LYAR

LYAR is a nucleolar zinc finger protein that couples ribosomal DNA transcription, chromatin remodeling, and transcription factor activity to cell growth and differentiation. It promotes rDNA transcription by recruiting BRD2–KAT7 and BRD4–KAT7 complexes to rDNA loci via association with upstream binding factor (UBF), increasing local histone H3 and H4 acetylation without affecting rDNA methylation or RNA Pol I subunit occupancy (PMID:31504794). LYAR also functions as a sequence-specific transcription factor at gene promoters (LGALS1, FSCN1, Aγ-globin), forms a complex with PRMT5 to suppress oxidative stress genes downstream of N-Myc (PMID:28686580, PMID:26413750, PMID:35069968), negatively regulates IFN-β innate immune signaling by binding phosphorylated IRF3 and impairing its DNA-binding capacity (PMID:31413131), and its loss activates the p53–p21 growth arrest pathway and impairs multi-lineage embryonic differentiation and preimplantation inner cell mass specification (PMID:22815056, PMID:41938621, PMID:41404914).

1. 1993 High

   Identification of LYAR as a nucleolar zinc finger protein whose overexpression drives tumorigenesis established that a previously unknown nucleolar factor could directly promote cell growth.

   Evidence cDNA cloning, immunolocalization to nucleolus, retroviral overexpression with nude mouse tumor assay in fibroblasts

   PMID:8491376

   Open questions at the time

   • DNA-binding target sites were not identified
   • Mechanism linking nucleolar localization to growth promotion was unknown
   • Endogenous loss-of-function phenotype not tested
2. 2012 Medium

   Gene-trap mutagenesis revealed that LYAR loss activates p53–p21 growth arrest and genetically interacts with p53 in neural tube closure, providing the first endogenous loss-of-function evidence that LYAR is required for normal growth and development.

   Evidence Gene-trap mutant MEFs with Western blot for p53/p21; compound Lyar/p53 mutant mice exhibiting exencephaly

   PMID:22815056

   Open questions at the time

   • Molecular link between LYAR loss and p53 stabilization was not defined
   • Single lab; independent confirmation in other mouse models not available
   • Whether nucleolar stress mediates the p53 response was untested
3. 2014 Medium

   Discovery that LYAR associates with 60S ribosomal subunits and stimulates translation in vitro extended its functional repertoire beyond transcription to translational control.

   Evidence Proteomic survey, subcellular fractionation and ultracentrifugation in rodent testis and cancer cells, in vitro translation assay

   PMID:24990247

   Open questions at the time

   • No ribosome profiling or in vivo translation data
   • Specificity of LYAR effect on particular mRNAs not addressed
   • Single lab finding without independent replication
4. 2015 Medium

   ChIP and reporter assays demonstrated that LYAR functions as a transcription factor at the LGALS1 promoter, establishing its role in transcriptional regulation of migration-related genes in colorectal cancer.

   Evidence ChIP, gene reporter assay, siRNA knockdown with rescue by ectopic galectin-1 in colorectal cancer cells

   PMID:26413750

   Open questions at the time

   • Genome-wide binding profile of LYAR was not determined
   • Whether LYAR activates LGALS1 in non-cancer contexts was unclear
   • Direct DNA-binding motif specificity not fully defined
5. 2017 High

   Placing LYAR downstream of N-Myc and in complex with PRMT5, with epistatic rescue by antioxidant treatment and CHAC1 knockdown, defined a pathway through which LYAR suppresses oxidative stress to maintain neuroblastoma cell viability.

   Evidence N-Myc ChIP on LYAR promoter, LYAR–PRMT5 co-IP, genome-wide expression profiling, NAC and CHAC1 siRNA rescue in neuroblastoma cells

   PMID:28686580

   Open questions at the time

   • Direct LYAR–PRMT5 target genes on chromatin were not mapped
   • Whether PRMT5 catalytic activity is required for LYAR function was not tested
   • Relevance outside neuroblastoma not demonstrated
6. 2018 High

   Demonstration that LYAR directly recruits BRD2 to the Nanog promoter via a specific interaction domain, and that this is required for proper differentiation kinetics, revealed a chromatin-recruitment mechanism linking LYAR to lineage specification.

   Evidence ChIP, domain deletion mutagenesis of Lyar, BET inhibitor treatment, differentiation assays in ESCs

   PMID:29505757

   Open questions at the time

   • Whether BRD2 recruitment by LYAR extends genome-wide beyond Nanog was unknown
   • Structural basis of the LYAR–BRD2 interaction was not resolved
   • Relationship to the rDNA-specific BRD2 recruitment discovered later was not yet connected
7. 2018 High

   Identification of LYAR as a host factor that interacts with influenza A vRNP subunits and enhances vRNP assembly revealed an unexpected role for this nucleolar protein in viral RNA replication.

