Human Molecular Genetics Advance Access originally published online on May 4, 2006
Human Molecular Genetics 2006 15(12):1984-1994; doi:10.1093/hmg/ddl121
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Exaggerated behavioral phenotypes in Fmr1/Fxr2 double knockout mice reveal a functional genetic interaction between Fragile X-related proteins
1Department of Molecular and Human Genetics and 2Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA and 3Department of Clinical Genetics, Erasmus University, 3000 DR Rotterdam, The Netherlands
* To whom correspondence should be addressed at: Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA. Tel: +1 7137986124; Fax: +1 7137986521; Email: rpaylor{at}bcm.tmc.edu
Received March 31, 2006; Accepted May 1, 2006
Individuals affected by Fragile X syndrome (FXS) experience cognitive impairment, hyperactivity, attention deficits, social anxiety and autistic-like behaviors. FXS results from the loss of expression of the Fragile X mental retardation (FMR1) gene, whose protein product FMRP is thought to play an important role in neuronal function and synaptic plasticity. Two paralogs of FMRP, FXR1P and FXR2P, have been identified, forming the Fragile X-related (FXR) family of proteins. Although the functions of FXR1P and FXR2P are not well understood, there are similarities among all three FXR proteins in gene structure, amino acid sequence, expression pattern and cellular functions. Mouse models have been described for loss of Fmrp, Fxr1p and Fxr2p, the mouse homologs of FMRP, FXR1P and FXR2P. In earlier studies, we found that Fmr1 knockout (KO) mice, which do not express Fmrp, and Fxr2 KO mice, which do not express Fxr2p, show similarities in some behavioral responses such as hyperactivity. To better understand the functional relationship between FMRP and FXR2P, we generated Fmr1 KO, Fxr2 KO, Fmr1/Fxr2 double KO and wild-type control mice as littermates on the same genetic background and examined them in several behavioral assays. Results show that Fmr1/Fxr2 double KO mice have exaggerated behavioral phenotypes in open-field activity, prepulse inhibition of acoustic startle response and contextual fear conditioning when compared with Fmr1 KO mice, Fxr2 KO mice or wild-type littermates. Our findings suggest that Fmr1 and Fxr2 genes contribute in a cooperative manner to pathways controlling locomotor activity, sensorimotor gating and cognitive processes.
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