ELEMENTS AND FACTORS INVOLVED IN TISSUE-SPECIFIC AND EMBRYONIC EXPRESSION OF THE LIVER TRANSCRIPTION FACTOR LFB1 IN XENOPUS-LAEVIS

LFB1 (HNF1) is a tissue-specific transcription factor found in the liv ers, stomachs, intestines, and kidneys of vertebrates. By analyzing th e promoter of the Xenopus LFB1 gene, we identified potential autoregul ation by LFB1 and regulation by HNF4, a transcription factor with a ti ssue distribution similar to that of LFB1. Injection of LFB1 promoter- chloramphenicol acetyltransferase constructs into Xenopus eggs reveale d embryonic activation that is restricted to the region of the develop ing larvae expressing endogeneous LFB1. Proper embryonic activation wa s also observed with a rat LFB1 promoter. Deletion analysis of the Xen opus and rat promoters revealed that in both promoters embryonic activ ation is absolutely dependent on the presence of an element that conta ins CCNCTCTC as the core consensus sequence. Since this element is rec ognized by the maternal factor OZ-1 previously described by N. Ovsenek , A. M. Zorn, and P. A. Krieg (Development 115:649-655, 1992), we migh t have identified the main constituents of a hierarchy that leads via LFB1 to the activation of tissue-specific genes during embryogenesis.