Development of the nervous system in C. elegans requires the ligand UNC-6 and its two receptors UNC-5 and UNC-40 as well as other molecules including members of the SLT-1 and the Wnt family pathways. Correct guidance of the axons of the DA and DB classes of motor neurons relies on UNC-6/Netrin and its receptor UNC-5. A mutation in
enu-3.1 enhanced the axon outgrowth defects of DB4, DB5 and DB6 in a strain lacking UNC-5. A mutation in
enu-3.1 also enhanced guidance of the ventrally directed processes of the AVM and PVM touch receptor neurons in a strain lacking UNC-40 but did not enhance the defects of a strain lacking UNC-6. The data suggest that ENU-3.1 works downstream of UNC-6 and parallel to UNC-40 in touch receptor neuron guidance. ENU-3.1 is a member of a family that contains six proteins in C. elegans. Five of the ENU-3 proteins are transmembrane proteins and a sixth is not. We have investigated the genetic mechanism of action of the ENU-3 proteins. We show that the ENU-3 protein family members are all involved in the outgrowth of the DA and DB motor neurons and they work parallel to the Netrin pathway for this function. When expressed in HeLa cells, two of the ENU-3 proteins were expressed in the ER and were localized in the nuclear membrane. The sixth member, ENU-3.6 was located proximal to the plasma membrane and resulted in the appearance of actin dependent processes on the surface of HeLa cells. It appears that the ENU-3 protein family is a part of a pathway that works parallel to the UNC-6 pathway of motor neuron axon outgrowth proteins and we continue to investigate function.