It has been estimated that approximately 15% of all mutations that lead to human genetic disease alter mRNA splicing. Our studies have focused on familial dysautonomia (FD), a hereditary sensory and autonomic neuropathy that is caused by a splice mutation in the IKBKAP gene. The mutation results in variable skipping of exon 20 in IKBKAP mRNA, which leads to a tissue-specific reduction of IKAP protein. The fact that FD patients retain the capacity to make both normal mRNA and protein offers an exciting, direct approach towards the development of therapies aimed at increasing levels of cellular IKAP via splicing modification. We have shown that kinetin, a plant cytokinin, enhances exon 20 inclusion and dramatically increases the amount of wild-type IKBKAP mRNA and IKAP protein in FD cells. Recent studies performed in our transgenic mouse models and in human FD carriers show that kinetin can improve IKBKAP splicing in vivo, setting the stage for clinical trials in FD patients. To better understand the role of the IKBKAP gene in vivo, an Ikbkap knock-out mouse model has been created. We demonstrate that deletion of mouse Ikbkap results in failure of embryogenesis, proving for the first time a crucial role for IKAP during mammalian development. Further, to replicate the tissue-specific splicing pattern found in FD, we have generated several transgenic mouse lines that carry either the human wild-type or mutant IKBKAP transgene. Mice carrying the human mutant IKBKAP transgene show a similar tissue-specific splicing pattern to that observed in FD patients, proving conservation of splicing mechanism. Importantly, introduction of the human wild-type and FD transgene into the Ikbkap knock-out line can completely rescue the lethal phenotype. Armed with these unique mouse models and the knowledge that we can directly target the splicing defect, we are now poised to characterize the transcriptional pathways that are disrupted in FD and to identify and target the genes that govern tissue-specific splicing. In the long-term these studies will contribute to the fundamental understanding of normal neuronal development as well as the regulation of disease- associated and tissue-specific splicing. Most importantly, however, they will lead to new targets for the development of therapeutics for FD and other diseases caused by aberrant regulation of mRNA splicing.
Familial Dysautonomia is a severe hereditary sensory and autonomic neuropathy that is caused by a mutations in the IKBKAP gene. The major mutation causes an mRNA splicing error that leads to a tissue-specific reduction of IKAP protein. We have generated several mouse models for FD, and studying these models will enable us to determine which genes are crucial for nervous system development.
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