ABSTRACT
The disks of vertebrate photoreceptors are produced by outgrowths of the plasma membrane. Hence genes that encode retinal proteins targeted to plasma membrane protrusions represent candidates for inherited retinal degenerations. One such candidate is the gene encoding human prominin (mouse)-like 1 (PROML1, previously known as AC133 antigen) which belongs to the prominin family of 5-transmembrane domain proteins. Murine prominin (prom) shows a strong preference for plasma membrane protrusions in a variety of epithelial cells whereas PROML1 is expressed in retinoblastoma cell lines and adult retina. In the present study, molecular genetic analyses of a pedigree segregating for autosomal recessive retinal degeneration indicated that the affected individuals were homozygous for a nucleotide 1878 deletion in PROML1. This alteration is predicted to result in a frameshift at codon 614 with premature termination of translation. Expression of a similar prom deletion mutant in CHO cells indicated that the truncated protein does not reach the cell surface. Immunocytochemistry revealed that prom is concentrated in the plasma membrane evaginations at the base of the outer segments of rod photoreceptors. These findings suggest that loss of prominin causes retinal degeneration, possibly because of impaired generation of the evaginations and/or impaired conversion of the evaginations to disks.
Subject(s)
Frameshift Mutation , Glycoproteins/genetics , Glycoproteins/metabolism , Peptides/genetics , Peptides/metabolism , Retinal Degeneration/genetics , AC133 Antigen , Animals , Antigens, CD , Cell Membrane/metabolism , Chromosomes, Human, Pair 4 , Consanguinity , Female , Gene Expression Regulation , Genetic Markers , Glycoproteins/immunology , Humans , India , Male , Mice , Mice, Inbred Strains , Pedigree , Peptides/immunology , Polydactyly/genetics , Rod Cell Outer Segment/metabolismABSTRACT
We report here the results of a preliminary screening programme to identify natural mutations in the ovine cystic fibrosis transmembrane conductance regulator (CFTR) gene. Nine regions of the ovine CFTR gene were screened, corresponding to human CFTR gene exons 4, 6b, 7, 9, 10, 11, 12, 17b and 20. DNA samples from up to 2000 individual sheep were examined by single-stranded conformation polymorphism (SSCP) of each exon. In addition to the mutation (R297Q) reported previously, we have found several interesting variants, including intronic DNA variants and exonic polymorphisms.
