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Fragile X Syndrome (FXS) presents with a constellation of phenotypes, including trouble regulating emotion and aggressive behaviors, disordered sleep, intellectual impairments, and atypical physical development. Genetic study of the X chromosome revealed that substantial repeat expansion of the 5′ end of the gene fragile X messenger ribonucleoprotein 1 (FMR1) promoted DNA methylation and, consequently, silenced expression of FMR1. Further analysis proved that shorter repeat expansions in FMR1 also manifested in disease at later stages in life. Treatment and therapy options do exist, but they only manage symptoms. Up to now, no cure for FMR1 disorders exists. In this review, we aim to provide an overview of FMR1 biology and the latest research focused on developing therapeutic interventions that can potentially prevent and/or reverse FXS. [ABSTRACT FROM AUTHOR]

Accumulating studies reveal that m6A RNA methylation plays a critical role in cancer pathogenesis and progression. METTL3 as a m6A methyltransferase acts as an oncogene in multiple malignancies including hepatocellular carcinoma (HCC). However, the role and underlying mechanism by which METTL3 contributes to HCC remains unclear. The association of METTL3 expression with clinicopathological characteristics and prognosis in patients with HCC was assessed by reverse transcription polymerase chain reaction, Western blot, and public TCGA dataset. MTT, colony formation, Transwell assays, and xenograft tumor models were executed to reveal the role of METTL3 in HCC. m6A dot blot, RNA immunoprecipitation (RIP), m6A methylated RIP, and Western blot assays were used to uncover the regulatory mechanism of METTL3 in HCC cells. We found that METTL3 was dramatically upregulated in HCC tissue samples and acted as an independent prognostic factor for poor survival and tumor recurrence in patients with HCC. Silencing of METTL3 repressed cell growth and invasion in vitro and in vivo, but restored expression of METTL3 boosted these effects. Mechanistical investigations revealed that METTL3 could directly interact with FMRP and harbor a positive correlation with FMRP expression. Knockdown of METTL3 reduced FMRP m6A levels as well as its mRNA and protein expression. FMRP overexpression drove cell colony formation and cell invasion and abolished METTL3 knockdown-induced antitumor effects and AKT/mTORC1 signaling inactivation. Elevated expression of FMRP could act as an independent prognostic factor for poor survival and tumor recurrence in patients with HCC. Our findings demonstrate that METTL3-mediated m6A modification of FMRP promotes growth and invasion of HCC cells and may provide a promising therapeutic target for HCC. [ABSTRACT FROM AUTHOR]

Circular RNAs (circRNAs) are covalently closed RNA molecules widely expressed in eukaryotes and deregulated in several pathologies, including cancer. Many studies point to their activity as microRNAs (miRNAs) and protein sponges; however, we propose a function based on circRNA-mRNA interaction to regulate mRNA fate. We show that the widely tumor-associated circHIPK3 directly interacts in vivo with the BRCA1 mRNA through the back-splicing region in human cancer cells. This interaction increases BRCA1 translation by competing for the binding of the fragile-X mental retardation 1 protein (FMRP) protein, which we identified as a BRCA1 translational repressor. CircHIPK3 depletion or disruption of the circRNA-mRNA interaction decreases BRCA1 protein levels and increases DNA damage, sensitizing several cancer cells to DNA-damage-inducing agents and rendering them susceptible to synthetic lethality. Additionally, blocking FMRP interaction with BRCA1 mRNA with locked nucleic acid (LNA) restores physiological protein levels in BRCA1 hemizygous breast cancer cells, underscoring the importance of this circRNA-mRNA interaction in regulating DNA-damage response. [Display omitted] • circHIPK3 and FMRP compete for a direct site-specific binding to the BRCA1 mRNA • circHIPK3 promotes BRCA1 expression, preventing FMRP-mediated translational inhibition • circHIPK3- BRCA1 interaction disruption sensitizes cancer cells to DNA-damaging drugs • FMRP- BRCA1 -binding disruption restores normal BRCA1 levels in BRCA1 hemizygous cells Grelloni et al. demonstrate that the tumor-associated circular RNA circHIPK3 and the RNA-binding protein FMRP compete for site-specific binding to the BRCA1 mRNA. CircHIPK3, by interacting with the BRCA1 transcript, prevents FMRP-mediated translational inhibition, thereby increasing BRCA1 protein levels. These interactions represent novel therapeutic targets to modulate BRCA1 levels. [ABSTRACT FROM AUTHOR]

Fragile X Syndrome (FXS) is the most common inherited form of intellectual disability and is caused by mutations in the gene encoding the Fragile X messenger ribonucleoprotein (FMRP). FMRP is an evolutionarily conserved and neuronally enriched RNA-binding protein (RBP) with functions in RNA editing, RNA transport, and protein translation. Specific target RNAs play critical roles in neurodevelopment, including the regulation of neurite morphogenesis, synaptic plasticity, and cognitive function. The different biological functions of FMRP are modulated by its cooperative interaction with distinct sets of neuronal RNA and protein-binding partners. Here, we focus on interactions between FMRP and components of the microRNA (miRNA) pathway. Using the Drosophila S2 cell model system, we show that the Drosophila ortholog of FMRP (dFMRP) can repress translation when directly tethered to a reporter mRNA. This repression requires the activity of AGO1, GW182, and MOV10/Armitage, conserved proteins associated with the miRNA-containing RNA-induced silencing complex (miRISC). Additionally, we find that untagged dFMRP can interact with a short stem-loop sequence in the translational reporter, a prerequisite for repression by exogenous miR-958. Finally, we demonstrate that dFmr1 interacts genetically with GW182 to control neurite morphogenesis. These data suggest that dFMRP may recruit the miRISC to nearby miRNA binding sites and repress translation via its cooperative interactions with evolutionarily conserved components of the miRNA pathway.

This study aimed to determine the association between severity of autism spectrum disorder (ASD) and cognitive, behavioral, and molecular measures in individuals with fragile X syndrome (FXS). Study inclusion criteria included individuals with FXS and (1) age 6-40 years, (2) full-scale IQ

