A mouse model of the fragile X premutation: Effects on behavior, dendrite morphology, and regional rates of cerebral protein synthesis

Section on Neuroadaptation and Protein Metabolism, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA.
Neurobiology of Disease (Impact Factor: 5.2). 04/2011; 42(1):85-98. DOI: 10.1016/j.nbd.2011.01.008
Source: PubMed

ABSTRACT Carriers of FMR1 premutation alleles have 55-200 CGG repeats in the 5' untranslated region of the gene. These individuals are at risk for fragile X associated primary ovarian insufficiency (females) and, in late life, fragile X associated tremor and ataxia syndrome (males, and to a lesser extent, females). Premutation carrier status can also be associated with autism spectrum disorder, attention deficit hyperactivity disorder, and some cognitive deficits. In premutation carriers, FMR1 mRNA levels are often higher than those with normal sized alleles. In contrast, in subjects with full mutation alleles, (>200 repeats) the FMR1 gene is silenced and FMR1 mRNA and its product, FMRP, are absent. We have studied a male knock-in (KI) mouse model of the fragile X premutation (120-140 repeats) during young adulthood. In comparison to wild type, KI mice were hyperactive, exhibited less anxiety in both the open field and the elevated zero maze, were impaired on the passive avoidance test, and showed some subtle deficits on a test of social interaction. Motor learning as assessed by the rotarod test was normal. Dendritic arbors were less complex and spine densities and lengths increased in medial prefrontal cortex, basal lateral amygdala, and hippocampus compared with wild type. Regional rates of cerebral protein synthesis measured in vivo in KI mice were increased. KI mice also had elevated levels of Fmr1 mRNA and decreased levels of FMRP. Our results highlight similarities in phenotype between KI and Fmr1 knockout mice and suggest that the decreased concentration of FMRP contributes to the phenotype in young adult KI mice.

