REGULATION AND FUNCTION OF THE TISSUE-SPECIFIC TRANSCRIPTION FACTOR HNF1-ALPHA (LFB1) DURING XENOPUS DEVELOPMENT

We review the data available on the structure, developmental appearanc e and embryonic regulation of the tissue-specific transcription factor HNF1 alpha (LFB1) in Xenopus. The expression of the HNF1 alpha gene s tarts early in embryogenesis shortly after mid-blastula transition and the protein accumulates in the region of the embryo where liver, pron ephros and gut - tissues that contain HNF1 alpha in the adult - are de veloping. The cofactor DCoH, known to stabilize dimer formation of HNF 1 alpha, is present as a maternal factor in the egg and has a partiall y distinct tissue distribution compared to HNF1 alpha. This implies th at DCoH does not only modulate HNF1 alpha dimerization but may also co operate with other transcription factors. By injecting HNF1 alpha prom oter CAT constructs into fertilized Xenopus eggs we obtained activatio n of the injected gene restricted to the region of the developing larv ae expressing endogenous HNF1 alpha. Deletion analysis allowed to defi ne the OZ-element that is essential for embryonic activation. This ele ment also occurs in other promoters activated at mid-blastula transiti on in the embryo and interacts with the maternal factor OZ-1. As the H NF1 alpha promoter also contains functional binding sites for HNF4 and HNF1, we postulate that all these transcription factors contribute to the cascade leading to proper embryonic activation of the HNF1 alpha gene.