Background: From previous experiments it is known that the murine dominant cataract mutants carrying the gene Cat2 have a decreased content of gamma-crystallin-specific transcripts in the juvenile lens, when the cataract is completely expressed. Moreover, the mutant locus has been mapped recently to chromosome 1, closely linked to the gamma E-crystallin gene (map distance 0.3 +/- 0.3 cM). In the present paper we describe the phenotypic changes and the gamma-crystallin expression in embryonic lenses of the Cat2nop mutants as an example for the Cat2 allelic series.
Methods: The technique of in situ hybridization was applied using a probe from the murine gamma D-crystallin gene, and, for control, from the murine alpha A-crystallin gene. Simultaneously, a series of lens sections was examined histologically.
Results: The presence of gamma-crystallin mRNA was demonstrated from embryonic day 13.5 (E13.5) onward, but in the mutants to a lower extent than in the wild-type lenses. However, the first morphological abnormality in the mutant lenses was observed as swelling of lens fibers at day E15.5. Progressive degeneration of the lens core followed, leading to a cataracta immatura.
Conclusion: The reduced level of gamma-crystallin transcripts is the first alteration observable during the embryonic development of the Cat2 mutant lenses: it precedes the morphological changes. This result represents an additional line of argument that the gamma-crystallin genes may be the target of the mutation in the Cat2 mice.