Parasite-host interactions in Caenorhabditis elegans
Parasites decrease host fitness, they evolve rapidly, and they are therefore believed to have a major impact on host evolution. At the same time, the presence of specific host defenses selects for parasites, which have evolved efficient countermeasures. In consideration of the ubiquity of parasitic organisms in nature, parasite-host interactions are expected to be both highly complex and dynamic. However, owing to the scarcity of suitable experimental systems, many aspects of the interaction are only poorly understand. Here, we employ the free-living soil nematode Caenorhabditis elegans as a model host, which is ideally suited for efficient performance of laboratory experiments, including comprehensive phenotypic and molecular genetic analyses (see C. elegans, Wormbook, Caenorhabditis Genetics Centre, or Wormbase).
Co-evolution between parasites and hosts should result in genotype-specific interactions. In this case, certain host genotypes can defend themselves efficiently towards only some parasite genotypes (towards which they are well adapted), but not others (towards which they are not adapted), whereas other host genotypes show exactly the opposite pattern. We were able to find such genotype-specific interactions towards two different parasitic bacteria: the Gram-negative Serratia marcescens and the Gram-positive Bacillus thuringiensis, both of which infect the worm intestines . We now use selection experiments (laboratory evolution experiments) to assess the impact of parasites on the dynamics of host evolution, in particular the host defense system, the extent of a possible trade-off between resistance and other host life-history traits (fertility, longevity), and the occurrence of outbreeding (expected to be essential for the generation of sufficient genetic diversity to keep up with a fast evolving parasite).
Understanding the mechanisms of worm defense is of paramount importance for interpretation of the dynamics of parasite-host interactions. Due to the availability of a whole array of molecular techniques and the whole genome sequence, C. elegans provides an ideal opportunity for molecular analysis of an organism’s defense system. We therefore also examine the genetic basis of the observed differences in immunity among natural C. elegans strains, using the microarray technology to identify candidate immunity genes and gene inactivation by RNA interference to examine the function of such candidate genes. Considering that only little information is as yet available on the immune system of lower invertebrates, including C. elegans, this work should provide novel insights into the evolution and function of the animal innate immune system. One previously identified pathway is of special interest: the insulin-like receptor pathway (daf-2 pathway) links resistance and longevity on one hand to development and reproductive rate on the other hand, and therefore it may represent the genetic switch for the trade-off among different life-history traits (fast reproduction versus longevity).
People involved:
Martina Hohloch, Leila Masri, Hinrich Schulenburg (PI)
Funding:
DFG grants SCHU 1415/1-1, SCHU 1415/1-2, SCHU 1415/3-1, SCHU 1415/3-2 (part of the DFG priority programme 1110 on innate immunity), and SCHU 1415/5-1; DAAD; Alexander-von-Humboldt foundation
Collaborators:
* Jonathan Ewbank and group in Marseille (microarrays and work on Serratia marcescens)
* Thomas Roeder and group in Kiel (pathogen recognition)
* Adrian Streit, Ralf Sommer, Tübingen (C. elegans genetics)
* Andreas Peschel, Friedrich Götz, Tübingen (Staph. aureus pathogenesis)
* Jan Kammenga, Wageningen (QTL analysis of C. elegans defence)
* Rüdiger Paul and group (inducible defence against pathogens)
* Erich Bornberg and group (genomic diversification of immunogenes)
Colleagues working on related topics in C. elegans:
* Jonathan Hodgkin and group in Oxford
* Man-Wah Tan and group in Stanford
* Raffi Aroian and group in San Diego
* Frederick Ausubel and group at Harvard University
* Danielle Garsin and group in Houston
* Alejandro Aballay and group at Duke University
* Creg Darby and group at the University of Alabama
Check out our publication list and C. elegans web resources.
