The expression of the human DACH gene is varied and complex — it is, for example, involved in the development of the brain, limbs and sensory organs — but the gene itself is suspiciously lacking in upstream control regions. Immediately upstream and downstream of the gene are two gene deserts of 1,330 and 870 kb, respectively. Arguing that the control regions of DACH could be buried somewhere in this genetic wasteland, the authors looked for evolutionary sequence conservation in a 2,630-kb region that includes the gene and these flanking deserts. Comparing the targeted sequences between human and mouse yielded 1,098 conserved sequences that were more than 100 base pairs long — this number was reduced to 32 when the analysis was extended to include frog, zebrafish and two species of pufferfish.
That 32 noncoding sequences are conserved across more than one billion years of vertebrate evolution is impressive. Proof of their regulatory role came when nine were tested in a transgenic mouse assay for the ability to modulate the expression of a marker gene that was placed downstream of a minimal promoter. Seven of these elements convincingly reproduced the expression pattern of the endogenous DACH gene, which indicated that the conserved sequences identified do indeed have enhancer function. This conclusion was further supported by the fact that the linear relationship of the newly discovered regulatory elements was identical in all of the animals tested, even though the order of the surrounding genes had been rearranged.
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