(Downloading may take up to 30 seconds.
If the slide opens in your browser, select File -> Save As to save it.)
Click on image to view larger version.

Fig. 5. A model for positive feedback. Initially BMP ligands, such as Dpp
and Scw, bind to the type I and type II signaling receptors. This signal
activates transcription of a cell surface BMP-binding protein (sbp), such as
Cv-2, that helps to present ligand to the signaling receptors. This may
account for the production of spatial bi-stability, as proposed by Ferguson
and Wang (Ferguson and Wang, 2005). P, phosphorylation. The question mark
indicates that the identity of this component is not yet established in the
embryo.