Transplantation of bone marrow mesenchymal stem cells (BMSCs) represents an encouraging strategy for the repair of spinal cord injury (SCI), however, its effectiveness on treating SCI remains controversial. Bilobalide isolated from Ginkgo biloba leaves shows significant neuroprotective effects. We examined the role and underlying mechanism of bilobalide in the efficacy of BMSC transplantation on SCI. Primary BMSCs were isolated from neonatal rats, and cell viability was assessed by MTT assay. Neuronal markers (MAP-2, NeuN, NSE and Tuj1), autophagy markers (LC3 and Beclin1), and Fragile X mental retardation protein (FMRP)/With-no-lysine kinase-1 (WNK1) signaling were measured using RT-qPCR and western blotting. The relationship of FMRP and WNK1 was estimated by RNA immunoprecipitation, while WNK1 mRNA stability was assessed with actinomycin D assay. In a SCI rat model, tissue injury was examined using HE and Nissl staining. Bilobalide treatment facilitated neural differentiation of BMSCs, as well as enhanced autophagy and inhibited WNK1 signaling. The promotive effect of bilobalide on BMSC differentiation was antagonized when overexpressing WNK1 or inhibiting autophagy. Bilobalide upregulated FMRP to promote WNK1 mRNA decay, thus reducing WNK1 expression. FMRP knockdown reversed the promoted functions of bilobalide on autophagy and neuronal differentiation in BMSCs. Additionally, compared to either monotherapy, simultaneous treatments with bilobalide and BMSCs further facilitated autophagy and neuronal differentiation, thereby enhancing the repair of SCI in rats. Bilobalide enhances autophagy activity to promote BMSC neuronal differentiation via FMRP/WNK1 axis, thus improving functional recovery following SCI, which indicates a promising therapeutic approach for SCI. [ABSTRACT FROM AUTHOR]

Fragile X mental retardation protein (FMRP) is a translational repressor encoded by FMR1. It targets bone morphogenetic protein receptor type II (BMPR2), which regulates granulosa cell (GC) function and follicle development. However, whether this interaction affects folliculogenesis remains unclear. Therefore, this study investigated the potential effect of FMRP-BMPR2 dysregulation in ovarian reserves and infertility. COV434 cells and patient-derived GCs were used to evaluate FMRP and BMPR2 expression. Similarly, FMR1, BMPR2, LIMK1, and SMAD expression were evaluated in GCs with normal (NOR) and poor (POR) ovarian responses. FMRP and BMPR2 were expressed in both cell types. They were co-localized to the nuclear membrane of COV434 cells and cytoplasm of primary GCs. FMR1 silencing increased the mRNA and protein levels of BMPR2. However, the mRNA levels of FMR1 and BMPR2 were significantly lower in the POR group. FMR1 and BMPR2 levels were strongly positively correlated in the NOR group but weakly correlated in the POR group. Additionally, SMAD9 expression was significantly reduced in the POR group. This study highlights the crucial role of FMR1/FMRP in the regulation of BMPR2 expression and its impact on ovarian function. These findings indicate that the disruption of FMRP-BMPR2 interactions may cause poor ovarian responses and infertility. [ABSTRACT FROM AUTHOR]

Ubiquitination is one of the most conserved post-translational modifications and together with mRNA translation contributes to cellular protein homeostasis (proteostasis). Temporal and spatial regulation of proteostasis is particularly important during synaptic plasticity, when translation of specificmRNAs requires tight regulation. Mutations in genes encoding regulators of mRNA translation and in ubiquitin ligases have been associated with several neurodevelopmental disorders. RNA metabolism and translation are regulated by RNA-binding proteins, critical for the spatial and temporal control of translation in neurons. Several ubiquitin ligases also regulate RNA-dependent mechanisms in neurons, with numerous ubiquitination events described in splicing factors and ribosomal proteins. Here we will explore how ubiquitination regulates translation in neurons, from RNA biogenesis to alternative splicing and how dysregulation of ubiquitin signaling can be the underlying cause of pathology in neurodevelopmental disorders, such as Fragile X syndrome. Finally we propose that targeting ubiquitin signaling is an attractive novel therapeutic strategy for neurodevelopmental disorders where mRNA translation and ubiquitin signaling are disrupted. [ABSTRACT FROM AUTHOR]

Perineuronal nets (PNNs) are mesh‐like structures on the surfaces of parvalbumin‐expressing inhibitory and other neurons, and consist of proteoglycans such as aggrecan, brevican, and neurocan. PNNs regulate the Excitatory/Inhibitory (E/I) balance in the brain and are formed at the closure of critical periods of plasticity during development. PNN formation is disrupted in Fragile X Syndrome, which is caused by silencing of the fragile X messenger ribonucleoprotein 1 (Fmr1) gene and loss of its protein product FMRP. FXS is characterized by impaired synaptic plasticity resulting in neuronal hyperexcitability and E/I imbalance. Here, we investigate how PNN formation is altered in FXS. PNNs are reduced in Fmr1 KO mouse brain when examined by staining for the lectin Wisteria floribunda agglutin (WFA) and aggrecan. Examination of PNNs by WFA staining at P14 and P42 in the hippocampus, somatosensory cortex, and retrosplenial cortex shows that they were reduced in these brain regions at P14 but mostly less so at P42 in Fmr1 KO mice. However, some differential FMRP regulation of PNN development in these brain regions persists, perhaps caused by asynchrony in PNN development between brain regions in wild‐type animals. During development, aggrecan PNN levels in the brain were reduced in all brain regions in Fmr1 KO mice. Aggrecan mRNA levels were unchanged at these times, suggesting that FMRP is normally an activator of aggrecan mRNA translation. This hypothesis is buttressed by the observations that FMRP binds aggrecan mRNA and that ribosome profiling data show that aggrecan mRNA is associated with reduced numbers of ribosomes in Fmr1 KO mouse brain, indicating reduced translational efficiency. Moreover, aggrecan mRNA poly(A) tail length is also reduced in Fmr1 KO mouse brain, suggesting a relationship between polyadenylation and translational control. We propose a model where FMRP modulates PNN formation through translational up‐regulation of aggrecan mRNA polyadenylation and translation. [ABSTRACT FROM AUTHOR]

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Fragile X syndrome (FXS), the most frequent monogenic form of intellectual disability, is caused by transcriptional silencing of the FMR1 gene that could render neuronal hyperexcitability. Here we show that pyramidal cells (PCs) in the dorsal CA1 region of the hippocampus elicited a larger action potential (AP) number in response to suprathreshold stimulation in juvenile Fmr1 knockout (KO) than wild‐type (WT) mice. Because Kv7/M channels modulate CA1 PC excitability in rats, we investigated if their dysfunction produces neuronal hyperexcitability in Fmr1 KO mice. Immunohistochemical and western blot analyses showed no differences in the expression of Kv7.2 and Kv7.3 channel subunits between genotypes; however, the current mediated by Kv7/M channels was reduced in Fmr1 KO mice. In both genotypes, bath application of XE991 (10 μM), a blocker of Kv7/M channels: produced an increased AP number, produced an increased input resistance, produced a decreased AP voltage threshold and shaped AP medium afterhyperpolarization by increasing mean velocities. Retigabine (10 μM), an opener of Kv7/M channels, produced opposite effects to XE991. Both XE991 and retigabine abolished differences in all these parameters found in control conditions between genotypes. Furthermore, a low concentration of retigabine (2.5 μM) normalized CA1 PC excitability of Fmr1 KO mice. Finally, ex vivo seizure‐like events evoked by 4‐aminopyiridine (200 μM) in the dorsal CA1 region were more frequent in Fmr1 KO mice, and were abolished by retigabine (5–10 μM). We conclude that CA1 PCs of Fmr1 KO mice exhibit hyperexcitability, caused by Kv7/M channel dysfunction, and increased epileptiform activity, which were abolished by retigabine. Key points: Dorsal pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice exhibit hyperexcitability.Kv7/M channel activity, but not expression, is reduced in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice.Kv7/M channel dysfunction causes hyperexcitability in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice by increasing input resistance, decreasing AP voltage threshold and shaping medium afterhyperpolarization.A Kv7/M channel opener normalizes neuronal excitability in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice.Ex vivo seizure‐like events evoked in the dorsal CA1 region were more frequent in Fmr1 KO mice, and such an epileptiform activity was abolished by a Kv7/M channel opener depending on drug concentration.Kv7/M channels may represent a therapeutic target for treating symptoms associated with hippocampal alterations in fragile X syndrome. [ABSTRACT FROM AUTHOR]

