Smn1^{tm6(SMN2)Mrph}

The Smn allele D contains four tandem SMN genes. The first is a hybrid gene in which a 2.2 kb segment of mouse genome containing exons 7 and 8 of the mouse Smn gene was replaced with a 1.3 kb fragment of human genomic DNA containing exons 7 and 8 of the human SMN2 gene. The next three are identical full-length, 42 kb copies of the human SMN2 gene. A selection cassette located downstream from the final human SMN2 polyadenylation signal was removed by FLPe expression in ES cells leaving a FRT site at the downstream junction between human and mouse DNA. Because exon 7 is derived from human SMN2, it is skipped in approx. 90% of the processed mRNA derived from each of the gene copies. (J:148685)