The neural receptor tyrosine phosphatases DPTP69D,
DPTP99A and DLAR are involved in motor axon guidance
in the Drosophila embryo. Here we analyze the requirements
for these three phosphatases in growth cone guidance decisions along the ISN and SNb motor pathways.
Any one of the three suffices for the progression of ISN
pioneer growth cones beyond their first intermediate target
in the dorsal muscle field. DLAR or DPTP69D 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 allow SNb axons
to leave the common ISN pathway at the exit junction.
When DLAR is not expressed, however, SNb axons
sometimes bypass their ventrolateral muscle targets after
leaving the common pathway, instead growing out as a
separate bundle adjacent to the ISN. This abnormal
guidance decision can be completely suppressed by also
removing DPTP99A, suggesting that DLAR turns off or
counteracts a DPTP99A signal that favors 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 phosphatases cooperate, while along another
nerve these same phosphatases can act in opposition to one
another
