sentences:  FGF-induced activation of FGFR1 also stimulates the activation of sprouty proteins SPRY1, SPRY2, SPRY3, and/or SPRY4 which in turn interact with GRB2, SOS1, and/or c-Raf to reduce or inhibit further cell stimulation by activated FGFR1 as well as other tyrosine kinase receptors such as the Epidermal growth factor receptor.These interactions serve as negative feedback loops to limit the extent of cellular activation.Mice genetically engineered to lack a functional "Fgfr1" gene (ortholog of the human "FGFR1" gene) die in utero before 10.5 days of gestation.