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Available from: Gloria E Hoffman, Aug 10, 2015
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    • "Conditions were optimized to minimize DAB reactivity in Fmr1 KO tissue. We reliably observed reduced FMRP levels in CGG KI mice both by western analysis and immunohistochemistry, consistent with previous reports (Tassone et al., 2000a; Kenneson et al., 2001; Entezam et al., 2007; Qin et al., 2011; Iliff et al., 2013; Ludwig et al., 2014; Pretto et al., 2014; Figure 1). In an effort to probe a potential role of altered FMRP expression in AD pathogenesis, we evaluated FMRP in a double transgenic model of AD which contains an additional copy of the human APP gene carrying the familial Swedish (K670N/M671L) missense mutation (Haass et al., 1995), and a deletion of exon 9 in the presenilin1 gene (Prihar et al., 1999). "
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    ABSTRACT: The FMR1 protein product, FMRP, is an mRNA binding protein associated with translational inhibition of target transcripts. One FMRP target is the amyloid precursor protein (APP) mRNA, and APP levels are elevated in Fmr1 KO mice. Given that elevated APP protein expression can elicit Alzheimer's disease (AD) in patients and model systems, we evaluated whether FMRP expression might be altered in Alzheimer's autopsy brain samples and mouse models compared to controls. In a double transgenic mouse model of AD (APP/PS1), we found no difference in FMRP expression in aged AD model mice compared to littermate controls. FMRP expression was also similar in AD and control patient frontal cortex and cerebellum samples. Fragile X-associated tremor/ataxia syndrome (FXTAS) is an age-related neurodegenerative disorder caused by expanded CGG repeats in the 5' untranslated region of the FMR1 gene. Patients experience cognitive impairment and dementia in addition to motor symptoms. In parallel studies, we measured FMRP expression in cortex and cerebellum from three FXTAS patients and found reduced expression compared to both controls and Alzheimer's patient brains, consistent with animal models. We also find increased APP levels in cerebellar, but not cortical, samples of FXTAS patients compared to controls. Taken together, these data suggest that a decrease in FMRP expression is unlikely to be a primary contributor to Alzheimer's disease pathogenesis.
    Frontiers in Genetics 10/2014; 5:360. DOI:10.3389/fgene.2014.00360
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    • "FXS is caused by trinucleotide repeat expansions of an X-linked gene, FMR1, which results in the transcriptional silencing and loss of the FMR1 protein product, the fragile X mental retardation protein (FMRP; reviewed in Penagarikano et al., 2007; Bagni et al., 2012). Brains of FXS patients and FMR1 knockout mice show abnormal morphology of dendritic spines (Rudelli et al., 1985; Hinton et al., 1991; Comery et al., 1997; Irwin et al., 2001, 2002; McKinney et al., 2005; Levenga et al., 2011) and dendritic arborizations (Braun and Segal, 2000; Galvez et al., 2003, 2005; Castr en et al., 2005; Restivo et al., 2005; Zarnescu et al., 2005; Thomas et al., 2008; Qin et al., 2011; Scotto- Lomassese et al., 2011; Till et al., 2012). "
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    ABSTRACT: Neuronal dendrites are structurally and functionally dynamic in response to changes in afferent activity. The fragile X mental retardation protein (FMRP) is an mRNA binding protein that regulates activity-dependent protein synthesis and morphological dynamics of dendrites. Loss and abnormal expression of FMRP occur in fragile X syndrome (FXS) and some forms of autism spectrum disorders. To provide further understanding of how FMRP signaling regulates dendritic dynamics, we have examined dendritic expression and localization of FMRP in the reptilian and avian nucleus laminaris (NL) and its mammalian analogue, the medial superior olive (MSO), in rodents and humans. NL/MSO neurons are specialized for temporal processing of low frequency sounds for binaural hearing, which is impaired in FXS. Protein BLAST analyses first demonstrate that the FMRP amino acid sequences in the alligator and chicken are highly similar to human FMRP with identical mRNA-binding and phosphorylation sites, suggesting that FMRP functions similarly across vertebrates. Immunocytochemistry further reveals that NL/MSO neurons have very high levels of dendritic FMRP in low frequency hearing vertebrates including alligator, chicken, gerbil, and human. Remarkably, dendritic FMRP in NL/MSO neurons often accumulates at branch points and enlarged distal tips, loci known to be critical for branch-specific dendritic arbor dynamics. These observations support an important role for FMRP in regulating dendritic properties of binaural neurons that are essential for low frequency sound localization and auditory scene segregation, and support the relevance of studying this regulation in nonhuman vertebrates that use low frequencies in order to further understand human auditory processing disorders. J. Comp. Neurol., 2013. © 2013 Wiley Periodicals, Inc.
    The Journal of Comparative Neurology 06/2014; 522(9). DOI:10.1002/cne.23520 · 3.51 Impact Factor
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    • "2.4.1. Conventional (non-microwave treated) nickel-diaminobenzadine tetrahydrochloride (Ni-DAB) labeling Immunolabeling of free-floating sections was performed with chromogenic substrate Ni-DAB as described in Qin et al. (2011). All primary antibodies were applied and incubated at room temperature for 1 h then 48 h at 4 • C. The corresponding biotinylated secondary antibody with concentration of 1:600 was applied for 1 h at room temperature. "
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    ABSTRACT: There is an accumulating literature demonstrating the application of microwaves across a wide spectrum of histological techniques. Although exposure to microwaves for short periods resulted in substantial acceleration of all procedures this technique still is not adopted widely. In part, this may be due to concerns over solutions that will avoid induction of thermal damage to the tissue when using standard microwave. Here, we offer a cooling setup that can be used with conventional microwave ovens. We utilized dry ice for effective cooling during microwave irradiation of tissue samples. To prevent overheating, the cups with tissue during exposure to microwaves were surrounded with powdered dry ice. Since the dry ice does not touch the walls of the cups, freezing is prevented. Overheating is avoided by alternating the microwave treatment with 1-2minute time periods when the cups are cooled outside of the microwave oven. This technique was used on mouse brain sections that were immunostained with microglia-specific CD68 antiserum and astrocyte labeling GFAP antibody. Both standard and microwave-assisted immonolabeling gave comparable results visualizing cells with fine processes and low background signal. Short incubation time in the microwave requires high concentrations of antibody for tissue immunostaining. We show that by prolonging the microwaving procedure we were able to reduce the antibody concentration to the levels used in standard immunostaining protocol. In summary, our technique gives a possibility to use a conventional microwave for rapid and effective immunolabeling resulting in reduced amount of antibody required for satisfactory immunostaining.
    Journal of neuroscience methods 07/2013; DOI:10.1016/j.jneumeth.2013.07.002 · 1.96 Impact Factor
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