Browsing by keyword "Fragile X syndrome"
Now showing items 1-5 of 5
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Do Fragile X Syndrome and Other Intellectual Disorders Converge at Aberrant Pre-mRNA SplicingFragile X Syndrome is a neuro-developmental disorder caused by the silencing of the FMR1 gene, resulting in the loss of its protein product, FMRP. FMRP binds mRNA and represses general translation in the brain. Transcriptome analysis of the Fmr1-deficient mouse hippocampus reveals widespread dysregulation of alternative splicing of pre-mRNAs. Many of these aberrant splicing changes coincide with those found in post-mortem brain tissue from individuals with autism spectrum disorders (ASDs) as well as in mouse models of intellectual disability such as PTEN hamartoma syndrome (PHTS) and Rett Syndrome (RTT). These splicing changes could result from chromatin modifications (e.g., in FXS, RTT) and/or splicing factor alterations (e.g., PTEN, autism). Based on the identities of the RNAs that are mis-spliced in these disorders, it may be that they are at least partly responsible for some shared pathophysiological conditions. The convergence of splicing aberrations among these autism spectrum disorders might be crucial to understanding their underlying cognitive impairments.
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EGFP insertional mutagenesis reveals multiple FXR2P fibrillar states with differing ribosome association in neuronsRNA-binding proteins (RBPs) function in higher-order assemblages such as RNA granules to regulate RNA localization and translation. The Fragile X homolog FXR2P is an RBP essential for formation of neuronal Fragile X granules that associate with axonal mRNA and ribosomes in the intact brain. However, the FXR2P domains important for assemblage formation in a cellular system are unknown. Here we used an EGFP insertional mutagenesis approach to probe for FXR2P intrinsic features that influence its structural states. We tested 18 different in-frame FXR2P(EGFP) fusions in neurons and found that the majority did not impact assemblage formation. However, EGFP insertion within a 23 amino acid region of the low complexity (LC) domain induced FXR2P(EGFP) assembly into two distinct fibril states that were observed in isolation or in highly-ordered bundles. FXR2P(EGFP) fibrils exhibited different developmental timelines, ultrastructures and ribosome associations. Formation of both fibril types was dependent on an intact RNA-binding domain. These results suggest that restricted regions of the LC domain, together with the RNA-binding domain, may be important for FXR2P structural state organization in neurons.
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FMRP Links Optimal Codons to mRNA stability in Neurons [preprint]Fragile X syndrome (FXS) is caused by inactivation of the FMR1 gene and loss of encoded FMRP, an RNA binding protein that represses translation of some of its target transcripts. Here we use ribosome profiling and RNA-seq to investigate the dysregulation of translation in the mouse brain cortex. We find that most changes in ribosome occupancy on hundreds of mRNAs are largely driven by dysregulation in transcript abundance. Many downregulated mRNAs, which are mostly responsible for neuronal and synaptic functions, are highly enriched for FMRP binding targets. RNA metabolic labeling demonstrates that in FMRP-deficient cortical neurons, mRNA downregulation is caused by elevated degradation, and is correlated with codon optimality. Moreover, FMRP preferentially binds mRNAs with optimal codons, suggesting that it stabilizes such transcripts through direct interactions via the translational machinery. Finally, we show that the paradigm of genetic rescue of FXS-like phenotypes in FMRP-deficient mice by deletion of the Cpeb1 gene is mediated by restoration of steady state RNA levels and consequent rebalancing of translational homeostasis. Our data establish an essential role of FMRP in codon optimality-dependent mRNA stability as an important factor in FXS.
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Genetic Rescue of Fragile X Syndrome Links FMRP Deficiency to Codon Optimality-Dependent RNA Destabilization [preprint]Fragile X syndrome (FXS) is caused by inactivation of FMR1 gene and loss of its encoded product the RNA binding protein FMRP, which generally represses translation of its target transcripts in the brain. In mouse models of FXS (i.e., Fmr1 knockout animals; Fmr1 KO), deletion of Cpeb1, which encodes a translational activator, mitigates nearly all pathophysiologies associated with the disorder. Here we reveal unexpected wide-spread dys-regulation of RNA abundance in Fmr1 KO brain cortex and its rescue to normal levels in Fmr1/Cpeb1 double KO mice. Alteration and restoration of RNA levels are the dominant molecular events that drive the observed dys-regulation and rescue of translation as measured by whole transcriptome ribosome occupany in the brain. The RNAs down-regulated and rescued in these animal models are highly enriched for FMRP binding targets and have an optimal codon bias that would predict their stability in wild type and possible instability in FMRP knock-out brain. Indeed, whole transcriptome analysis of RNA metabolic rates demonstrates a codon optimality-dependent elevation of RNA destruction in FMRP knock-out cortical neurons. This elevated RNA destruction leads to a massive reshuffling of the identities of stabilizing versus destabilizing codons in neurons upon loss of FMRP. Our results show a widespread RNA instability in FXS, which results from the uncoupling of codon optimality, ribosome occupancy, and RNA degradation mechanisms. Re-establishment of the linkage among these events is likely required by the genetic rescue of the disorder.
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New Therapeutic Options for Fragile X SyndromePURPOSE OF REVIEW: The purpose of this review is to provide an overview of current research and clinical practice guidelines in fragile X syndrome (FXS) with regard to therapeutic approaches in the management of this condition. The authors summarize and discuss findings from relevant preclinical studies and results from clinical trials in human subjects with FXS. Additionally, we provide an outline of the basic framework for understanding and providing educational and psychosocial supports for these individuals. RECENT FINDINGS: Current treatments in FXS are largely symptom based and focused on managing associated psychiatric and behavioral co-morbidities. While data from animal studies has been promising in providing targeted treatments to correct the underlying deficits at the cellular level, there have not been as robust findings in human trials. There are several targeted treatments for FXS currently under development. SUMMARY: Individuals with FXS present with several behavioral challenges including anxiety, social withdrawal, ADHD, hyperarousal, self-injury, and aggression. Therapeutic services are often necessary, such as behavioral intervention, speech and language therapy, occupational therapy, and individualized educational support; adjunctive psychopharmacologic treatment is often helpful as well. It is important to address these symptoms and weigh the evidence for the use of medications that target the underlying neurobiology and pathophysiology of the syndrome.