Ferroptosis is a unique modality of regulated cell death that is driven by iron-dependent phospholipid peroxidation. N6-methyladenosine (m6A) RNA modification participates in varieties of cellular processes. However, it remains elusive whether m6A reader Fragile X Mental Retardation Protein (FMRP) are involved in the modulation of ferroptosis in breast cancer (BC). In this study, we found that FMRP expression was elevated and associated with poor prognosis and pathological stage in BC patients. Overexpression of FMRP induced ferroptosis resistance and exerted oncogenic roles by positively regulating a critical ferroptosis defense gene SLC7A11. Mechanistically, upregulated FMRP catalyzes m6A modification of SLC7A11 mRNA and further influences the SLC7A11 translation through METTL3-dependent manner. Further studies revealed that FMRP interacts with splicing factor hnRNPM to recognize the splice site and then modulated the exon skip splicing event of SLC7A11 transcript. Interestingly, SLC7A11-S splicing variant can effectively promote FMRP overexpression-induced ferroptosis resistance in BC cells. Moreover, our clinical data suggested that FMRP/hnRNPM/SLC7A11 expression were significantly increased in the tumor tissues, and this signal axis was important evaluation factors closely related to the worse survival and prognosis of BC patients. Overall, our results uncovered a novel regulatory mechanism by which high FMRP expression protects BC cells from undergoing ferroptosis. Targeting the FMRP–SLC7A11 axis has a dual effect of inhibiting ferroptosis resistance and tumor growth, which could be a promising therapeutic target for treating BC.

Motor skill learning induces changes in synaptic structure and function in the primary motor cortex (M1). In the fragile X syndrome (FXS) mouse model an impairment in motor skill learning and associated formation of new dendritic spines was previously reported. However, whether modulation of synaptic strength through trafficking of AMPA receptors (AMPARs) with motor skill training is impaired in FXS is not known. Here, we performed in vivo imaging of a tagged AMPA receptor subunit, GluA2, in layer (L)2/3 neurons in the primary motor cortex of wild-type (WT) and Fmr1 knock-out (KO) male mice at different stages of learning a single forelimb-reaching task. Surprisingly, in the Fmr1 KO mice, despite impairments in learning there was no deficit in motor skill training-induced spine formation. However, the gradual accumulation of GluA2 in WT stable spines, which persists after training is completed and past the phase of spine number normalization, is absent in the Fmr1 KO mouse. These results demonstrate that motor skill learning not only reorganizes circuits through formation of new synapses, but also strengthens existing synapses through accumulation of AMPA receptors and GluA2 changes are better associated with learning than new spine formation.

Fragile X syndrome (FXS) is caused by epigenetic silencing of the X-linked fragile X messenger ribonucleoprotein 1 (FMR1) gene located on chromosome Xq27.3, which leads to the loss of its protein product, fragile X messenger ribonucleoprotein (FMRP). It is the most prevalent inherited form of intellectual disability and the highest single genetic cause of autism. Since the discovery of the genetic basis of FXS, extensive studies using animal models and human pluripotent stem cells have unveiled the functions of FMRP and mechanisms underlying FXS. However, clinical trials have not yielded successful treatment. Here we review what we have learned from commonly used models for FXS, potential limitations of these models, and recommendations for future steps. [ABSTRACT FROM AUTHOR]

Ubiquitination is one of the most conserved post-translational modifications and together with mRNA translation contributes to cellular protein homeostasis (proteostasis). Temporal and spatial regulation of proteostasis is particularly important during synaptic plasticity, when translation of specific mRNAs requires tight regulation. Mutations in genes encoding regulators of mRNA translation and in ubiquitin ligases have been associated with several neurodevelopmental disorders. RNA metabolism and translation are regulated by RNA-binding proteins, critical for the spatial and temporal control of translation in neurons. Several ubiquitin ligases also regulate RNA-dependent mechanisms in neurons, with numerous ubiquitination events described in splicing factors and ribosomal proteins. Here we will explore how ubiquitination regulates translation in neurons, from RNA biogenesis to alternative splicing and how dysregulation of ubiquitin signaling can be the underlying cause of pathology in neurodevelopmental disorders, such as Fragile X syndrome. Finally we propose that targeting ubiquitin signaling is an attractive novel therapeutic strategy for neurodevelopmental disorders where mRNA translation and ubiquitin signaling are disrupted.

This study contributes to a greater understanding of the utility of molecular biomarkers to identify clinical phenotypes of fragile X syndrome (FXS). Correlations of baseline clinical trial data (molecular measures-FMR1 mRNA, CYFIP1 mRNA, MMP9 and FMRP protein expression levels, nonverbal IQ, body mass index and weight, language level, NIH Toolbox, adaptive behavior rating, autism, and other mental health correlates) of 59 participants with FXS ages of 6-32 years are reported. FMR1 mRNA expression levels correlated positively with adaptive functioning levels, expressive language, and specific NIH Toolbox measures. The findings of a positive correlation of MMP-9 levels with obesity, CYFIP1 mRNA with mood and autistic symptoms, and FMR1 mRNA expression level with better cognitive, language, and adaptive functions indicate potential biomarkers for specific FXS phenotypes. These may be potential markers for future clinical trials for targeted treatments of FXS.

