Vertebrate lenses are transparent because they contain tightly packed primary and secondary lens fibre cells. These cells, which are generated from lens epithelial cells during embryogenesis and throughout adult life,respectively, mature by losing their nuclei and other organelles in a process that uses components of the apoptotic pathway. However, something stops them from completing apoptosis. Morozov and Wawrousek now report thatα-crystallin, a major lens protein, suppresses caspase activity in secondary lens fibre cells and prevents their disintegration (see ).α-Crystallin consists of two subunits: αA and αB.αB-crystallin inhibits caspase 3 in vitro but its in vivo effects are unknown. Morozov and Wawrousek report that morphological abnormalities develop in the secondary lens fibre cells of αA/αB-crystallin double knockout mice, which are opaque at birth, and provide data that suggest that these abnormalities result from increased caspase 3 and caspase 6 activity. They also show that there is increased apoptosis in the lenses of the mutant mice and conclude that α-crystallin is an anti-apoptotic agent in the vertebrate lens.
