| A program of gene discovery was initiated for the planorbid snail Biomphalaria glabrata and for the primary sporocysts of its two trematode parasites, Schistosoma mansoni and Echinostoma paraensei , to study the molecular mechanisms that underlie the interactions between the infection/invasion strategies employed by larval trematodes and the subsequent defense response of their snail hosts.;Using suppression subtractive hybridization (SSH) a cDNA library was constructed that had enhanced representation of gene transcripts likely to be more abundant during the successful defense response of resistant versus susceptible B. glabrata snails against S. mansoni infection. In particular, transcripts for FREP2 and two protease inhibitors were likely to be expressed more abundantly in the response of resistant versus susceptible snails. Quantitative PCR (gPCR) analysis before and after exposure to S. mansoni indicated several transcription patterns are associated with the two different snail reactions to infection, including: constitutive differences in expression, upregulation in resistant snails, and downregulation in susceptible snails.;SSH yielded subtracted sporocyst cDNA libraries of the trematodes E. paraensei and S. mansoni. Sixty-nine and 89 unique sequences were recovered from the E. paraensei and S. mansoni SSH-libraries, respectively. Greater than 70% of the E. paraensei sequences were novel, although one sequence had similarity to a putative inhibitor of nitric oxide synthase, implying defense against a host hemocyte attack. The largest subsets of identifiable S. mansoni sequences indicated an emphasis on detoxification/stress response and protein translation/degradation. gPCR measurements of transcript abundance in various ontogenetic stages revealed five of the six transcripts ( E. paraensei) and seven of eight (S. mansoni) are developmentally regulated, with increased expression in sporocysts. Comparisons between the species' sporocyst SSH libraries indicate that echinostomes transcribe many genes that have no homologues in S. mansoni, which indicates possible additional mechanisms employed to facilitate successful infection. This study has identified several new gene products indicated to influence outcome of trematode infections in snails, relating to development of trematode sporocysts and snail defense factors. These will serve as valuable tools to guide further studies of a novel and important model for understanding at a molecular level the nature of host-parasite interactions. |
