P70 S6 Kinase 1-dependent alterations in cortical mRNA translation in fragile X syndrome mice
Ontology highlight
ABSTRACT: Fragile X syndrome (FXS) is caused by loss of the fragile X mental retardation protein (FMRP). The mechanism by which FMRP regulates messenger RNA (mRNA) translation remains disputed. We observed reduced ribosome footprint abundance in the majority of differentially translated genes in cortices of FXS mice, which was correlated with an increased rate of ribosome translocation that was normalized by inhibition of p70 S6 Kinase 1 (S6K1). We also show that alterations in translation efficiencies across mRNAs in FXS mouse cortices exhibit a positive to negative gradation with coding sequence length, which is prevented by the genetic reduction of S6K1. Our findings reveal the identity of dysregulated mRNAs and a molecular mechanism by which reduction of S6K1 prevents altered translation in FXS.
Project description:Translation activation of local synaptic mRNA is critical to learning and memory. Despite extensive studies on how phosphorylations of ribosome units and translation factors enable fast response to exogenous stimuli, our knowledge on molecular pathways utilized by RNA binding proteins (RBPs) to control translation of specific mRNAs remains incomplete. We have previously found that YTHDF1 regulates depolarization-induced protein synthesis by promoting translation of N6-methyladenosine (m6A)-modified transcripts. Here we report an unexpected mechanism that the stimuli-induced neuronal translation is mediated by phosphorylation of a YTHDF1-binding protein FMRP. Phosphorylation of FMRP serine 499 induced by neuronal depolarization alters the condensing behavior of prion-like protein YTHDF1. Unphosphorylated FMRP sequesters YTHDF1 away from the translation initiation complex, whereas the stimulation-induced FMRP phosphorylation releases YTHDF1 to form translational active condensates with the ribosome to activate translation of YTHDF1 target transcripts. In fragile X syndrome (FXS) models characterized with low FMRP expression, we observed YTHDF1-mediated hyperactive translation, which notably impacts FXS pathophysiology. Developmental defects in an FXS forebrain organoid model could be reversed by a selective small-molecule inhibitor of YTHDF1 which acts by suppressing its condensation in neurons. We characterized transcriptome-wide translation alterations with the inhibitor treatment in organoids and identified targets that explain alleviated FXS pathology. Our study thus reveals FMRP and its phosphorylation as an important regulator of the activity-dependent translation during neuronal development and stimulation, and identifies YTHDF1 as a potential therapeutic target for FXS in which developmental defects caused by FMRP depletion could be reversed through YTHDF1 inhibition.
Project description:Fragile X syndrome (FXS) is caused by the loss of fragile X mental retardation protein (FMRP), a translation-inhibitor RNA binding protein. The impact of FMRP-deficiency on neural function is widespread, including its regulation of adult neural stem cell (aNSC) differentiation. To assess FMRP activity, we performed ribosome profiling of aNSCs from normal and Fmr1 knockout mice, which revealed diverse gene expression changes at the mRNA and translation levels. Many mitosis and neurogenesis genes were dysregulated primarily at the mRNA level, while numerous synaptic genes were mostly dysregulated at the translation level. Translational “buffering” was also evident, whereby changes in ribosome association with mRNA is compensated by alterations in RNA abundance. Our data revealed that FMRP-regulated neurogenesis is mediated by the transcriptional factor necdin and that FMRP determines mitochondrial mRNA expression and energy homeostasis. Thus, FMRP controls diverse transcriptional and post-transcriptional gene expression programs critical for the adult neural stem cell differentiation.
Project description:Fragile X syndrome (FXS) is caused by the absence of the fragile X mental retardation protein (FMRP). We have previously generated FXS-induced pluripotent stem cells (iPSCs) from patients' fibroblasts. In this study, we aimed at unraveling the molecular phenotype of the disease. Our data revealed aberrant regulation of neural differentiation and axon guidance genes in FXS-derived neurons, which are regulated by the RE-1 silencing transcription factor (REST). Moreover, we found REST to be elevated in FXS-derived neurons. As FMRP is involved in the microRNA (miRNA) pathway we employed microRNA-array analyses and uncovered several miRNAs dysregulated in FXS-derived neurons. We found hsa-mir-382 to be down-regulated in FXS-derived neurons, and introduction of mimic-mir-382 into these neurons was sufficient to repress REST and up-regulate its axon guidance target genes. Our data link, FMRP and REST, through the miRNA pathway, and show a new aspect in the development of FXS. Affimetrix miRNA array of two WT and two fragile X syndrome derived neurons
Project description:Loss of functional fragile X mental retardation protein (FMRP) causes fragile X syndrome (FXS) and is the leading monogenic cause of autism spectrum disorders and intellectual disability. FMRP is most notably a translational repressor and is thought to inhibit translation elongation by stalling ribosomes as FMRP-bound polyribosomes from brain tissue are resistant to puromycin and nuclease treatment. Here, we present data showing that the C-terminal non-canonical RNA-binding domain of FMRP is essential and sufficient to induce puromycin-resistant mRNA•ribosome complexes. Given that stalled ribosomes can stimulate ribosome collisions and no-go mRNA decay (NGD), we tested the ability of FMRP to drive NGD of its target transcripts in neuroblastoma cells. Indeed, FMRP and ribosomal proteins, but not PABPC1, were enriched in isolated nuclease-resistant disomes compared to controls. Using siRNA knockdown and RNA-seq, we identified 16 putative FMRP-mediated NGD substrates, many of which encode proteins involved in neuronal development and function. Increased mRNA stability of the putative substrates was also observed when either FMRP was depleted or NGD was prevented via RNAi. Taken together, these data support that FMRP stalls ribosomes and can stimulate NGD in cells, albeit on a small number of transcripts, revealing an unappreciated role of FMRP that would be misregulated in FXS when FMRP is lost.
