| Abstract: |
The idea that point mutations in exons may affect splicing is intriguing and adds an additional layer of complexity when evaluating their possible effects. Even in the best-studied examples, the molecular mechanisms are not fully understood. Here, we use patient cells, model minigenes, and in vitro assays to show that a missense mutation in exon 5 of the medium-chain acyl-CoA dehydrogenase (MCAD) gene primarily causes exon skipping by inactivating a crucial exonic splicing enhancer (ESE), thus leading to loss of a functional protein and to MCAD deficiency. This ESE functions by antagonizing a juxtaposed exonic splicing silencer (ESS) and is necessary to define a suboptimal 3′ splice site. Remarkably, a synonymous polymorphic variation in MCAD exon 5 inactivates the ESS, and, although this has no effect on splicing by itself, it makes splicing immune to deleterious mutations in the ESE. Furthermore, the region of MCAD exon 5 that harbors these elements is nearly identical to the exon 7 region of the survival of motor neuron (SMN) genes that contains the deleterious silent mutation in SMN2, indicating a very similar and finely tuned interplay between regulatory elements in these two genes. Our findings illustrate a mechanism for dramatic context-dependent effects of single-nucleotide polymorphisms on gene-expression regulation and show that it is essential that potential deleterious effects of mutations on splicing be evaluated in the context of the relevant haplotype. © 2007 by The American Society of Human Genetics. All rights reserved. |
| Keywords: |
controlled study; gene mutation; human cell; sequence analysis; single nucleotide polymorphism; exon; missense mutation; exons; mutation, missense; polymorphism, single nucleotide; case report; gene; cell survival; nerve tissue proteins; genetic variability; transcription, genetic; haplotype; gene expression regulation; rna-binding proteins; molecular sequence data; infant; infant, newborn; genes, brca1; gene inactivation; 3' untranslated region; rna stability; immunity; dna primers; sequence homology, nucleic acid; point mutation; rna splicing; genetic polymorphism; motoneuron; cyclic amp response element-binding protein; enhancer region; enhancer elements, genetic; medium chain acyl coenzyme a dehydrogenase; mcad gene; smn2 gene; acyl-coa dehydrogenase; lipid metabolism, inborn errors; muscular atrophy, spinal; silencer elements, transcriptional; smn complex proteins; survival of motor neuron 2 protein
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