Comparison of Caenorhabditis elegans NLP peptides with arthropod neuropeptides Steven J. Husson * , Marleen Lindemans * , Tom Janssen and Liliane Schoofs Functional Genomics and Proteomics, Department of Biology, Katholieke Universiteit Leuven, Naamsestraat 59, B-3000 Leuven, Belgium Neuropeptides are small messenger molecules that can be found in all metazoans, where they govern a diverse array of physiological processes. Because neuropeptides seem to be conserved among pest species, selected peptides can be considered as attractive targets for drug discovery. Much can be learned from the model system Caenorhabditis elegans because of the availability of a sequenced genome and state-of-the-art postgenomic technologies that enable characterization of endogen- ous peptides derived from neuropeptide-like protein (NLP) precursors. Here, we provide an overview of the NLP peptide family in C. elegans and discuss their resemblance with arthropod neuropeptides and their relevance for anthelmintic discovery. The search for new anthelmintics Worldwide helminth infections of humans, domestic live- stock and agricultural products still have a tremendous impact on the world economy and on health. Currently, three major classes of anthelmintics are widely used: benzimidazoles (e.g. albendazole and mebendazole), imi- dazothiazoles (e.g. levamisole) and macrocyclic lactones (e.g. avermectins, milbemycins and ivermectins). However, a huge increase in resistance to existing anthelmintics has obliged us to look for new key drug targets and potential lead compounds [1]. To find potentially interesting drug targets, the availability of genomic sequences is invaluable because they form the base for high-throughput screens. After the publication of the first genomic sequence of a multicellular organism, Caenorhabditis elegans, in 1998 [2], efforts have been undertaken to unravel nucleotide sequence data from parasitic nematodes. The first initiat- ives focused on expressed sequence tag (EST) libraries – initially, only those of the filarial worms Brugia malayi [3] and Onchocerca volvulus [4], which cause elephantiasis and river blindness, respectively. The vast ocean of nucleo- tide information, together with recently published or ongoing genome-sequencing projects from parasite species such as B. malayi [5], provides an unprecedented oppor- tunity to mine for putative drug targets [6]. Successful application of the RNA interference (RNAi) technology in B. malayi offers the promise of assessing gene functions in parasitic species [7]. Combining bioinformatics and unra- veling gene functions by RNAi can be considered as an effective genome-wide strategy for identifying new mol- ecular targets for anthelmintic discovery. Of note, amino- acetonitrile derivatives (AADs) have recently been discov- ered as a new chemical class of synthetic anthelmintics using a solid in vitro screen [8]. These novel drug candi- dates seem to have a completely novel mode of action, which is efficacious against a wide variety of livestock- pathogenic nematodes. Because the AADs target nema- tode-specific acetylcholine receptor subunits, low toxicity to mammals has been observed. The neuropeptidergic signaling machinery might also be of particular interest because biologically active neuro- peptides have been demonstrated to be important for orchestrating a wide diversity of behaviors [9]. Although at first sight, nematodes, platyhelminths and arthropods seem to be simple organisms, they all contain a surpris- ingly complex neuropeptidergic signaling system. This is reflected not only in the presence of a wide variety of neuropeptide-encoding genes but also in the highly regulated proteolytic processing of the resulting peptide precursors to yield the bioactive peptides (Box 1) and the initiation of a specific signaling pathway by binding to their cognate G-protein-coupled receptors (GPCRs). The FMRFamide-like peptides, or FLPs (which have been studied extensively in nematodes [10], platyhel- minths [11] and insects [12]), represent promising oppor- tunities for the identification and development of targets for pest control [13,14]. Inactivation of the C. elegans flp-1 gene, for example, results in uncoordinated movements, hyperactivity and insensitivity to high osmolarity [15] and causes egg-laying defects [16], illustrating the potential of these signaling molecules as putative drug targets. Here, we focus on a second class of neuropeptides, derived from the so-called ‘neuropeptide-like protein’ (NLP) precursors. Initially, 32 nlp genes were found by mining the C. elegans genome for precursor genes encoding neuropeptides that display sequence resemblance with peptides from other species [17]. Four to five years later, additional NLP peptides could be identified by mass spec- trometry, microarray analysis and bioinformatics, bring- ing the total number of nlp genes to 47 [18–21]. Although the NLP family is still expanding, the availability of pep- tide sequences without knowledge of their in vivo physio- logical functions can be tantalizing. Because only a few knockouts are available for nlp genes, it is hard to gain functional information. However, a lot can be learned from Review Corresponding author: Husson, S.J. (steven.husson@bio.kuleuven.be) * These authors contributed equally to this article. 1471-4922/$ – see front matter ß 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.pt.2008.12.009 Available online 9 March 2009 171