Fig. 2
Basic pharmacological and cross-species reactivity studies of C. elegans and human neuropeptides and receptors in vitro. a Live-cell fluorescence microscopy of C. elegans NPR, human NPY and RFamide receptor::eYFP fusion proteins (yellow) shows similar receptor expression in transfected HEK293 cells and export to the plasma membrane. Images are representative of three independent experiments, and were acquired and processed identically. Nuclei were stained with Hoechst33342 (blue), scale bar = 10 μm. b C. elegans receptors recognize the human G protein repertoire and show distinct coupling preferences. Coupling specificity was deduced from second messenger production (cAMP or inositol phosphate (IP)) in response to FLP-5-1, FLP-15-2, FLP-18-5, and FLP-21, and qualitative data is depicted as color gradient (original numerical data are shown in Additional file 1: Tables S4 and S5). Coupling of NPR-5b to Gα16 and GαΔ6qi4myr via inositol phosphate accumulation is not readily accessible due to endogenous Gαq-coupling and was thus not determined (shaded). c Cross-species activation profiles of selected human and C. elegans receptors with different neuropeptides. Activation profiles were based on data from second messenger assays according to the endogenous G protein-coupling (original data can be found in Additional file 1: Tables S6–S9). Shown is a color-coded interaction matrix based on a two-concentration (0.1 μM; 10 μM) peptide screen as a coarse measure of peptide potency. The two lightest shades of green indicate partial receptor activation after stimulation with 10 μM peptide but no response to 0.1 μM of peptide (estimated EC50 > 10 μM assuming normal curve steepness and full agonism). Mid-grade colors display submaximal activation at 0.1 μM peptide and up to full activation at 10 μM (estimated EC50 0.1 μM), while the darkest shade represents full activation in response to 0.1 μM of peptide (estimated EC50 < 100 nM). Few peptide/receptor combinations elicited identical, but submaximal responses at 0.1 and 10 μM concentration, indicative of partial agonism, and are marked with an asterisk (*). For more details on matrix generation in B and C, see Methods