Cross-talk among embryonic signaling pathways and experimental inhibitors. Potential cross-talk among embryonic signaling pathways (transforming growth factor (TGF)-β, Hedgehog (Hh), Notch, Wnt, and ErbB) is shown. The expansive potential for signaling cross-talk suggests that signaling pathways do not function in isolation, but instead are parts of a complex signaling network. Cross-talk can lead to both enhancing and inhibitory interactions between pathways. The actions of experimental pathway inhibitors are shown in yellow. Positive interactions are shown in green, while negative interactions are shown in red.