scholarly journals Fragile X Premutation rCGG Repeats Impairs Synaptic Growth and Synaptic Transmission at Drosophila larval Neuromuscular Junction

2020 ◽  
Author(s):  
Sajad Ahmad Bhat ◽  
Adil Yousuf ◽  
Zeeshan Mushtaq ◽  
Vimlesh Kumar ◽  
Abrar Qurashi
Keyword(s):  
Synaptic Transmission ◽  
Neuromuscular Junctions ◽  
Fragile X ◽  
Protein A ◽  
Model Systems ◽  
Synaptic Growth ◽  
Developmental Abnormalities ◽  
Fragile X Premutation ◽  
Cgg Repeats ◽  
Larval Neuromuscular Junction

AbstractFragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive neurodegenerative disease manifesting in the premutation (PM) carriers of the FMR1 gene with alleles bearing 55-200 CGG repeats. The discovery of a broad spectrum of clinical and cell developmental abnormalities among PM carriers with or without FXTAS, and in model systems suggests that neurodegeneration seen in FXTAS could be the inevitable end-result of pathophysiological processes set during early development. Hence, it is imperative to trace early pathological abnormalities. Our previous studies have shown that transgenic Drosophila carrying human-derived fragile X premutation-length CGG repeats are sufficient to cause neurodegeneration. Here, we used the same transgenic Drosophila model to understand the effects of fragile X premutation-length CGG repeats on the structure and function of the developing nervous system. We show that presynaptic expression of the premutation length CGG repeats restricts synaptic growth, reduces the number of synaptic boutons, leads to aberrant presynaptic varicosities, and impairs synaptic transmission at the larval neuromuscular junctions (NMJs). The postsynaptic analysis shows both glutamate receptor and subsynaptic reticulum proteins are normal. However, a high percentage of boutons show the reduced density of Bruchpilot protein, a key component of presynaptic active zones required for vesicle release. The electrophysiological analysis shows a significant reduction in the quantal content, a measure of total synaptic vesicles released per excitation potential. Together these findings endorse that synapse perturbation caused by rCGG repeats mediate presynaptically during larval NMJ development.

scholarly journals Near-cognate initiation generates FMRpolyG from CGG repeats in Fragile X associated Tremor Ataxia Syndrome

2020 ◽  
Author(s):  
Yuan Zhang ◽  
M. Rebecca Glineburg ◽  
Venkatesha Basrur ◽  
Kevin Conlon ◽  
Deborah A. Hall ◽  
...  
Keyword(s):  
Fragile X ◽  
Model Systems ◽  
Initiation Factor ◽  
Amino Terminal ◽  
Human Samples ◽  
Cgg Repeats ◽  
Cellular Environment ◽  
Ataxia Syndrome ◽  
Signature Peptides ◽  
Ran Translation

AbstractRepeat associated non-AUG (RAN) translation of FMR1 5’ UTR CGG repeats produces toxic homo-polymeric proteins that accumulate within ubiquitinated inclusions in Fragile X-associated tremor/ataxia syndrome (FXTAS) patient brains and model systems. The most abundant RAN product, FMRpolyG, initiates predominantly at an ACG codon located just 5’ to the repeat. Methods to accurately measure FMRpolyG in FXTAS patients are lacking. Here we used data dependent acquisition (DDA) and parallel reaction monitoring (PRM) mass spectrometry coupled with stable isotope labeled standard peptides (SIS) to identify potential signature FMRpolyG fragments in patient cells and tissues. Following immunoprecipitation (IP) enrichment, we detected FMRpolyG signature peptides by PRM in transfected cells, FXTAS human samples and patient derived stem cells, but not in controls. Surprisingly, we identified two amino-terminal peptides: one beginning with methionine (Ac-MEAPLPGGVR) initiating at an ACG, and a second beginning with threonine (Ac-TEAPLPGGVR), initiating at a GUG. Abundance of the threonine peptide was enhanced relative to the methionine peptide upon activation of the integrated stress response. In addition, loss of the eIF2 alternative factor, eIF2A, or enhanced expression of initiation factor eIF1, preferentially suppressed GUG initiated FMRpolyG synthesis. These data demonstrate that FMRpolyG is quantifiable in human samples and that RAN translation on FMR1 initiates at specific near cognate codons dependent on available initiation factors and cellular environment.

