THE XENOPUS DORSALIZING FACTOR NOGGIN VENTRALIZES DROSOPHILA EMBRYOS BY PREVENTING DPP FROM ACTIVATING ITS RECEPTOR

noggin is expressed in the Spemann organizer region of the Xenopus emb ryo and can promote dorsal cell fates within the mesoderm and neural d evelopment within the overlying ectoderm. Here, we show that noggin pr omotes 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 recepto rs to demonstrate that noggin blocks dpp signaling upstream of dpp rec eptor activation. These results suggest a mechanistic basis for the ac tion of Spemann's organizer during Xenopus development and provide fur ther support for the conservation of dorsal-ventral patterning mechani sms between arthropods and chordates.