ANTI-DORSALIZING MORPHOGENETIC PROTEIN IS A NOVEL TGF-BETA HOMOLOG EXPRESSED IN THE SPEMANN ORGANIZER

We have identified a novel growth factor in Xenopus, which is most clo sely related to human Bone Morphogenetic Protein-3. Its expression pea ks during gastrulation, most prominently in the Spemann organizer, and persists in the posterior neural floor plate and prechordal plate dur ing neurulation, Injection of the corresponding mRNA into dorsal blast omeres results in dose-dependent suppression of dorsal and anterior st ructures, even in the presence of lithium chloride, Overexpression of the gene downregulates the dorsalizing factors noggin, goosecoid and f ollistatin, as web as the dorsal markers NCAM, muscle actin and MyoD; conversely, ventral markers are induced, We therefore designate this g ene product Anti-Dorsalizing Morphogenetic Protein (ADMP). Though deve lopment of dorsoanterior structures is suppressed when exogenous ADMP is injected, the gene is induced by lithium chloride treatment or acti vin, both of which are known to produce the opposite effect. Thus, the expression of ADMP resembles that of several dorsalizing signals, but its product exerts dorsal-suppressing activity, This suggests that AD MP may moderate organizer-associated dorsalizing influences. These fin dings are also consistent with the recently advanced proposal of dorsa lly expressed inhibitory activin-like signals.