title: Alternative Splicing Shapes the Phenotype of a Mutation in BBS8 To Cause Nonsyndromic Retinitis Pigmentosa.
abstract: Bardet-Biedl syndrome (BBS) is a genetic disorder affecting multiple systems and organs in the body. Several mutations in genes associated with BBS affect only photoreceptor cells and cause nonsyndromic retinitis pigmentosa (RP), raising the issue of why certain mutations manifest as a systemic disorder whereas other changes in the same gene affect only a specific cell type. Here, we show that cell-type-specific alternative splicing is responsible for confining the phenotype of the A-to-G substitution in the 3' splice site of BBS8 exon 2A (IVS1-2A>G mutation) in the BBS8 gene to photoreceptor cells. The IVS1-2A>G mutation leads to missplicing of BBS8 exon 2A, producing a frameshift in the BBS8 reading frame and thus eliminating the protein specifically in photoreceptor cells. Cell types other than photoreceptors skip exon 2A from the mature BBS8 transcript, which renders them immune to the mutation. We also show that the splicing of Bbs8 exon 2A in photoreceptors is directed exclusively by redundant splicing enhancers located in the adjacent introns. These intronic sequences are sufficient for photoreceptor-cell-specific splicing of heterologous exons, including an exon with a randomized sequence.
authors.affiliation: Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Murphy
authors.affiliation: Department of Ophthalmology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA.
authors.forename: Ratnesh
authors.initials: R
authors.lastname: Singh
authors.affiliation: Department of Ophthalmology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA.
authors.forename: Saravanan
authors.initials: S
authors.lastname: Kolandaivelu
authors.affiliation: Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA Department of Ophthalmology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA Center for Neuroscience, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA ramamurthyv@wvuhealthcare.com pstoilov@hsc.wvu.edu.
authors.forename: Visvanathan
authors.initials: V
authors.lastname: Ramamurthy
authors.affiliation: Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA ramamurthyv@wvuhealthcare.com pstoilov@hsc.wvu.edu.
authors.forename: Peter
authors.initials: P
authors.lastname: Stoilov
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D000831:Animals, Newborn / Q000033:anatomy & histology / Q000235:genetics; D003315:Cornea / Q000378:metabolism*; D003598:Cytoskeletal Proteins; D004742:Enhancer Elements, Genetic; D005091:Exons; D016368:Frameshift Mutation; D051379:Mice; D008810:Mice, Inbred C57BL; D008869:Microtubule-Associated Proteins / Q000235:genetics* / Q000378:metabolism; D009928:Organ Specificity; D010786:Photoreceptor Cells / Q000378:metabolism*; D012174:Retinitis Pigmentosa / Q000235:genetics* / Q000473:pathology
chemical_list: D003598:Cytoskeletal Proteins; D008869:Microtubule-Associated Proteins; C561225:Ttc8 protein, mouse