Evolution of crystallins: expression of lens-specific proteins in the blind mammals mole (Talpa europaea) and mole rat (Spalax ehrenbergi)

The mole (Talpa europaea; Insectivora) and the mole rat (Spalax ehrenbergi;Rodentia) both have degenerated eyes as a convergent adaptation tosubterranean life. The rudimentary eye lenses of these blind mammals nolonger function in a visual process. The crystallin genes, which display alens-specific expression pattern, were studied in these blind mammals andin related species with normal eyes by hybridizing their genomic DNAs withprobes obtained from cDNA clones for alpha A-, alpha B-, and betaBp-crystallins from calf and gamma 3- crystallin from the rat. For allcrystallin genes examined, the hybridization signals of mole and mole ratgenomic DNA were comparable, respectively, with those of shrew and of ratand mouse, normal-vision representatives of the orders Insectivora andRodentia. The expression of the crystallins at the protein level was testedby using antiserum specific for alpha-crystallin in immunofluorescencereactions on lens sections of mole and mole rat eyes and by using antiseraagainst the beta- and gamma-crystallins on sections of the mole eye. Allantisera gave positive fluorescence reactions exclusively with lens tissueof these blind mammals, indicating that the crystallins are still normallyexpressed despite the fact that these lenses have had no function in avisual process in these mammals for at least many million years. Thesefindings apparently imply that some unknown selective advantage hasconserved the crystallin genes and their expression after the loss ofnormal function of the lenses.