Use of modified U1 small nuclear RNA for rescue from exon 7 skipping caused by 5′-splice site mutation of human cathepsin A gene

Cathepsin A (CTSA) is a multifunctional lysosomal enzyme, and its hereditary defect causes an autosomal recessive disorder called galactosialidosis. In a certain number of galactosialidosis patients, a base substitution from adenine to guanine is observed at the +3 position of the 7th intron (IVS7 + 3a > g) of the CTSA gene. With this mutation, a splicing error occurs; and consequently mRNA lacking the 7th exon is produced. This skipping of exon 7 causes a frame shift of the transcripts, resulting in a non-functional CTSA protein and hence galactosialidosis. This mutation seems to make the interaction between the 5'-splice site of intron 7 of pre-mRNA and U1 small nuclear RNA (U1 snRNA) much weaker. In the present study, to produce properly spliced mRNA from the CTSA gene harboring this IVS7 + 3a > g mutation, we examined the possible usefulness of modified U1 snRNA that could interact with the mutated 5'-splice site. Toward this goal, we first prepared a model system using a mutant CTSA mini gene plasmid for delivery into HeLa cells. Then, we examined the effectiveness of modified U1 snRNA on the formation of properly spliced mRNA from this mutant CTSA mini gene. As a result, we succeeded in obtaining improved formation of properly spliced CTSA mRNA. Our results suggest the usefulness of modified U1 snRNA for rescue from exon 7 skipping caused by the IVS7 + 3a > g mutation of the CTSA gene.