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The Journal of Neuroscience, September 28, 2005, 25(39):8908-8916; doi:10.1523/JNEUROSCI.0932-05.2005
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Development/Plasticity/Repair
A Reduced Number of Metabotropic Glutamate Subtype 5 Receptors Are Associated with Constitutive Homer Proteins in a Mouse Model of Fragile X Syndrome
Raffaella Giuffrida,1
Sebastiano Musumeci,3
Simona D'Antoni,1,5
Carmela Maria Bonaccorso,2,3
Anna Maria Giuffrida-Stella,1
Ben A. Oostra,4 and
Maria Vincenza Catania3,5
1Department of Chemical Sciences, Section of Biochemistry and Molecular Biology and 2Department of Physiological Sciences, University of Catania, 95125 Catania, Italy, 3Department of Neurology, Oasi Maria Santissima Institute for Research on Mental Retardation and Brain Aging (Istituto di Ricovero e Cura a Carattere Scientifico), 94018 Troina (EN), Italy, 4Department of Clinical Genetics, Erasmus Medical Center, 3000 DR Rotterdam, The Netherlands, and 5Institute of Neurological Sciences, Section of Catania, Consiglio Nazionale delle Ricerche, 95123 Catania, Italy
Fragile X (FRAX) syndrome is a common inherited form of mental retardation resulting from the lack of fragile X mental retardation protein (FMRP) expression. The consequences of FMRP absence in the mechanism underlying mental retardation are unknown. Here, we tested the hypothesis that glutamate receptor (GluR) expression might be altered in FRAX syndrome. Initial in situ hybridization and Western blotting experiments did not reveal differences in mRNA levels and protein expression of AMPA and NMDA subunits and metabotropic glutamate subtype 5 (mGlu5) receptors between control and Fmr1 knock-out (KO) mice during postnatal development. However, a detergent treatment (1% Triton X-100) revealed a selective reduction of mGlu5 receptor expression in the detergent-insoluble fraction of synaptic plasma membranes (SPMs) from KO mice, with no difference in the expression of NR2A, GluR1, GluR2/3, GluR4, and Homer proteins. mGlu5 receptor expression was also lower in Homer immunoprecipitates from Fmr1 KO SPMs. Homer, but not NR2A, mGlu5, and GluR1, was found to be less tyrosine phosphorylated in Fmr1 KO than control mice. Our data indicate that, in FRAX syndrome, a reduced number of mGlu5 receptors are tightly linked to the constituents of postsynaptic density and, in particular, to the constitutive forms of Homer proteins, with possible consequent alterations in synaptic plasticity.
Key words: mental retardation; synaptosomes; synaptic plasticity; glutamate receptors; Homer; tyrosine phosphorylation
Received Aug 18, 2003;
revised August 11, 2005;
accepted August 14, 2005.
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