Expression of GATA6 has been found during embryonic development in many mammalian species. In mouse embryonic development, GATA6 is a primitive endoderm (PrE) marker. However, the expression and effect of GATA6 in ruminant ungulates has not been well characterized. In this report, the expression of GATA6 mRNA was examined in the uteri of ruminants. GATA6 mRNA was detected in days 17, 20, and 22 (day 0=day of estrus) bovine conceptuses and in days 15, 17, and 21 ovine conceptuses. In both cases, GATA6 mRNA increased on day 22 or 21 after conceptus attachment to the uterine epithelium. GATA6 mRNA was also detected in bovine trophoblast CT-1 or F3 cells and ovine trophoblast oTr cells. In transient transfection analyses using the upstream region of the bovine IFNT gene (bIFNT, IFN-tau-c1), GATA6 overexpression was effective in the up-regulation of the bIFNT construct that had been transfected into human choriocarcinoma JEG3 or bovine ear-derived fibroblast EF cells. The observation in which GATA6 increased IFNT transcription suggests that in addition to lineage specification, GATA6 may have acquired ruminant-specific functions involving the control of trophoblast gene expression.