Human Molecular Genetics Advance Access originally published online on May 5, 2004
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Human Molecular Genetics, 2004, Vol. 13, No. 13 1291-1302
DOI: 10.1093/hmg/ddh150
Human Molecular Genetics, Vol. 13, No. 13 © Oxford University Press 2004; all rights reserved
Fxr1 knockout mice show a striated muscle phenotype: implications for Fxr1p function in vivo
1Department of Clinical Genetics and 2Department of Pathology, Erasmus University, Rotterdam, The Netherlands, 3Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA and 4Institut de Genetique et de Biologie Moleculaire et Cellulaire, CNRS/INSERM/ULP, Illkirch, France
Received January 23, 2004; Accepted April 25, 2004
FXR1 is one of the two known homologues of FMR1. FXR1 shares a high degree of sequence homology with FMR1 and also encodes two KH domains and an RGG domain, conferring RNA-binding capabilities. In comparison with FMRP, very little is known about the function of FXR1P in vivo. Mouse knockout (KO) models exist for both Fmr1 and Fxr2. To study the function of Fxr1 in vivo, we generated an Fxr1 KO mouse model. Homozygous Fxr1 KO neonates die shortly after birth most likely due to cardiac or respiratory failure. Histochemical analyses carried out on both skeletal and cardiac muscles show a disruption of cellular architecture and structure in E19 Fxr1 neonates compared with wild-type (WT) littermates. In WT E19 skeletal and cardiac muscles, Fxr1p is localized to the costameric regions within the muscles. In E19 Fxr1 KO littermates, in addition to the absence of Fxr1p, costameric proteins vinculin, dystrophin and 
-actinin were found to be delocalized. A second mouse model (Fxr1+neo), which expresses strongly reduced levels of Fxr1p relative to WT littermates, does not display the neonatal lethal phenotype seen in the Fxr1 KOs but does display a strongly reduced limb musculature and has a reduced life span of 
18 weeks. The results presented here point towards a role for Fxr1p in muscle mRNA transport/translation control similar to that seen for Fmrp in neuronal cells.
* To whom correspondence should be addressed. Tel: +1 7137984787; Fax: +1 7137981116; Email: nelson@bcm.tmc.edu
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