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In recent decades, numerous studies have sought to better understand the mechanisms underlying the compatibility between Biomphalaria glabrata and Schistosoma mansoni. The developments of comparative transcriptomics, comparative genomics, interactomics and more targeted approaches have enabled researchers to identify a series of candidate genes. However, no molecular comparative work has yet been performed on multiple populations displaying different levels of compatibility. Here, we seek to fill this gap in the literature. We focused on B. glabrata FREPs and S. mansoni SmPoMucs, which were previously demonstrated to be involved in snail/schistosome compatibility. We studied the expression and polymorphisms of these factors in combinations of snail and schistosome isolates that display different levels of compatibility. We found that the polymorphism and expression levels of FREPs and SmPoMucs could be linked to the compatibility level of S. mansoni. These data and our complementary results obtained by RNA-seq of samples from various snail strains indicate that the mechanism of compatibility is much more complex than previously thought, and that it is likely to be highly variable within and between populations. This complexity must be taken into account if we hope to identify the molecular pathways that are most likely to be good targets for strategies aimed at blocking transmission of the parasite through the snail intermediate host.

The co-evolutionary dynamics that exist in host-parasite interactions sometimes lead to compatibility polymorphisms, the molecular bases of which are rarely investigated. To identify key molecules that are involved in this phenomenon in the Schistosoma mansoni/Biomphalaria glabrata model, we developed a comparative proteomics approach using the larval stages that interact with the invertebrate host. We used qualitative and quantitative analyses to compare the total proteomes of primary sporocysts from compatible and incompatible parasite strains. The differentially expressed proteins thus detected belong to three main functional groups: (i) scavengers of reactive oxygen species, (ii) components of primary metabolism, and (iii) mucin-like proteins. We discuss the putative roles played by these protein families as determinants of compatibility polymorphism. Since mucins are known to play key roles in the host-parasite interplay, we consider the newly discovered S. mansoni mucin-like proteins (SmMucin-like) as the most promising candidates for influencing the fate of host-parasite interactions. An analysis of their expression is presented in a paper published in the same journal issue.