WINGED-HELIX, HEDGEHOG AND BMP GENES ARE DIFFERENTIALLY EXPRESSED IN DISTINCT CELL-LAYERS OF THE MURINE YOLK-SAC

The visceral yolk sac plays a critical role in normal embryogenesis, y et little is known about the specific molecules that regulate its deve lopment. We show here that four winged-helix genes (HNF-3 alpha, HNF-3 beta, HNF-3 gamma and HFH-4) are restricted to visceral endoderm. In the absence of HNF-3 beta, visceral endoderm forms but the morphogenet ic movements by which the embryo becomes enclosed within its yolk sac are disrupted and serum protein gene transcription is greatly reduced. Hedgehog and Bmp genes, which encode signaling molecules known to pla y multiple roles in embryonic development, are also differentially exp ressed in the closely apposed yolk sac mesoderm and endoderm layers. O ur results suggest that similar mechanisms may be utilized to mediate inductive interactions in both extraembryonic and embryonic tissues. ( C) 1997 Elsevier Science Ireland Ltd.