Tolloid gets Sizzled competing with Chordin

BMP Signaling: Lighting up the Way for Embryonic Dorsoventral Patterning

One of the most significant events during early embryonic development is the establishment of a basic embryonic body plan, which is defined by anteroposterior, dorsoventral (DV), and left-right axes. It is well-known that the morphogen gradient created by BMP signaling activity is crucial for DV axis patterning across a diverse set of vertebrates. The regulation of BMP signaling during DV patterning has been strongly conserved across evolution. This is a remarkable regulatory and evolutionary feat, as the BMP gradient has been maintained despite the tremendous variation in embryonic size and shape across species. Interestingly, the embryonic DV axis exhibits robust stability, even in face of variations in BMP signaling. Multiple lines of genetic, molecular, and embryological evidence have suggested that numerous BMP signaling components and their attendant regulators act in concert to shape the developing DV axis. In this review, we summarize the current knowledge of the function and regulation of BMP signaling in DV patterning. Throughout, we focus specifically on popular model animals, such as Xenopus and zebrafish, highlighting the similarities and differences of the regulatory networks between species. We also review recent advances regarding the molecular nature of DV patterning, including the initiation of the DV axis, the formation of the BMP gradient, and the regulatory molecular mechanisms behind BMP signaling during the establishment of the DV axis. Collectively, this review will help clarify our current understanding of the molecular nature of DV axis formation.

Scaling of dorsal-ventral patterning in the Xenopus laevis embryo

Scaling of pattern with size has been described and studied for over a century, yet its molecular basis is understood in only a few cases. In a recent, elegant study, Inomata and colleagues proposed a new model explaining how bone morphogenic protein (BMP) activity gradient scales with embryo size in the early Xenopus laevis embryo. We discuss their results in conjunction with an alternative model we proposed previously. The expansion-repression mechanism (ExR) provides a conceptual framework unifying both mechanisms. Results of Inomata and colleagues implicate the chordin-stabilizing protein sizzled as the expander molecule enabling scaling, while we attributed this role to the BMP ligand Admp. The two expanders may work in concert, as suggested by the mathematical model of Inomata et al. We discuss approaches for differentiating the contribution of sizzled and Admp to pattern scaling.

Extracellular BMP-antagonist regulation in development and disease: tied up in knots

Developmental processes are regulated by the bone morphogenetic protein (BMP) family of secreted molecules. BMPs bind to serine/threonine kinase receptors and signal through the canonical Smad pathway and other intracellular effectors. Integral to the control of BMPs is a diverse group of secreted BMP antagonists that bind to BMPs and prevent engagement with their cognate receptors. Tight temporospatial regulation of both BMP and BMP-antagonist expression provides an exquisite control system for developing tissues. Additional facets of BMP-antagonist biology, such as crosstalk with Wnt and Sonic hedgehog signaling during development, have been revealed in recent years. In addition, previously unappreciated roles for the BMP antagonists in kidney fibrosis and cancer have been elucidated. This review provides a description of BMP-antagonist biology, together with highlights of recent novel insights into the role of these antagonists in development, signal transduction and human disease.

The extracellular regulation of bone morphogenetic protein signaling

In many cases, the level, positioning and timing of signaling through the bone morphogenetic protein (BMP) pathway are regulated by molecules that bind BMP ligands in the extracellular space. Whereas many BMP-binding proteins inhibit signaling by sequestering BMPs from their receptors, other BMP-binding proteins cause remarkably context-specific gains or losses in signaling. Here, we review recent findings and hypotheses on the complex mechanisms that lead to these effects, with data from developing systems, biochemical analyses and mathematical modeling.