Nematodes are important: parasitic nematodes threaten the health of plants, animals and humans on a global scale; interstitial nematodes pervade sediment and soil ecosystems in overwhelming numbers; and Caenorhabditis elegans is a favourite experimental model system. A lack of clearly homologous characters and the absence of an informative fossil record have prevented us from deriving a consistent evolutionary framework for the phylum. Here we present a phylogenetic analysis, using 53 small subunit ribosomal DNA sequences from a wide range of nematodes. With this analysis, we can compare animal-parasitic, plant-parasitic and free-living taxa using a common measurement. Our results indicate that convergent morphological evolution may be extensive and that present higher-level classification of the Nematoda will need revision. We identify five major clades within the phylum, all of which include parasitic species. We suggest that animal parasitism arose independently at least four times, and plant parasitism three times. We clarify the relationship of C. elegans to major parasitic groups; this will allow more effective exploitation of our genetic and biological knowledge of this model species.

The activity of the DAF-2 insulin-like receptor is required for Caenorhabditis elegans reproductive growth and normal adult life span. Informatic analysis identified 37 C. elegans genes predicted to encode insulin-like peptides. Many of these genes are divergent insulin superfamily members, and many are clustered, indicating recent diversification of the family. The ins genes are primarily expressed in neurons, including sensory neurons, a subset of which are required for reproductive development. Structural predictions and likely C-peptide cleavage sites typical of mammalian insulins suggest that ins-1 is most closely related to insulin. Overexpression of ins-1, or expression of human insulin under the control of ins-1 regulatory sequences, causes partially penetrant arrest at the dauer stage and enhances dauer arrest in weak daf-2 mutants, suggesting that INS-1 and human insulin antagonize DAF-2 insulin-like signaling. A deletion of the ins-1 coding region does not enhance or suppress dauer arrest, indicating a functional redundancy among the 37 ins genes. Of five other ins genes tested, the only other one bearing a predicted C peptide also antagonizes daf-2 signaling, whereas four ins genes without a C peptide do not, indicating functional diversity within the ins family. Insulin and its related proteins define a superfamily of secreted proteins that share a structural motif stabilized by a set of stereotypical disulfide bonds (Blundell and Humbel 1980;Murray-Rust et al. 1992). Insulin superfamily genes are ubiquitous in vertebrates, and have been identified in invertebrates, including insects, molluscs, and the nematode Caenorhabditis elegans (Duret et al. 1998;Gregoire et al. 1998;Smit et al. 1998;Kawano et al. 2000). Seven members of the insulin superfamily have been identified in humans, including insulin (Brown et al. 1955), insulin-like growth factors (IGFs) I and II (Rinderknecht and Humbel 1978a,b), relaxins HI and HII (Bedarkar et al. 1977;Schwabe and McDonald 1977), early placenta insulin-like peptide (EPIL) (Chassin et al. 1995;Koman et al. 1996), and relaxin-like factor (Bullesbach and Schwabe 1995). These hormones mediate diverse functions. Insulin is a metabolic hormone that acts on target tissues to increase glucose uptake and energy storage, IGFs are mitogenic stimulators that control cell survival and proliferation, and relaxin causes dilation of the symphysis pubis before parturition and vasodilation. No function is yet known for either EPIL or relaxin-like factor. Bombyxin in silk moths (Satake et al. 1997), and the neurons that secrete locust and molluscan insulin-related proteins (Smit et al. 1988;Lagueux et al. 1990) regulate metabolism, implicating insulin-like proteins in metabolic control broadly in animal phylogeny. The insulin-like proteins that regulate metabolism, insulin in vertebrates, bombyxin from silk moths, molluscan MIP, and locust LIRP, appear to be processed proteolytically to remove an internal C peptide (Smit et al. 1988;Lagueux et al. 1990;Kondo et al. 1996). This proc...

In C. elegans, tol-1 is important for development and pathogen recognition, as is Toll in Drosophila, but remarkably for the latter rôle, it functions in the context of a behavioral mechanism that keeps worms away from potential danger.

No abstract