Human Molecular Genetics Advance Access published online on March 27, 2009
Human Molecular Genetics, doi:10.1093/hmg/ddp157
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A SMN missense mutation complements SMN2 restoring snRNPs and rescuing SMA mice
1 Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, OH, 43210 USA 2 Department of Neurology, The Ohio State University, Columbus, OH, 43210 USA 3 Center for Motor Neuron Biology and Disease, Department of Pathology and Cell Biology, Columbia University Medical Center, New York, NY 10032, USA 4 Department of Neuroscience and Center for Molecular Neurobiology, The Ohio State University, Columbus OH 43210, USA 5 Departments of Neurology and Pediatrics, The John Hopkins Hospital, Baltimore, MD, 21287 USA 6 The Jackson Laboratory, 600 Main Street, Bar Harbor, Maine 04609, USA
* To whom correspondence should be addressed at: Department of Molecular and Cellular Biochemistry, 363 Hamilton Hall, 1645 Neil Ave, Columbus, OH, 43210 USA. Tel +1 6146884759; Fax: +1 6142924118 Email: burghes.1{at}osu.edu
Received January 26, 2009; Revised March 25, 2009; Accepted March 25, 2009
Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disease. Loss of the survival motor neuron (SMN1) gene, in the presence of the SMN2 gene causes SMA. SMN functions in snRNP assembly in all cell types, however, it is unclear how this function results in specifically motor neuron cell death. Lack of endogenous mouse SMN (Smn) in mice results in embryonic lethality. Introduction of 2 copies of human SMN2 results in a mouse with severe SMA, while 1 copy of SMN2 is insufficient to overcome embryonic lethality.
We show that SMN(A111G), an allele capable of snRNP assembly, can rescue mice that lack Smn and contain either one or two copies of SMN2 (SMA mice). The correction of SMA in these animals was directly correlated with snRNP assembly activity in spinal cord, as was correction of snRNA levels. These data support snRNP assembly as being the critical function affected in SMA and suggests that the levels of snRNPs are critical to motor neurons.
Furthermore, SMN(A111G) cannot rescue Smn-/- mice without SMN2 suggesting that both SMN(A111G) and SMN from SMN2 undergo intragenic complementation in vivo to function in heteromeric complexes that have greater function than either allele alone. The oligomer composed of limiting full-length SMN and SMN(A111G) has substantial snRNP assembly activity. Also, the SMN(A2G) and SMN(A111G) alleles in vivo did not complement each other leading to the possibility that these mutations could affect the same function.
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