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Reduced cortical synaptic plasticity and GluR1 expression associated with fragile X mental retardation protein
Jianxue Li1, Marc R Pelletier, Jose-Luis Perez Velazquez
1Division of Cellular and Molecular Biology, Toronto Western Research Institute, University of Toronto, Toronto, Ontario M5T 2S8, Canada.
Abstract:
Lack of expression of the fragile X mental retardation protein (FMRP), due to silencing of the FMR1 gene, causes the Fragile X syndrome. Although FMRP was characterized previously to be an RNA binding protein, little is known about its function or the mechanisms underlying the Fragile X syndrome. Here we report that the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor subunit, GluR1, was decreased in the cortical synapses, but not in the hippocampus or cerebellum, of FMR1 gene knockout mice. Reduced long-term potentiation (LTP) was also found in the cortex but not in the hippocampus. Another RNA binding protein, FXR; the N-methyl-D-aspartate receptor subunit, NR2; and other learning-related proteins including c-fos, synapsin, myelin proteolipid protein, and cAMP response element binding protein were not different between FMR1 gene knockout and wild-type mice. These findings suggest that the depressed cortical GluR1 expression and LTP associated with FMRP deficiency could contribute to the Fragile X phenotype.
Insights
Fragile X syndrome results from a lack of fragile X mental retardation protein (FMRP). This study found reduced GluR1 expression and long-term potentiation (LTP) in the cortex of affected mice, suggesting a role in the syndrome's phenotype.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Background:
- Fragile X syndrome is caused by the absence of fragile X mental retardation protein (FMRP), a known RNA-binding protein.
- The precise function of FMRP and the molecular mechanisms underlying Fragile X syndrome remain incompletely understood.
Purpose of the Study:
- To investigate the role of FMRP in synaptic plasticity and protein expression in the brain.
- To identify specific molecular changes associated with FMRP deficiency in a mouse model.
Main Methods:
- Utilized FMR1 gene knockout mice to model Fragile X syndrome.
- Compared cortical and hippocampal synaptic protein expression (specifically GluR1) between knockout and wild-type mice.
- Assessed long-term potentiation (LTP) in cortical and hippocampal tissues.
Main Results:
- Cortical synapses showed decreased expression of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor subunit, GluR1, in FMR1 knockout mice.
- Reduced long-term potentiation (LTP) was observed in the cortex but not the hippocampus of knockout mice.
- Expression levels of other proteins, including FXR, NR2, c-fos, synapsin, myelin proteolipid protein, and CREB, were unchanged.
Conclusions:
- FMRP deficiency leads to reduced GluR1 expression and impaired cortical LTP.
- These synaptic alterations in the cortex may contribute to the characteristic phenotype of Fragile X syndrome.