The present study has given us a first glimpse of the transcriptome of the adult stage of the bovine lungworm, D. viviparus
, and represents a starting point for studies in a number of different fundamental and applied areas. We used a comprehensive EST analysis pipeline, ESTExplorer, for this purpose, for functional annotation at the DNA and protein levels [13
]. From this single study of 5271 ESTs, we have identified 55 novel sequences (1.4%), with high confidence, with no known homologue in any other nematode or mammal for which sequence data are presently available in public databases. These molecules are particularly interesting, as they may represent genes that may be specific to parasitism or to the species. However, such molecules are very challenging to work on, as their potential functions cannot be predicted using current bioinformatic approaches. However, there is considerable scope in exploring such molecules in the future, using a combination of genomic and proteomic approaches. Insights into such molecules and/or their interaction with the bovine host could provide opportunities for developing novel intervention approaches.
From a systematic viewpoint, D. viviparus
, belongs to the Metastrongyloidea ("metastrongyles" or "lungworms") based on nuclear ribosomal DNA sequence data [47
], as distinct from the Trichostrongyloidea (mainly in the stomach and small intestine), Strongyloidea (mostly in the large intestine) and Ancylostomatoidea (small intestine), and thus represents, from biological, host-parasite relationship and molecular evolutionary perspectives, a very interesting species for comparative genomic analysis with nematodes from these superfamilies. Therefore, this nematode brings a number of important benefits for future investigations, particularly for genome sequencing and for subsequent comparative evolutionary analyses. Indeed, D. viviparus
, among other strongylid nematodes, has recently been selected for whole genome sequencing, to be carried out at the Genome Sequencing Center of Washington University in St Louis, USA [48
]. For D. viviparus
, the genomic information from the present study underpins future microarray analyses, focused on exploring the transcriptional profiles among different stages (e.g., larval versus
adult stages; hypobiotic stages versus
those which are not arrested; free-living (L1s and L2s) versus
late larval stages), sexes (female versus
male) and tissues (e.g., germline versus
intestine) of the parasite. Such studies, particularly those of the molecules differentially transcribed and expressed during the transition to parasitism, the invasion of the host and hypobiosis, could provide unique insights into such key molecular developmental and reproductive processes. While there is some controversy regarding the applicability and usefulness of RNAi to some parasitic nematodes, such as the Strongylida [11
], comparative studies of gene-silencing and transgenesis in C. elegans
are considered useful for exploring the function and regulation of some relatively conserved parasite genes, provided data are interpreted with caution [10
]. This is particularly the case with the continued increase in genome sequence information.
With the future availability of whole genome sequence data for D. viviparus
, it will also be possible to carry out meaningful mass spectroscopic analyses of differentially expressed proteins [49
], allowing large-scale analysis of proteins from small amounts of parasite material. Such analyses will enable the link to be made between the regulation of transcription and translation and, importantly, in the study of parasites, will allow the analysis of proteins expressed within short time frames within or external to the host animal, or within organs or micro-environments within the parasite [51
]. Hence, the application of an integrated bioinformatic-genomic-phenomic-proteomic ("systems biology") approach, focusing on developmental processes and mechanisms, could enhance our understanding of the molecular biology of moulting, invasion of and establishment in the host, hypobiosis (arrested development), and sexual differentiation, maturation and behaviour of D. viviparus
. Clearly, progress in such fundamental areas could lead to the development of exciting new ways of treating, controlling or preventing this lungworm and other parasitic nematodes, by blocking or disrupting key biological pathways in them.