TGF-beta signals from the membrane to the nucleus through serine/threonine kinase receptors and their downstream effectors, termed SMAD proteins. The activated TGF-beta receptor induces phosphorylation of two such proteins, Smad2 and Smad3, which form hetero-oligomeric complex(es) with Smad4/DPC4 that translocate to the nucleus, where they then regulate transcriptional responses. However, the mechanisms by which the intracellular signals of TGF-beta are switched off are unclear. Here we report the identification of Smad7, which is related to Smad6. Transfection of Smad7 blocks responses mediated by TGF-beta in mammalian cells, and injection of Smad7 RNA into Xenopus embryos blocks activin/TGF-beta signalling. Smad7 associates stably with the TGF-beta receptor complex, but is not phosphorylated upon TGF-beta stimulation. TGFbeta-mediated phosphorylation of Smad2 and Smad3 is inhibited by Smad7, indicating that the antagonistic effect of Smad7 is exerted at this important regulatory step. TGF-beta rapidly induces expression of Smad7 mRNA, suggesting that Smad7 may participate in a negative feedback loop to control TGF-beta responses.

Carbon nanotubes (CNTs), tubular molecular entities that consist of sp(2)-hybridized carbon atoms, are currently produced as mixtures that contain tubes of various diameters and different sidewall structures. The electronic and optical properties of CNTs are determined by their diameters and sidewall structures and so a controlled synthesis of uniform-diameter, single-chirality CNTs-a significant chemical challenge-would provide access to pure samples with predictable properties. Here we report a rational bottom-up approach to synthesize structurally uniform CNTs using carbon nanorings (cycloparaphenylenes) as templates and ethanol as the carbon source. The average diameter of the CNTs formed is close to that of the carbon nanorings used, which supports the operation of a 'growth-from-template' mechanism in CNT formation. This bottom-up organic chemistry approach is intrinsically different from other conventional approaches to making CNTs and, if it can be optimized sufficiently, offers a route to the programmable synthesis of structurally uniform CNTs.

The family of TGF-beta signalling molecules play inductive roles in various developmental contexts. One member of this family, Drosophila Decapentaplegic (Dpp) serves as a morphogen that patterns both the embryo and adult. We have now isolated a gene, Daughters against dpp (Dad), whose transcription is induced by Dpp. Dad shares weak homology with Drosophila Mad (Mothers against dpp), a protein required for transduction of Dpp signals. In contrast to Mad or the activated Dpp receptor, whose overexpression hyperactivates the Dpp signalling pathway, overexpression of Dad blocks Dpp activity. Expression of Dad together with either Mad or the activated receptor rescues phenotypic defects induced by each protein alone. Dad can also antagonize the activity of a vertebrate homologue of Dpp, bone morphogenetic protein, as evidenced by induction of dorsal or neural fate following overexpression in Xenopus embryos. We conclude that the pattern-organizing mechanism governed by Dpp involves a negative-feedback circuit in which Dpp induces expression of its own antagonist, Dad. This feedback loop appears to be conserved in vertebrate development.

Plants achieve mineral ion homeostasis by means of a hydrophobic barrier on endodermal cells called the Casparian strip, which restricts lateral diffusion of ions between the root vascular bundles and the soil. We identified a family of sulfated peptides required for contiguous Casparian strip formation in Arabidopsis roots. These peptide hormones, which we named Casparian strip integrity factor 1 (CIF1) and CIF2, are expressed in the root stele and specifically bind the endodermis-expressed leucine-rich repeat receptor kinase GASSHO1 (GSO1)/SCHENGEN3 and its homolog, GSO2. A mutant devoid of CIF peptides is defective in ion homeostasis in the xylem. CIF genes are environmentally responsive. Casparian strip regulation is not merely a passive process driven by root developmental cues; it also serves as an active strategy to cope with adverse soil conditions.