Fragile X Syndrome (FXS) is the best-known form of inherited intellectual disability caused by the loss-of-function mutation in a single gene. The FMR1 gene mutation abolishes the expression of Fragile X Messenger Ribonucleoprotein (FMRP), which regulates the expression of many synaptic proteins. Cortical pyramidal neurons in postmortem FXS patient brains show abnormally high density and immature morphology of dendritic spines; this phenotype is replicated in the Fmr1 knockout (KO) mouse. While FMRP is well-positioned in the dendrite to regulate synaptic plasticity, intriguing in vitro and in vivo data show that wild type neurons embedded in a network of Fmr1 KO neurons or glia exhibit spine abnormalities just as neurons in Fmr1 global KO mice. This raises the question: does FMRP regulate synaptic morphology and dynamics in a cell-autonomous manner, or do the synaptic phenotypes arise from abnormal pre-synaptic inputs? To address this question, we combined viral and mouse genetic approaches to delete FMRP from a very sparse subset of cortical layer 5 pyramidal neurons (L5 PyrNs) either during early postnatal development or in adulthood. We then followed the structural dynamics of dendritic spines on these Fmr1 KO neurons by in vivo two-photon microscopy. We found that, while L5 PyrNs in adult Fmr1 global KO mice have abnormally high density of thin spines, single-cell Fmr1 KO in adulthood does not affect spine density, morphology, or dynamics. On the contrary, neurons with neonatal FMRP deletion have normal spine density but elevated spine formation at 1 month of age, replicating the phenotype in Fmr1 global KO mice. Interestingly, these neurons exhibit elevated thin spine density, but normal total spine density, by adulthood. Together, our data reveal cell-autonomous FMRP regulation of cortical synaptic dynamics during adolescence, but spine defects in adulthood also implicate non-cell-autonomous factors.

Fragile X syndrome (FXS) is a global neurodevelopmental disorder caused by the expansion of CGG trinucleotide repeats (≥200) in the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene. FXS is the hallmark of Fragile X-associated disorders (FXD) and the most common monogenic cause of inherited intellectual disability and autism spectrum disorder. There are several animal models used to study FXS. In the FXS model of Drosophila, the only ortholog of FMR1, dfmr1, is mutated so that its protein is missing. This model has several relevant phenotypes, including defects in the circadian output pathway, sleep problems, memory deficits in the conditioned courtship and olfactory conditioning paradigms, deficits in social interaction, and deficits in neuronal development. In addition to FXS, a model of another FXD, Fragile X-associated tremor/ataxia syndrome (FXTAS), has also been established in Drosophila. This review summarizes many years of research on FXD in Drosophila models.

Abstract Fragile X syndrome (FXS) is the leading cause of inherited autism and intellectual disabilities. Aberrant protein synthesis due to the loss of fragile X messenger ribonucleoprotein (FMRP) is the major defect in FXS, leading to a plethora of cellular and behavioral abnormalities. However, no treatments are available to date. In this study, we found that activation of metabotropic glutamate receptor 7 (mGluR7) using a positive allosteric modulator named AMN082 represses protein synthesis through ERK1/2 and eIF4E signaling in an FMRP-independent manner. We further demonstrated that treatment of AMN082 leads to a reduction in neuronal excitability, which in turn ameliorates audiogenic seizure susceptibility in Fmr1 KO mice, the FXS mouse model. When evaluating the animals’ behavior, we showed that treatment of AMN082 reduces repetitive behavior and improves learning and memory in Fmr1 KO mice. This study uncovers novel functions of mGluR7 and AMN082 and suggests the activation of mGluR7 as a potential therapeutic approach for treating FXS.

Maternal microbial dysbiosis has been implicated in adverse postnatal health conditions in offspring, such as obesity, cancer, and neurological disorders. We observed that the progeny of mice fed a Westernized diet (WD) with low fiber and extra fat exhibited higher frequencies of stereotypy, hyperactivity, cranial features and lower FMRP protein expression, similar to what is typically observed in Fragile X Syndrome (FXS) in humans. We hypothesized that gut dysbiosis and inflammation during pregnancy influenced the prenatal uterine environment, leading to abnormal phenotypes in offspring. We found that oral in utero supplementation with a beneficial anti-inflammatory probiotic microbe, Lactobacillus reuteri, was sufficient to inhibit FXS-like phenotypes in offspring mice. Cytokine profiles in the pregnant WD females showed that their circulating levels of pro-inflammatory cytokine interleukin (Il)-17 were increased relative to matched gravid mice and to those given supplementary L. reuteri probiotic. To test our hypothesis of prenatal contributions to this neurodevelopmental phenotype, we performed Caesarian (C-section) births using dissimilar foster mothers to eliminate effects of maternal microbiota transferred during vaginal delivery or nursing after birth. We found that foster-reared offspring still displayed a high frequency of these FXS-like features, indicating significant in utero contributions. In contrast, matched foster-reared progeny of L. reuteri-treated mothers did not exhibit the FXS-like typical features, supporting a key role for microbiota during pregnancy. Our findings suggest that diet-induced dysbiosis in the prenatal uterine environment is strongly associated with the incidence of this neurological phenotype in progeny but can be alleviated by addressing gut dysbiosis through probiotic supplementation.

Silencing of the fragile X messenger ribonucleoprotein 1 (FMR1) gene and a consequent lack of FMR protein (FMRP) synthesis are associated with fragile X syndrome, one of the most common inherited intellectual disabilities. FMRP is a multifunctional protein that is involved in many cellular functions in almost all subcellular compartments under both normal and cellular stress conditions in neuronal and non-neuronal cell types. This is achieved through its trafficking signals, nuclear localization signal (NLS), nuclear export signal (NES), and nucleolar localization signal (NoLS), as well as its RNA and protein binding domains, and it is modulated by various post-translational modifications such as phosphorylation, ubiquitination, sumoylation, and methylation. This review summarizes the recent advances in understanding the interaction networks of FMRP with a special focus on FMRP stress-related functions, including stress granule formation, mitochondrion and endoplasmic reticulum plasticity, ribosome biogenesis, cell cycle control, and DNA damage response. [ABSTRACT FROM AUTHOR]

Fragile X syndrome (FXS) is the leading cause of inherited autism and intellectual disabilities. Aberrant protein synthesis due to the loss of fragile X messenger ribonucleoprotein (FMRP) is the major defect in FXS, leading to a plethora of cellular and behavioral abnormalities. However, no treatments are available to date. In this study, we found that activation of metabotropic glutamate receptor 7 (mGluR7) using a positive allosteric modulator named AMN082 represses protein synthesis through ERK1/2 and eIF4E signaling in an FMRP-independent manner. We further demonstrated that treatment of AMN082 leads to a reduction in neuronal excitability, which in turn ameliorates audiogenic seizure susceptibility in Fmr1 KO mice, the FXS mouse model. When evaluating the animals’ behavior, we showed that treatment of AMN082 reduces repetitive behavior and improves learning and memory in Fmr1 KO mice. This study uncovers novel functions of mGluR7 and AMN082 and suggests the activation of mGluR7 as a potential therapeutic approach for treating FXS. [ABSTRACT FROM AUTHOR]

