Evolution of Crystallins: Expression of Lens-Specific Proteins in the Blind Mammals Mole (Talpa europaea) and Mole Rat (Spalax eIwe&ergi)’

The mole (Talpa europaea; Insectivora) and the mole rat (Spalax ehrenbergi; Rodentia) both have degenerated eyes as a convergent adaptation to subterranean life. The rudimentary eye lenses of these blind mammals no longer function in a visual process. The crystallin genes, which display a lens-specific expression pattern, were studied in these blind mammals and in related species with normal eyes by hybridizing their genomic DNAs with probes obtained from cDNA clones for CGA-, aB-, and PBp-crystallins from calf and y3-crystallin from the rat. For all crystallin genes examined, the hybridization signals of mole and mole rat genomic DNA were comparable, respectively, with those of shrew and of rat and mouse, normal-vision representatives of the orders Insectivora and Rodentia. The expression of the crystallins at the protein level was tested by using antiserum specific for a-crystallin in immunofluorescence reactions on lens sections of mole and mole rat eyes and by using antisera against the p-and y-crystallins on sections of the mole eye. All antisera gave positive fluorescence reactions exclusively with lens tissue of these blind mammals, indicating that the crystallins are still normally expressed despite the fact that these lenses have had no function in a visual process in these mammals for at least many million years. These findings apparently imply that some unknown selective advantage has conserved the crystallin genes and their expression after the loss of normal function of the lenses. Introduction In the past 2 decades much information has become available on the evolutionary changes of genes and proteins. Most of this information has been obtained from comparative studies of functionally normal proteins and their genes. But what happens with genes and proteins that have lost their biological function in the course of evolution? What types of changes do they undergo-and at what rates-as compared with their functional counterparts? Such knowledge might complement our understanding of neutral and adaptive processes in molecular evolution.