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1 Division of Biology and Biomedical Sciences, Washington University School of Medicine, St. Louis, United States
2 Pediatrics, Washington University School of Medicine, Saint Louis, Missouri, United States
3 Children's Hospital and Program for Developmental and Reproductive Biology, University of Helsinki, Finland
* To whom correspondence should be addressed. E-mail: simon_t{at}kids.wustl.edu.
GATA-4, GATA-5, and GATA-6 are endodermal zinc-finger transcription factors that activate numerous enterocytic genes. GATA-4 and GATA-6 but not GATA-5 are present in enterocytes of adult mice, and we now report the simultaneous presence of all three GATA factors in enterocytes of mice before weaning age. An immunohistochemical survey detected enterocytic GATA-4 and GATA-6 at birth and one week of age, and GATA-5 at one week but not birth. Interactions among GATA factors were explored utilizing a transgene constructed from the proximal promoter of the rat liver fatty acid binding protein gene (Fabpl). GATA-4 and GATA-5 but not GATA-6 activate the Fabpl transgene through a cognate binding site at -128. A dose-response assay revealed a maximum in transgene activation by both factors, where additional factor did not further increase transgene activity. At saturated levels of GATA-4, however, additional transgene activation was achieved by adding GATA-5 expression construct, and vice versa. Similar cooperativity occurred with GATA-5 and GATA-6. Identical interactions were observed with a synthetic target transgene consisting of a single GATA site upstream of a minimal promoter. Furthermore, GATA-4 and GATA-5 or GATA-5 and GATA-6 bound to each other in solution. These results are consistent with tethering of one GATA factor to the Fabpl promoter through interaction with a second GATA factor to produce increased target gene activation. Cooperative target gene activation was specific to an intestinal cell line and may represent a mechanism by which genes are activated in the intestinal epithelium during the period before weaning.
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