ISOLATION OF XENOPUS HGF GENE PROMOTER AND ITS FUNCTIONAL-ANALYSIS INEMBRYOS AND ANIMAL CAPS

Previously, we isolated Xenopus HGF (hepatocyte growth factor) cDNA an d showed in Xenopus embryos that expression of this gene starts at the late gastrula stage mainly in the ventral mesoderm, and furthermore t hat the expression is induced in animal cap by activin A and bFGF (bas ic fibroblast growth factor). Here we have cloned the Xenopus HGF gene , covering a 14 kb 5'-upstream region and a 0.2 kb 5'-coding region. W ithin about 0.5 kb of the 5'-flanking region, the Xenopus HGF gene con tained a TATA-like element AATGAAA, one putative NF-1 binding site, tw o NF-IL-6 binding motif sequences, one putative TGF-beta-dependent inh ibitory element (TIE) and one AP-1 binding site. A recombinant circula r plasmid consisting of a 1.7 kb HGF promoter region and the bacterial chloramphenicol acetyltransferase (CAT) gene was first expressed at t he late gastrula stage in the ventral mesoderm, as was the endogenous HGF gene. The expression of the fusion gene was induced in animal cap cells by activin A and bFGF although induction by the latter was not s o strong. Using a series of 5'-deletion constructs introduced into ani mal caps, silencer elements, which seem to be essential for the gene's regionally correct expression, and the element responsible for induct ion by activin ware found. The results show that the HGF gene promoter isolated here contains elements which may endow the gene with the reg ulative function for its temporally and spatially regulated expression , although the element necessary for induction by bFGF seems to be mis sing.