Objective: Fragile X Syndrome (FXS) is a hereditary form of autism spectrum disorder. It is caused by a trinucleotide repeat expansion in the Fmr1 gene, leading to a loss of Fragile X Protein (FMRP) expression. The loss of FMRP causes auditory hypersensitivity: FXS patients display hyperacusis and the Fmr1‐ knock‐out (KO) mouse model for FXS exhibits auditory seizures. FMRP is strongly expressed in the cochlear nucleus and other auditory brainstem nuclei. We hypothesize that the Fmr1‐KO mouse has altered gene expression in the cochlear nucleus that may contribute to auditory hypersensitivity. Methods: RNA was isolated from cochlear nuclei of Fmr1‐KO and WT mice. Using next‐generation sequencing (RNA‐seq), the transcriptomes of Fmr1‐KO mice and WT mice (n = 3 each) were compared and analyzed using gene ontology programs. Results: We identified 270 unique, differentially expressed genes between Fmr1‐KO and WT cochlear nuclei. Upregulated genes (67%) are enriched in those encoding secreted molecules. Downregulated genes (33%) are enriched in neuronal function, including synaptic pathways, some of which are ideal candidate genes that may contribute to hyperacusis. Conclusion: The loss of FMRP can affect the expression of genes in the cochlear nucleus that are important for neuronal signaling. One of these, Kcnab2, which encodes a subunit of the Shaker voltage‐gated potassium channel, is expressed at an abnormally low level in the Fmr1‐KO cochlear nucleus. Kcnab2 and other differentially expressed genes may represent pathways for the development of hyperacusis. Future studies will be aimed at investigating the effects of these altered genes on hyperacusis. Level of Evidence: N/A Laryngoscope, 134:1363–1371, 2024 [ABSTRACT FROM AUTHOR]

Fragile X syndrome (FXS) is the most common inherited cause of Intellectual Disability. There is a broad phenotype that includes deficits in cognition and behavioral changes, alongside physical characteristics. Phenotype depends upon the level of mutation in the FMR1 (fragile X messenger ribonucleoprotein 1) gene. The molecular understanding of the impact of the FMR1 gene mutation provides an opportunity to target treatment not only at symptoms but also on a molecular level. We conducted a systematic review to provide an up-to-date narrative summary of the current evidence for pharmacological treatment in FXS. The review was restricted to randomized, blinded, placebo-controlled trials. The outcomes from these studies are discussed and the level of evidence assessed against validated criteria. The initial search identified 2377 articles, of which 16 were included in the final analysis. Based on this review to date there is limited data to support any specific pharmacological treatments, although the data for cannabinoids are encouraging in those with FXS and in future developments in gene therapy may provide the answer to the search for precision medicine. Treatment must be person-centered and consider the combination of medical, genetic, cognitive, and emotional challenges. [ABSTRACT FROM AUTHOR]

The fragile X syndrome (FXS) represents the most prevalent form of inherited intellectual disability and is the first monogenic cause of autism spectrum disorder. FXS results from the absence of the RNA-binding protein FMRP (fragile X messenger ribonucleoprotein). Neuronal migration is an essential step of brain development allowing displacement of neurons from their germinal niches to their final integration site. The precise role of FMRP in neuronal migration remains largely unexplored. Using live imaging of postnatal rostral migratory stream (RMS) neurons in Fmr1-null mice, we observed that the absence of FMRP leads to delayed neuronal migration and altered trajectory, associated with defects of centrosomal movement. RNA-interference-induced knockdown of Fmr1 shows that these migratory defects are cell-autonomous. Notably, the primary Fmrp mRNA target implicated in these migratory defects is microtubule-associated protein 1B (MAP1B). Knocking down MAP1B expression effectively rescued most of the observed migratory defects. Finally, we elucidate the molecular mechanisms at play by demonstrating that the absence of FMRP induces defects in the cage of microtubules surrounding the nucleus of migrating neurons, which is rescued by MAP1B knockdown. Our findings reveal a novel neurodevelopmental role for FMRP in collaboration with MAP1B, jointly orchestrating neuronal migration by influencing the microtubular cytoskeleton.

By adulthood, most males with fragile X syndrome (FXS) require support to navigate day-to-day settings. The present study cross-sectionally: (1) characterized the profile of daily living skills in males with FXS and (2) examined associated participant characteristics (i.e., fragile X mental retardation protein [FMRP] expression, nonverbal cognition, language, autism symptomatology, and anxiety symptomatology) using the Waisman-Activities of Daily Living questionnaire. Males with FXS (n = 57, ages 15-23 years) needed more help/support in the areas of domestic and community daily livings skills, than in the area of personal daily living skills. Significant associations were observed between reduced daily living skills and lower nonverbal cognition, receptive language, expressive language, and increased autism symptomatology. Receptive language emerged as the strongest unique predictor of daily living skill performance.

Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by the full mutation as well as highly localized methylation of the fragile X mental retardation 1 (FMR1) gene on the long arm of the X chromosome. Children with FXS are commonly co-diagnosed with Autism Spectrum Disorder, attention and learning problems, anxiety, aggressive behavior and sleep disorder, and early interventions have improved many behavior symptoms associated with FXS. In this review, we performed a literature search of original and review articles data of clinical trials and book chapters using MEDLINE (1990-2021) and ClinicalTrials.gov. While we have reviewed the biological importance of the fragile X mental retardation protein (FMRP), the FXS phenotype, and current diagnosis techniques, the emphasis of this review is on clinical interventions. Early non-pharmacological interventions in combination with pharmacotherapy and targeted treatments aiming to reverse dysregulated brain pathways are the mainstream of treatment in FXS. Overall, early diagnosis and interventions are fundamental to achieve optimal clinical outcomes in FXS.

Individuals with the fragile X premutation report symptoms of chronic pain from multiple systems, have increased incidence of comorbid conditions where pain is a prominent feature, and pathophysiology that supports disrupted pain regulation, inflammation, and energy imbalance. Less is known about how pain manifests for the subpopulation of carriers that develop the motor and cognitive changes of fragile X-associated tremor and ataxia syndrome (FXTAS), and how pain may differ between men and women. We gathered data collected from 104 males and females with FXTAS related to chronic pain, comorbid conditions related to pain, and medications used for pain control to further explore the types of pain experienced and to better characterize how individuals with the fragile X premutation experience pain sensation across genders. We found that women experience significantly more pain symptoms than men, particularly allodynia (20 vs. 2.0%, p = 0.008), peripheral neuropathy pain (43.9 vs. 25.4%, p = 0.0488), migraine (43.9 vs. 14.5%, p = 0.0008), fibromyalgia (26.8 vs. 0%, p = 0.0071) and back pain (48.5 vs. 23.4%, p = 0.008). We found onset of peripheral neuropathy predicts the onset of ataxia (β = 0.63 ± 0.25, p = 0.019) and tremor (β = 0.56 ± 0.17, p = 0.004) across gender. Women also report significantly more anxiety (82.9 vs. 39.7%, p < 0.001), which has implications for ideal pain treatment. These pain symptoms need to be recognized in the medical history and treated appropriately, with consideration for overlapping comorbidities.

