COMPETITION AND COOPERATION AMONG RECEPTOR TYROSINE PHOSPHATASES CONTROL MOTONEURON GROWTH CONE GUIDANCE IN DROSOPHILA

The neural receptor tyrosine phosphatases DPTP69D, DPTP99A and DLAR ar e involved in motor axon guidance in the Drosophila embryo, Here we an alyze the requirements for these three phosphatases in growth cone gui dance decisions along the ISN and SNb motor pathways, Any one of the t hree suffices for the progression of ISN pioneer growth cones beyond t heir first intermediate target in the dorsal muscle field, DLAR or DPT P69D can facilitate outgrowth beyond a second intermediate target, and DLAR is uniquely required for formation of a normal terminal arbor, A different pattern of partial redundancy among the three phosphatases is observed for the SNb pathway, Any one of the three suffices to allo w SNb axons to leave the common ISN pathway at the exit junction, When DLAR is not expressed, however, SNb axons sometimes bypass their vent rolateral muscle targets after leaving the common pathway, instead gro wing out as a separate bundle adjacent to the ISN, This abnormal guida nce decision can be completely suppressed by also removing DPTP99A, su ggesting that DLAR turns off or counteracts a DPTP99A signal that favo rs the bypass axon trajectory, Our results show that the relationships among the tyrosine phosphatases are complex and dependent on cellular context, At growth cone choice points along one nerve, two phosphatas es cooperate, while along another nerve these same phosphatases can ac t in opposition to one another.