Functional properties and evolutionary splicing constraints on a composite exonic regulatory element of splicing in CFTR exon 12.
In general, splicing regulatory elements are defined as Enhancers or Silencers depending on their positive or negative effect upon exon inclusion. Often, these sequences are usually present separate from each other in exonic/intronic sequences. The Composite Exonic Splicing Regulatory Elements (CERES) represent an extreme physical overlap of enhancer/silencer activity. As a result, when CERES elements are mutated the consequences on the splicing process are difficult to predict. Here, we show that the functional activity of the CERES2 sequence in CFTR exon 12 is regulated by the binding, in very close proximity to each other, of several SR and hnRNP proteins. Moreover, our results show that practically the entire exon 12 sequence context participate in its definition. The consequences of this situation can be observed at the evolutionary level by comparing changes in conservation of different splicing elements in different species. In conclusion, our study highlights how it is increasingly difficult to define many exonic sequences by simply breaking them down in isolated enhancer/silencer or even neutral elements. The real picture is close to one of continuous competition between positive and negative factors where affinity for the target sequences and other dynamic factors decide the inclusion or exclusion of the exon.
Haque
Ariful
A
International Centre for Genetic Engineering and Biotechnology, 34149 Trieste, Italy.
Buratti
Emanuele
E
Baralle
Francisco E
FE
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D005091:Exons; D006367:HeLa Cells; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000378:metabolism; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D012326:RNA Splicing; D016601:RNA-Binding Proteins / Q000378:metabolism; D038621:Regulatory Sequences, Ribonucleic Acid; D000068103:Serine-Arginine Splicing Factors
C505032:CFTR protein, human; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D038621:Regulatory Sequences, Ribonucleic Acid; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000068103:Serine-Arginine Splicing Factors