http://repub.eur.nl/res/aut/5592/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/28597/ 2010-09-01T00:00:00Z http://repub.eur.nl/res/pub/25385/ 2009-08-15T00:00:00Z Lack of the FMR1 gene product causes fragile X syndrome, the commonest inherited cause of mental impairment. We know little of the roles that fragile X related (FXR) gene family members (FMR1, FXR2 and FXR1) play during embryonic development. Although all are expressed in the brain and testis, FXR1 is the principal member found in striated and cardiac muscle. The Fxr1 knockout mice display a striated muscle phenotype but it is not known why they die shortly after birth; however, a cardiac cause is possible. The zebrafish is an ideal model to investigate the role of fxr1 during development of the heart. We have carried out morpholino knockdown of fxr1 and have demonstrated abnormalities of striated muscle development and abnormal development of the zebrafish heart, including failure of looping and snapping of the atrium from its venous pole. In addition, we have measured cardiac function using high-speed video microscopy and demonstrated a significant reduction in cardiac function. This cardiac phenotype has not been previously described and suggests that fxr1 is essential for normal cardiac form and function. http://repub.eur.nl/res/pub/18468/ 2009-02-15T00:00:00Z Fragile X syndrome is one of the most common forms of mental retardation, yet little is known about the physiological mechanisms causing the disease. In this study, we probed the ionotropic glutamate receptor content in synapses of hippocampal CA1 pyramidal neurons in a mouse model for fragile X (Fmr1 KO2). We found that Fmr1 KO2 mice display a significantly lower AMPA to NMDA ratio than wild-type mice at 2 weeks of postnatal development but not at 6-7 weeks of age. This ratio difference at 2 weeks postnatally is caused by down-regulation of the AMPA and up-regulation of the NMDA receptor components. In correlation with these changes, the induction of NMDA receptor-dependent long-term potentiation following a low-frequency pairing protocol is increased in Fmr1 KO2 mice at this developmental stage but not later in maturation. We propose that ionotropic glutamate receptors, as well as potentiation, are altered at a critical time point for hippocampal network development, causing long-term changes. Associated learning and memory deficits would contribute to the fragile X mental retardation phenotype. http://repub.eur.nl/res/pub/10782/ 2007-01-15T00:00:00Z The human FMR1 gene contains a CGG repeat in its 5′ untranslated region. The repeat length in the normal population is polymorphic (5–55 CGG repeats). Lengths beyond 200 CGGs (full mutation) result in the absence of the FMR1 gene product, FMRP, through abnormal methylation and gene silencing. This causes Fragile X syndrome, the most common inherited form of mental retardation. Elderly carriers of the premutation, defined as a repeat length between 55 and 200 CGGs, can develop a progressive neurodegenerative syndrome: Fragile X-associated tremor/ataxia syndrome (FXTAS). In FXTAS, FMR1 mRNA levels are elevated and it has been hypothesised that FXTAS is caused by a pathogenic RNA gain-offunction mechanism. We have developed a knock in mouse model carrying an expanded CGG repeat (98 repeats), which shows repeat instability and displays biochemical, phenotypic and neuropathological characteristics of FXTAS. Here, we report further repeat instability, up to 230 CGGs. An expansion bias was observed, with the largest expansion being 43 CGG units and the largest contraction 80 CGG repeats. In humans, this length would be considered a full mutation and would be expected to result in gene silencing. Mice carrying long repeats (∼230 CGGs) display elevated mRNA levels and decreased FMRP levels, but absence of abnormal methylation, suggesting that modelling the Fragile X full mutation in mice requires additional repeats or other genetic manipulation. http://repub.eur.nl/res/pub/13369/ 2004-07-01T00:00:00Z FXR1 is one of the two known homologues of FMR1. FXR1 shares a high degree of sequence homology with FMR1 and also encodes two KH domains and an RGG domain, conferring RNA-binding capabilities. In comparison with FMRP, very little is known about the function of FXR1P in vivo. Mouse knockout (KO) models exist for both Fmr1 and Fxr2. To study the function of Fxr1 in vivo, we generated an Fxr1 KO mouse model. Homozygous Fxr1 KO neonates die shortly after birth most likely due to cardiac or respiratory failure. Histochemical analyses carried out on both skeletal and cardiac muscles show a disruption of cellular architecture and structure in E19 Fxr1 neonates compared with wild-type (WT) littermates. In WT E19 skeletal and cardiac muscles, Fxr1p is localized to the costameric regions within the muscles. In E19 Fxr1 KO littermates, in addition to the absence of Fxr1p, costameric proteins vinculin, dystrophin and alpha-actinin were found to be delocalized. A second mouse model (Fxr1 + neo), which expresses strongly reduced levels of Fxr1p relative to WT littermates, does not display the neonatal lethal phenotype seen in the Fxr1 KOs but does display a strongly reduced limb musculature and has a reduced life span of approximately 18 weeks. The results presented here point towards a role for Fxr1p in muscle mRNA transport/translation control similar to that seen for Fmrp in neuronal cells. http://repub.eur.nl/res/pub/10126/ 2003-01-01T00:00:00Z Recent studies have reported that alleles in the premutation range in the FMR1 gene in males result in increased FMR1 mRNA levels and at the same time mildly reduced FMR1 protein levels. Some elderly males with premutations exhibit an unique neurodegenerative syndrome characterized by progressive intention tremor and ataxia. We describe neurohistological, biochemical and molecular studies of the brains of mice with an expanded CGG repeat and report elevated Fmr1 mRNA levels and intranuclear inclusions with ubiquitin, Hsp40 and the 20S catalytic core complex of the proteasome as constituents. An increase was observed of both the number and the size of the inclusions during the course of life, which correlates with the progressive character of the cerebellar tremor/ataxia syndrome in humans. The observations in expanded-repeat mice support a direct role of the Fmr1 gene, by either CGG expansion per se or by mRNA level, in the formation of the inclusions and suggest a correlation between the presence of intranuclear inclusions in distinct regions of the brain and the clinical features in symptomatic premutation carriers. This mouse model will facilitate the possibilities to perform studies at the molecular level from onset of symptoms until the final stage of the disease.