High-level activation by a duodenum-specific enhancer requires functional GATA binding sites

The purine metabolic gene adenosine deaminase (ADA) is expressed at high levels in a well-defined spatiotemporal pattern in the villous epithelium of proximal small intestine. A duodenum-specific enhancer module responsible for this expression pattern has been identified in the second intron of the human ADA gene. It has previously been shown that binding of the factor PDX-1 is essential for function of this enhancer. The studies presented here examine the proposed roles of GATA factors in the enhancer. Site-directed mutagenesis of the enhancer's GATA binding sites crippled enhancer function in 10 lines of transgenic mice, with 9 of the lines demonstrating <1% of normal activity. Detailed studies along the longitudinal axis of mouse small intestine indicate that GATA-4 and GATA-5 mRNA levels display a reciprocal pattern, with low levels of GATA-6 throughout. Interestingly, gel shift studies with duodenal nuclear extracts showed binding only by GATA-4.