Gastropod-associated nematodes have been previously studied and documented worldwide, with some species forming host-specific association as obligate parasites of molluscs while others form intermediate and temporary association. Philippinella moellendorffi from Imelda, Zamboanga Sibugay, Philippines, were collected, washed and maintained in the laboratory until death. Cadavers were placed on nutrient agar to allow nematode proliferation. Nematode pure culture was obtained using one gravid female for propagation. Morphology and molecular analyses (18S ribosomal DNA (rDNA) and D2–D3 expansion segments of 28S rDNA) were employed as diagnostic tools in identifying the nematode species isolated from P. moellendorffi. The newly isolated nematode was identified as Caenorhabditis brenneri, thus designated as C. brenneri strain IZSP from the Philippines. This is the first record of C. brenneri isolated from the terrestrial slug P. moellendorffi.

Transgenesis for Strongyloides and Parastrongyloides was accomplished in 2006 and is based on techniques derived for Caenorhabditis elegans over two decades earlier. Adaptation of these techniques has been possible because Strongyloides and related parasite genera carry out at least one generation of free-living development, with adult males and females residing in soil contaminated by feces from an infected host. Transgenesis in this group of parasites is accomplished by microinjecting DNA constructs into the syncytia of the distal gonads of free-living females. In Strongyloides stercoralis, plasmid-encoded transgenes are expressed in promoter-regulated fashion in the F1 generation following gene transfer but are silenced subsequently. Stable inheritance and expression of transgenes in S. stercoralis requires their integration into the genome, and stable lines have been derived from integrants created using the piggyBac transposon system. More direct investigations of gene function involving expression of mutant transgene constructs designed to alter intracellular trafficking and developmental regulation have shed light on the function of the insulin-regulated transcription factor Ss-DAF-16. Transgenesis in Strongyloides and Parastrongyloides opens the possibility of powerful new methods for genome editing and transcriptional manipulation in this group of parasites. Proof of principle for one of these, CRISPR/Cas9, is presented in this review.

The DNA from a number of free-living and parasitic nematode species was examined to determine the genomic number and distribution of DNA sequences encoding two evolutionary conserved proteins; the major sperm protein (MSP) and nematode actin. Ascaris and Caenorhabditis MSP cDNA sequences and Ascaris genomic actin sequences were used to probe Southern blots of Eco RI and Hin d III digested nematode DNA. The number of MSP genes varied widely between the 1 MSP gene in Ascaris and the 60 MSP genes in Caenorhabditis. Filarial nematodes appeared to have 1—4 MSP genes while the plant and insect parasitic species showed from 5–12 MSP-hybridizing restriction fragments. Mammalian intestinal parasites showed between 1 and 13 bands hybridizing with the MSP probes. Blots probed to estimate the number of actin genes showed that, with the exception of Ascaris which contains more than 20 germ line sequences that encode actin, all of the nematodes tested had between 3 and 9 bands that hybridized to the Ascaris genomic actin probe. The possible use of highly conserved sequences such as MSP and actin to differentiate between nematode species in diagnostic and taxonomic studies is discussed.

There is increasing interest in the use of the free-living nematode Caenorhabditis elegans as a tool for parasitic nematode research and there are now a number of compelling examples of its successful application. C. elegans has the potential to become a standard tool for molecular helminthology researchers, just as yeast is routinely used by molecular biologists to study vertebrate biology. However, in order to exploit C. elegans in a meaningful manner, we need a detailed understanding of the extent to which different aspects of C. elegans biology have been conserved with particular groups of parasitic nematodes. This review first considers the current state of knowledge regarding the conservation of genome organisation across the nematode phylum and then discusses some recent evolutionary development studies in free-living nematodes. The aim is to provide some important concepts that are relevant to the extrapolation of information from C. elegans to parasitic nematodes and also to the interpretation of experiments that use C. elegans as a surrogate expression system. In general, examples have been specifically chosen because they highlight the importance of careful experimentation and interpretation of data. Consequently, the focus is on the differences that have been found between nematode species rather than the similarities. Finally, there is a detailed discussion of the current status of C. elegans as a heterologous expression system to study parasite gene function and regulation using successful examples from the literature.