Gene expression in the embryonic Xenopus liver

In recent years, significant progress has been made in uncovering the molecular basis of endoderm specification in Xenopus. Much less is understood, however, about endodermal patterning and how endoderm-derived organs such as the liver are formed. Progress has been hampered by the lack of good molecular markers of presumptive liver tissue. Here, we have examined the embryonic expression of a number of marker genes during liver organogenesis, including the transcription factors hex, sox17 alpha, and hnf3 beta, as well as a number of proteins specific to the adult liver. Interestingly, sox17 alpha appears to specifically mark the gall bladder precursors. At 7 days of development expression of the liver differentiation markers albumin, alpha 1-microglobulin/bikunin precursor, fibrinogen, transferrin and transthyretin is restricted to the differentiating liver bud. Surprisingly, however, at 3 days of development most of these genes have a more widespread endodermal expression pattern. In addition to expression in the undifferentiated liver bud they were expressed extensively throughout the presumptive intestinal tissue, which may reflect some general feature of how the hepatic gene program is developmentally regulated. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.