PATTERNING THE EXPRESSION OF A TISSUE-SPECIFIC TRANSCRIPTION FACTOR IN EMBRYOGENESIS - HNF1-ALPHA GENE ACTIVATION DURING XENOPUS DEVELOPMENT

Tissue-specific transcription factors play an essential role in establ ishing cell identity during development. We review our knowledge of th e molecular events involved in the activation of the gene encoding the tissue-specific transcription factor HNF1 alpha (LFB1). The available data suggest that the maternal factors OZ-1, HNF4 alpha and HNF4 beta act as initial activators of the HNF1 alpha promoter. We present evid ence suggesting that the mesoderm-inducing factor activin A plays a cr itical role by acting through the HNF4 binding site of the HNF1 alpha promoter. The activity of this embryonic morphogen seems to form a gra dient opposing the distribution of the maternal HNF4 proteins that are concentrated at the animal pole of the egg. After zygotic gene transc ription the HNF1 alpha-related transcription factor HNF1 beta accumula tes faster than HNF1 alpha itself and thus is likely to contribute to the activation of the HNF1 alpha transcription via the HNF1 binding si te. The cofactor of the HNF1 proteins (DCoH) is present throughout dev elopment and thus cannot limit the activation potential of HNF1 alpha in early development. Our results provide a detailed description of se tting up the expression pattern of a tissue-specific transcription fac tor during embryogenesis. (C) 1997 Elsevier Science Ireland Ltd.