A model of mRNA splicing in adult lysosomal storage disease (glycogenosis type II).
Glycogenosis type II is a recessively inherited disorder caused by mutations in the acid maltase (GAA) gene. Clinically, three different phenotypes are recognized: Infantile, juvenile and adult forms. A majority of compound heterozygous adult-onset patients carry a t-13g mutation in intron 1 associated with splicing out the first coding exon (exon 2). We have studied the mechanism of this mutation in a model system with wild-type and mutant minigenes expressed in a GAA deficient cell line. We have demonstrated that the mutation does not prevent normal splicing; low levels of correctly spliced mRNA are generated with the mutant construct. The data explain why the mutation is restricted to a milder, adult-onset phenotype. We also demonstrate that splicing out of exon 2 occurs with the wild-type construct, and thus represents alternative splicing which takes place in normal cells. Three splice variants (SV1, SV2 and SV3) are made with both the mutant and the wild-type constructs. Furthermore, as shown by RNAse protection assay, these mRNA variants are less abundant with the mutant construct. Thus, a major effect of the mutation appears to be a low splicing efficiency, since the total amount of all the transcripts generated from the mutant construct is reduced compared with the wild type. The removal of approximately 90% of the intron 1 (2.6 kb) sequence resulted in a dramatic increase in the levels of correctly spliced mRNA, indicating that the intron may contain a powerful transcriptional repressor.
Raben
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N
Arthritis and Rheumatism Branch, National Institute of Arthritis, Musculoskeletal, and Skin Diseases, National Institutes of Health, Bethesda, Maryland, USA.
Nichols
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RC
Martiniuk
F
F
Plotz
P H
PH
D000328:Adult; D017668:Age of Onset; D017398:Alternative Splicing; D002461:Cell Line, Transformed; D005091:Exons / Q000235:genetics; D005347:Fibroblasts; D015870:Gene Expression; D006009:Glycogen Storage Disease Type II / Q000235:genetics*; D006801:Humans; D007438:Introns / Q000235:genetics; D017354:Point Mutation / Q000235:genetics*; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics*; D017384:Sequence Deletion
D012333:RNA, Messenger