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 among the predominant proteins of the vertebrate eye lens. In vitro, the alpha-crystallins, which are isolated together as a high molecular mass aggregate, exhibit a number of properties, the most interesting of which is their ability to function as molecular chaperones for other proteins. Here we begin to examine the in vivo functions of alpha-crystallin by generating mice with a targeted disruption of the alpha A gene. Mice that are homozygous for the disrupted allele produce no detectable alpha A in their lenses, based on protein gel electrophoresis and immunoblot analysis. Initially, the alpha A-deficient lenses appear structurally normal, but they are smaller than the lenses of wild-type littermates. 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 inclusion bodies in the central lens fiber cells. The inclusions react strongly with antibodies to alpha B but not significantly with antibodies to beta- or gamma-crystallins. In addition, immunoblot analyses demonstrate that a significant portion of the alpha B in alpha A-/- lenses shifts into the insoluble fraction. These studies suggest that alpha A is essential for maintaining lens transparency, possibly by ensuring that alpha B or proteins closely associated with this small heat shock protein remain soluble.
Brady
J P
JP
National Eye Institute, National Institutes of Health, Bethesda, MD 20892-2730, USA.
Garland
D
D
Duglas-Tabor
Y
Y
Robison
W G
WG
Groome
A
A
Wawrousek
E F
EF
D000818:Animals; D001483:Base Sequence; D002386:Cataract / Q000235:genetics*; D003459:Crystallins / Q000032:analysis* / Q000235:genetics* / Q000502:physiology; D015870:Gene Expression; D006360:Heat-Shock Proteins / Q000032:analysis*; D002479:Inclusion Bodies / Q000737:chemistry*; D007908:Lens, Crystalline / Q000737:chemistry* / Q000254:growth & development; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data
D003459:Crystallins; D006360:Heat-Shock Proteins