Tissue-specific activity of the blind mole rat and the two nucleotide-mutated mouse [alpha]B-crystallin promoter in transgenic mice

The [alpha]B-crystallin and HspB2 genes are located [approximately equal to] 0.9 kb apart in a head-to-head arrangement in mammals. Previous experiments have shown that a truncated -668/+45 [alpha]B-crystallin enhancer/promoter fragment from blind mole rats (Spalax ehrenbergl), which have nonfunctional lenses, lacks lens activity and has enhanced muscle activity in transgenic mice. Here we show that the full-length mole rat [alpha]B-crystallin intergenic region behaves similarly in transgenic mice. A two-nucleotide mutation ([sup.-273]CA [right arrow] G) in the mouse [alpha]B-crystallin enhancer/promoter fragment mimicking the wild-type mole rat sequence functionally converted the mouse promoter fragment to that of the wild-type mole rat promoter when tested in transgenic mice. The reciprocal mutation in the mole rat promoter fragment ([sup.-272]G [right arrow] CA) did not affect its activity. Oligonucleotides from the wild-type mouse and mole rat [alpha]B-crystallin promoter region under study formed distinct complexes with nuclear proteins from cultured cells. The mouse mutant sequence lost binding ability, whereas the mutated mole rat sequence gained the ability to form a complex similar in size to that of the wild-type mouse oligonucleotide. Our data support the idea that blind mole rats' [alpha]B-crystallin promoter activity was modified during the evolution of subterranean life and shows that tissue-specific promoter activity can be modulated by changing as few as two apparently neutral nucleotides in the mouse [alpha]B-crystallin enhancer region, implying the importance of the context of regulatory sequences for promoter activity. evolution | gene expression | lens | muscle