Growth cones integrate signaling from multiple guidance cues

Nerve growth factor (NGF) and semaphorin3A (Sema3A) are guidance cues found in pathways and targets of developing dorsal root ganglia (DRG) neurons. DRG growth cone motility is regulated by cytoplasmic signaling triggered by these molecules. We investigated interactions of NGF and Sema3A in modulating growth cone behaviors of axons extended from E7 chick embryo DRGs. Axons extending in collagen matrices were repelled by Sema3A released from transfected HEK293 cells. However, if an NGF-coated bead was placed adjacent to Sema3A-producing cells, axons converged at the NGF bead. Growth cones of DRGs raised in 10(-9) M NGF were more resistant to Sema3A-induced collapse than when DRGs were raised in 10(-11) M NGF. After overnight culture in 10(-11) M NGF, 1-hr treatment with 10-9 M NGF also increased growth cone resistance to Sema3A. Pharmacological studies indicated that the activities of ROCK and PKG participate in the cytoskeletal alterations that lead to Sema3A-induced growth cone collapse, whereas PKA activity is required for NGF-mediated reduction of Sema3A-induced growth cone collapse. These results support the idea that growth cone responses to a guidance cue can be modulated by interactions involving coincident signaling by other guidance cues.