Striatal Function in Fragile X Syndrome

Abstract

Fragile X syndrome (FXS) is the leading genetic cause of autism caused by a mutation of the Fmr1 gene. This mutation results in the loss of fragile X mental retardation protein (FMRP) which associates with and regulates four percent of brain mRNAs. Symptoms associated with FXS in humans range from physical characteristics, such as enlarged ears and pronounced forehead and chin, to behavioral characteristics, such as stereotypies and social deficits. Using total fragile X mental retardation 1 knockout (Fmr1 KO) mice, a model for FXS, and/or conditional Fmr1 KO mice, social and natural reward behavioral assays were performed, followed by RNA and protein analyses of FMRP targets with known roles in synaptic function, to further define these characteristics. Results from these experiments showed a trend towards significant social deficits in mice lacking FMRP specifically in cholinergic neurons. Protein analysis revealed differences of expression across cytosolic and synaptic fractions for activity-regulated cytoskeleton-associated protein (ARC), Ras-related C3 botulinum toxin substrate 1 (RAC1), postsynaptic density-95 (PSD-95), as well as for an unidentified band labeled by the ARC antibody. Quantitative (q)PCR analysis identified differences of expression at the RNA level for targets diacylglycerol kinase kappa (Dgkκ) and SH3 and multiple ankyrin repeat domains 2, or Shank2. Overall, these results point to a possible role for FMRP in cholinergic cells in elements of social behavior and raise questions about its role at translational and transcriptional levels.