Enhancer analysis of the mouse HNF-3 beta gene: Regulatory elements for node/notochord and floor plate are independent and consist of multiple sub-elements

Background: Axial pattern formation in vertebrate embryos depends on signals from the node and, later, from the notochord and floor plate. Previous studies have shown that HNF-3 beta, a member of the winged-helix transcription factor family, plays key roles in the development of all three organizing centres. Results: Enhancer analysis of HNF-3 beta has therefore been performed using lacZ reporter gene constructs in transgenic mouse embryos. This has led to the identification of independent node/notochord and floor plate enhancers, at positions far upstream (-15 to -14kb) and downstream (+6 to +11kb) of the transcription start site, respectively. The node/notochord enhancer activity has been localized to a 520bp fragment. Floor plate gene expression requires a combination of two separate fragments of the enhancer. Deletion analysis of one of these fragments (400bp) has identified sub-regions required for the initiation and the maintenance of floor plate expression, and for the suppression of ectopic expression within the neural tube. Conclusion: We conclude that HNF-3 beta gene expression in the node/notochord and in the floor plate are controlled through different enhancers, which consist of positive and negative elements.