scholarly journals An Origin of DNA Replication in the Promoter Region of the Human Fragile X Mental Retardation (FMR1) Gene

2006 ◽  
Vol 27 (2) ◽  
pp. 426-437 ◽  
Author(s):  
Steven J. Gray ◽  
Jeannine Gerhardt ◽  
Walter Doerfler ◽  
Lawrence E. Small ◽  
Ellen Fanning
Keyword(s):  
Mental Retardation ◽  
Dna Replication ◽  
Fragile X Syndrome ◽  
Fragile X ◽  
Model Systems ◽  
Fmr1 Gene ◽  
Fragile X Mental Retardation ◽  
Cgg Repeats ◽  
Origin Of Dna Replication ◽  
Transformed Cell Lines

ABSTRACT Fragile X syndrome, the most common form of inherited mental retardation in males, arises when the normally stable 5 to 50 CGG repeats in the 5′ untranslated region of the fragile X mental retardation protein 1 (FMR1) gene expand to over 200, leading to DNA methylation and silencing of the FMR1 promoter. Although the events that trigger local CGG expansion remain unknown, the stability of trinucleotide repeat tracts is affected by their position relative to an origin of DNA replication in model systems. Origins of DNA replication in the FMR1 locus have not yet been described. Here, we report an origin of replication adjacent to the FMR1 promoter and CGG repeats that was identified by scanning a 35-kb region. Prereplication proteins Orc3p and Mcm4p bind to chromatin in the FMR1 initiation region in vivo. The position of the FMR1 origin relative to the CGG repeats is consistent with a role in repeat maintenance. The FMR1 origin is active in transformed cell lines, fibroblasts from healthy individuals, fibroblasts from patients with fragile X syndrome, and fetal cells as early as 8 weeks old. The potential role of the FMR1 origin in CGG tract instability is discussed.

Abnormal GABA-mediated and cerebellar inhibition in women with the fragile X premutation

2013 ◽  
Vol 109 (5) ◽  
pp. 1315-1322 ◽  
Author(s):  
Virginia Conde ◽  
Francisco J. Palomar ◽  
María José Lama ◽  
Raquel Martínez ◽  
Fátima Carrillo ◽  
...  
Keyword(s):  
Primary Motor Cortex ◽  
Fragile X ◽  
Intracortical Inhibition ◽  
Noninvasive Brain Stimulation ◽  
Cgg Repeat ◽  
Afferent Inhibition ◽  
Fragile X Premutation ◽  
Cgg Repeats ◽  
Structural Abnormalities ◽  
Cerebellar Inhibition

The fragile X syndrome is a mutation-driven developmental disorder caused by a repetition over 200 times of the CGG trinucleotide situated in the 5′-untranslated region of the fragile X mental retardation 1 gene ( FMR1). The interval between 55 and 199 CGG repeats, which is over the normal range but below full mutation, is named fragile X premutation. Recent studies have focused on the asymptomatic state of fragile X premutation carriers and their potentially relevant preclinical features. However, the underlying neurological mechanisms leading to altered functions in fragile X premutation carriers are still poorly understood. In this study, we wanted to test the hypothesis that asymptomatic women who carry the fragile X premutation present GABAergic and cerebellar abnormalities compared with healthy women without the premutation. We performed noninvasive brain stimulation protocols on both asymptomatic fragile X premutation carriers and controls comprising of measures of GABAA- and GABAB-mediated intracortical inhibition, afferent inhibition, and cerebello-motor functional interactions. Premutation carriers presented an absence of cerebellar inhibition over primary motor cortex as well as a reduced GABAA-mediated intracortical and afferent inhibition compared with healthy nonpremutated controls. These alterations are most probably dependent on a dysfunctional GABAergic mechanism associated with the fragile X premutation condition as previously found in CGG-repeat animal models. Furthermore, the lack of cerebello-motor inhibition could be related to the cerebellar structural abnormalities previously found in carriers of the premutation.

