Sprouty was initially characterized as a negative regulator of FGFR signaling in Drosophila. Human cells contain four genes encoding Sprouty proteins, of which Spry2 is the best studied and most widely expressed. Spry proteins modulate the duration and extent of signaling through the MAPK cascade after FGF stimulation, although the mechanism appears to depend on the particular biological context. Some studies have suggested that Sprouty binds to GRB2 and interferes with the recruitment of GRB2-SOS1 to the receptor, while others have shown that Sprouty interferes with the MAPK cascade at the level of RAF activation. In addition to modulating the MAPK pathway in response to FGF stimulation, Sprouty itself appears to be subject to complex post-translational modification that regulates its activity and stability.