes Nodal/TGF-beta signaling during vertebrate mesendoderm patterning, with combined overexpression in zebrafish producing cyclopia and knockdown expanding anterior axial mesendoderm (PMID:15257293). Beyond signaling, NOMO is a structural element of a ~360 kDa ribosome-associated translocon assembled around Sec61, TMCO1, CCDC47, Nicalin, and TMEM147 that engages multi-pass membrane protein biogenesis, with loss of NOMO reducing levels of the multi-pass client EAAT1 (PMID:32820719). Its luminal architecture of consecutive immunoglobulin-like domains forms a 'beads on a string' structure that sets ER intermembrane distance and maintains ER sheet morphology; NOMO depletion collapses ER morphology, generates LAMP1-positive holes, and triggers autophagy markers, placing it in the ER-shaping network alongside Atlastin2 and Climp63 (PMID:34224731). A critical interface between distal Ig domains allows NOMO to bear single-piconewton-range forces and act as a mechanical element required for myogenesis, with interface mutants failing to rescue C2C12 differentiation (PMID:40663102). In zebrafish, loss of nomo causes chondrodysplasia with downregulation of cartilage and skeletal developmental genes, identifying NOMO as a positive regulator of chondrogenesis-related transcription in vivo (PMID:30539698).

1. 2004 High

   Established the first function for NOMO by showing it partners with Nicalin to antagonize Nodal/TGF-beta signaling, explaining a developmental patterning role that was previously unknown.

   Evidence Zebrafish ectopic expression and morpholino knockdown, cell-based Nodal/Activin reporter assay, epistasis with Lefty

   PMID:15257293

   Open questions at the time

   • Molecular mechanism by which the complex inhibits Nodal signaling not defined
   • Direct biochemical interaction with pathway receptors not shown
2. 2007 Medium

   Resolved how the Nicalin-NOMO complex is built and maintained, showing Nicalin governs assembly and post-transcriptionally stabilizes NOMO, which is otherwise produced in excess and degraded.

   Evidence RNAi knockdown and overexpression with Western blot analysis of post-transcriptional regulation at the ER

   PMID:17261586

   Open questions at the time

   • Degradation pathway for unassembled NOMO not identified
   • Stoichiometry of the complex not determined
3. 2010 High

   Expanded the complex to include TMEM147 as a core component and demonstrated hierarchical assembly beginning with a Nicalin-NOMO intermediate.

   Evidence Affinity purification with mass spectrometry, reciprocal knockdown/overexpression, ER localization

   PMID:20538592

   Open questions at the time

   • Functional contribution of TMEM147 to NOMO activity not dissected
   • Structural arrangement of the trimeric complex unresolved at this stage
4. 2020 High

   Placed NOMO within a defined ~360 kDa translocon and assigned it a role in multi-pass membrane protein biogenesis, moving it from a signaling modulator to a biogenesis machine component.

   Evidence Cryo-EM, ribosome co-purification, high-throughput mRNA sequencing, genetic knockout with EAAT1 client readout

   PMID:32820719

   Open questions at the time

   • Specific catalytic or substrate-handling step performed by NOMO not defined
   • Client repertoire dependent specifically on NOMO not fully mapped
5. 2021 High

   Defined the structural basis by which NOMO maintains ER morphology, showing its luminal Ig-domain array sets intermembrane distance and that depletion collapses ER sheets and triggers autophagy.

   Evidence Overexpression, siRNA depletion, live-cell imaging, in vitro reconstitution with domain insertion, epistasis with Atlastin2 and Climp63

   PMID:34224731

   Open questions at the time

   • Whether ER-shaping and translocon roles are coupled or separable not resolved
   • Mechanism linking ER collapse to autophagy induction unknown
6. 2018 Medium

   Connected NOMO to skeletal development in vivo, showing it positively regulates chondrogenesis-related gene expression and is required to prevent chondrodysplasia.

   Evidence CRISPR/Cas9 knockout in zebrafish, whole-mount in situ hybridization, qRT-PCR, alcian staining

   PMID:30539698

   Open questions at the time

   • Mechanism linking NOMO loss to downregulation of sox9/dlx/col genes not established
   • Whether this reflects the Nodal, translocon, or ER-shaping role unclear
7. 2025 High

   Demonstrated that NOMO is a mechanical force-bearing element of the ER, identifying an Ig-domain interface that bears piconewton forces and is required for myogenesis across species.

   Evidence FRET-based tension sensors, Ig-domain interface mutagenesis, C2C12 myogenesis rescue, C. elegans motility loss-of-function

   PMID:40663102

   Open questions at the time

   • Source and direction of the forces NOMO bears not fully defined
   • How mechanosensing feeds into muscle differentiation signaling unknown
8. 2025 Low

   Began linking NOMO to cancer therapy resistance by placing it upstream of Chk2-pathway activation and apoptosis sensitization in lung cancer cells.

   Evidence siRNA knockdown, viability and apoptosis assays, antibody array for phospho-kinase profiling

   PMID:41151896

   Open questions at the time

   • Single siRNA approach without mechanistic rescue
   • Direct link between NOMO and Chk1/Chk2 phosphorylation not established
   • Semi-quantitative antibody array readout

• How NOMO's distinct activities—Nodal antagonism, translocon participation, ER shaping, and mechanosensing—are integrated or specified in different tissues remains unresolved.
• Whether one structural property underlies all functions or they are separable is unknown
• Tissue-specific partner requirements not defined
• Functional distinctions among NOMO1/2/3 paralogs not characterized