Mutations in one of the duplicated Survival of Motor Neuron (SMN) genes lead to the progressive loss of motor neurons and subsequent development of Spinal Muscular Atrophy (SMA), a common, usually fatal, pediatric disease. Homozygous absence of the telomeric copy (SMN1) correlates with development of SMA because differential splicing of the centromeric copy (SMN2) predominantly produces a biologically inactive protein isoform. The low amounts of SMN produced from SMN2 are adequate for a fetus to develop, but are insufficient to maintain healthy motor neurons throughout life. One of the biological functions of SMN is to catalyze the biosynthesis of components of the spliceosome, an enzymatic machinery that removes introns from pre-mRNAs. Indeed using animal models it was demonstrated that purified building blocks of the spliceosome are sufficient to rescue developmental defect caused by reduced levels of SMN. These experiments demonstrated that elevated levels of the splicing machinery are essential for proper differentiation of stem cells into motor neurons.
Based on these observations we hypothesize that alternative pre-mRNA splicing of several genes set in stone a developmental pathway that imprints unique gene expression features throughout motor neuron differentiation and maintenance. In this application we propose to test this hypothesis by analyzing genome-wide alternative pre-mRNA splicing during the differentiation of human embryonic stem cells into motor neurons.
Verification of the hypothesis will provide new insights into the biological processes that specify longevity of motor neurons and direct future research to identify alternative targets for SMA and other neurological disease therapy.
Recent experiments demonstrated that pre-mRNA splicing is required to establish gene expression profiles that dictate the longevity of developing motor neurons. The ability to differentiate human embryonic stem cells into motor neurons in cell culture permits an evaluation of gene expression and alternative pre-mRNA splicing throughout the differentiation process. This unique opportunity is available in part because the state of California actively supports research using human embryonic stem cells. The results obtained from this proposal will establish gene expression and alternative splicing maps that link defined developmental events with gene expression and motor neuron differentiation. The resulting signature profiles will enable future studies investigating motor neuron longevity and they will likely identity new molecular targets to battle various motor neuron diseases that have in common premature motor neuron death. As such, the information gained from the proposed experiments would maintain California’s leading status in stem cell research and may provide the intellectual framework for the development of new therapeutic developments in the private sector. An additional benefit to California citizens could be the availability of cutting edge technologies in clinical trials carried out at California's research centers.