We have cloned the Xenopus laevis homologue of the LFB3/HNF1β transcription factor. RNase protection and in situ hybridisation experiments show that XLFB3 transcription starts in the gastrulating endoderm at stage 10.5 (mid-gastrula). At later stages, XLFB3 transcripts within the endoderm are restricted to mid- and hindgut and to their derivative organs and tissues. XLFB3 is also expressed in the neuroectoderm and in the pronephros anlage. XLFB3 is not expressed in the rostral part of all three germ layers, with coincident anterior borders that are shifted anteriorly by treatment of developing embryos with retinoic acid. XLFB3 is a useful marker of early endoderm differentiation and its expression pattern along the antero-posterior axis, as well as the response to retinoic acid treatment, suggests a role in early morphogenesis.
