The generation of a conditional Fmr1 knock out mouse model to study Fmrp function in vivo.
ABSTRACT The FMR1 gene, mutated in Fragile X syndrome patients, has been modeled in mice with a neomycin cassette inserted in exon 5 of the mouse Fmr1 gene creating an Fmr1 knockout (Fmr1 KO) allele. This results in animals lacking Fmr1 protein (Fmrp) expression in all tissues. We have created a new, more versatile Fmr1 in vivo KO model (Fmr1 KO2) and generated conditional Fmr1 KO (CKO) mice by flanking the promoter and first exon of Fmr1 with lox P sites. This enables us to create a null allele in specific cell types and at specific time points by crossing Fmr1 CKO mice with tissue specific or inducible cre-recombinase expressing mice. The new Fmr1 KO2 line does not express any Fmrp and also lacks detectable Fmr1 transcripts. Crossing the Fmr1 CKO line with a Purkinje cell-specific cre-recombinase expresser produces mice that are null for Fmr1 in Purkinje neurons but wild type in all other cell types.
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ABSTRACT: Fragile X syndrome (FXS) is considered the leading inherited cause of intellectual disability and autism. In FXS, the fragile X mental retardation 1 (FMR1) gene is silenced and the fragile X mental retardation protein (FMRP) is not expressed, resulting in the characteristic features of the syndrome. Despite recent advances in understanding the pathophysiology of FXS, there is still no cure for this condition; current treatment is symptomatic. Preclinical research is essential in the development of potential therapeutic agents. This review provides an overview of the preclinical evidence supporting metabotropic glutamate receptor 5 (mGluR5) antagonists as therapeutic agents for FXS. According to the mGluR theory of FXS, the absence of FMRP leads to enhanced glutamatergic signaling via mGluR5, which leads to increased protein synthesis and defects in synaptic plasticity including enhanced long-term depression. As such, efforts to develop agents that target the underlying pathophysiology of FXS have focused on mGluR5 modulation. Animal models, particularly the Fmr1 knockout mouse model, have become invaluable in exploring therapeutic approaches on an electrophysiological, behavioral, biochemical, and neuroanatomical level. Two direct approaches are currently being investigated for FXS treatment: reactivating the FMR1 gene and compensating for the lack of FMRP. The latter approach has yielded promising results, with mGluR5 antagonists showing efficacy in clinical trials. Targeting mGluR5 is a valid approach for the development of therapeutic agents that target the underlying pathophysiology of FXS. Several compounds are currently in development, with encouraging results.Psychopharmacology 11/2013; DOI:10.1007/s00213-013-3330-3 · 3.99 Impact Factor
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ABSTRACT: Background / Purpose: The aim of this study was to investigate the mechanism(s) by which neural differentiation is impaired during embryonic development of FX affected fetuses and how the developmentally regulated silencing of FMR1 expression is related to mental retardation. Main conclusion: Neural differentiation induced FMR1 down regulation in FX-hESC, similar to the natural process. Abnormal neurogenesis & aberrant gene expression were found already at early stages of differentiation, leading to poor neuronal maturation. FX-neurons were electrophysiologically functional and contained the appropriate synaptic machinery but displayed poor spontaneous synaptic activity and no response to glutamate.Developmental Biology 01/2013; · 3.64 Impact Factor
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ABSTRACT: Fragile X syndrome (FXS) is the leading monogenic cause of intellectual disability and autism. The disease is a result of lack of expression of the fragile X mental retardation protein. Brain tissues of patients with FXS and mice with FMRP deficiency have shown an abnormal dendritic spine phenotype. We investigated the dendritic spine length and density of hippocampal CA1 pyramidal neurons in 2-, 10-, and 25-week-old Fmr1 knockout (KO). Next, we studied the effects of long-term treatment with an mGluR5 antagonist, AFQ056/Mavoglurant, on the spine phenotype in adult Fmr1 KO mice. We observed alterations in the spine phenotype during development, with a decreased spine length in 2-week-old Fmr1 KO mice compared with age-match wild-type littermates, but with increased spine length in Fmr1 KO mice compared with 10- and 25-week-old wild-type controls. No difference was found in spine density at any age. We report a rescue of the abnormal spine length in adult Fmr1 KO mice after a long-term treatment with AFQ056/Mavoglurant. This finding suggests that long-term treatment at later stage is sufficient to reverse the structural spine abnormalities and represents a starting point for future studies aimed at improving treatments for FXS.Psychopharmacology 12/2012; 231(6). DOI:10.1007/s00213-012-2947-y · 3.99 Impact Factor