AlphaB-crystallin in lens development and muscle integrity: a gene knockout approach

To study the role of alphaB-crystallin (alphaB) in the developing lens and its importance in lens structure and function.

Gene targeting in embryonic stem cells was used to generate mouse lines in which the alphaB gene and its protein product were absent. Gene structure and expression were characterized by genomic Southern blot, immunoblot, and Northern blot analyses, and two-dimensional gel electrophoresis. The gene knockout mice were screened for cataract with slit lamp biomicroscopy, and dissected lenses were examined with dark-field microscopy. Lenses and other tissues were analyzed by standard histology and immunohistochemistry. Chaperone activity was determined by heating lens homogenate supernatants and measuring absorbance changes.

In an unexpected result, lenses in the alphaB gene knockout mice developed normally and were remarkably similar to wild-type mouse lenses. All the other crystallins were present. The thermal stability of a lens homogenate supernatant was mildly compromised, and when oxidatively stressed in vivo with hyperbaric oxygen, the knockout lenses reacted similarly to wild type. In targeting the alphaB gene, the adjacent HSPB2 gene, which is not expressed in the lens, was also disrupted. Loss of alphaB and/or HSPB2 function leads to degeneration of some skeletal muscles.

AlphaB is not essential for normal development of a transparent lens in the mouse, and therefore is more dispensable to the lens than the closely related alphaA-crystallin. It may play a small role in maintaining transparency throughout life. alphaB and/or the closely related HSPB2 is required to maintain muscle cell integrity in some skeletal muscles.