The alpha-crystallins comprise a large fraction of the soluble protein in the vertebrate lens where they were, for many years, believed to function solely as structural proteins. This small family of crystallins is encoded by only two genes, the alpha-A- and alpha-B-crystallin genes and is collectively referred to as alpha-crystallin. They are related to the small heat shock proteins, and in vitro, they exhibit molecular chaperon activity; autokinase activity; and single-stranded, DNA-binding activity; and they interact with and affect the state of several cytoskeletal components. Alpha-crystallin, especially alpha-B-crystallin, has been shown to be a normal constituent of many nonlenticular tissues and has been detected in cytoplasmic inclusion bodies found in several human pathological conditions. To understand the major roles of alpha-crystallin in vivo, we are functionally deleting alpha-crystallin proteins by disrupting or """"""""knocking out"""""""" their genes in mice. We are attempting to elucidate the in vivo functions of alpha-A- and alpha-B-crystallin in (1) lens development and morphogenesis; (2) maintaining a stable, transparent lens throughout the life of an organism (i.e., preventing cataract); (3) the nonlenticular tissues where they are normally present; and (4) nonlenticular pathological conditions. We have generated mice lacking alpha-A-crystallin and mice lacking alpha-B-crystallin. We are presently crossing them to generate mice that are deficient in both alpha-A- and alpha-B-crystallin. Our research has demonstrated that neither alpha-A-crystallin nor alpha-B-crystallin is essential for survival of the laboratory mouse. Because alpha-B-crystallin is highly expressed during embryogenesis in the developing heart and other structures and is a normal constituent of adult heart, skeletal muscle, and several other organs, it was thought to be an essential protein. Analysis of alpha-A-/- mice reveals that lens development occurs relatively normally, and although the wet weight of alpha-A-/- lenses are approximately 35 percent less than that of controls, the gross architecture of the lens is normal, exhibiting an anterior epithelial layer and elongated fiber cells. Dense proteinaceous cytoplasmic inclusion bodies (1 to 3 microns in diameter) form in the fiber cells of these lenses as early as 2 to 4 weeks of age. Alpha-B-crystallin, and modified forms of this protein, has been identified as the major constituent of purified cytoplasmic inclusion bodies. Lens translucence becomes apparent later at 8 to 10 weeks of age.
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