TARGETED DISRUPTION OF THE MOUSE ALPHA-A-CRYSTALLIN GENE INDUCES CATARACT AND CYTOPLASMIC INCLUSION-BODIES CONTAINING THE SMALL HEAT-SHOCK PROTEIN ALPHA-B-CRYSTALLIN

alpha A-crystallin (alpha A) and alpha B-crystallin (alpha B) are amon g the predominant proteins of the vertebrate eye lens. In vitro, the a lpha-crystallins, which are isolated together as a high molecular mass aggregate, exhibit a number of properties, the most interesting of wh ich is their ability to function as molecular chaperones for other pro teins. Here we begin to examine the in vivo functions of alpha-crystal lin by generating mice with a targeted disruption of the alpha A gene. Mice that are homozygous for the disrupted allele produce no detectab le alpha A in their lenses, based on protein gel electrophoresis and i mmunoblot analysis. Initially, the alpha A-deficient lenses appear str ucturally normal, but they are smaller than the lenses of wild-type li ttermates. alpha A(-/-) lenses develop an opacification that starts in the nucleus and progresses to a general opacification with age. Light and transmission electron microscopy reveal the presence of dense inc lusion bodies in the central lens fiber cells. The inclusions react st rongly with antibodies to alpha B but not significantly with antibodie s to beta- or gamma-crystallins. In addition, immunoblot analyses demo nstrate that a significant portion of the alpha B in alpha A(-/-) lens es shifts into the insoluble fraction. These studies suggest that alph a A is essential for maintaining lens transparency, possibly by ensuri ng that alpha B or proteins closely associated with this small heat sh ock protein remain soluble.