Transcriptional regulation of the murine k-fgf gene

Embryonal carcinoma (EC) cells provide a useful model system for studying the roles of growth factors during early mammalian development. In 1988, we determined that EC cells express a member of the fibroblast growth factor (FGF) family that cannot be detected after EC cells undergo differentiation. Attempts to understand how differentiation regulates the production of FGFs led to the finding that EC cells express the fibroblast growth factor k-FGF (FGF-4), whereas there is a large decrease in the steady state levels of k-FGF mRNA when EC cells differentiate. This suggested that transcription of the k-fgf gene is repressed when EC cells differentiate. To investigate this possibility, we prepared a series of reporter gene constructs containing various regions of the murine k-fgf gene. These constructs were transfected into two mouse EC cell lines and one mouse embryonic stem (ES) cell line. We determined that the mouse 5' flanking region cannot support expression of the reporter gene. In both EC and ES cell lines, expression of the reporter gene is elevated greatly by the addition of a 316 bp region from the third exon of the murine k-fgf gene. Sequence analysis of the 316 bp region identified one and possibly two conserved octamer binding motifs. These sequences are likely to be involved in regulation of the k-fgf gene, because differentiation of EC cells is known to reduce the expression of octamer binding proteins, including Oct-3. To test the possible role of octamer binding proteins, we examined the expression of our reporter gene constructs in F9-differentiated cells and in PYS-2 cells.(ABSTRACT TRUNCATED AT 250 WORDS)