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RB Hough, A Avivi, J Davis, J Alma, E Nevo, J Piatigorsky; Adaptive Changes of Small Heat Shock Protein/B-Crystallin Promoter Activity of the Blind Mole Rat to Subterranean Life . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3598.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The mouse αB-crystallin gene is highly expressed in the lens and to a lesser extent in heart and skeletal muscle. Although mole rats have degenerated, subcutaneous eyes and are visually blind, their lenses express low levels of crystallins. Our goal is to characterize the mole rat αB-crystallin promoter with respect to evolutionary adaptation to life underground. Methods: The expression of αB-crystallin in the mole rat eye was examined by immunohistochemistry, and the proteins of the mole rat eye were examined by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). The nucleotide region (-943/+45) of the mole rat αB-crystallin gene was cloned by using polymerase chain reaction (PCR). The firefly luciferase reporter gene was used to test the activity of the mole rat (-668/+45) and the mouse (-661/+45) αB-crystallin promoters in cell lines and transgenic mice. Results: Although we can detect αB-crystallin in the mole rat lens by immunohistochemistry, SDS-PAGE shows that all crystallins, including αB-crystallin, are barely detectable in the newborn or the adult eye. The nucleotide sequence of the mole rat αB-crystallin promoter (-668/+45) is 82 %, 83% and 78% identical to that of the rat, mouse and human, respectively. Transfection experiments using N/N1003A rabbit lens, αTN-4 mouse lens, and C2C12 mouse myoblast cell lines suggested that the mole rat promoter has preferentially reduced lens activity while maintaining muscle activity. In transgenic mouse experiments using the firefly luciferase reporter gene, the mole rat αB-crystallin promoter/enhancer selectively lost its high lens activity after 13.5 days of embryogenesis (E13.5), and appears to have increased its activity in the muscle 13-fold. Conclusion: Minor sequence modifications of the mole rat αB-crystallin promoter are associated with profound changes in promoter activity presumably resulting from adaptation to a subterranean environment. These changes are possibly adaptive, economizing metabolic expenses, by saving expression of αB-crystallin in the degenerated lens and by increasing expression in the muscle, thereby increasing fitness.
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