Thorsten Schedletzky and Alexander Gottschalk. We have previously identified novel proteins associated with the levamisole receptor, one of two nicotinic acetylcholine receptors (nAChRs) acting at the neuromuscular junction (NMJ) of Caenorhabditis elegans, using a tandem affinity approach, mass spectromety and RNAi-based functional screening (Gottschalk et al., 2005). Two of the proteins that show altered nicotine-sensitivity after knock-down are the multisubstrate adaptor protein SOC-1 and the polo-like kinase PLK-2.
soc-1(
n1789) mutants show resistance to nicotine and levamisole in paralysis assays. As it is well known that SOC-1 acts downstream of the EGL-15 fibroblast growth factor (FGF) receptor tyrosine kinase (RTK), we tested
egl-15 as well as other positive regulators of the FGF pathway. We could show that
soc-1 is connected not only to EGL-15 signalling in clustering of levamisole receptors at the NMJ, but also to a second RTK, CAM-1, and that it also affects clustering of GABAA receptors, potentially through a third, as yet unknown RTK. A SOC-1::GFP fusion is strongly expressed in amphid sheath and socket cells, but nevertheless rescues the
soc-1 phenotype in
clr-1;
soc-1 double mutants. We try to detect SOC-1 in other cells, using a specific antibody.. Currently, we are screening for other receptor tyrosine kinases in C. elegans causing a nicotine or levamisole resistance phenotype, to identify novel upstream regulators of SOC-1, that may be involved in nAChR and/or GABAA receptor clustering at the NMJ.. PLKs are kinases generally involved in cell-division and chromosome segregation, however, vertebrate PLK-2 homologues (Fnk and Snk) also affect synaptic plasticity.
plk-2(
tm1395) mutants are weakly nicotine and levamisole resistant. Characterization of
plk-2(
tm1395) by electrophysiology, however, indicated only a trend towards reduced currents induced by cholinergic agonists in muscle (see abstract by J. Liewald).
plk-2 mutants also show a high incidence of males (him) phenotype, indicating indeed a role in centrosome duplication and chromosome segregation. Consistently, PLK-2::GFP appears to be expressed both in dividing and non-dividing cells, including muscle.. Reference: Gottschalk A, Almedom R, Schedletzky T, Anderson SD, Yates JR, and Schafer WR (2005) EMBO J 24: 2566-2578