{"doi":"10.7302/6080","title":"Repeat-Associated Non-AUG Translation of CGG Repeats in Native Neuronal Function and Disease","abstract":"As much as a third of the human genome is comprised of repetitive DNA. Short tandem repeats (STRs; 2-6 base pairs per repeating unit) comprise between 1-3% of the genome and are often associated with disease upon expansion. However, little is known about the native roles played by STRs in regulating neuronal gene expression. A CGG repeat in the Fragile X messenger ribonucleoprotein 1 (FMR1) 5’ UTR is present in all humans at <55 repeats, but upon expansion to a premutation range (55-200 repeats), causes neurodegeneration in Fragile X-associated Tremor/Ataxia Syndrome (FXTAS). Toxicity of the CGG premutation expansion is linked in part to aberrant translation initiation upstream of the repeat in a process known as repeat-associated non-AUG (RAN) translation, which produces homopolymeric peptides found in inclusions in patient tissues. While RAN translation is primarily studied at expanded repeats, recent work has shown that RAN translation can occur at native repeat lengths, and therefore may have native biological functions in addition to the pathogenic one. Here, we describe three mechanisms by which CGG RAN translation may affect native gene expression and regulation. First, we show that RAN translation of native and expanded CGG repeats regulates downstream translation of the main open reading frame (mORF) of FMR1 and production of FMR1 protein (FMRP), reminiscent of an inhibitory upstream (u) ORF (uORF). Using luciferase reporters for FMR1 translation, we showed that metabotropic glutamate receptor (mGluR)-mediated activity-dependent FMRP synthesis in rodent and human neurons requires both the CGG repeat and CGG RAN initiation sites. To exploit this uORF-life regulation to therapeutic ends, we generated non-cleaving antisense oligonucleotides (ASOs) that blocked endogenous RAN translation, enhanced endogenous FMRP, suppressed repeat toxicity and prolonged survival in patient stem cell-derived neurons. These findings delineate a native function for CGG repeats and RAN translation in regulating basal and activity-dependent FMRP synthesis and demonstrate the therapeutic potential of modulating CGG RAN translation in fragile X-associated disorders. Second, we observed a +1 translational frameshift within the CGG repeat from the arginine to glycine reading frame, dependent on RNA sequence and surrounding structural features. Chimeric R/G peptides that generated by frameshifting at CGG repeats formed distinct structures than those formed by either pure arginine or glycine, and induced toxicity in cultured rodent neurons. This work suggests that CGG repeats support translational frameshifting to produce novel, chimeric peptides with distinct properties that may contribute to CGG repeat-associated toxicity in FXTAS and related disorders. Third, we demonstrated that both RAN translation and FMRP synthesis can occur through 5’ m7G cap-dependent and cap-independent mechanisms. Intriguingly, cap-independent translation is most efficient in neurons and is influenced by both repeat length and the RAN translation reading frame. Internal ribosomal entry site (IRES) activity is modestly reduced in reporters without a CGG repeat, suggesting that repeats modulate but do not alone provide the template for neuronal 5’ m7G cap-independent initiation. Together, these projects demonstrate that CGG repeats in FMR1 impact gene expression by both modulating translational initiation (through RAN translation of uORFs and by modulating IRES activity) and by influencing translational elongation (by triggering translational frameshifting). These findings support a model where short tandem repeats throughout the genome natively regulate neuronal gene expression while triggering dysregulation and neurodegeneration in the setting of a repeat expansion to elicit human neurological disease. disease.","journal":"Deep Blue (University of Michigan)","year":2022,"id":314537,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":0,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9403,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2022-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":827220,"name":"Shannon E. Wright","orcid":"0000-0002-7388-1617","position":0,"is_corresponding":true}],"reference_count":0,"raw_metadata":null,"created_at":"2026-07-19T00:33:52.047924Z","pmid":null,"pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}