Molecular and phenotypic reassessment of an infrequently used mouse model for spinal muscular atrophy

Proximal spinal muscular atrophy (SMA) results from loss of the survival molar neuron 1 (SMN1) gene, with retention of its nearly identical homolog. SMN2. There is a direct correlation between disease severity and SMN2 copy number Mice do not have a Smn2 gene. and thus cannot naturally replicate the disorder However, two murine models of SMA have been generated using SMN2-BAC transgenic mice bred onto a mutant Smn background In these instances mice die shortly after birth, have variable phenotypes within the same litter. or completely correct the SMA phenotype Both models have been imported to The Jackson Laboratory for distribution to the research community To ensure that similar results ate obtained after importation to The Jackson Laboratory to what was originally reported in the literature. we have begun a molecular and phenotypic evaluation of these mouse models Here we report our findings for the SMA mouse model that has been deposited by the Li group from Taiwan These mice. JAX stock number TJL-005058. are homozygous for the SMN2 transgene, Tg(SMN2)2Hung, and a targeted Smn allele that lacks exon 7, Smn1(tmlHung) Our findings are consistent with those reported originally for this line and clarify some of the original data In addition, we have cloned and mapped the integration site for Tg(SMN2)2Hung to Chromosome 4, and provide a simple genotyping assay that is specific to the junction fragment. Finally. based upon the survival data from Out generic crosses, we suggest that tills underused SMA model may be a useful compliment or alternative to the more commonly used "delta7" SMA mouse We provide bleeding schemes in which two genotypes of mice call be generated so that 50% of the fitter will be SMA-like pups while 50% will be controls (C) 2009 Elsevier Inc All rights reserved