Characterization of a new, dominant V124E mutation in the mouse alpha A-crystallin-encoding gene

Purpose. During an ethylnitrosourea (ENU) mutagenesis screening, mice were tested for the occurrence of dominant cataracts. The purpose of the study w as morphologic description, mapping of the mutant gene, and characterizatio n of the underlying molecular lesion in a particular mutant, Aey7. Methods. Isolated lenses were photographed and histologic sections of the e ye were analyzed according to standard procedures. Linkage analysis was per formed with a set of microsatellite markers covering all autosomal chromoso mes. cDNA was amplified after reverse transcription of tens mRNA. For PCR, cDNA or genomic DNA was used as a template. Results. Nuclear opacity and posterior suture anomaly were visible at eye o pening and progressed to a nuclear and zonular cataract at 2 months of age. The opacity as well as the microphthalmia was more pronounced in the homoz ygotes than in the heterozygotes. The mutation was mapped to chromosome 17 between the markers D16Mit133 and D17Mit180. This position made the alphaA- crystaflin-encoding gene (Cryaa) an excellent candidate gene. Sequence anal ysis revealed a mutation of a T to an A at position 371 in the Cryaa cDNA. The mutation was confirmed by an additional MnlI restriction site in the ge nomic DNA of homozygous mutants leading to replacement of Val with Glu at c odon 124 affecting the C-terminal region of, the alphaA-crystallin. Conclusions. The Aey7 mutant represents the first dominant mouse cataract m utation affecting the Cryaa gene. The mutation leads to progressive opacifi cation of the lens. Compared with the beta- and gamma -crystallin-encoding genes, mutations in the alpha -crystallin-encoding genes are rare.