Obesity is a pediatric epidemic that is more prevalent in children with developmental disabilities. We hypothesize that soy protein-based diets increase weight gain and alter neurobehavioral outcomes. Our objective herein was to test matched casein- and soy protein-based purified ingredient diets in a mouse model of fragile X syndrome, Fmr1KO mice. The experimental methods included assessment of growth; 24-7 activity levels; motor coordination; learning and memory; blood-based amino acid, phytoestrogen and glucose levels; and organ weights. The primary outcome measure was body weight. We find increased body weight in male Fmr1KO from postnatal day 6 (P6) to P224, male wild type (WT) from P32–P39, female Fmr1KO from P6–P18 and P168–P224, and female Fmr1HET from P9–P18 as a function of soy. Activity at the beginning of the light and dark cycles increased in female Fmr1HET and Fmr1KO mice fed soy. We did not find significant differences in rotarod or passive avoidance behavior as a function of genotype or diet. Several blood-based amino acids and phytoestrogens were significantly altered in response to soy. Liver weight was increased in WT and adipose tissue in Fmr1KO mice fed soy. Activity levels at the beginning of the light cycle and testes weight were greater in Fmr1KO versus WT males irrespective of diet. DEXA analysis at 8-months-old indicated increased fat mass and total body area in Fmr1KO females and lean mass and bone mineral density in Fmr1KO males fed soy. Overall, dietary consumption of soy protein isolate by C57BL/6J mice caused increased growth, which could be attributed to increased lean mass in males and fat mass in females. There were sex-specific differences with more pronounced effects in Fmr1KO versus WT and in males versus females. [ABSTRACT FROM AUTHOR]

There is increasing interest in retinoic acid (RA) as a regulator of the complex biological processes underlying the cognitive functions performed by the brain. The importance of RA in brain function is underlined by the brain's high efficiency in converting vitamin A into RA. One crucial action of RA in the brain is dependent on RA receptor a (RARa) transport out of the nucleus, where it no longer regulates transcription but carries out non-genomic functions. RARa, when localised in the cytoplasm, particularly in neuronal dendrites, acts as a translational suppressor. It regulates protein translation as a crucial part of the mechanism maintaining homoeostatic synaptic plasticity, which is characterised by neuronal changes necessary to restore and balance the excitability of neuronal networks after perturbation events. Under normal conditions of neurotransmission, RARa without ligand suppresses the translation of proteins. When neural activity is reduced, RA synthesis is stimulated, and RA signalling via RARa derepresses the translation of proteins and synergistically with the fragile X mental retardation protein allows the synthesis of Ca2+ permeable a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors that re-establish normal levels of synaptic activity. Homoeostatic synaptic plasticity underlies many cognitive processes, so its impairment due to dysregulation of RA signalling may be involved in neurodevelopmental disorders such as autism, which is also associated with FMRP. A full understanding of RA signalling control of homoeostatic synaptic plasticity may point to treatments. [ABSTRACT FROM AUTHOR]

Fragile X Syndrome (FXS) is the most common inherited form of intellectual disability and is caused by mutations in the gene encoding the Fragile X messenger ribonucleoprotein (FMRP). FMRP is an evolutionarily conserved and neuronally enriched RNA-binding protein (RBP) with functions in RNA editing, RNA transport, and protein translation. Specific target RNAs play critical roles in neurodevelopment, including the regulation of neurite morphogenesis, synaptic plasticity, and cognitive function. The different biological functions of FMRP are modulated by its cooperative interaction with distinct sets of neuronal RNA and protein-binding partners. Here, we focus on interactions between FMRP and components of the microRNA (miRNA) pathway. Using the Drosophila S2 cell model system, we show that the Drosophila ortholog of FMRP (dFMRP) can repress translation when directly tethered to a reporter mRNA. This repression requires the activity of AGO1, GW182, and MOV10/Armitage, conserved proteins associated with the miRNA-containing RNA-induced silencing complex (miRISC). Additionally, we find that untagged dFMRP can interact with a short stem-loop sequence in the translational reporter, a prerequisite for repression by exogenous miR-958. Finally, we demonstrate that dFmr1 interacts genetically with GW182 to control neurite morphogenesis. These data suggest that dFMRP may recruit the miRISC to nearby miRNA binding sites and repress translation via its cooperative interactions with evolutionarily conserved components of the miRNA pathway. [ABSTRACT FROM AUTHOR]

A deficiency of FMRP, a canonical RNA-binding protein, causes the development of Fragile X Syndrome (FXS), which is characterised by multiple phenotypes, including neurodevelopmental disorders, intellectual disability, and autism. Due to the alternative splicing of the encoding FMR1 gene, multiple FMRP isoforms are produced consisting of full-length predominantly cytoplasmic (i.e., iso1) isoforms involved in translation and truncated nuclear (i.e., iso6) isoforms with orphan functions. However, we recently implicated nuclear FMRP isoforms in DNA damage response, showing that they negatively regulate the accumulation of anaphase DNA genomic instability bridges. This finding provided evidence that the cytoplasmic and nuclear functions of FMRP are uncoupled played by respective cytoplasmic and nuclear isoforms, potentially involving specific interactions. While interaction partners of cytoplasmic FMRP have been reported, the identity of nuclear FMRP isoform partners remains to be established. Using affinity purification coupled with mass spectrometry, we mapped the nuclear interactome of the FMRP isoform iso6 in U2OS. In doing so, we found FMRP nuclear interaction partners to be involved in RNA processing, pre-mRNA splicing, ribosome biogenesis, DNA replication and damage response, chromatin remodeling and chromosome segregation. By comparing interactions between nuclear iso6 and cytoplasmic iso1, we report a set of partners that bind specifically to the nuclear isoforms, mainly proteins involved in DNA-associated processes and proteasomal proteins, which is consistent with our finding that proteasome targets the nuclear FMRP iso6. The specific interactions with the nuclear isoform 6 are regulated by replication stress, while those with the cytoplasmic isoform 1 are largely insensitive to such stress, further supporting a specific role of nuclear isoforms in DNA damage response induced by replicative stress, potentially regulated by the proteasome. [ABSTRACT FROM AUTHOR]

FMRP is a multifunctional protein encoded by the Fragile X Messenger Ribonucleoprotein 1 gene (FMR1). The inactivation of the FMR1 gene results in fragile X syndrome (FXS), a serious neurodevelopmental disorder. FMRP deficiency causes abnormal neurite outgrowth, which is likely to lead to abnormal learning and memory capabilities. However, the mechanism of FMRP in modulating neuronal development remains unknown. We found that FMRP enhances the translation of 4EBP2, a neuron-specific form of 4EBPs that inactivates eIF4E by inhibiting the interaction between eIF4E and eIF4G. Depletion of 4EBP2 results in abnormal neurite outgrowth. Moreover, the impairment of neurite outgrowth upon FMRP depletion was overcome by the ectopic expression of 4EBP2. These results suggest that FMRP controls neuronal development by enhancing 4EBP2 expression at the translational level. In addition, treatment with 4EGI-1, a chemical that blocks eIF4E activity, restored neurite length in FMRP-depleted and 4EBP2-depleted cells. In conclusion, we discovered that 4EBP2 functions as a key downstream regulator of FMRP activity in neuronal development and that FMRP represses eIF4E activity by enhancing 4EBP2 translation. [ABSTRACT FROM AUTHOR]

