Survey of transcripts expressed by the invasive juvenile stage of the liver fluke Fasciola hepatica

Abstract

BackgroundThe common liver fluke Fasciola hepatica is the agent of a zoonosis with significant economic consequences in livestock production worldwide, and increasing relevance to human health in developing countries. Although flukicidal drugs are available, re-infection and emerging resistance are demanding new efficient and inexpensive control strategies. Understanding the molecular mechanisms underlying the host-parasite interaction provide relevant clues in this search, while enlightening the physiological adaptations to parasitism. Genomics and transcriptomics are still in their infancy in F. hepatica, with very scarce information available from the invasive newly excysted juveniles (NEJ). Here we provide an initial glimpse to the transcriptomics of the NEJ, the first stage to interact with the mammalian host.ResultsWe catalogued more than 500 clusters generated from the analysis of F. hepatica juvenile expressed sequence tags (EST), several of them not detected in the adult stage. A set of putative F. hepatica specific transcripts, and a group of sequences conserved exclusively in flatworms were identified. These novel sequences along with a set of parasite transcripts absent in the host genomes are putative new targets for future anti-parasitic drugs or vaccine development.Comparisons of the F. hepatica sequences with other metazoans genomes or EST databases were consistent with the basal positioning of flatworms in the bilaterian phylogeny. Notably, GC content, codon usage and amino acid frequencies are remarkably different in Schistosomes to F. hepatica and other trematodes.Functional annotation of predicted proteins showed a general representation of diverse biological functions. Besides proteases and antioxidant enzymes expected to participate in the early interaction with the host, various proteins involved in gene expression, protein synthesis, cell signaling and mitochondrial enzymes were identified. Differential expression of secreted protease gene family members between juvenile and adult stages may respond to different needs during host colonization.ConclusionThe knowledge of the genes expressed by the invasive stage of Fasciola hepatica is a starting point to unravel key aspects of this parasite's biology. The integration of the emerging transcriptomics, and proteomics data and the advent of functional genomics tools in this organism are positioning F. hepatica as an interesting model for trematode biology.

Reducing the future threat from (liver) fluke: realistic prospect or quixotic fantasy?

“…Despite the limited amount of sequence data available in the databases for Fasciola, there have been a number of recent efforts to analyse the transcriptome and proteome of the fluke, at different stages in the life cycle (Gourbal et al, 2008;Cancela et al, 2010;Hernández-González et al, 2010;Young et al, 2010Young et al, , 2011. The technologies have the potential to identify proteins, based on sequence homology with known molecules in other organisms.…”

“…Fasciola hepatica secretes a variety of cathepsins-10 cathepsin B proteases and at least 5 cathepsin L proteases. The individual cathepsins show a pattern of expression during the mammalian phase of the life cycle that is strongly linked to the migration and development of the fluke, with the cathepsin B proteases predominating in the earlier stages, while the cathepsin L proteases are the only forms produced by the adult stage (Cancela et al, , 2010Robinson et al, 2008aRobinson et al, ,b, 2009Beckham et al, 2009;see Fig. 2 in Robinson et al, 2009).…”

The miRnome of Fasciola hepatica juveniles endorses the existence of a reduced set of highly divergent micro RNAs in parasitic flatworms

“…During the invasion process the invasive NEJs are confronted with different environments in their passage from the intestine to the liver. It has been demonstrated that changes in gene expression underlie the early stages of invasion (Cancela et al, 2008(Cancela et al, , 2010 but little is known of how these processes are regulated.…”

Juvenile-specific cathepsin proteases in Fasciola spp.: their characteristics and vaccine efficacies

“…Later, three cathepsin B isotypes were identified from stage-specific cDNA libraries of F. gigantica and named FgCatB1, FgCatB2, and FgCatB3 (Meemon et al 2004). The orthologous cathepsin B isotypes (CB1, CB2, CB3) were then identified in juvenile F. hepatica (Cancela et al 2008(Cancela et al , 2010. RT-PCR and phylogenetic analyses demonstrated that these isotypes were stagespecific (Meemon et al 2004;Cancela et al 2008;Smooker et al 2010).…”