Ethylnitrosourea-induced base pair substitution affects splicing of the mouse gammaE-crystallin encoding gene leading to the expression of a hybrid protein and to a cataract.
A novel ENU-induced mutation in the mouse leading to a nuclear and cortical opacity of the eye lens (ENU418) was mapped to proximal chromosome 1 by a genome-wide mapping approach. It suggests that the cluster of gamma-crystallin encoding genes (Cryg) and the betaA2-crystallin encoding gene Cryba2 are excellent candidate genes. An A --> G exchange in the middle of intron 1 of the Cryge gene was found as the only alteration cosegregating with the cataractous phenotype. The mutation was confirmed by the presence of a novel restriction site for ApaI in the corresponding genomic DNA fragment. The mutation represses splicing of intron 1; the additional 92 bp in the corresponding cDNA leads to a frameshift and the expression of a novel hybrid protein containing 3 amino acids of the gammaE-crystallin at the N terminus, but 153 novel amino acids. The Cryge(ENU418) protein has a calculated molecular mass of approximately 15.6 kD and an alkaline isoelectric point (pH 10.1) and is predicted to have two hydrophobic domains. Western blot analysis using a polyclonal antibody against the hydrophilic C-terminal part of the Cryge(ENU418)-specific protein demonstrated its stable expression in the cataractous lenses; it was not found in the wild types. Histological analysis of the cataractous lenses indicated that the expression of the new protein disrupts the cellular structure of the eye lens.
Graw
Jochen
J
GSF-National Research Center for Environment and Health, Institute of Mammalian Genetics, D-85764 Neuherberg, Germany. graw@gsf.de
Neuhäuser-Klaus
Angelika
A
Löster
Jana
J
Klopp
Norman
N
Favor
Jack
J
D000477:Alkylating Agents / Q000494:pharmacology; D000818:Animals; D001483:Base Sequence; D002386:Cataract / Q000235:genetics*; D002874:Chromosome Mapping; D003459:Crystallins / Q000235:genetics*; D005038:Ethylnitrosourea / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000187:drug effects; D012326:RNA Splicing / Q000187:drug effects*; D011993:Recombinant Fusion Proteins / Q000235:genetics*; D038222:gamma-Crystallins
D000477:Alkylating Agents; D003459:Crystallins; D011993:Recombinant Fusion Proteins; C107256:crystallin gammaE; D038222:gamma-Crystallins; D005038:Ethylnitrosourea