Project description:The molecular mechanism(s) leading to Purkinje neuron loss in the neurodegenerative disorder Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS) are limited by the complex morphology of this cell type. Purkinje neurons are notoriously difficult to isolate and maintain in culture presenting considerable difficultly to identify molecular changes in response to riboCGG repeat-containing mRNA that induces neurotoxicity in FXTAS. Several studies have uncovered a number of RNA binding proteins involved in translation that aberrantly interact with the toxic RNA; however, whether these interactions alter the translational profile of cells has not been investigated. Here we employ bacTRAP translational profiling to demonstrate that Purkinje neurons ectopically expressing 90 CGG repeats exhibit a dramatic change in their translational profile even prior to the onset of riboCGG-induced phenotypes. This approach identified nearly 500 transcripts that are differentially associated with ribosomes in r(CGG)90-expressing mice. Functional annotation cluster analysis revealed broad ontologies enriched in the r(CGG)90 list, including RNA binding and response to stress. Intriguingly, a transcript for the Tardbp gene, implicated in a number of other neurodegenerative disorders, exhibits altered association with ribosomes in the presence of r(CGG)90 repeats. We therefore tested and showed that reduced association of Tardbp mRNA with the ribosomes results in a loss of TDP-43 protein expression in r(CGG)90–expressing Purkinje neurons. Furthermore, we showed that TDP-43 could modulate the rCGG repeat-mediated toxicity in a Drosophila model that we developed previously. These findings together suggest translational dysregulation may be an underlying mechanism of riboCGG-induced neurotoxicity and provide insight into the pathogenicity of FXTASBAC-trap studies of Purkinje cels in normal and mutant mice Looking for cell type specific gene expression differences caused by mutation in FMR1 using BAC-Trap RNA capture assay. A cutoff value of 4.5 for mean probe_set mean across all 18 hybridizations was used to determine a cutoff for expression in Purkinje cells. This 16040 corresponded to a mean value of at least 3.4323 in the 4week time point. L7CGG90Fmr1:Pcp2 BAC (r(CGG)90 BAC) and wild-type:L7/Pcp2 BAC (WT BAC) transgenic mice used in this study have a 50% C57B6 and 50% FVB genetic background and were derived from the same parents by crossing L7CGG90Fmr1 heterozygote transgenics (100% C57B6 background) with L7/Pcp2eEGFPL10a BAC homozygous transgenics (100% FVB background). All mice reported were F1 progeny and were therefore hemizygous for one or both transgenes. Littermate wild-type mice were used for all experiments whenever possible.

Project description:The molecular mechanism(s) leading to Purkinje neuron loss in the neurodegenerative disorder Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS) are limited by the complex morphology of this cell type. Purkinje neurons are notoriously difficult to isolate and maintain in culture presenting considerable difficultly to identify molecular changes in response to riboCGG repeat-containing mRNA that induces neurotoxicity in FXTAS. Several studies have uncovered a number of RNA binding proteins involved in translation that aberrantly interact with the toxic RNA; however, whether these interactions alter the translational profile of cells has not been investigated. Here we employ bacTRAP translational profiling to demonstrate that Purkinje neurons ectopically expressing 90 CGG repeats exhibit a dramatic change in their translational profile even prior to the onset of riboCGG-induced phenotypes. This approach identified nearly 500 transcripts that are differentially associated with ribosomes in r(CGG)90-expressing mice. Functional annotation cluster analysis revealed broad ontologies enriched in the r(CGG)90 list, including RNA binding and response to stress. Intriguingly, a transcript for the Tardbp gene, implicated in a number of other neurodegenerative disorders, exhibits altered association with ribosomes in the presence of r(CGG)90 repeats. We therefore tested and showed that reduced association of Tardbp mRNA with the ribosomes results in a loss of TDP-43 protein expression in r(CGG)90–expressing Purkinje neurons. Furthermore, we showed that TDP-43 could modulate the rCGG repeat-mediated toxicity in a Drosophila model that we developed previously. These findings together suggest translational dysregulation may be an underlying mechanism of riboCGG-induced neurotoxicity and provide insight into the pathogenicity of FXTASBAC-trap studies of Purkinje cels in normal and mutant mice Looking for cell type specific gene expression differences caused by mutation in FMR1 using BAC-Trap RNA capture assay. A cutoff value of 4.5 for mean probe_set mean across all 18 hybridizations was used to determine a cutoff for expression in Purkinje cells. This 16040 corresponded to a mean value of at least 3.4323 in the 4week time point.

Dataset Information

TRAP-seq from hippocampus isolated from WT and Fmr1-/y mice bred to Snap25-EGFPL10a mice

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