Adaptive evolution of small heat shock protein/alpha B-crystallin promoter activity of the blind subterranean mole rat, Spalax ehrenbergi.

Blind mole rats have degenerated subcutaneous eyes that are visually nonfunctional. In this investigation, we have compared the tissue specificity of the small heat shock protein (shsp)/alphaB-crystallin promoter of the mole rat superspecies, Spalax ehrenbergi, with that of the mouse. Earlier experiments showed that mouse shsp/alphaB-crystallin promoter/enhancer activity is high in the lens and moderate in the heart and skeletal muscle of transgenic mice. Here, we show in transgenic mouse experiments using the firefly luciferase reporter gene that, despite relatively few changes in sequence, the mole rat shsp/alphaB-crystallin promoter/enhancer has selectively lost lens activity after 13.5 days of embryogenesis (E13.5). The ratios of mole rat/mouse promoter activity were 0.01 for lens, 1.7 for heart, and 13.6 for skeletal muscle in 8-wk-old transgenic mice. Our data indicate that the shsp/alphaB-crystallin promoter/enhancer has undergone adaptive changes corresponding to the subterranean evolution of the blind mole rat. We speculate that selective pressures on metabolic economy may have contributed to these tissue-specific modifications of promoter/enhancer function during adaptation to life underground.