LRK-1/LRRK2 regulates axon termination in C. elegans neurons.
(A) Schematic of primary structures of human LRRK2 and C. elegans LRK-1 proteins, as labelled. Positions of PD-associated familial missense mutations in LRRK2 and of deletion alleles in LRK-1, are shown. (B) Axonal processes of C. elegans mechanosensory neurons (ALM and AVM) were marked by selective expression of GFP using the mec-7 promoter (Pmec-7::GFP) and visualized by fluorescence microscopy. ALM neurons extend a single axon that normally terminates at a distance from the tip of the nose (yellow arrowhead) in WT worms. However, in lrk-1 mutants, ALM axon frequently overextends to the tip of the nose and subsequently reverses course, resulting in a hook-like structure (white arrowhead). Schematic drawing of the ALM and AVM axon structures is shown at the bottom; anterior is to the right; scale bar = 50 μm. (C) Two independent lrk-1 mutant strains (km17 and tm1898) cultured at 20 °C showed overextension of ALM axons. This was rescued by transgenic expression of LRK-1 under its own promoter (Plrk-1::lrk-1) or of human wild-type LRRK2 (Psnb-1::LRRK2) under the synaptobrevin promoter. Percentages exhibiting overextension of ALM axons are shown. Is: chromosomally integrated strain, ex: extrachromomally overexpressing strain. Data represent mean ± SEM, *p < 0.05, **p < 0.01; Samples numbers n are listed to the right of bar graphs. (D) Overextension of ALM axons was more frequently observed in nematodes cultured at 25 °C than at 20 °C and this temperature-sensitive overextension was rescued by transgenic expression of LRK-1 or human LRRK2. Data represent mean ± SEM, *p < 0.05, **p < 0.01.