Octamer-dependent regulation of the kFGF gene in embryonal carcinoma and embryonic stem cells.

Expression of kFGF, which belongs to the family of fibroblast growth factor genes, is restricted to undifferentiated embryonal carcinoma and embryonic stem cells. Stem cell specific expression of kFGF is controlled by a distally localized enhancer, conferring both positive and negative regulation to the kFGF and tk promoters. This enhancer contains a consensus octamer binding sequence that controls positive regulation in EC and ES cells. The octamer sequence binds Oct1 and Oct4 in nuclear extracts from undifferentiated EC cells, while only Oct1 is bound in nuclear extracts from RA differentiated cells. These results suggest that the kFGF gene is a target for positive regulation by Oct4 and implicate Oct4 as target for regulation by the retinoic acid receptors.