wdr-23 was identified in an RNAi screen for genes that cause resistance to the paralytic effects of the acetylcholine (ACh) esterase inhibitor aldicarb. WDR-23 is a conserved protein composed of seven WD-40 repeats predicted to form a beta-propeller.
wdr-23 is expressed broadly, including in cholinergic motor neurons (CMNs), head neurons, body wall muscle, vulval muscle, skin cells and gut cells. Two isoforms of
wdr-23 exist, A and B, and share the seven WD-40 repeat domains, but differ at the N-terminus. In CMNs, WDR-23A::GFP is seen localized to punctuate structures in axons and in cell bodies, while WDR-23B::GFP expression is restricted to the nucleus. In axons, WDR-23A::GFP partially co-localizes with the active zone marker SYD-2/Liprin. While WDR-23A::GFP normally localizes to the active zone, it co-localizes with synaptic vesicle markers in mutants that disrupt exocytosis. We have characterized a
wdr-23 deletion allele,
tm1817, provided by the Mitani lab, which causes a frame shift and early truncation of the protein after the second WD-40 repeat.
wdr-23 mutants are scrawny, slow growing, and resistant to aldicarb, but not resistant to the paralytic effects of the muscle agonist levamisole. We have fully rescued the movement, growth and aldicarb defects by re-expressing WDR-23A cDNA under the
snb-1 promoter. In a wild type background, over-expression of WDR-23A under the
snb-1 promoter causes hypersensitivity to aldicarb. Further, we see an accumulation of the synaptic vesicle marker SNB-1::GFP in
wdr-23 mutants that is similar to that seen in known exocytosis mutants, suggesting that
wdr-23 plays a role in exocytosis. The human homologue of WDR-23, WDR23, binds to the DDB1/CUL4 ubiquitin ligase complex and is proposed to function as a linker to target proteins destined for degredation. The worm homologue of DDB1, DDB-1, has been reported to be expressed in some neurons. We are testing whether these proteins interact in neurons and looking for potential degradation targets using co-immunoprecipitation. We are testing whether this interaction is functional in neurotransmission by assaying for ACh secretion in mutants where these proteins cannot interact. Together, our findings suggest that
wdr-23 is a novel conserved regulator of synaptic transmission and may be required for targeting synaptic proteins for degradation.