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability. FXS is an X-linked, neurodevelopmental disorder caused by a CGG trinucleotide repeat expansion in the 5' untranslated region (UTR) of the Fragile X Mental Retardation gene, FMR1. Greater than 200 CGG repeats results in epigenetic silencing of the gene leading to the deficiency or absence of Fragile X mental retardation protein (FMRP). The loss of FMRP is considered the root cause of FXS. The relationship between neurological function and FMRP expression in peripheral blood mononuclear cells (PBMCs) has not been well established. Assays to detect and measure FMR1 and FMRP have been described; however, none are sufficiently sensitive, precise, or quantitative to properly characterize the relationships between cognitive ability and CGG repeat number, FMR1 mRNA expression, or FMRP expression measured in PBMCs. To address these limitations, two novel immunoassays were developed and optimized, an electro-chemiluminescence immunoassay and a multiparameter flow cytometry assay. Both assays were performed on PMBCs isolated from 27 study participants with FMR1 CGG repeats ranging from normal to full mutation. After correcting for methylation, a significant positive correlation between CGG repeat number and FMR1 mRNA expression levels and a significant negative correlation between FMRP levels and CGG repeat expansion was observed. Importantly, a high positive correlation was observed between intellectual quotient (IQ) and FMRP expression measured in PBMCs.

Fragile X syndrome (FXS) [OMIM 300624] is a common X-linked inherited syndrome with an incidence only second to that of trisomy 21. More than 95% of fragile X syndrome is caused by reduced or absent fragile X intellectual disability protein 1 (FMRP) synthesis due to dynamic mutation expansion of the CGG triplet repeat in the 5'UTR and abnormal methylation of the FMR1 (fragile X messenger ribonucleoprotein 1) gene [OMIM 309550]. Less than 5% of cases are caused by abnormal function of the FMRP due to point mutations or deletions in the FMR1 gene. In a proband with clinical suspicion of FXS and no CGG duplication, we found the presence of c.585_586del (p.Lys195AsnfsTer8) in exon 7 of the FMR1 gene using whole exome sequencing (WES). This variant resulted in frameshift and a premature stop codon after 8 aberrant amino acids. This variant is a novel pathogenic mutation, as determined by pedigree analysis, which has not been reported in any database or literature. [ABSTRACT FROM AUTHOR]

Children with fragile X syndrome (FXS) exhibit deficits in a variety of cognitive processes within the executive function domain. As working memory (WM) is known to support a wide range of cognitive, learning and adaptive functions, WM computer-based training programs have the potential to benefit people with FXS and other forms of intellectual and developmental disability (IDD). However, research on the effectiveness of WM training has been mixed. The current study is a follow-up "deep dive" into the data collected during a randomized controlled trial of Cogmed (Stockholm, Sweden) WM training in children with FXS. Analyses characterized the training data, identified training quality metrics, and identified subgroups of participants with similar training patterns. Child, parent, home environment and training quality metrics were explored in relation to the clinical outcomes during the WM training intervention. Baseline cognitive level and training behavior metrics were linked to gains in WM performance-based assessments and also to reductions in inattention and other behaviors related to executive functioning during the intervention. The results also support a recommendation that future cognitive intervention trials with individuals with IDD such as FXS include additional screening of participants to determine not only baseline feasibility, but also capacity for training progress over a short period prior to inclusion and randomization. This practice may also better identify individuals with IDD who are more likely to benefit from cognitive training in clinical and educational settings.

The fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder seen in older premutation (55-200 CGG repeats) carriers of FMR1. The premutation has excessive levels of FMR1 mRNA that lead to toxicity and mitochondrial dysfunction. The clinical features usually begin in the 60 s with an action or intention tremor followed by cerebellar ataxia, although 20% have only ataxia. MRI features include brain atrophy and white matter disease, especially in the middle cerebellar peduncles, periventricular areas, and splenium of the corpus callosum. Neurocognitive problems include memory and executive function deficits, although 50% of males can develop dementia. Females can be less affected by FXTAS because of a second X chromosome that does not carry the premutation. Approximately 40% of males and 16% of female carriers develop FXTAS. Since the premutation can occur in less than 1 in 200 women and 1 in 400 men, the FXTAS diagnosis should be considered in patients that present with tremor, ataxia, parkinsonian symptoms, neuropathy, and psychiatric problems. If a family history of a fragile X mutation is known, then FMR1 DNA testing is essential in patients with these symptoms.

Abstract FMRP, an RNA-binding protein, has previously shown to be involved in regulation of circadian rhythms in flies and mice. However, the molecular mechanism remains elusive. Here we demonstrate that core circadian component Per1 mRNA was a target of FMRP and the association leads to reduced PER1 expression. In Fmr1 KO mice, the oscillation of PER1 protein expression was significantly affected in a temporal and tissue-dependent pattern when compared to WT mice. Our work thus identified Per1 mRNA as a novel target of FMRP and suggested a potential role of FMRP in regulation of circadian function.

Abstract Background Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability in males and the most common single gene cause of autism. This X-linked disorder is caused by an expansion of a trinucleotide CGG repeat (> 200 base pairs) on the promotor region of the fragile X messenger ribonucleoprotein 1 gene (FMR1). This leads to the deficiency or absence of the encoded protein, fragile X messenger ribonucleoprotein 1 (FMRP). FMRP has a central role in the translation of mRNAs involved in synaptic connections and plasticity. Recent studies have demonstrated the benefit of therapeutics focused on reactivation of the FMR1 locus towards improving key clinical phenotypes via restoration of FMRP and ultimately disease modification. A key step in future studies directed towards this effort is the establishment of proof of concept (POC) for FMRP reactivation in individuals with FXS. For this, it is key to determine the feasibility of repeated collection of tissues or fluids to measure FMR1 mRNA and FMRP. Methods Individuals, ages 3 to 22 years of age, with FXS and those who were typically developing participated in this single-site pilot clinical biomarker study. The repeated collection of hair follicles was compared with the collection of blood and buccal swabs for detection of FMR1 mRNA and FMRP and related molecules. Results There were n = 15 participants, of whom 10 had a diagnosis of FXS (7.0 ± 3.56 years) and 5 were typically developing (8.2 ± 2.77 years). Absolute levels of FMRP and FMR1 mRNA were substantially higher in healthy participants compared to full mutation and mosaic FXS participants and lowest in the FXS boys. Measurement of FMR1 mRNA and FMRP levels by any method did not show any notable variation by collection location at home versus office across the various sample collection methodologies of hair follicle, blood sample, and buccal swab. Conclusion Findings demonstrated that repeated sampling of hair follicles in individuals with FXS, in both, home, and office settings, is feasible, repeatable, and can be used for measurement of FMR1 mRNA and FMRP in longitudinal studies.

