Aey2, a new mutation in the beta B2-crystallin-encoding gene of the mouse

PURPOSE. During an ethylnitrosourea (ENU) mutagenesis screen, mice were tes ted for the occurrence of dominant cataracts. One particular mutant was fou nd that caused progressive opacity and was referred to as Aey2. The purpose of the study was to provide a morphologic description, to map the mutant g ene, and to characterize the underlying molecular lesion. METHODS. Isolated lenses were photographed, and histologic sections of the eye were analyzed according to standard procedures. Linkage analysis was pe rformed using a set of microsatellite markers covering all autosomal chromo somes, cDNA from candidate genes was amplified after reverse transcription of lens mRNA. RESULTS. The cortical opacification visible at eye opening progressed to an anterior suture cataract and reached its final phenotype as total opacity at 8 weeks of age. There was no obvious difference between heterozygous and homozygous mutants. The mutation was mapped to chromosome 5 proximal to th e marker D5Mit138 (8.7 +/- 4.2 centimorgan [cM]) and distal to D5Mit15 (12. 8 +/- 5.4 cM). No recombinations were observed to the markers D5Mit10 and D 5Mit25. This position makes the genes within the beta A4/betaB-crystallin g ene cluster excellent candidate genes. Sequence analysis revealed a mutatio n of T -->A at position 553 in the Crybb2 gene, leading to an exchange of V al for Glu. It affects the same region of the Crybb2 gene as in the Philly mouse. Correspondingly, the loss of the fourth Greek key motif is to be exp ected. CONCLUSIONS. The Aey2 mutant represents the second allele of Crybb2! in mic e. Because an increasing number of beta- and gamma -crystallin mutations ha ve been reported, a detailed phenotype-genotype correlation will allow a cl earer functional understanding of beta- and gamma -crystallins.