Growth Hormone Splicing and Treatment of Disease Using RNA Interference
Splicing is the regulated removal of introns and the concurrent ligation of exons to produce mature mRNA transcripts. Variability in this tightly regulated process is responsible for an extraordinarily diverse proteome from a relatively small mammalian genome. Alternative splicing can lead to differential exon inclusion or exclusion, as can aberrant splicing, and such transcripts therefore differ from constitutively spliced transcripts. Where mistakes in splicing cause disease, the resulting mutant transcripts appear to be ideal targets for RNA interference (RNAi). In the case of inappropriate exon inclusion, small interfering RNAs (siRNAs) can be targeted to specific exons. When exon skipping prevails, siRNAs can be designed complementary to the specific exon-exon junctions that are not present in normal transcripts. The human growth hormone gene, GH-1, nicely illustrates these points. Constitutive splicing of all 5 exons produces the normal hormone but aberrant skipping of exon 3 can lead to the production of a dominant negative isoform and associated Isolated Growth Hormone Deficiency type II (IGHD II). This thesis describes research into understanding the causes of exon 3 skipping and shows that siRNAs targeting the unique exon 2-exon 4 sequence in mutant transcripts can prevent onset of IGHD II in a mouse model.