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Biomphalaria glabrata is the major intermediate snail host for Schistosoma mansoni, one of the important schistosomes infecting man. Much remains to be discovered concerning specific molecules mediating the defence events in these intermediate hosts, triggered by invading schistosomes. An expressed sequence tag (EST) gene discovery strategy known as ORESTES has been employed to identify transcripts that might be involved in snail-schistosome interactions in order to examine gene expression patterns in infected B. glabrata. Over 3930 ESTs were sequenced from cDNA libraries made from both schistosome-exposed and unexposed snails using different tissue types, producing a database of 1843 non-redundant clones. The non-redundant set has been assessed for gene ontology and KEGG pathway assignments. This approach has revealed a number of signalling, antioxidant and immune-related gene homologues that, based on current understanding of molluscan and other comparative systems, might play an important role in the molluscan defence response towards infection.

The freshwater tropical snail Biomphalaria glabrata is an intermediate host for Schistosoma mansoni, the causative agent of human intestinal schistosomiasis, and strains differ in their susceptibility to parasite infection. Changes in gene expression in response to parasite infection have been simultaneously examined in a susceptible strain (NHM1742) and a resistant strain (NHM1981) using a newly developed fluorescent-based differential display method. Such RNA profiling techniques allow the examination of changes in gene expression in response to parasite infection, without requiring previous sequence knowledge, or selecting candidate genes that may be involved in the complex neuroendocrine or defence systems of the snail. Thus, novel genes may be identified. Ten transcripts were initially identified, present only in the profiles derived from snails of the resistant strain when exposed to infection. The differential expression of five of these genes, including HSP70 and several novel transcripts with one containing at least two globin-like domains, has been confirmed by semi-quantitative RT-PCR.

During its life cycle, the helminth parasite Schistosoma mansoni uses the freshwater snail Biomphalaria glabrata as an intermediate host to reproduce asexually generating cercariae for infection of the human definitive host. Following invasion of the snail, the parasite develops from a miracidium to a mother sporocyst and releases excretory-secretory products (ESPs) that likely influence the outcome of host infection. To better understand molecular interactions between these ESPs and the host snail defence system, we determined gene expression profiles of haemocytes from S. mansoni-resistant or -susceptible strains of B. glabrata exposed in vitro to S. mansoni ESPs (20 μg/ml) for 1 h, using a 5K B. glabrata cDNA microarray. Ninety-eight genes were found differentially expressed between haemocytes from the two snail strains, 57 resistant specific and 41 susceptible specific, 60 of which had no known homologue in GenBank. Known differentially expressed resistant-snail genes included the nuclear factor kappa B subunit Relish, elongation factor 1α, 40S ribosomal protein S9, and matrilin; known susceptible-snail specific genes included cathepsins D and L, and theromacin. Comparative analysis with other gene expression studies revealed 38 of the 98 identified genes to be uniquely differentially expressed in haemocytes in the presence of ESPs, thus identifying for the first time schistosome ESPs as important molecules that influence global snail host-defence cell gene expression profiles. Such immunomodulation may benefit the schistosome, enabling its survival and successful development in the snail host. [ABSTRACT FROM AUTHOR]

The outcome of infection in the host snail Biomphalaria glabrata with the digenean parasite Schistosoma mansoni is determined by the initial molecular interplay occurring between them. The mechanisms by which schistosomes evade snail immune recognition to ensure survival are not fully understood, but one possibility is that the snail internal defence system is manipulated by the schistosome enabling the parasite to establish infection. This study provides novel insights into the nature of schistosome resistance and susceptibility in B. glabrata at the transcriptomic level by simultaneously comparing gene expression in haemocytes from parasite-exposed and control groups of both schistosome-resistant and schistosomesusceptible strains, 2 h post exposure to S. mansoni miracidia, using an novel 5 K cDNA microarray. Differences in gene expression, including those for immune/stress response, signal transduction and matrix/adhesion genes were identified between the two snail strains and tests for asymmetric distributions of gene function also identified immune-related gene expression in resistant snails, but not in susceptible. Gene set enrichment analysis revealed that genes involved in mitochondrial electron transport, ubiquinone biosynthesis and electron carrier activity were consistently up-regulated in resistant snails but down-regulated in susceptible. This supports the hypothesis that schistosome-resistant snails recognize schistosomes and mount an appropriate defence response, while in schistosome-susceptible snails the parasite suppresses this defence response, early in infection. [ABSTRACT FROM AUTHOR]

Abstract: Analysis of differential gene expression in salmon (Salmo salar) blood following infection with the monogenean parasite Gyrodactylus salaris, resulted in the isolation of a thymidylate kinase gene not previously described from fish and which showed similarity to an LPS-inducible thymidylate kinase gene isolated from mouse macrophages. This salmon TYKi-like gene may play a role in an innate generalised response to pathogen infection as it was upregulated in salmon following infection with the parasite, and also in response to injection with the immunostimulants LPS and Poly I:C, used to emulate bacterial and viral infections, respectively. The possible role of this gene in the biosynthesis of mitochondrial DNA in activated macrophages, in response to G. salaris infection is discussed. [Copyright &y& Elsevier]

Abstract: Suppressive subtractive hybridisation was used to examine the genetic basis of susceptibility and resistance of the Atlantic salmon (Salmo salar) to Gyrodactylus salaris infection. Selected immune relevant genes are listed and two genes, for myeloid leukemia differentiation protein (Mcl-1) and opioid growth factor receptor (OGFr), obtained from the susceptible salmon library were characterised. Both sequences showed high amino acid identity and similarity with human and mouse isoforms, and their possible involvement in the response of salmon to G. salaris is discussed. Quantitative reverse transcriptase-PCR was performed for both genes. Upregulation of Mcl-1 in B1 backcross salmon of the susceptible phenotypic category compared with resistant salmon was demonstrated. The possible relationship of the salmon Mcl-1 and cytokines (interleukin 1β) in the G. salaris-induced host response is discussed. Potential involvement of OGFr in the depletion of mucous cells during prolonged and heavy G. salaris infection, via suppression of DNA synthesis and profound decrease in basal cell proliferation, is proposed. However, only two of six susceptible fish showed high upregulation of OGFr, which might indicate that its expression is localised to sites of wounds resulting from a heavy burden of G. salaris. [Copyright &y& Elsevier]