Abstract
The nematode Ascaridia galli (order Ascaridida) is an economically important intestinal parasite responsible for increased food consumption, reduced performance and elevated mortality in commercial poultry production. This roundworm is an emerging problem in several European countries on farms with laying hens, as a consequence of the recent European Union (EU) ban on conventional battery cages. As infection is associated with slow development of low levels of acquired protective immunity, parasite control relies on repeated use of dewormers (anthelmintics). Benzimidazoles (BZ) are currently the only anthelmintic registered in the EU for use in controlling A. galli and there is an obvious risk of overuse of one drug class, selecting for resistance. Thus we developed a reference transcriptome of A. galli to investigate the response in gene expression before and after exposure to the BZ drug flubendazole (FLBZ). Transcriptional variations between treated and untreated A. galli showed that transcripts annotated as mitochondrial glutamate dehydrogenase and cytochrome P450 were significantly down-regulated in treated worms, whereas transcripts homologous to heat shock proteins (HSP), catalase, phosphofructokinase, and a multidrug resistance P-glycoprotein (PGP1) were significantly up-regulated in treated worms. Investigation of candidate transcripts responsible for anthelmintic resistance in livestock nematodes led to identification of several tubulins, including six new isoforms of beta-tubulin, and several ligand-gated ionotropic receptors and ABC-transporters. We discovered several transcripts associated with drug binding and processing genes, but further characterisation using a larger set of worms exposed to BZs in functional assays is required to determine how these are involved in drug binding and metabolism.
Highlights
Nematodes are elongated, cylindrical and bilaterally symmetrical organisms surrounded by a non-cellular cuticle over a layer of muscle cells covering a pseudocoel filled with an intestine and genitalia [1]
In total 6,291 out of 301,681 transcripts were included in this top-90% subset, indicating that a large amount of the assembled transcripts were expressed at rather low levels
Baseline information about gene expression is of fundamental importance for ongoing research on identification of mechanisms involved in the uptake and metabolism of anthelmintic drugs in target nematodes
Summary
Nematodes (roundworms) are elongated, cylindrical and bilaterally symmetrical organisms surrounded by a non-cellular cuticle over a layer of muscle cells covering a pseudocoel filled with an intestine and genitalia [1]. The genome of nematodes ranges in size from 50 to 250 Mb [4], but the variation across this phylum is probably even larger because genome size has so far only been estimated for a limited number of species. Genome size was recently shown to be 312 Mb in barber’s pole worm, Haemonchus contortus [5]. This is a highly pathogenic nematode of sheep and one of the best studied parasitic nematodes [6]. The genome is nearly seven times larger (~2100 Mb) in the ascarid Parascaris equorum of horses [7], illustrating a remarkable/significant variation in genome size between different species
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