A gene trap integration provides an early in situ marker for hepatic specification of the foregut endoderm

We report the characterization of a gene trap integration that provides an in situ marker for one of the earliest events in liver development. Express ion of the reporter gene is observed at the nine-somite stage in the hepati c field of the foregut endoderm. At 10.5 days post-coitus expression is obs erved exclusively and at high levers in the majority of cells in the develo ping liver bud. As development proceeds the proportion of expressing cells decreases with expression in adult liver being restricted to a few sporadic cells. This therefore provides the earliest, most specific in situ marker of the hepatic lineage reported to date and will be useful in the further c haracterization of the inductive events involved in hepatic specification. Molecular characterization of the gene trap insertion suggests that the exp ression pattern is the result of alternative promoter use in the ankyrin re peat-containing gene, gtar. (C) 2001 Elsevier Science Inland Ltd. All right s reserved.