Aberrant alternative splicing of mRNAs results in dysregulated gene expression in multiple neurological disorders. Here, we show that hundreds of mRNAs are incorrectly expressed and spliced in white blood cells and brain tissues of individuals with fragile X syndrome (FXS). Surprisingly, the FMR1 (Fragile X Messenger Ribonucleoprotein 1) gene is transcribed in >70% of the FXS tissues. In all FMR1- expressing FXS tissues, FMR1 RNA itself is mis- spliced in a CGG expansion--dependent manner to generate the little- known FMR1- 217 RNA isoform, which is comprised of FMR1 exon 1 and a pseudo- exon in intron 1. FMR1- 217 is also expressed in FXS premutation carrier--derived skin fibroblasts and brain tissues. We show that in cells aberrantly expressing mis- spliced FMR1, antisense oligonucleotide (ASO) treatment reduces FMR1- 217, rescues full- length FMR1 RNA, and restores FMRP (Fragile X Messenger RibonucleoProtein) to normal levels. Notably, FMR1 gene reactivation in transcriptionally silent FXS cells using 5- aza- 2'- deoxycytidine (5- AzadC), which prevents DNA methylation, increases FMR1- 217 RNA levels but not FMRP. ASO treatment of cells prior to 5- AzadC application rescues full- length FMR1 expression and restores FMRP. These findings indicate that misregulated RNA- processing events in blood could serve as potent biomarkers for FXS and that in those individuals expressing FMR1- 217, ASO treatment may offer a therapeutic approach to mitigate the disorder. [ABSTRACT FROM AUTHOR]

Different mutations in the RNA‐binding protein Pumilio1 (PUM1) cause divergent phenotypes whose severity tracks with dosage: a mutation that reduces PUM1 levels by 25% causes late‐onset ataxia, whereas haploinsufficiency causes developmental delay and seizures. Yet PUM1 targets are derepressed to equal degrees in both cases, and the more severe mutation does not hinder PUM1's RNA‐binding ability. We therefore considered the possibility that the severe mutation might disrupt PUM1 interactions, and identified PUM1 interactors in the murine brain. We find that mild PUM1 loss derepresses PUM1‐specific targets, but the severe mutation disrupts interactions with several RNA‐binding proteins and the regulation of their targets. In patient‐derived cell lines, restoring PUM1 levels restores these interactors and their targets to normal levels. Our results demonstrate that dosage sensitivity does not always signify a linear relationship with protein abundance but can involve distinct mechanisms. We propose that to understand the functions of RNA‐binding proteins in a physiological context will require studying their interactions as well as their targets. Synopsis: Different variants in a gene can alter protein expression to different degrees, producing milder or more severe phenotypes. Here, two variants of the RNA‐binding protein PUM1 are shown to act via distinct molecular mechanisms: deregulation of direct targets or disruption of PUM1 interactors and their targets. Mild PUM1 loss de‐represses PUM1's direct targets.PUM1 haploinsufficiency disrupts native interactions and downstream targets.Dosage sensitivity can reflect distinct mechanisms rather than linear change in severity.To understand RNA‐binding proteins requires investigation of both their targets and interactors. [ABSTRACT FROM AUTHOR]

Fragile X Syndrome (FXS) is the most common form of inherited intellectual disability (ID) and a primary genetic cause of autism spectrum disorder (ASD). FXS arises from the silencing of the FMR1 gene causing the lack of translation of its encoded protein, the Fragile X Messenger RibonucleoProtein (FMRP), an RNA-binding protein involved in translational control and in RNA transport along dendrites. Although a large effort during the last 20 years has been made to investigate the cellular roles of FMRP, no effective and specific therapeutic intervention is available to treat FXS. Many studies revealed a role for FMRP in shaping sensory circuits during developmental critical periods to affect proper neurodevelopment. Dendritic spine stability, branching and density abnormalities are part of the developmental delay observed in various FXS brain areas. In particular, cortical neuronal networks in FXS are hyper-responsive and hyperexcitable, making these circuits highly synchronous. Overall, these data suggest that the excitatory/inhibitory (E/I) balance in FXS neuronal circuitry is altered. However, not much is known about how interneuron populations contribute to the unbalanced E/I ratio in FXS even if their abnormal functioning has an impact on the behavioral deficits of patients and animal models affected by neurodevelopmental disorders. We revise here the key literature concerning the role of interneurons in FXS not only with the purpose to better understand the pathophysiology of this disorder, but also to explore new possible therapeutic applications to treat FXS and other forms of ASD or ID. Indeed, for instance, the reintroduction of functional interneurons in the diseased brains has been proposed as a promising therapeutic approach for neurological and psychiatric disorders. [ABSTRACT FROM AUTHOR]

Silencing of the fragile X messenger ribonucleoprotein 1 (FMR1) gene and a consequent lack of FMR protein (FMRP) synthesis are associated with fragile X syndrome, one of the most common inherited intellectual disabilities. FMRP is a multifunctional protein that is involved in many cellular functions in almost all subcellular compartments under both normal and cellular stress conditions in neuronal and non-neuronal cell types. This is achieved through its trafficking signals, nuclear localization signal (NLS), nuclear export signal (NES), and nucleolar localization signal (NoLS), as well as its RNA and protein binding domains, and it is modulated by various post-translational modifications such as phosphorylation, ubiquitination, sumoylation, and methylation. This review summarizes the recent advances in understanding the interaction networks of FMRP with a special focus on FMRP stress-related functions, including stress granule formation, mitochondrion and endoplasmic reticulum plasticity, ribosome biogenesis, cell cycle control, and DNA damage response.

Fragile X syndrome (FXS) is an X-linked neurodevelopmental condition associated with intellectual disability and behavioral problems due to the lack of the Fragile X mental retardation protein (FMRP), which plays a crucial role in synaptic plasticity and memory. A desirable in vitro cell model to study FXS would be one that can be generated by simple isolation and culture method from a collection of a non-invasive donor specimen. Currently, the various donor-specific cells can be isolated mainly from peripheral blood and skin biopsy. However, they are somewhat invasive methods for establishing cell lines from the primary subject material. In this study, we characterized a cost-effective and straightforward method to derive epithelial cell lines from urine samples collected from participants with FXS and healthy controls (TD). The urine-derived cells expressed epithelial cell surface markers via fluorescence-activated cell sorting (FACS). We observed inter, and the intra-tissue CGG mosaicism in the PBMCs and the urine-derived cells from participants with FXS potentially related to the observed variations in the phenotypic and clinical presentation FXS. We characterized these urine-derived epithelial cells for FMR1 mRNA and FMRP expression and observed some expression in the lines derived from full mutation mosaic participants. Further, FMRP expression was localized in the cytoplasm of the urine-derived epithelial cells of healthy controls. Deficient FMRP expression was also observed in mosaic males, while, as expected, no expression was observed in cells derived from participants with a hypermethylated full mutation.