Transcriptional hierarchy in Xenopus embryogenesis: HNF4 a maternal factor involved in the developmental activation of the gene encoding the tissue specific transcription factor HNF1α (LFB1)

Abstract

The tissue specific transcription factor HNF1α (LFB1) expressed in liver, kidney, stomach and gut gets transcriptionally activated in Xenopus shortly after zygotic transcription starts. By microinjection into fertilized Xenopus eggs, a HNF1α promoter fragment is activated in the middle part of developing larvae, reflecting the activation pattern of the endogenous HNF1α gene. Mutational analysis of the HNF1α promoter shows that HNF1 and HNF4 binding sites are essential for proper embryonic regulation. Since by injecting HNF4 mRNA into fertilized eggs the endogenous HNF1α gene is activated ectopically and HNF4 is present as a maternal protein within an animal to vegetal gradient in the embryo, we assume that HNF4 initiates a transcriptional hierarchy involved in determination of different cell fates.