title: Synonymous mutations in CFTR exon 12 affect splicing and are not neutral in evolution.
abstract: It is well established that exonic sequences contain regulatory elements of splicing that overlap with coding capacity. However, the conflict between ensuring splicing efficiency and preserving the coding capacity for an optimal protein during evolution has not been specifically analyzed. In fact, studies on genomic variability in fields as diverse as clinical genetics and molecular evolution mainly focus on the effect of mutations on protein function. Synonymous variations, in particular, are assumed to be functionally neutral both in clinical diagnosis and when measuring evolutionary distances between species. Using the cystic fibrosis transmembrane conductance regulator (CFTR) exon 12 splicing as a model, we have established that about one quarter of synonymous variations result in exon skipping and, hence, in an inactive CFTR protein. Furthermore, comparative splicing evaluation of mammalian sequence divergences showed that artificial combinations of CFTR exon 12 synonymous and nonsynonymous substitutions are incompatible with normal RNA processing. In particular, the combination of the mouse synonymous with the human missense variations causes exon skipping. It follows that there are two sequential levels at which evolutionary selection of genomic variants take place: splicing control and protein function optimization.
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34012 Trieste, Italy.
authors.forename: Franco
authors.initials: F
authors.lastname: Pagani
authors.forename: Michela
authors.initials: M
authors.lastname: Raponi
authors.forename: Francisco E
authors.initials: FE
authors.lastname: Baralle
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics*; D019143:Evolution, Molecular; D005091:Exons / Q000235:genetics*; D015870:Gene Expression; D014644:Genetic Variation; D006801:Humans; D008322:Mammals / Q000235:genetics*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation / Q000235:genetics*; D009841:Oligonucleotides; D012326:RNA Splicing / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012641:Selection, Genetic; D016415:Sequence Alignment
chemical_list: C505032:CFTR protein, human; D009841:Oligonucleotides; D019005:Cystic Fibrosis Transmembrane Conductance Regulator