Lens development in a dominant X-linked congenital cataract of the mouse.

Xcat is a recently identified mouse mutation causing X-linked dominant congenital cataract. The mutation is of particular interest as a possible animal model for the human X-linked cataract syndrome. Using light microscopy, we examined the histological changes of mutant lenses at selected intervals between embryonic (E) day 14 and postnatal (P) day 21. At E14, primary fiber formation completely fills the former lens vesicle in both normal and mutant mice, but in affected animals the primary fibers are irregularly arranged and show small foci of cellular disintegration. Progressive degeneration of primary fibers occurs from E15 to E18 and, during late gestation, secondary lens fibers also begin to degenerate. The lens epithelium and newly differentiated fibers, however, show no evident abnormality. Postnatally, most of the lens substance becomes amorphous; the cataractous process terminates in rupture of the posterior lens capsule by P21. Analysis of crystallin and cytoskeletal proteins of postnatal cataractous lenses revealed no significant abnormalities when compared to normal lenses. The observed sequence of histological changes indicates that the Xcat mutation affects the differentiation of lens fiber cells at some point after their initial elongation.