In humans, a highly homologous gene, SMN2, which lies centromeric to SMN1 on chromosome www.selleckchem.com/products/Bosutinib.html 5q, partially but poorly compensates for reduced SMN levels. While five nucleotides, none of which lead to an amino acid change, differentiate SMN2 from SMN1, SMN2 mRNA, through alternative splicing, results predominantly in transcripts lacking exon 7, thereby leading to a truncated, unstable

protein (Lorson et al., 2010). Only 10% of the transcripts are translated into functional full-length SMN protein. As a result, SMN2 normally contributes little to the overall levels of full-length SMN protein. However, copy numbers of the SMN2 gene in the human genome are variable, ranging from 0 to 4 copies in the genome. Higher SMN2 copy numbers result in increased full-length protein levels, which correlate with milder phenotypes in patients (Mailman et al., 2002). As such, current targets for therapy have focused on drugs that either promote overall SMN2 expression or promote exon 7 inclusion (Sendtner, 2010). While transgenic mouse models exist, mice lack SMN2 and homozygous knockout of SMN1 leads to embryonic lethality, which has necessitated generating PD0332991 transgenic mice that harbor human SMN2 (Hsieh-Li et al., 2000 and Monani et al., 2000). To create a patient-specific iPS cell model of SMA, skin fibroblasts were obtained from a child with SMA type 1. The subject was 3 years old at the time of sample collection

and had two copies of SMN2. Fibroblasts from his unaffected mother were also reprogrammed to iPS cells by lentiviral transduction of OCT4, SOX2, NANOG, and LIN28 ( Ebert et al., 2009). One iPS clone from the SMA child

(iPS-SMA) and the unaffected mother (WT-iPS) was subsequently used in their studies. As expected, SMA fibroblasts and iPS cells lacked SMN1 expression, expressed the alternatively spliced delta exon 7 mRNA, and demonstrated reduced levels of full-length those SMN contributed by SMN2 expression. Following directed differentiation of iPS cells to spinal motor neurons, no significant differences in motor neuron numbers were seen after a total of 4 weeks of in vitro differentiation. At 6 weeks, the total numbers of neurons, based on the overall number of cells positive for neuronal marker TUJ1, were equivalent between WT and SMA (15.78% in WT and 15.55% in SMA). However, when cultures were specifically evaluated for motor neurons based on coexpression of TUJ1 and ChAT, motor neuron numbers were reduced from the SMA cultures (4.3% in SMA versus 24.2% in WT). In addition, SMA-iPS motor neurons were smaller in soma size and synapse formation appeared to be compromised ( Ebert et al., 2009). To demonstrate that SMN production could pharmacologically be altered in this disease line, two drugs known to increase SMN production were tested. SMN can be localized to discrete, punctuate structures called “gems” (Liu and Dreyfuss, 1996).