Proper development of the nervous system requires directed axonal outgrowth. During development in C. elegans, the DD and VD D-type GABAergic motor neuron axons are directed anteriorly along the ventral nerve cord. The 6 DD neurons form during embryogenesis and the 13 VD neurons form later at the end of the L1 stage. Previously, we found that
fmi-1/Flamingo, the single C. elegans member of the Celsr-like cadherin superfamily interacts synergistically with Wnt pathway components to regulate anteroposterior (A/P) axonal outgrowth of the DD and VD neurons. In mutant animals, some DD and VD neurons exhibit posteriorly-directed neurite (Pdn) outgrowth instead of the stereotypical anterior neurite (AN). We conducted a forward enhancer genetic screen in
mig-5/Disheveled mutants for new mutations that synergistically increased the occurrence of Pdns. One of the alleles recovered was a nonsense mutation in the cell-adhesion molecule
syg-2. To simplify our genetic analyses, we focused entirely on Pdns that occurred in the tail of the animal, where there are normally no GABAergic axons present. We found that, individually, loss of function in either
mig-5 or
syg-2 resulted in a Pdn in approximately 2% of animals, while 28% of the double mutants had a Pdn. Mutations in
syg-1 also demonstrated synergy with
mig-5, resulting in a similar penetrance to the
syg-2;
mig-5 double mutants. To test a second component of the Wnt signaling pathway, we used
lin-17/frizzled. Loss of
lin-17 function resulted in a Pdn in roughly ~ 20% of animals, while 46% and 55% of
syg-2;
lin-17 and
syg-1;
lin17 animals exhibited Pdns, respectively. The
syg-1syg-2;
lin-17 triple mutant exhibited a 55% penetrance of the Pdn phenotype, indicating that
syg-1 and
syg-2 are in a common genetic pathway. Finally, we sought to determine whether the DDs or VDs were contributing to the Pdns observed. To do so, we compared the penetrance of Pdns in L1 stage animals to adults. Our previous work showed that the DD neurons were not affected by loss of function in
fmi-1, however both DD and VD neurons are affected in
mig-5;
fmi-1 double mutants. Recent results indicate that that
mig-5 affects all D-type neurons, while
syg-1 and
syg-2 more specifically affect DDs in both a
mig-5 and
lin-17 background, while
fmi-1 is VD selective. Currently, we are examining where
syg-1 and
syg-2 are functioning during GABAergic axon development. Our results provide novel insights as to how neurons with the same morphology may use different patterning cues during nervous system development.