unc-51 and
unc-14 mutants of C. elegans have defects in axon guidance of many neurons. We previously reported that
unc-51 encoded a novel serine/threonine kinase, and that
unc-14 encoded a novel protein. In addition, we showed that these genes were expressed in many neurons, and that UNC-51 directly bound UNC-14. Their protein structures and localizations imply that UNC-51 and UNC-14 plays important roles in signal transduction on axon guidance, however, the molecular functions are largely unknown. In order to analyze their functions, we searched for their interacting proteins by using yeast two hybrid system. We newly identified a catalytic subunit of protein phophatase 2A (PP2A-C) as an UNC-51 and UNC-14 interacting protein. At previous meeting, we reported that PP2A-C is encoded by
let-92.
let-92 mutants was 100% early larval lethal. We analyzed morphology of DD/VD neurons of dead
let-92(
s504) larvae, and found that
s504 had minor guidance defects in them. We found that abundant maternal LET-92 and
let-92 mRNA was provided maternally, which might result in the minor defects of axon morphology. In order to avoid the maternal effect, we took RNAi analysis by using
rrf-3(
pk1426) mutants that are hypersensitive to RNAi. Strong
let-92(RNAi) was 100% embryonic lethal, therefore, we analyzed the larval lethal escapers. We found that the
let-92(RNAi) escapers had severe guidance defects of DD/VD neurons. The typical feature was detachment of the ventral and dorsal nerve cords from their normal positions. A
let-92 promoter::GFP fusion gene was expressed in almost all cells. The expression was strong in many neurons. To analyze the subcellular localization of LET-92 in DD/VD neurons, we expressed GFP::LET-92 in DD/VD neurons, and found that GFP::LET-92 strongly localized at the cytoplasm. We also expressed GFP::UNC-51 and GFP::UNC-14 in DD/VD neurons, and found that they also strongly localized at the cytoplasm. As PP2A-C interacts with some serine/threonine kinases and regulates the kinase activity, LET-92 may regulate kinase activity of UNC-51. The strong localization of LET-92, UNC-51 and UNC-14 to cytoplasm imply that they may work in cytoplasm of neurons. As UNC-51 is a homolog of yeast
apg1p required for autophagy that is a catabolic membrane trafficking, LET-92, UNC-51 and UNC-14 may participate in such membrane trafficking.