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Acta Neuropathol Commun. 2019 Feb 26;7(1):27. doi: 10.1186/s40478-019-0677-7.

Astroglial-targeted expression of the fragile X CGG repeat premutation in mice yields RAN translation, motor deficits and possible evidence for cell-to-cell propagation of FXTAS pathology.

Author information

1
Department of Neurological Surgery, University of California, Davis, Davis, CA, USA.
2
Department of Psychiatry and Behavioral Sciences, University of California, Davis, Davis, CA, USA.
3
Department of Clinical Genetics, Erasmus MC, Rotterdam, The Netherlands.
4
Graduate Program in Neuroscience, University of California, Davis, Davis, CA, USA.
5
Program in Neuroscience and Behavior, Department of Psychology and Education, Mount Holyoke College, South Hadley, MA, USA.
6
Division of Biostatistics, Department of Public Health Sciences, University California Davis, Davis, CA, USA.
7
Departments of Neurology, Neurobiology, and Cell Biology, and the Duke Center for Neurodegeneration & Neurotherapeutics, Duke University School of Medicine, Durham, NC, USA.
8
Department of Neurology, University of Washington School of Medicine, Seattle, WA, USA.
9
Department of Biochemistry and Molecular Medicine, University of California, Davis, Davis, CA, USA.
10
Department of Neurological Surgery, University of California, Davis, Davis, CA, USA. rfberman@ucdavis.edu.

Abstract

The fragile X premutation is a CGG trinucleotide repeat expansion between 55 and 200 repeats in the 5'-untranslated region of the fragile X mental retardation 1 (FMR1) gene. Human carriers of the premutation allele are at risk of developing the late-onset neurodegenerative disorder, fragile X-associated tremor/ataxia syndrome (FXTAS). Characteristic neuropathology associated with FXTAS includes intranuclear inclusions in neurons and astroglia. Previous studies recapitulated these histopathological features in neurons in a knock-in mouse model, but without significant astroglial pathology. To determine the role of astroglia in FXTAS, we generated a transgenic mouse line (Gfa2-CGG99-eGFP) that selectively expresses a 99-CGG repeat expansion linked to an enhanced green fluorescent protein (eGFP) reporter in astroglia throughout the brain, including cerebellar Bergmann glia. Behaviorally these mice displayed impaired motor performance on the ladder-rung test, but paradoxically better performance on the rotarod. Immunocytochemical analysis revealed that CGG99-eGFP co-localized with GFAP and S-100ß, but not with NeuN, Iba1, or MBP, indicating that CGG99-eGFP expression is specific to astroglia. Ubiquitin-positive intranuclear inclusions were found in eGFP-expressing glia throughout the brain. In addition, intracytoplasmic ubiquitin-positive inclusions were found outside the nucleus in distal astrocyte processes. Intriguingly, intranuclear inclusions, in the absence of eGFP mRNA and eGFP fluorescence, were present in neurons of the hypothalamus and neocortex. Furthermore, intranuclear inclusions in both neurons and astrocytes displayed immunofluorescent labeling for the polyglycine peptide FMRpolyG, implicating FMRpolyG in the pathology found in Gfa2-CGG99 mice. Considered together, these results show that Gfa2-CGG99 expression in mice is sufficient to induce key features of FXTAS pathology, including formation of intranuclear inclusions, translation of FMRpolyG, and deficits in motor function.

KEYWORDS:

Electron microscopy of inclusions; FMRpolyG; FXTAS; Fragile X premutation; Glia; Mouse model; Neurodegeneration; Non-cell-autonomous; RAN translation

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