scholarly journals Short antisense oligonucleotides alleviate the pleiotropic toxicity of RNA harboring expanded CGG repeats

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Magdalena Derbis ◽  
Emre Kul ◽  
Daria Niewiadomska ◽  
Michał Sekrecki ◽  
Agnieszka Piasecka ◽  
...  
Keyword(s):  
Motor Behavior ◽  
Neurodegenerative Disorder ◽  
Therapeutic Potential ◽  
Cell Damage ◽  
Fragile X ◽  
Nuclear Proteins ◽  
Mirna Biogenesis ◽  
Loop Formation ◽  
Cgg Repeats ◽  
Initiation Of Translation

AbstractFragile X-associated tremor/ataxia syndrome (FXTAS) is an incurable neurodegenerative disorder caused by expansion of CGG repeats in the FMR1 5’UTR. The RNA containing expanded CGG repeats (rCGGexp) causes cell damage by interaction with complementary DNA, forming R-loop structures, sequestration of nuclear proteins involved in RNA metabolism and initiation of translation of polyglycine-containing protein (FMRpolyG), which forms nuclear insoluble inclusions. Here we show the therapeutic potential of short antisense oligonucleotide steric blockers (ASOs) targeting directly the rCGGexp. In nuclei of FXTAS cells ASOs affect R-loop formation and correct miRNA biogenesis and alternative splicing, indicating that nuclear proteins are released from toxic sequestration. In cytoplasm, ASOs significantly decrease the biosynthesis and accumulation of FMRpolyG. Delivery of ASO into a brain of FXTAS mouse model reduces formation of inclusions, improves motor behavior and corrects gene expression profile with marginal signs of toxicity after a few weeks from a treatment.

scholarly journals Molecular Pathogenesis and Peripheral Monitoring of Adult Fragile X-Associated Syndromes

2021 ◽  
Vol 22 (16) ◽  
pp. 8368
Author(s):  
Luis M. Valor ◽  
Jorge C. Morales ◽  
Irati Hervás-Corpión ◽  
Rosario Marín
Keyword(s):  
Neurodegenerative Disorder ◽  
Late Onset ◽  
Fragile X ◽  
Endocrine System ◽  
Molecular Pathogenesis ◽  
Adult Women ◽  
Adult Men ◽  
Cgg Repeats ◽  
Reproductive Impairment ◽  
Ataxia Syndrome

Abnormal trinucleotide expansions cause rare disorders that compromise quality of life and, in some cases, lifespan. In particular, the expansions of the CGG-repeats stretch at the 5’-UTR of the Fragile X Mental Retardation 1 (FMR1) gene have pleiotropic effects that lead to a variety of Fragile X-associated syndromes: the neurodevelopmental Fragile X syndrome (FXS) in children, the late-onset neurodegenerative disorder Fragile X-associated tremor-ataxia syndrome (FXTAS) that mainly affects adult men, the Fragile X-associated primary ovarian insufficiency (FXPOI) in adult women, and a variety of psychiatric and affective disorders that are under the term of Fragile X-associated neuropsychiatric disorders (FXAND). In this review, we will describe the pathological mechanisms of the adult “gain-of-function” syndromes that are mainly caused by the toxic actions of CGG RNA and FMRpolyG peptide. There have been intensive attempts to identify reliable peripheral biomarkers to assess disease progression and onset of specific pathological traits. Mitochondrial dysfunction, altered miRNA expression, endocrine system failure, and impairment of the GABAergic transmission are some of the affectations that are susceptible to be tracked using peripheral blood for monitoring of the motor, cognitive, psychiatric and reproductive impairment of the CGG-expansion carriers. We provided some illustrative examples from our own cohort. Understanding the association between molecular pathogenesis and biomarkers dynamics will improve effective prognosis and clinical management of CGG-expansion carriers.

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