Fig. 1. Signalling specificity in the TGF-ß superfamily. Classification of the mammalian Smad signalling cascade into activin–TGF-ß (maroon) and BMP (blue) pathways. Representative examples of mammalian ligands (pink shading), type II receptors (red shading), type I receptors (orange shading), R-Smads (green shading), Co-Smads (bright green shading) and I-Smads (grey shading) are depicted in pathways linked by arrows or signs of inhibition. Bifurcation of the TGF-ß pathway at the level of type I receptors towards both TGF-ß and BMP Smads is marked by an asterisk. Nomenclature of proteins not detailed in the text are growth and differentiation factors (GDFs), Mullerian inhibiting substance (MIS), activin type II and type IIB receptor (ActRII/IIB), TGF-ß type II receptor (TßRII), BMP type II receptor (BMPRII), MIS type II receptor (MISRII), activin receptor-like kinases 1 to 6 (ALK1-ALK6). For references see ten Dijke et al. (ten Dijke et al., 2000).
