FIG. 8.

Model of the network that activates the MAP kinase by FGF8. The figure illustrates a role for the feed-forward loop mediated by interaction of CRKL and FGFR1 in organizing the output through the MAP kinase ERK1/2. Note that RAF1 and MEK1 function as tandem AND-gates that integrate signals effectively from FGFR1. Although cell-matrix adhesion can also participate in this network (shaded in gray), cells stimulated by FGF8 can escape from this requirement. This is a simplified model that does not show additional regulatory pathways mediated by other signaling modifiers.