Gene expression profiles in the cerebellum of transgenic mice over expressing the human FMR1 gene with CGG repeats in the normal range

Abstract

ABSTRACT. Modifications in the GABA pathway are considered to be responsible for motor alterations in animal models for fragile X-associated tremor ataxia syndrome. We analyzed the expression profile in the cerebellum in a transgenic mouse model that over expresses the human FMR1 gene with CGG repeats in the normal range. We used the "GeneChip Mouse Gene 1.0 ST Array" from Affymetrix analyzing 28,853 well-described and -characterized genes. Based on data from the comparative analysis of the expression profile, we detected a significant gradient with a P value <0.1 and changes in expression equal to or greater than 1.5 times compared to the control mouse genes. There were significant changes in the expression of 104 genes, among which 72% had decreased and 28% had increased expression. With the exception of GabarapL2, no changes in expression of genes from the GABA pathway were observed, which may explain the absence of an altered motor phenotype in these mice. These results further support the view that toxic effects in fragile X-associated tremor ataxia syndrome are due to expansion of CGG repeats rather than increased mRNA levels, since in the transgenic mice the FMR1 mRNA levels were increased 20-100 times compared with those of control littermates.

Mouse models of the fragile X premutation and fragile X-associated tremor/ataxia syndrome

“…These findings support the notion that overall abundance of a CGG repeat molecule may be important for generating a pathological phenotype [36]. To investigate the potential deleterious effects produced by overexpression of FMR1 mRNA with a normal CGG repeat length, transgenic mice that overexpress FMR1 mRNA bearing a normal length CGG29 repeat have been generated [41]. The CGG29 transgenic mouse was obtained by pronuclear injection of a construct containing the human FMR1 cDNA with 29 CGG repeats under control of a SV40/T7 promoter.…”

“…Microarray analysis in the cerebellum of transgenic mice that overexpress human FMR1 with a normal range CGG29 repeat has also been carried out, but there were no clear changes in the GABAergic system compared to controls. Among GABA-related genes, only up-regulation of the GABA A receptor-associated protein-like 2 ( Gabarapl2 ) gene was observed [41]. These results provide additional support that pathology in CGG KI mice, at least in the GABA system, is due to expansion of CGG repeats rather than increased mRNA levels, given that FMR1 mRNA levels were increased 20 to 100 times in these transgenic mice compared with those of WT littermates.…”

“…Up-regulation of Let-7 miRNA has been also been reported in a Drosophila model of FXTAS [88]. This is important because several miRNAs are up-regulated in human premutation carriers [89], although they differed from those observed in CGG transgenic mice [41]. …”

“…Toxicity appears to be the result of the expanded CGG repeat per se , and not of overexpression of FMR1 . This is supported by the fact that ectopic expression of a CGG repeat expansion in the premutation range is sufficient to induce formation of intranuclear inclusions, reduce cell viability, trigger neuronal death (for example, Purkinje cell loss) and produce behavioral deficits [34,59,107], whereas overexpression of Fmr1 mRNA without a CGG repeat expansion does not appear to be toxic [41]. Similar RNA toxicity has been suggested to underlie the pathology in several repeat diseases, including the myotonic muscular dystrophies.…”

In silico, in vitro, and in vivo Approaches to Identify Molecular Players in Fragile X Tremor and Ataxia Syndrome

“…A Drosophila model shows that repeat length is a direct cause of pathology since longer repeats show extreme retina pathology while short repeats result in little pathology (Jin et al, 2003). To confirm these findings in mice, transgenic mice were generated overexpressing FMR1 mRNA with a normal length CGG repeat consisting of 29CGGs (Fernandez et al, 2012). Human FMR1 cDNA with 29CGG repeats under control of a SV40/T7 promoter was injected in oocytes to generate these transgenic 29CGG mice with 20-100 fold increase in FMR1 mRNA in tissues such as liver, cerebral cortex and cerebellum.…”