Recent genetic evidence suggests that tyrosine kinases and tyrosine ph
osphatases can control the guidance of specific growth cones. Within a
family of related phosphatases or kinases, individual members can hav
e partially redundant functions. Receptor phosphatases can work togeth
er at one guidance choice point, but in opposition at another. The spe
cific combination of kinases and phosphatases active in a growth cone
may be an important determinant of pathway choice. One mechanism by wh
ich these proteins could control guidance decisions is through regulat
ion of adhesion between growth cones and axons.