noggin is expressed in the Spemann organizer region of the Xenopus embryo and can promote dorsal cell fates within the mesoderm and neural development within the overlying ectoderm. Here, we show that noggin promotes ventral development in Drosophila, specifying ventral ectoderm and CNS in the absence of all endogenous ventral-specific zygotic gene expression. We utilize constitutively active forms of the dpp receptors to demonstrate that noggin blocks dpp signaling upstream of dpp receptor activation. These results suggest a mechanistic basis for the action of Spemann's organizer during Xenopus development and provide further support for the conservation of dorsal-ventral patterning mechanisms between arthropods and chordates.
Bibliographical noteFunding Information:
Correspondence should be addressed to E. L. F. We thank Kathryn Anderson for many helpful discussions, Nipam Patel for advice and use of equipment for photomicroscopy, Kavita Arora for providing the CyO P[ry + dpp Hin+ ] P[wg–lacZ] balancer chromosome, and John Wozney for the gift of BMP4 protein. We thank Kathryn Anderson, Jeremy Green, John Hudson, Kallie Keith, Anthony Mahowald, Steven Podos, and Christopher Wright for helpful comments on the manuscript. This work was supported by a grant from the Medical Research Council (MRC) of Canada to J. L. W. and by grants from the National Institutes of Health to M. B. O.'C. (GM47462), E. M. D. R. (HD21503), and E. L. F. (GM50838). S. A. H. was supported by a fellowship from the Women's Board of the University of Chicago Cancer Research Center. J. L. W. is an MRC Scholar, E. M. D. R. is a Howard Hughes Medical Institute Investigator, and E. L. F. is a Pew Scholar in the Biomedical Sciences.