Two secreted signaling molecules, Xwnt-8 and BMP-4, play an essential role in the dorso-ventral patterning of the mesoderm in Xenopus. Here we investigate how the Wnt-8 and the BMP-4 pathways are connected and how they regulate target genes in the lateral and ventral marginal zone. BMP-4 regulates the transcription of Xwnt-8 in a threshold dependent manner. High levels of BMP-4 induce the expression of the Wnt antagonist sizzled in the ventral marginal zone, independent of Xwnt-8 signaling. Xwnt-8 induces the early muscle marker myf-5 in the lateral marginal zone in a BMP independent manner. The expression of the homeobox gene Xvent-1 can be modulated through both the BMP-4 and the Xwnt-8 pathways. The spatial distribution and the level of BMP-4 activity in the lateral and ventral marginal zone is reflected in the dynamic expression pattern of Xwnt-8. The data support the view that Xwnt-8 is involved in the specification of lateral (somitogenic) mesoderm and BMP-4 in the specification of ventral mesoderm. Copyright (C) 1999 Elsevier Science Ireland Ltd.
Bibliographical noteFunding Information:
We wish to thank Randall Moon, Douglas Melton, Mark Kirschner, Chris Wright, Mike Jones and Dale Frank for probes and cDNA clones. Also we would like to thank Eddy De Robertis for the fruitful discussions during the early stages of this work, Ursula Müller for technical assistance and Sarah Cramton for critically reading the manuscript. This work was supported in part by a grant from the Council for Tobacco Research Inc. USA to A. Fainsod.
- Mesoderm patterning