Members of the transforming growth factor-beta (TGF-beta) superfamily, including TGF-beta, bone morphogenetic proteins (BMPs), activins and nodals, are vital for regulating growth and differentiation. These growth factors transduce their signals through pairs of transmembrane type I and type II receptor kinases. Here, we have cloned a transmembrane protein, BAMBI, which is related to TGF-beta-family type I receptors but lacks an intracellular kinase domain. We show that BAMBI is co-expressed with the ventralizing morphogen BMP4 (refs 5, 6) during Xenopus embryogenesis and that it requires BMP signalling for its expression. The protein stably associates with TGF-beta-family receptors and inhibits BMP and activin as well as TGF-beta signalling. Finally, we provide evidence that BAMBI's inhibitory effects are mediated by its intracellular domain, which resembles the homodimerization interface of a type I receptor and prevents the formation of receptor complexes. The results indicate that BAMBI negatively regulates TGF-beta-family signalling by a regulatory mechanism involving the interaction of signalling receptors with a pseudoreceptor.

We have identified a novel homeobox gene, that

In a large-scale gene expression screen 1765 randomly picked cDNAs were analyzed by whole-mount in situ hybridization in Xenopus embryos. Two hundred and seventy three unique, differentially expressed genes were identified, 204 of which are novel in Xenopus. Partial DNA sequences and expression patterns were documented and assembled into a database, 'AXelDB'. Approximately 30% of cDNAs analyzed represent differentially expressed genes and about 5% show highly regionalized expression. Novel marker genes and potential developmental regulators were found. Differential expression of mitochondrial genes was observed. Marker genes were used to study regionalization of the entire gastrula as well as the tail forming region and the epidermis of the tailbud embryo. Four 'synexpression' groups representing genes with shared, complex expression pattern that predict molecular pathways involved in patterning and differentiation were identified. According to their probable functional significance these groups are designated as Delta1, Bmp4, ER-import and Chromatin group. Within synexpression groups, a likely function of genes without sequence similarity can be predicted. The results indicate that synexpression groups have strong prognostic value. A cluster analysis was made by comparing gene expression patterns to derive a novel parameter, 'tissue relatedness'. In conclusion, this study describes a semi-functional approach to investigate genes expressed during early development and provides global insight into embryonic patterning.