   Evidence AP-MS, co-IP, subcellular fractionation showing LYAR relocalization, viral RNA synthesis assays upon LYAR knockdown

   PMID:30209172

   Open questions at the time

   • Specific vRNP subunit interface with LYAR was not mapped
   • Whether LYAR supports replication of other RNA viruses was not tested
   • Mechanism of LYAR nucleolar-to-nucleoplasm translocation upon infection not defined
8. 2019 High

   Comprehensive mechanistic dissection showed that LYAR recruits both BRD2–KAT7 and BRD4–KAT7 acetyltransferase complexes to rDNA via UBF, selectively enhancing H3/H4 acetylation and rRNA transcription — resolving how LYAR promotes ribosome biogenesis at the chromatin level.

   Evidence Co-IP, ChIP-seq, ChIP-qPCR, siRNA knockdown, histone modification analysis, rRNA synthesis assay

   PMID:31504794

   Open questions at the time

   • Structural basis of LYAR–UBF and LYAR–BRD4 interactions not resolved
   • Whether this mechanism operates in all cell types or is context-dependent was not examined
   • Connection between local histone acetylation changes and RNA Pol I processivity was not directly tested
9. 2019 High

   Discovery that LYAR binds phosphorylated IRF3 and suppresses IFN-β transcription and NF-κB signaling defined LYAR as a negative regulator of innate antiviral immunity, extending its function beyond growth and ribosome biogenesis.

   Evidence Co-IP of LYAR with phospho-IRF3, reporter assays, siRNA knockdown, viral infection assays

   PMID:31413131

   Open questions at the time

   • Whether LYAR–IRF3 interaction is direct or bridged was not fully resolved
   • In vivo immune phenotype of LYAR loss was not tested
   • Relationship between innate immune suppression and LYAR's nucleolar functions unclear
10. 2019 Medium

    Biophysical characterization of LYAR binding to the 5′-GGTTAT-3′ motif in the Aγ-globin 5′-UTR, disrupted by rs368698783, provided quantitative evidence for sequence-specific DNA recognition by LYAR and its potential relevance to hemoglobin regulation.

    Evidence Surface plasmon resonance with recombinant and endogenous LYAR, molecular docking

    PMID:31300855

    Open questions at the time

    • Functional consequence of LYAR binding on Aγ-globin expression was not tested in cells
    • Clinical significance of rs368698783 was not established
    • Whether this motif represents a general LYAR recognition sequence genome-wide was not addressed
11. 2021 Medium

    Identification of FSCN1 as a direct LYAR transcriptional target linked LYAR-driven tumor migration to fatty acid metabolism through downstream regulation of FASN and SCD.

    Evidence Microarray, ChIP, reporter assay, siRNA knockdown with rescue, xenograft in colorectal cancer cells

    PMID:35069968

    Open questions at the time

    • Whether LYAR directly regulates FASN/SCD or acts solely via FSCN1 was not distinguished
    • Metabolomic confirmation of fatty acid changes upon LYAR manipulation was not provided
    • Single lab; independent validation needed
12. 2026 Medium

    CRISPR knockout of Lyar in mouse ESCs confirmed p53–p21 activation and further demonstrated that LYAR is required for multi-lineage (mesoderm, endoderm, ectoderm) differentiation capacity, while preimplantation studies showed LYAR-dependent rRNA synthesis is critical for inner cell mass specification.

    Evidence CRISPR/Cas9 KO in ESCs with cell cycle/apoptosis analysis, embryoid body differentiation, and siRNA microinjection at pronuclear/2-cell stage with EU staining for nascent rRNA

    PMID:41404914 PMID:41938621

    Open questions at the time

    • Both studies from single labs; independent replication pending
    • Whether p53 activation upon LYAR loss is a direct nucleolar stress response or indirect was not determined
    • Transcriptomic or epigenomic changes at rDNA loci in LYAR-null embryos were not profiled

• A structural model of LYAR's zinc finger domain bound to DNA, and a unified understanding of how its nucleolar, transcriptional, and immune-regulatory functions are coordinated across cell types, remain unresolved.
• No crystal or cryo-EM structure of LYAR or its complexes is available
• Genome-wide LYAR ChIP-seq in multiple cell types has not been reported
• Whether the p53 activation upon LYAR loss reflects nucleolar stress signaling has not been formally tested