Project description: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. These results leads to a further study to profile RNA metabolism rates in Fragile X neurons.
Project description:Fragile-X Syndrome (FXS) is a multi-organ disease leading to mental retardation, macro-orchidism in males, and premature ovarian insufficiency in female carriers. FXS is also a prominent monogenic disease associated with autism spectrum disorders (ASD). FXS is typically caused by the loss of FRAGILE X-MENTAL RETARDATION 1 (FMR1) expression, which encodes for the RNA-binding protein (RBP), FMR1 (or FMRP). We report the discovery of the RNA recognition elements (RREs), binding sites, and mRNA targets for wild-type and I304N mutant FMRP isoforms as well as its paralogs, FXR1 and FXR2. RRE frequency, ratio, and distribution determine target mRNA association with FMRP. Among highly-enriched targets, we identified many genes involved in ASD and demonstrate that FMRP can affect their protein levels in cell culture, mice, and human brain. Unexpectedly, we discovered that these targets are also dysregulated in Fmr1-/- mouse ovaries, showing signs of premature follicular overdevelopment. These results indicate that FMRP targets shared signaling pathways across different cellular contexts. As it is become increasingly appreciated that signaling pathways are important to FXS and ASD, our results here provide an invaluable molecular guide towards the pursuit of novel therapeutic targets for these devastating neurological disorders. The mRNA profile of RNA recovered from FLAG-antibody immunoprecipitated FMRP was compared to the mRNA profile of the starting lysate material.
Project description:Fragile-X Syndrome (FXS) is a multi-organ disease leading to mental retardation, macro-orchidism in males, and premature ovarian insufficiency in female carriers. FXS is also a prominent monogenic disease associated with autism spectrum disorders (ASD). FXS is typically caused by the loss of FRAGILE X-MENTAL RETARDATION 1 (FMR1) expression, which encodes for the RNA-binding protein (RBP), FMR1 (or FMRP). We report the discovery of the RNA recognition elements (RREs), binding sites, and mRNA targets for wild-type and I304N mutant FMRP isoforms as well as its paralogs, FXR1 and FXR2. RRE frequency, ratio, and distribution determine target mRNA association with FMRP. Among highly-enriched targets, we identified many genes involved in ASD and demonstrate that FMRP can affect their protein levels in cell culture, mice, and human brain. Unexpectedly, we discovered that these targets are also dysregulated in Fmr1-/- mouse ovaries, showing signs of premature follicular overdevelopment. These results indicate that FMRP targets shared signaling pathways across different cellular contexts. As it is become increasingly appreciated that signaling pathways are important to FXS and ASD, our results here provide an invaluable molecular guide towards the pursuit of novel therapeutic targets for these devastating neurological disorders. PAR-CLIP profiling for wild-type and I304N mutant FMRP isoforms as well as paralogs, FXR1 and FXR2.
Project description:N6-methyladenosine (m6A) is a prevalent mRNA modification essential for post-transcriptional regulation. Fragile X syndrome (FXS), the leading genetic cause of intellectual disability, arises from FMR1 gene silencing and loss of FMRP, which has been shown to antagonize m6A readers. However, the impact of FMRP loss on transcriptome-wide m6A modifications in human FXS remains unknown. Using cortical neurons derived from healthy subjects and FXS patient-induced pluripotent stem cells, we found that FXS neurons exhibited synaptic and neuronal network defects, mirroring clinical EEG data from the same FXS patients. FMRP deficiency led to increased translation of m6A writers, resulting in transcriptome-wide hypermethylation, primarily affecting synapse-associated transcripts and increasing mRNA decay. Treatment with an m6A writer inhibitor rescued synaptic defects in FXS neurons, highlighting its therapeutic potential. Our findings uncover an epi-transcriptomic mechanism by which FMRP deficiency disrupts m6A modifications in FXS, contributing to FXS pathogenesis, and suggest a promising avenue for m6A-targeted therapies.
Project description:N6-methyladenosine (m6A) is a prevalent mRNA modification essential for post-transcriptional regulation. Fragile X syndrome (FXS), the leading genetic cause of intellectual disability, arises from FMR1 gene silencing and loss of FMRP, which has been shown to antagonize m6A readers. However, the impact of FMRP loss on transcriptome-wide m6A modifications in human FXS remains unknown. Using cortical neurons derived from healthy subjects and FXS patient-induced pluripotent stem cells, we found that FXS neurons exhibited synaptic and neuronal network defects, mirroring clinical EEG data from the same FXS patients. FMRP deficiency led to increased translation of m6A writers, resulting in transcriptome-wide hypermethylation, primarily affecting synapse-associated transcripts and increasing mRNA decay. Treatment with an m6A writer inhibitor rescued synaptic defects in FXS neurons, highlighting its therapeutic potential. Our findings uncover an epi-transcriptomic mechanism by which FMRP deficiency disrupts m6A modifications in FXS, contributing to FXS pathogenesis, and suggest a promising avenue for m6A-targeted therapies.
Project description:Loss of the neuronal RNA binding protein FMRP causes Fragile X Syndrome (FXS), the most common cause of inherited intellectual disability, yet it is unknown which brain regions and cell types within them contribute to disease pathophysiology. We used conditional tagging of FMRP and CLIP (cTag FMRP CLIP) to examine FMRP targets specifically in CA1 hippocampal neurons, a critical cell type for learning and memory known to have altered synaptic function in FXS. Integrating this data with analysis of ribosome-bound transcripts from the same neuronal population revealed CA1-enriched binding of autism-relevant mRNAs, and unexpected CA1-specific regulation of transcripts encoding circadian proteins.